Amy L Stuart | University of South Florida (original) (raw)

Traffic air pollution, urban form and equity by Amy L Stuart

Journal of Transport & Health, 2022

To enable human mobility, economic vitality, and population well-being in growing cities, well-pl... more To enable human mobility, economic vitality, and population well-being in growing cities, well-planned transportation infrastructure is essential. However, transportation systems can also have detrimental impacts on health and equity, including through increased air pollution and its unequal social distribution. This study focuses on estimating air quality and equity impacts of an ongoing large-scale metropolitan transportation program (known as “Tampa Bay Next”). Our objective was to characterize and quantify the air pollution levels and population exposures resulting from an interstate freeway expansion planned under Tampa Bay Next, which includes added toll lanes. Specifically, we estimated changes in individual human exposures to oxides of nitrogen (NOx) due to the proposed freeway changes, using an integrated suite of high-resolution models for travel demand, emissions, pollutant dispersion, and exposure. Inequity in the distribution of exposures among racioethnic and income groups was also estimated using a few measures of inequality. Results indicate that the planned freeway expansion may slightly decrease the ambient daily NOx emissions, concentrations, and exposures on average, while increasing exposure densities during peak periods in areas surrounding downtown Tampa. Group-average exposures also decreased for all population subgroups under the planned expansion scenario. However, disparities in exposure for the black and the below-poverty groups increased. Results suggest that a detailed analysis of exposures may be needed to ensure large-scale transportation improvement programs reduce inequity, even when average impacts on air quality and exposures are positive or neutral.

International Journal of Environmental Research and Public Health, 2021

Within the existing relationship among urban environment, health, and poverty, it is necessary to... more Within the existing relationship among urban environment, health, and poverty, it is necessary to clarify and characterize the influence that the physical environment has on community socioeconomic outcomes. Given that Detroit has one of the highest poverty rates among large metropolitan areas in the United States, this study aims to identify environmental and urban features that have influenced poverty in this city by assessing whether changes in household income are associated with characteristics of the built environment. The difference of median household income (DMHI) between 2017 and 2013 and 27 environmental and urban variables were investigated using both geographic distribution mapping and statistical correlation analysis. Results suggest that proximity of housing to job opportunity areas, as well as to certain educational and health-related facilities, were positively related to increasing household incomes. These findings outline a healthy urban design that may benefit co...

Environmental Pollution, 2019

On the accuracy and potential of Google Maps location history data to characterize individual mob... more On the accuracy and potential of Google Maps location history data to characterize individual mobility for air pollution health studies, Environmental Pollution (2019), doi:

The objective of this study was to model the potential impacts of alternative transit-oriented ur... more The objective of this study was to model the potential impacts of alternative transit-oriented urban design scenarios on community exposures to roadway air pollution. We used a modeling framework developed previously for the study area that includes activity-based travel demand modeling (Tampa Bay ABM), a dynamic traffic assignment model (MATSim), a mobile-source emissions model (MOVES), a line-source dispersion model (RLINE), and a population exposure estimator to simulate ambient concentrations and population exposure to oxides of nitrogen (NOx) under alternate urban design scenarios for Hillsborough County, Florida. Data from the 2040 transit plan envisioned by the Tampa Bay Area Regional Transportation Authority were added to the modeling system along with reassignment of household residence locations to parcels near to both employment centers and transit stops. Scenarios included a low-transit scenario (S1) that used the 2040 base residential distribution with 2010 bus services, an enhanced-transit scenario (S2) that applied the proposed 2040 bus services, and a compact-growth scenario (S3) that increased the residential density in S2 by redistributing 37% households to be near to jobs and bus stops. Results show slightly higher shares for active modes of travel for S2 and S3 compared to S1, with an increase of 7.1% for walking and 1.8% for transit under S3 specifically. Measures of travel under S3, including daily total travel distance and travel time, decreased compared to S1 by 9% and 2.1%, respectively. Pollution results were more mixed. Daily total emissions of NOx and its overall mean ambient concentration were lower for S3 than S1 (by 11% and 9%, respectively), but mean population exposure was higher (by 29%), due to the collocation of people and pollution. Enhanced diesel bus services alone increased emissions, concentrations, and exposures to NOx. This study suggests that a multi-faceted approach may be needed to ensure beneficial pollution outcomes of transportation and urban design interventions.

Science of The Total Environment, 2017

'Smart' growth and electric vehicles are potential solutions to the negative impacts of worldwide... more 'Smart' growth and electric vehicles are potential solutions to the negative impacts of worldwide urbanization on air pollution and health. However, the effects of planning strategies on distinct types of pollutants, and on human exposures, remain understudied. The goal of this work was to investigate the potential impacts of alternative urban designs for the area around Tampa, Florida USA, on emissions, ambient concentrations, and exposures to oxides of nitrogen (NO x), 1,3-butadiene, and benzene. We studied three potential future scenarios: sprawling growth, compact growth, and 100% vehicle fleet electrification with compact growth. We projected emissions in the seven-county region to 2050 based on One Bay regional visioning plan data. We estimated pollutant concentrations in the county that contains Tampa using the CALPUFF dispersion model. We applied residential population projections to forecast acute (highest hour) and chronic (annual average) exposure. The compact scenario was projected to result in lower regional emissions of all pollutants than sprawl, with differences of-18%,-3%, and-14% for NO x , butadiene, and benzene, respectively. Within Hillsborough County, the compact form also had lower emissions, concentrations, and exposures than sprawl for NO x (-16% /-5% for acute /chronic exposures, respectively), but higher exposures for butadiene (+41% / +30%) and benzene (+21% / +9%). The addition of complete vehicle fleet electrification to the compact scenario mitigated these in-county increases for the latter pollutants, lowering predicted exposures to butadiene (-25% /-39%) and benzene (-5% /-19%), but also resulted in higher exposures to NO x (+81% / +30%) due to increased demand on power plants. These results suggest that compact forms may have mixed impacts on exposures and health. 'Smart' urban designs should consider multiple pollutants and the diverse mix of pollutant sources. Cleaner power generation will also likely be needed to support aggressive adoption of electric vehicles.

Impacts of Estimated Travel Activity on Air Pollutant Concentrations and Human Exposures in the T... more Impacts of Estimated Travel Activity on Air Pollutant Concentrations and Human Exposures in the Tampa Region Sashikanth Gurram, sgurram@mail.usf.edu Amy Stuart, als@ usf.edu; Abdul Pinjari, apinjari@usf.edu Department of Civil & Environmental Engineering, University of South Florida 4202 East Fowler Avenue, Tampa, Florida USA 33620 Department of Environmental & Occupational Health, University of South Florida 13201 Bruce B. Downs Blvd., MDC 56, Tampa, Florida USA 33612

Motor vehicles emit a complex mixture of noxious chemicals that contribute to cardiovascular and ... more Motor vehicles emit a complex mixture of noxious chemicals that contribute to cardiovascular and respiratory disease and excess mortality. Commuting may be important to pollution exposure because concentrations of many traffic-related pollutants are higher near roads (HEI, 2010) and average time in commute in the U.S. has been increasing (Jarosz and Cortes, 2014). Active travel, including bicycling and walking, is one promising strategy for reducing emissions of traffic-related pollution, and improving population health through daily exercise. However, studies suggest that active commuters could be at higher risk of pollutant-related health effects due to higher breathing rates and longer transit times than automobile commuters (Hatzopoulou et al., 2013; Johan de Hartog et al., 2010). Available routes of travel for each mode could also play a role because they affect travel times. Hence, more data are needed under real commuting conditions on the impacts of commute mode and route on...

Journal of Exposure Science and Environmental Epidemiology, 2016

Traffic-related air pollution is associated with increased mortality and morbidity, yet few studi... more Traffic-related air pollution is associated with increased mortality and morbidity, yet few studies have examined strategies to reduce individual exposure while commuting. The present study aimed to quantify how choice of mode and route type affects personal exposure to air pollutants during commuting. We analyzed within-person difference in exposures to multiple air pollutants (black carbon (BC), carbon monoxide (CO), ultrafine particle number concentration (PNC), and fine particulate matter (PM2.5)) during commutes between the home and workplace for 45 participants. Participants completed 8 days of commuting by car and bicycle on direct and alternative (reduced traffic) routes. Mean within-person exposures to BC, PM2.5, and PNC were higher when commuting by cycling than when driving, but mean CO exposure was lower when cycling. Exposures to CO and BC were reduced when commuting along alternative routes. When cumulative exposure was considered, the benefits from cycling were attenuated, in the case of CO, or exacerbated, in the case of particulate exposures, owing to the increased duration of the commute. Although choice of route can reduce mean exposure, the effect of route length and duration often offsets these reductions when cumulative exposure is considered. Furthermore, increased ventilation rate when cycling may result in a more harmful dose than inhalation at a lower ventilation rate.Journal of Exposure Science and Environmental Epidemiology advance online publication, 28 October 2015; doi:10.1038/jes.2015.68.

The Science of the Total Environment, 2016

Air pollution exposure has been linked to numerous adverse health effects, with some disadvantage... more Air pollution exposure has been linked to numerous adverse health effects, with some disadvantaged subgroups disproportionately burdened. The objective of this work was to characterize distributions of emissions and concentrations of a few important urban air toxics at high spatiotemporal resolution in order to assess exposure and inequality. Benzene, 1,3-butadiene, formaldehyde, and acetaldehyde were the focus pollutants, with oxides of nitrogen (NOx) estimated for comparisons. Primary pollutant emissions were estimated for the full spectrum of source types in the Tampa area using a hybrid approach that is most detailed for major roadways and includes hourly variations in vehicle speed. Resultant pollutant concentrations were calculated using the CALPUFF dispersion model, and combined with CMAQ model output to account for secondary formation of formaldehyde and acetaldehyde. Census demographic data were applied to estimate residential pollution exposures and inequality among popula...

Air Quality, Atmosphere & Health, 2014

Daily exposures to ambient oxides of nitrogen were estimated here for residents of Hillsborough C... more Daily exposures to ambient oxides of nitrogen were estimated here for residents of Hillsborough County, FL. The 2009 National Household Travel Survey provided geocoded data on fixed activity locations during each person-day sampled. Routes between activity locations were calculated from transportation network data, assuming the quickest travel path. To estimate daily exposure concentrations for each person-day, the exposure locations were matched with diurnally and spatially varying ambient pollutant concentrations derived from CALPUFF dispersion model results. The social distribution of exposures was analyzed by comparing frequency distributions of grouped daily exposure concentrations and by regression modeling. To investigate exposure error, the activity-based exposure estimates were also compared with estimates derived using residence location alone. The mean daily activity-based exposure concentration for the study sample was 17 μg/m 3 , with values for individual person-day records ranging from 7.0 to 43 μg/m 3 . The highest mean exposure concentrations were found for the following groups: black (20 μg/m 3 ), below poverty (18 μg/m 3 ), and urban residence location (22 μg/m 3 ). Urban versus rural residence was associated with the largest increase in exposure concentration in the regression (8.3 μg/m 3 ). Time in nonresidential activities, including travel, was associated with an increase of 0.2 μg/m 3 per hour. Time spent travelling and at nonresidential locations contributed an average of 6 and 24 %, respectively, to the daily estimate. A mean error of 3.6 %, with range from −64 to 58 %, was found to result from using residence location alone. Exposure error was highest for those who travel most, but lowest for the sociodemographic subgroups with higher mean exposure concentrations (including blacks and those from below poverty households). This work indicates the importance of urbanicity to social disparities in activity-based air pollution exposures. It also suggests that exposure error due to using residence location may be smaller for more exposed groups.

Journal of the Air & Waste Management Association, 2013

Intra-urban differences in concentrations of oxides of nitrogen (NO(x)) and exposure disparities ... more Intra-urban differences in concentrations of oxides of nitrogen (NO(x)) and exposure disparities in the Tampa area were investigated across temporal scales through emissions estimation, dispersion modeling, and analysis of residential subpopulation exposures. A hybrid estimation method was applied to provide link-level hourly on-road mobile source emissions. Ambient concentrations in 2002 at 1 km resolution were estimated using the CALPUFF dispersion model. Results were combined with residential demographic data at the block-group level, to investigate exposures and inequality for select racioethnic, age, and income population subgroups. Results indicate that on-road mobile sources contributed disproportionately to ground-level concentrations and dominated the spatial footprint across temporal scales (annual average to maximum hour). The black, lower income (less than 40Kannually),andHispanicsubgroupshadhigherestimatedexposuresthanthecountyaverage;thewhiteandhigherincome(greaterthan40K annually), and Hispanic subgroups had higher estimated exposures than the county average; the white and higher income (greater than 40Kannually),andHispanicsubgroupshadhigherestimatedexposuresthanthecountyaverage;thewhiteandhigherincome(greaterthan60K) subgroups had lower than average exposures. As annual average concentration increased, the disparity between groups generally increased. However for the highest 1-hr concentrations, reverse disparities were also found. Current studies of air pollution exposure inequality have not fully considered differences by time scale and are often limited in spatial resolution. The modeling methods and the results presented here can be used to improve understanding of potential impacts of urban growth form on health and to improve urban sustainability. Results suggest focusing urban design interventions on reducing on-road mobile source emissions in areas with high densities of minority and low income groups.

Journal of Environmental Management, Aug 1, 2011

Environmental equity has been identified as a challenge and goal of national to global air qualit... more Environmental equity has been identified as a challenge and goal of national to global air quality management. Here, relationships between traffic-related air pollution measures and the social demographics of elementary schools are investigated. Ogawa passive samplers were used to measure ambient nitrogen dioxide (NO2) levels near 75 randomly selected elementary schools in the county containing Tampa, FL over one week in March 2008. Concentrations were determined using colorimetric reaction using Hach nitrite reagent and photometric detection at 545 nm. NO2 levels, two metrics of traffic (highest annual average daily traffic count within 500 m and 1000 m), and school enrollment data by demographic subgroup (racial/ethnic and socioeconomic) were then compared. Data were analyzed for distribution statistics, linear correlations, and differences in subgroup category means. Weighted average values of NO2 and traffic count were also calculated for each subgroup. All measured NO2 levels were low, with a mean of 2.7 ppbv and range from 0.8 to 4.7 ppbv. Values were largest at sites near downtown. Results from all analyses show comparatively higher potential exposures to measured NO2 and traffic count for black schoolchildren, and lower values for white and Asian/Pacific Islander schoolchildren. The economically disadvantaged and Hispanic subgroups were also associated with higher levels of NO2 and traffic counts, but the relationship was not as strong or robust. Although measured NO2 levels were low and the differences between groups are small, results suggest disparities by racial/ethnic and economic status in children’s exposures to air pollution for the Tampa area.

Journal of environmental health

Passive diffusive samplers were used to collect ambient benzene for a one-week sampling period (A... more Passive diffusive samplers were used to collect ambient benzene for a one-week sampling period (April 27 to May 4, 2011) at 11 locations throughout a city park in the Tampa, Florida, area. Concentrations were determined through gas chromatography with mass spectrometry. Spatial variability within the park and its contribution to uncertainty in health risk estimates were studied. Measured concentrations ranged from 0.23 to 0.34 microg/m3. The relative percentage differences for samplers collocated with a regulatory reference monitor and with a duplicate were 3% and 14%, respectively. The spatial variability over the park was small with a coefficient of variation of 11%. The concentration variation due to sampler placement contributes less to uncertainty in health risk estimates than the uncertainty associated with the inhalation unit risk parameter (39% versus 170% relative percent differences over the ranges studied). Results suggest that there is a limit to the spatial resolution n...

Air, Soil and Water Research, 2011

Radiello passive diffusive aldehyde samplers were used to measure ambient formaldehyde and acetal... more Radiello passive diffusive aldehyde samplers were used to measure ambient formaldehyde and acetaldehyde levels, approximately every 0.7 km in a 10 km2 sampling area in Hillsborough County, Florida from January 21 to 28, 2010. Samples were analyzed for aldehyde-DNPH derivatives via high performance liquid chromatography with ultraviolet detection. Concentrations were compared with values at a regulatory fixed-site monitor. Distribution statistics, concentration ratios, and spatial contours were calculated to investigate spatial variability. Mean aldehyde concentrations were 2.4 and 1.1 μg/m3 for formaldehyde and acetaldehyde, respectively. Observed spatial concentration patterns were similar for both aldehydes and suggest the influence of nearby roadway emissions. Overall, the spatial variation was small, with coefficients of variation of 13% and 22%, respectively. Results here provide methods and data for understanding exposures to aldehydes at high spatial resolution.

Journal of Environmental Management, 2011

Environmental equity has been identified as a challenge and goal of national to global air qualit... more Environmental equity has been identified as a challenge and goal of national to global air quality management. Here, relationships between traffic-related air pollution measures and the social demographics of elementary schools are investigated. Ogawa passive samplers were used to measure ambient nitrogen dioxide (NO 2 ) levels near 75 randomly selected elementary schools in the county containing Tampa, FL over one week in March 2008. Concentrations were determined using colorimetric reaction using Hach nitrite reagent and photometric detection at 545 nm. NO 2 levels, two metrics of traffic (highest annual average daily traffic count within 500 m and 1000 m), and school enrollment data by demographic subgroup (racial/ethnic and socioeconomic) were then compared. Data were analyzed for distribution statistics, linear correlations, and differences in subgroup category means. Weighted average values of NO 2 and traffic count were also calculated for each subgroup. All measured NO 2 levels were low, with a mean of 2.7 ppbv and range from 0.8 to 4.7 ppbv. Values were largest at sites near downtown. Results from all analyses show comparatively higher potential exposures to measured NO 2 and traffic count for black school children, and lower values for white and Asian or Pacific Islander school children. The economically disadvantaged and Hispanic subgroups were also associated with higher levels of NO 2 and traffic counts, but the relationship was not as strong or robust. Although measured NO 2 levels were low and the differences between groups are small, results suggest disparities by racial/ethnic and economic status in children's exposures to air pollution for the Tampa area.

Journal of the Air & Waste Management Association, 2009

The potential for inequities between population subgroups in air pollution exposures and in regul... more The potential for inequities between population subgroups in air pollution exposures and in regulatory protection because of small-scale intraurban differences in outdoor air pollution and air quality monitoring are studied here. The focus subgroups are blacks, Hispanics, whites, and the population living below poverty, with Tampa, FL, used as the case study area for quantitative analyses. A geographical database is developed for the surrounding county that includes population demographics, source locations, monitor locations, and air pollutant concentrations. Data included are residential population demographics at the block-group spatial scale from the year 2000 U.S. Census, U.S. Environmental Protection Agency (EPA) Toxic Releases Inventory source locations and air source release amounts, EPA Air Quality System monitoring data, and Florida major highway source locations and roadway traffic data. This database is applied for analysis of the spatial relationships between residence locations of population subgroups and outdoor air pollution surrogates. A quantitative index to evaluate the inequity between subpopulations is developed and applied. Findings include that blacks, Hispanics, and people living in poverty are disproportionately living closer to sources of air pollution and further from regulatory air quality monitoring sites compared with the overall county population. Conversely, whites are disproportionately living away from sources and near monitoring sites. Analysis of the regulatory monitoring guidelines indicates that recent changes in those guidelines may exacerbate existent inequities. The results suggest disparities in exposures to air pollution, disparities in regulatory monitoring representation, and the need for more monitoring and analyses at smaller spatial scales.

Journal of Transport & Health, 2022

International Journal of Environmental Research and Public Health, 2021

Environmental Pollution, 2019

Science of The Total Environment, 2017

Journal of Exposure Science and Environmental Epidemiology, 2016

The Science of the Total Environment, 2016

Air Quality, Atmosphere & Health, 2014

Journal of the Air & Waste Management Association, 2013

Journal of Environmental Management, Aug 1, 2011

Journal of environmental health

Air, Soil and Water Research, 2011

Journal of Environmental Management, 2011

Environmental equity has been identified as a challenge and goal of national to global air qualit... more Environmental equity has been identified as a challenge and goal of national to global air quality management. Here, relationships between traffic-related air pollution measures and the social demographics of elementary schools are investigated. Ogawa passive samplers were used to measure ambient nitrogen dioxide (NO 2 ) levels near 75 randomly selected elementary schools in the county containing Tampa, FL over one week in March 2008. Concentrations were determined using colorimetric reaction using Hach nitrite reagent and photometric detection at 545 nm. NO 2 levels, two metrics of traffic (highest annual average daily traffic count within 500 m and 1000 m), and school enrollment data by demographic subgroup (racial/ethnic and socioeconomic) were then compared. Data were analyzed for distribution statistics, linear correlations, and differences in subgroup category means. Weighted average values of NO 2 and traffic count were also calculated for each subgroup. All measured NO 2 levels were low, with a mean of 2.7 ppbv and range from 0.8 to 4.7 ppbv. Values were largest at sites near downtown. Results from all analyses show comparatively higher potential exposures to measured NO 2 and traffic count for black school children, and lower values for white and Asian or Pacific Islander school children. The economically disadvantaged and Hispanic subgroups were also associated with higher levels of NO 2 and traffic counts, but the relationship was not as strong or robust. Although measured NO 2 levels were low and the differences between groups are small, results suggest disparities by racial/ethnic and economic status in children's exposures to air pollution for the Tampa area.

Journal of the Air & Waste Management Association, 2009

Transportation Research Part A: Policy and Practice, 2019

Emerging transportation technologies (e.g. connected vehicles) and services (e.g. shared mobility... more Emerging transportation technologies (e.g. connected vehicles) and services (e.g. shared mobility) provide efficient, sustainable and cost-effective alternatives to traditional travel modes. However, whether these innovative technologies bring benefits to different population groups in an equal and reasonable manner is still an open question. This report aims to tackle this question and is divided into the following two parts: transportation equity literature review and a case study on bike-sharing systems. The first part of the report comprehensively surveys the literature about methodologies for analyzing transportation equity for traditional and emerging transportation technologies in terms of economy, environment and public health. It is found that existing methodologies can be unified into a 3-step equity analysis framework. Research gaps and future research directions are also discussed. The second part of the report closes one of the research gaps mentioned in the first part of report by using disaggregated data for equity measurement. This part of report developes a comprehensive equity assessment framework on bike sharing accessibility in southern Tampa with individual-level data. The report compares the equity outcomes of the proposed approach and serveral benchmarks, and interpretes results of horizontal equity and vertical equity analysis. The results justify the importance of using disaggregated tour data, also reveal some equity issues in southern Tampa.

Transportation Research Interdisciplinary Perspectives, 2020

Emerging transportation technologies (e.g., electric vehicles) and services (e.g., shared mobilit... more Emerging transportation technologies (e.g., electric vehicles) and services (e.g., shared mobility) provide efficient, sustainable and cost-effective alternatives to traditional travel modes. However, whether these innovative technologies bring benefits to different population groups in an equal and reasonable manner is still an open question. The various methods applied to evaluate the equity performance of these systems are also not clearly comparable. In this paper, we comprehensively review methods from the existing literature for assessing the equity of a few important system outcomes: accessibility, traffic emissions, and safety. We also identify the existing challenges of analyzing equity for emerging transportation technologies. We unify the existing methodologies into a three-step framework that includes population measurement, cost/benefit measurement and equity assessment, and we summarize the applicable measurements for each step, in detail. A handful of literature focusing on emerging transportation technologies, such as shared mobility and autonomous vehicles, were also identified and surveyed; the methodologies used were found to fit with the three-step framework. We summarize the major findings and discuss promising directions for developing more sophisticated equity assessment methodologies for emerging transportation technologies. Overall, based on a comprehensive review, this paper contributes a framework for assessing the equity of transportation systems that integrates accessibility, traffic emissions, and safety outcomes. The summarized framework can be an overview resource to assist researchers and transportation planners who require equity analysis methods. The research gaps identified also provide directions for equity research on emerging transportation technologies.

Science of The Total Environment, 2021

Poly-brominated diphenyl ethers (PBDEs), dioxins, furans and current-use pesticides (CUPs) are co... more Poly-brominated diphenyl ethers (PBDEs), dioxins, furans and current-use pesticides (CUPs) are common organic pollutants that have received global scrutiny due to their association with adverse environmental and health impacts. However, there is limited previous work assessing their environmental fates in the context of tropical multi-use watersheds. The aim of this study was to estimate the effect of forests on long-term environmental fate for some PBDEs, dioxins, furans and CUPs for a case study watershed of a tropical developing country (the Rio Cobre River drainage basin, Jamaica). Specifically, a dynamic, 16-compartment environmental multimedia model, RioShed, was developed and applied to calculate compartmental concentrations, as well as some long-term environmental fate metrics. Results indicate that the presence of tropical forests, especially those that are evergreen, reduced the atmospheric concentrations, atmospheric long-range transport potential, and the overall persistence of the study pollutants. Reductions in atmospheric concentrations by tropical forests were most enhanced for the more polar CUPs. Forest parameters that notably influenced soil concentration and/or overall persistence included the canopy drip parameter, the leaf area index and the wax erosion rate. The results of this research are expected to inform land-use and environmental management of the study area and similar tropical regions.

Journal of Environmental Management, 2019

There is limited research characterizing the fates of persistent organic pollutants in tropical m... more There is limited research characterizing the fates of persistent organic pollutants in tropical multi-use watersheds. This study aimed to evaluate the role of forests in the environmental fates of select polybrominated diphenyl ethers (PBDEs) for a case study tropical drainage basin, the Rio Cobre watershed. Field samples of deposition, soil, litterfall and the atmosphere of a forest and nearby clearing were analyzed for the presence of the PBDEs (PBDE-28, 47, 99, 100, 153, 154, 183 and 209), which are routinely detected in the environment. The mean air and litterfall concentrations of these PBDEs were generally lower in the forest than in the clearing, whereas the deposition flux rate and soil concentrations were higher in the forest. The results suggest that the forest filtered the PBDEs by transferring them from the atmosphere to the soil, despite the tropical nature of the study site.

Environmental Monitoring and Assessment, 2011

The Low Carbon Development Strategy proposed in June 2009 by the government of Guyana in response... more The Low Carbon Development Strategy proposed in June 2009 by the government of Guyana in response to the Reducing Emissions from Deforestation and Forest Degradation in Developing Countries program has triggered evaluation of forest-related activities, thereby acting as a catalyst for improvements in Guyana's small-to medium-scale gold mining industry. This has also shed light on areas committed to conservation, something that has also been handled by Non Governmental Organizations. This paper compares water quality and mercury concentrations in sediment from four main areas in Guyana, two that are heavily mined for gold using mercury amalgamation methods (Arakaka and Mahdia) and two that are considered conservation areas (Iwokrama and Konashen). Fifty-three sediment and soil mercury loadings ranged from 29 to 1,200 ng/g and averaged 215 ± 187 ng/g for all sites with similar averages in conservation and mining areas. Sediment loadings are within the range seen in French Guiana and Suriname, but conservation area samples had higher loadings than the corresponding uncontaminated baselines. Type of ore and location in the mining process seemed to influence mercury loadings. Mercury sediment loadings were slightly positively correlated with pH (correlation coefficient = 0.2; p value < 0.001) whereas no significant correlations were found with dissolved oxygen or turbidity.

Mercury is a pervasive global pollutant with debilitating health outcomes, and an exposure pathwa... more Mercury is a pervasive global pollutant with debilitating health outcomes, and an exposure pathway that transcends social and economic boundaries. Wet deposition processes are central to the entry of mercury into aquatic ecosystems, where it bioaccumulates in piscivorous species. Fish consumption is the leading route to mercury exposure for vulnerable populations such as women of child-bearing age, subsistence fisher folk, and those consuming high seafood diets. However, substantial uncertainties exist in attributing deposition levels to local versus long-range emission sources. Here, we investigate the deposition and sources contributing to mercury loading in the Tampa Bay region. Positive matrix factorization (PMF) receptor analysis was applied to one year of special precipitation event data from the Bay Regional Atmospheric Chemistry Experiment, for a site in Tampa, to apportion source influence types. An 11-factor model was found to account for maximum uncertainties in the 25-sp...

Mercury contamination is a global environmental problem that has been responsible for some very v... more Mercury contamination is a global environmental problem that has been responsible for some very visible community health impacts. Although many detrimental effects of mercury are recognized, the factors that lead to continued human exposures are still poorly understood. These factors include its cycling in the environment and the economic, political, and cultural issues that sustain its use, release, and consumption. Here, we present an interdisciplinary research and graduate education project whose objective is to elucidate these interacting factors while training students to integrate knowledge and practice across disciplines. The project involves graduate students and professors from environmental health, geography, and environmental engineering. The research is primarily being conducted by students, in part through a course developed for the project with a case study focus of the Tampa Bay area. Our methods include systems modeling, field measurements with laboratory analysis, a...

Atmospheric Research, 2016

In this paper, sources of mercury deposition to the Tampa area (Florida, USA) are investigated by... more In this paper, sources of mercury deposition to the Tampa area (Florida, USA) are investigated by analysis of one year (March 2000-March 2001) of daily wet deposition data. HYSPLIT back-trajectory modeling was performed to assess potential source locations for high versus low concentration events in data stratified by precipitation level. Positive matrix factorization (PMF) was also applied to apportion the elemental compositions from each event and to identify sources. Increased total mercury deposition was observed during summer months, corresponding to increased precipitation. However, mercury concentration in deposited samples was not strongly correlated with precipitation amount. Back-trajectories show air masses passing over Florida land in the short (12 h) and medium (24 h) term prior to deposition for high mercury concentration events. PMF results indicate that eleven factors contribute to the deposited elements in the event data. Diagnosed elemental profiles suggest the sources that contribute to mercury wet deposition at the study site are coal combustion (52% of the deposited mercury mass), municipal waste incineration (23%), medical waste incineration (19%), and crustal dust (6%). Overall, results suggest that sources local to the county and in Florida likely contributed substantially to mercury deposition at the study site, but distant sources may also contribute.

Mercury is a persistent environmental contaminant whose most toxic form, methyl mercury, strongly... more Mercury is a persistent environmental contaminant whose most toxic form, methyl mercury, strongly bioaccumulates and biomagnifies in aquatic ecosystems, making consumption of predatory fish the leading route to toxic human exposures . Mitigation of mercury exposure requires attribution of observed levels of mercury (Hg) in the environment to emission sources. Of particular interest is identifying the relative contributions to deposition to sensitive watersheds of local anthropogenic sources versus distant sources. Existing uncertainties in the scientific literature on the point is detrimental to adequate control at all management levels, from international to local. Previous research specifically addressing the relative contributions is somewhat contradictory.

Annals of Epidemiology, 2017

Every additional infection reduced the odds of ALL by 4% (OR¼0.96, 95%CI: 0.94, 0.98) in studies ... more Every additional infection reduced the odds of ALL by 4% (OR¼0.96, 95%CI: 0.94, 0.98) in studies with self-reported data; whereas every additional infection increased the odds of ALL by 11% (OR¼1.11, 95%CI: 1.07, 1.15) in studies with administrative/medical records data. Conclusions: There was no overall effect between infections and childhood ALL, however, qualitative difference between subgroup effects indicate a potential infectious etiology for ALL that may depend on how infections were ascertained. Future research will need to address the challenges in measuring infectious exposures, and to reduce the knowledge gaps identified.

Environmental Research, 2015

A growing number of studies have investigated the association between air pollution and the risk ... more A growing number of studies have investigated the association between air pollution and the risk of birth defects, but results are inconsistent. The objective of this study was to examine whether maternal exposure to ambient PM2.5 or benzene increases the risk of selected birth defects in Florida. We conducted a retrospective cohort study of singleton infants born in Florida from 2000 to 2009. Isolated and non-isolated birth defect cases of critical congenital heart defects, orofacial clefts, and spina bifida were identified from the Florida Birth Defects Registry. Estimates of maternal exposures to PM2.5 and benzene for all case and non-case pregnancies were derived by aggregation of ambient measurement data, obtained from the US Environmental Protection Agency Air Quality System, during etiologically relevant time windows. Multivariable Poisson regression was used to estimate adjusted prevalence ratios (aPRs) and 95% confidence intervals (CIs) for each quartile of air pollutant exposure. Compared to the first quartile of PM2.5 exposure, higher levels of exposure were associated with an increased risk of non-isolated truncus arteriosus (aPR4th Quartile, 8.80; 95% CI, 1.11-69.50), total anomalous pulmonary venous return (aPR2nd Quartile, 5.00; 95% CI, 1.10-22.84), coarctation of the aorta (aPR4th Quartile, 1.72; 95% CI, 1.15-2.57; aPR3rd Quartile, 1.60; 95% CI, 1.07-2.41), interrupted aortic arch (aPR4th Quartile, 5.50; 95% CI, 1.22-24.82), and isolated and non-isolated any critical congenital heart defect (aPR3rd Quartile, 1.13; 95% CI, 1.02-1.25; aPR4th Quartile, 1.33; 95% CI, 1.07-1.65). Mothers with the highest level of exposure to benzene were more likely to deliver an infant with an isolated cleft palate (aPR4th Quartile, 1.52; 95% CI, 1.13-2.04) or any orofacial cleft (aPR4th Quartile, 1.29; 95% CI, 1.08-1.56). An inverse association was observed between exposure to benzene and non-isolated pulmonary atresia (aPR4th Quartile, 0.19; 95% CI, 0.04-0.84). Our results suggest a few associations between exposure to ambient PM2.5 or benzene and specific birth defects in Florida. However, many related comparisons showed no association. Hence, it remains unclear whether associations are clinically significant or can be causally related to air pollution exposures.

Spatial and Spatio-temporal Epidemiology, 2016

We investigate uncertainty in estimates of pregnant women's exposure to ambient PM 2.5 and benzen... more We investigate uncertainty in estimates of pregnant women's exposure to ambient PM 2.5 and benzene derived from central-site monitoring data. Through a study of live births in Florida during 20 0 0-20 09, we discuss the selection of spatial and temporal scales of analysis, limiting distances, and aggregation method. We estimate exposure concentrations and classify exposure for a range of alternatives, and compare impacts. Estimated exposure concentrations were most sensitive to the temporal scale of analysis for PM 2.5 , with similar sensitivity to spatial scale for benzene. Using 1-12 versus 3-8 weeks of gestational age as the exposure window resulted in reclassification of exposure by at least one quartile for up to 37% of mothers for PM 2.5 and 27% for benzene. The largest mean absolute differences in concentration resulting from any decision were 0.78 μg/m 3 and 0.44 ppbC, respectively. No bias toward systematically higher or lower estimates was found between choices for any decision.

Birth defects research, Jan 15, 2018

To identify the live-birth prevalence, trends, correlates, and neonatal and 1-year survival rates... more To identify the live-birth prevalence, trends, correlates, and neonatal and 1-year survival rates of congenital diaphragmatic hernia. Using a population-based, retrospective cohort study design, we examined 1,025 cases of congenital diaphragmatic hernia from the 1998-2012 Florida Birth Defects Registry. We used Poisson and joinpoint regression models to compute prevalence ratios and temporal trends, respectively. Kaplan-Meier survival curves and Cox proportional hazards regression were used to describe neonatal and 1-year survival and estimate hazard ratios representing the predictors of infant survival. The birth prevalence of congenital diaphragmatic hernia was 3.19 per 10,000 live births (95% confidence interval [CI]: 3.00-3.39); there was a 4.2% yearly increase among multiple cases only. Among all cases, maternal education less than high school (prevalence ratio: 1.25, 95% CI: 1.02-1.53), high school/associate degree/GED (prevalence ratio: 1.15, 95% CI: 1.01-1.32), multiple birt...

Birth Defects Research, 2019

BACKGROUND Congenital diaphragmatic hernia (CDH) is a rare musculoskeletal birth defect with a pr... more BACKGROUND Congenital diaphragmatic hernia (CDH) is a rare musculoskeletal birth defect with a prevalence of 2.61 per 10,000 in the United States. There is limited evidence for ambient air pollutants in the etiology of CDH in humans. OBJECTIVES We investigated the role of maternal exposure to ambient cadmium as a risk factor for CDH (overall and stratified by isolated and non-isolated subtypes) in Florida and whether maternal smoking during pregnancy was an effect modifier of this association. METHODS We conducted a population-based, retrospective cohort study using data from the 1999-2012 Florida Birth Defects Registry linked to the National Air Toxic Assessment database. Analyses included chi-square tests; multilevel Poisson regression models to calculate measures of association between cadmium and CDH; and stratified analyses to examine effect modification by maternal smoking status. RESULTS The study population consisted of 2,591,395 live births including 840 CDH cases. We did not find evidence for an association between maternal exposure to ambient cadmium concentration and CDH. We observed a 24% increased risk of CDH among isolated cases in the highest quartile of cadmium exposure (95% confidence interval [CI]: 1.00, 1.55). Although we were limited by small sample size for CDH cases, we found that among mothers who smoked during pregnancy, exposure to the highest quartile of cadmium was associated with more than two times higher risk for CDH among overall (95%CI: 1.04, 4.39) and isolated (95%CI: 1.07, 5.57) cases. CONCLUSIONS Additional research is needed to elucidate the mechanism by which maternal ambient cadmium exposure may increase the risk of CDH in offspring, and the extent to which maternal smoking during pregnancy modifies this association.

Atmospheric Environment, 2007

We study the use of ensemble-based Kalman filtering of chemical observations for constraining met... more We study the use of ensemble-based Kalman filtering of chemical observations for constraining meteorological uncertainties and for selecting targeted observations. Using a coupled model of two dimensional sea breeze dynamics and chemical tracer transport, we perform three numerical experiments. First, we investigate the chemical tracer forecast uncertainties associated with meteorological initial condition error. We find that the ensemble variance and error builds during the transition between land and sea breeze phases of the circulation. Second, we investigate the effects on the forecast variance and error of assimilating tracer concentration observations extracted from a truth simulation for a network of surface locations. We find that assimilation reduces the variance and error in both the observed variable (chemical tracer concentrations) and unobserved meteorological variables (vorticity and buoyancy). Finally, we investigate the potential value to the forecast of targeted observations. We calculate an impact factor that maximizes the total decrease in model uncertainty summed over all state variables.

Journal of Geophysical Research, 2007

This study explores the sensitivity of grid model ozone simulations of Houston area ozone to smal... more This study explores the sensitivity of grid model ozone simulations of Houston area ozone to small perturbations of meteorological variables that are realistic in structure and evolution.

Ensemble-based Kalman filtering (EnKF) is a data assimilation technique that is undergoing signif... more Ensemble-based Kalman filtering (EnKF) is a data assimilation technique that is undergoing significant investigation for many environmental modeling applications. Here, we study the use of EnKF for constraining meteorological uncertainties in a two-dimensional sea breeze and chemical tracer model forecast. For this work, we have augmented a nonlinear meteorological model of a sea breeze circulation with a tracer transport algorithm. With the coupled model, we perform three numerical experiments. First, we investigate the chemical tracer forecast uncertainties associated with meteorological initial condition error. We use a 50 member ensemble forecast in which member initial conditions were chosen by statistically sampling a time series of data, in a `climatological' initialization scheme, to represent the variance in the maximum diurnal heating (local noon). We find that the ensemble variance builds during the transition between land and sea breeze phases of the circulation. Second, we investigate the effects on the forecast variance and error of assimilating tracer concentration observations from a network of surface locations. Observations were extracted from an arbitrarily-chosen 51st member used as the truth simulation. We find that the EnKF assimilation reduces the variance and error in both meteorological variables (vorticity and buoyancy) and in chemical tracer concentrations. Finally, we investigate the potential value to the forecast of added targeted observations by post-processing analysis that determines an uncertainty norm throughout the spatial and temporal domain. The norm uses covariance information generated through the ensemble forecast to maximize the total decrease in model uncertainty summed over all state variables. By comparing the distributions of the uncertainty norm with and without data assimilation of the network observations, we find that the overall uncertainty decreased, but locations of optimal targeted observations remained similar. Our analysis also demonstrates the potential usefulness of EnKF data assimilation for planning targeted observations.

Journal of Geophysical Research: Atmospheres, 2001

By using a three-dimensional convective cloud model to simulate the July 10, 1996, Stratospheric-... more By using a three-dimensional convective cloud model to simulate the July 10, 1996, Stratospheric-Troposphedc Experiment: Radiation, Aerosols, and Ozone-Deep Convection experiment storm, we investigate the fate of tracers of varying solubilities in midlatitude convection. The tracer distribution resulting from the interactions of the soluble tracers with the cloud hydrometeors is illustrated for two cases. The first case assumes that the dissolved tracer in the cloud water or rain completely degasses when the parent hydrometeor is converted to ice, snow, or hail through microphysical processes. The second case assumes that the dissolved tracer is retained in the ice, snow, or hail. We find that when soluble tracers are degassed, both low-and high-solubility tracers are transported to the upper troposphere. When tracers are retained in ice hydrometeors, the highly soluble tracers are not ultimately transported to the upper troposphere but, instead, are precipitated out of the upper troposphere by snow and hail. Tracers of low solubility are transported upward, similar to passive tracer transport. The key microphysical processes that control these results are the accretion of cloud water by snow and hail. For the simulation in which retention of tracers in ice was considered, highly soluble scalars (10 '5 M atm-•) have a scavenging efficiency > 55% and have a mass change in the upper troposphere (8-15 km mean sea level) of-0.5 x 10 • kg to 0 for a 3-hour period, while a passive scalar has a mass change of 2.3 x 105 kg. 1. Introduction Deep convection has been known to be a primary mechanism of moving trace gas species from the boundary layer to the free troposphere [e.g., Dickerson et al., 1987; Chatfield and Crutzen, 1984]. Chemical consequences of the transport of boundary layer air to the upper and middle troposphere on the regional scale can be to attain ozone (Oa) concentrations greater than if the atmosphere were undisturbed by convection [Pickering et al., 1992b]. Recently, it has been hypothesized that deep convection can affect the odd hydrogen (HOx) budget in the upper troposphere [Prather and Jacob, 1997; Jaegl• et al., 1997]. However, studies have not examined in detail how deep convection processes the HOx precursors, such as methyl hydrogen peroxide (CHaOOH), hy

Phase partitioning during freezing affects the transport and distribution of volatile chemical sp... more Phase partitioning during freezing affects the transport and distribution of volatile chemical species in convective clouds. This consequently can have impacts on tropospheric chemistry, air quality, pollutant deposition, and climate change. Here, we discuss the development, evaluation, and application of a mechanistic model for the study and prediction of volatile chemical partitioning during steady-state hailstone growth. The model estimates the fraction of a chemical species retained in a two-phase freezing hailstone. It is based upon mass rate balances over water and solute for accretion under wet-growth conditions. Expressions for the calculation of model components, including the rates of super-cooled drop collection, shedding, evaporation, and hail growth were developed and implemented based on available cloud microphysics literature. Solute fate calculations assume equilibrium partitioning at air-liquid and liquid-ice interfaces. Currently, we are testing the model by performing mass balance calculations, sensitivity analyses, and comparison to available experimental data. Application of the model will improve understanding of the effects of cloud conditions and chemical properties on the fate of dissolved chemical species during hail growth.

Journal of Atmospheric Chemistry, 2006

Partitioning of volatile chemicals among the gas, liquid, and solid phases during freezing of liq... more Partitioning of volatile chemicals among the gas, liquid, and solid phases during freezing of liquid water in clouds can impact trace chemical distributions in the troposphere and in precipitation. We describe here a numerical model of this partitioning during the freezing of a supercooled liquid drop. Our model includes the time-dependent calculation of the coupled processes of crystallization kinetics, heat transport, and solute mass transport, for a freezing hydrometeor particle. We demonstrate the model for tracer partitioning during the freezing of a 1000 μm radius drop on a 100 μm ice substrate, under a few ambient condition scenarios. The model effectively simulates particle freezing and solute transport, yielding results that are qualitatively and quantitatively consistent with previous experimental and theoretical work. Results suggest that the ice shell formation time is governed by heat loss to air and not by dendrite propagation, and that the location of ice nucleation is not important to freezing times or the effective partitioning of chemical solutes. Even for the case of nucleation at the center of the drop, we found that dendrites propagated rapidly to form surface ice. Freezing then proceeded from the outside in. Results also indicate that the solid-liquid interfacial surface area is not important to freezing times or the effective partitioning of chemical solutes, and that the rate aspects of trapping are more important than equilibrium solid-liquid partitioning to the effective partitioning resulting from freezing.

Journal of Geophysical Research, 2004

Partitioning of volatile chemicals among the gas, liquid, and solid phases during the conversion ... more Partitioning of volatile chemicals among the gas, liquid, and solid phases during the conversion of liquid water to ice in clouds can impact distributions of chemicals in precipitation and in the poststorm troposphere. In this paper, we extend a theoretical scaling model of chemical retention during hydrometeor freezing to all dry growth riming conditions. We account for spreading of drops

Journal of Geophysical Research, 2003

1] Partitioning of volatile chemicals among the gas, liquid, and solid phases during the conversi... more 1] Partitioning of volatile chemicals among the gas, liquid, and solid phases during the conversion of liquid water to ice in clouds can impact the poststorm distributions of chemicals in the troposphere and in precipitation. In this paper, we use a timescale-based methodology to determine the key physical parameters involved in retention and derive the dependence of retention on these parameters for nonrime freezing and rime freezing when droplet spreading is minimal. We calculate a dimensionless retention indicator for SO 2 , H 2 O 2 , NH 3 , and HNO 3 , for a variety of conditions relevant to natural clouds. We find that solute properties, particularly the effective Henry's constant, likely have a large impact on retention. Chemicals with very high effective Henry's constants (e.g., HNO 3 ) will likely be retained completely under all conditions. For chemicals with lower effective Henry's constants, freezing conditions (including pH, temperature, magnitude of the hydrometeor velocity in air, and drop size) will likely have significant impacts on retention, while air pressure has only a small effect. The dependence on velocity and drop size depends on the limiting mass transport regime and is nonmonotonic due to the competing effects of ventilation on heat and mass transport. The formation of a complete or partial ice shell likely also affects retention significantly. Comparison of our results with available experimental data provides possible explanations of the trends and apparent disagreement found in the studies. The theory-based analysis and methodology presented in this paper can be used to improve experimental design and parameterization of retention in cloud models.

Journal of Geophysical Research, 2007

1] By using a three-dimensional convective cloud model to simulate the 10 July 1996, Stratospheri... more 1] By using a three-dimensional convective cloud model to simulate the 10 July 1996, Stratospheric-Tropospheric Experiment: Radiation, Aerosols, and Ozone-Deep Convection experiment storm, we investigate the fate of formaldehyde (CH 2 O), formic acid (HCOOH), hydrogen peroxide (H 2 O 2 ), and methyl hydrogen peroxide (CH 3 OOH) in an isolated thunderstorm. CH 2 O, H 2 O 2 , and CH 3 OOH are important HO x radical and ozone (O 3 ) precursors in the upper troposphere. Thus, determining their source strength to the upper troposphere is important for estimating O 3 production. The model simulates O 3 -NO x -CH 4 chemistry (no nonmethane hydrocarbon chemistry) which is affected by the cloud microphysics and production of NO x by lightning. The retention of the soluble species within ice, snow, and hail during drop freezing results in less transport of the species to the upper troposphere than when the species is degassed during drop-freezing processes. Aqueous-phase chemistry is found to be inadequate in producing sufficient quantities of HCOOH so that HCOOH could serve as a reliable indicator of cloud-processed air. The production of nitrogen oxides by lightning has little to no effect on convective outflow mixing ratios of CH 2 O, H 2 O 2 , and CH 3 OOH within 100 km of the convective cores. Thus, it is unlikely that lightning affects concentrations of HO x precursors near active convection. Scavenging of CH 2 O and H 2 O 2 significantly affects their concentrations in the convective outflow, although H 2 O 2 mixing ratios were still similar to CH 3 OOH indicating that both peroxides can contribute equally to O 3 production downwind of convection.

Clouds are able to modify the distribution of chemical species in many ways Through air motions a... more Clouds are able to modify the distribution of chemical species in many ways Through air motions associated with clouds chemical species are trans ported from the boundary layer to the free tropo sphere Highly soluble species may dissolve into the cloud water and rain and ultimately be deposited on the ground in the precipitation Because of the inter action of the cloud hydrometeors chemical species may be captured by the precipitating ice particles Photolysis rates are altered by the scattering and at tenuation of solar radiation The cloud hydromete ors may serve as locations for aqueous and ice phase reactions Deep convection is usually thought to transport insoluble chemical species from the boundary layer to the upper troposphere and to rain out highly soluble species By using a non hydrostatic three dimensional convective cloud model coupled to a simple chemical reaction mechanism we examine the importance of aqueous chemistry microphysical processes and modi ed photolysis rates...

Environmental Research Letters, 2009

We develop and apply a mechanistic model for the study and prediction of volatile chemical partit... more We develop and apply a mechanistic model for the study and prediction of volatile chemical partitioning during wet growth of a hailstone. The model estimates the fraction of a chemical's mass in the impinging drops that is retained in a two-phase hailstone. It is derived from mass and rate balances over solute and water for steady accretion conditions. We applied the model using a modified Monte Carlo ensemble simulation approach to study the impact of chemical, environmental, and hail-specific input variables on the predicted retention fraction for six atmospherically relevant volatile chemical species, sulfur dioxide, hydrogen peroxide, ammonia, nitric acid, formaldehyde, and formic acid. Individual input variables found to significantly influence retention are the ice-liquid interface supercooling, the liquid water content of the hail, and the effective Henry's constant. The retention fraction increased with increasing values of these variables. Conversely, the ice-liquid distribution coefficient and hail diameter were found to have negligible effects on solute retention. The overall range of simulated retention fraction was from 1 × 10 −8 to 1, while ensemble mean retentions for fixed values of individual input variables ranged from 9 × 10 −7 to 0.3. No single variable was found to control the extremes; rather they are due to combinations of model input variables.

Agu Fall Meeting Abstracts, Dec 1, 2003

Thunderstorms can significantly impact chemical distributions in the troposphere by 1) redistribu... more Thunderstorms can significantly impact chemical distributions in the troposphere by 1) redistribution of air and hydrometeors containing trace chemicals and 2) providing a multi-phase environment for chemical phase changes and reactions. Interactions between ice-containing hydrometeors and chemicals are not well understood. Laboratory and field measurements of chemical partitioning during freezing provide greatly varying estimates of the retention efficiency of volatile solutes. In this work, we develop the theory of volatile chemical partitioning during hydrometeor freezing (termed 'freezing retention'), apply it for a variety of freezing conditions and chemicals, and compare the results to available experimental data. By analyzing the hydrometeor-scale processes involved in retention for non-rime freezing, dry-growth riming, and wet-growth riming, we investigated the factors that control it. For non-rime freezing, we developed a theoretical dimensionless number to indicate retention, derived its dependence on conditions and chemical properties, and calculated its value for several freezing cases for SO2, H2O2, NH3, and HNO3. Retention is apparently highly chemical specific, controlled largely by the effective Henry's constant (and hence the drop pH for dissociating chemicals). Chemicals with high effective Henry's constants (HNO3) will be fully retained during freezing, while chemicals with lower effective Henry's constants (SO2) will undergo some loss. For chemicals that undergo loss, the degree of retention depends on freezing conditions. Retention likely increases with decreasing temperature and exhibits a maximum at intermediate drop sizes and ventilation. For dry-growth riming, we extended the development to predict retention and compared predicted values to experimental data from several measurement studies. The model agrees well with the data and provides a quantitative explanation for the differences in measured retention. For wet-growth riming, we developed a steady-state retention model. It suggests retention is dependent on the fraction unfrozen water in the riming hydrometeor. This work provides theory-based hypotheses regarding the dependence of retention on physical factors and chemical properties that can be used to develop robust parameterization in cloud models.

In this dissertation, I investigate volatile chemical partitioning during hydrometeor freezing (t... more In this dissertation, I investigate volatile chemical partitioning during hydrometeor freezing (termed 'freezing retention'). Three-dimensional convective cloud simulations of soluble tracer and reactive chemical redistribution were performed for one field project storm. Two bounding parameterizations of freezing retention, (1) complete solute degassing from the solid hydrometeor and (2) complete solute retention, were compared. Retention during freezing led to more scavenging, more ground deposition, and less upward vertical transport of moderately to highly soluble species (Henry's constants greater than 10 5 M/atm). Sedimentation in hail and rain played a significant role in species redistribution. By analyzing the hydrometeor-scale processes involved in retention for non-rime freezing, dry-growth riming, and wet-growth riming, I investigated the factors that control it. For non-rime freezing, I developed a theoretical dimensionless number to indicate retention, de...

Interactions of chemicals with the ice phase in tropospheric clouds are poorly understood. Recent... more Interactions of chemicals with the ice phase in tropospheric clouds are poorly understood. Recent research indicates that volatile chemical partitioning during cloud hydrometeor freezing and riming may significantly impact cloud transport of soluble chemicals (e.g. HNO3, H2O2, SO2, aldehydes, and carboxylic acids) important to acid precipitation, the oxidizing capacity of the troposphere, and global climate change. In previous work, we have developed theory-based models and parameterizations of chemical partitioning during non-rime freezing and dry-growth riming. In this work, we develop a steady-state model for partitioning during wet-growth riming. Our model is adapted from a model used to predict the salinity of sea-spray ice and is based on solute mass and rate balances over a wet-growth riming hail particle. It accounts for drop impingement on the hydrometeor, hail growth, evaporation from hail, and shedding of liquid water. It also accounts for chemical partitioning between the water, air, and ice phases. Our model predicts that the retention efficiency (the ratio of a solute's mass in hail to that in the impinging supercooled drops) for wet-growth riming will be a function of the liquid water content of the hail, the solute effective Henry's law constant, the effective ice-water distribution coefficient, and the rates of impingement, growth, and shedding. Application of this model within cloud-scale convective storm simulations will help elucidate the impacts of cloud transport and processing on tropospheric chemistry.

Proceedings of World Environmental and Water Resources Congress 2009 - World Environmental and Water Resources Congress 2009: Great Rivers, 2009

Florida. Her area of interests include the development of treatment technologies for inorganic co... more Florida. Her area of interests include the development of treatment technologies for inorganic contaminant remediation with a special emphasis on arsenic in drinking water and in landfill leachate; investigating the effect of climate change on mercury fate in aquatic environments; and understanding the effect of water storage containers on water quality in developing countries. She has an ongoing interest in multidisciplinary projects that encourage sustainable development and provide affordable and efficient technology to developing areas, especially with respect to improving water quality and reducing the incidence of water borne diseases and water related diseases and other health complications. She believes in holistic approaches to providing engineering solutions which incorporate women's perspectives and needs and which build local capacity. In Guyana, she works on projects with NGOs like WWF-Guianas,

ISEE Conference Abstracts, 2013

Background: Air pollutant concentrations vary temporally and spatially and, as such, regional out... more Background: Air pollutant concentrations vary temporally and spatially and, as such, regional outdoor air monitors do a poor job of representing personal exposures indoors and outdoors. Because par...

Background Hazardous air pollutants (HAP) have been associated with a wide variety of adverse hea... more Background Hazardous air pollutants (HAP) have been associated with a wide variety of adverse health effects, from minor irritation of respiratory tissues to chronic asthma. Formaldehyde, a volatile organic HAP, present abundantly in the lower atmosphere is known to cause serious health effects. Health impact assessments (HIA) for criteria pollutants are routinely performed by United States Environmental Protection Agency (USEPA) using Benefits Mapping Analysis Program (BenMAP). BenMAP can be modified to perform local HIA for formaldehyde using local data. Study Purpose The main objective of this research is to develop a method which can estimate impact on health outcomes due to change in local formaldehyde. The primary focus is to develop concentration response (CR) functions necessary in BenMAP for performing formaldehyde HIA. Methodology Detailed review of published literature on health effects of Formaldehyde and documentation on BenMAP was performed. Using published literature ...

The purpose of this research was to evaluate five transportation planning processes used in Flori... more The purpose of this research was to evaluate five transportation planning processes used in Florida to determine how greenhouse gas (GHG) emissions considerations can be incorporated into the processes. These included the federal metropolitan planning organization long range transportation planning process (MPO LRTP) and transportation improvement programming (TIP) with application of federal Clean Air Act (CAA) air quality conformity analysis;

Environmental Science & Technology, 2005

We investigate the impact on effective terrorism response of the viability degradation of biologi... more We investigate the impact on effective terrorism response of the viability degradation of biological weapons agents in the environment. We briefly review the scientific understanding and modeling of agent environmental viability degradation. In general, agent susceptibility to viability loss is greatest for vegetative bacteria, intermediate for viruses, and least for bacterial spores. Survival is greatest in soil and progressively decreases in the following environments: textiles, water, hard surfaces, and air. There is little detailed understanding of loss mechanisms. We analyze the time behavior and sensitivity of four mathematical models that are used to represent environmental viability degradation (the exponential, probability, and first-and second-order catastrophic decay models). The models behave similarly at short times (<30 min for our example case) but diverge to significantly different values at intermediate to long times. Hence, for a release event in which the majority of atmospheric exposure or deposition occurs over very short times, the current response models likely provide a good representation of the hazard. For longer time phenomena, including decontamination, the current model capabilities are likely insufficient. Finally, we implement each model in a simple numerical integration of anthrax dispersion, viability degradation, and dose response. Decay models spanning the current knowledge of airborne degradation result in vastly different predicted hazard areas. This confounds attempts to determine necessary medical and decontamination measures. Hence, the current level of understanding and representation of environmental viability degradation in response models is inadequate to inform appropriate emergency response measures.