Steve Mara - Academia.edu (original) (raw)

Papers by Steve Mara

AAAR 28th Annual Conference., Oct 26, 2009

AGU Fall Meeting Abstracts, Dec 1, 2019

AGU Fall Meeting Abstracts, Dec 1, 2019

Journal of the Air & Waste Management Association, Jun 7, 2016

This paper discusses results from a vehicular emissions research study of over 350 vehicles condu... more This paper discusses results from a vehicular emissions research study of over 350 vehicles conducted in three communities in Los Angeles, CA, in 2010 using vehicle chase measurements. The study explores the real-world emission behavior of light-duty gasoline vehicles, characterizes real-world super-emitters in the different regions, and investigates the relationship of on-road vehicle emissions with the socioeconomic status (SES) of the region. The study found that in comparison to a 2007 earlier study in a neighboring community, vehicle emissions for all measured pollutants had experienced a significant reduction over the years, with oxides of nitrogen (NO X) and black carbon (BC) emissions showing the largest reductions. Mean emission factors of the sampled vehicles in low-SES communities were roughly 2-3 times higher for NO X , BC, carbon monoxide, and ultrafine particles, and 4-11 times greater for fine particulate matter (PM 2.5) than for vehicles in the high-SES neighborhood. Further analysis indicated that the emission factors of vehicles within a technology group were also higher in low-SES communities compared to similar vehicles in the high-SES community, suggesting that vehicle age alone did not explain the higher vehicular emission in low-SES communities. Evaluation of the emission factor distribution found that emissions from 12% of the sampled vehicles were greater than five times the mean from all of the sampled fleet, and these vehicles were consequently categorized as "real-world super-emitters." Low-SES communities had approximately twice as many super-emitters for most of the pollutants as compared to the high-SES community. Vehicle emissions calculated using model-year-specific average fuel consumption assumptions suggested that approximately 5% of the sampled vehicles accounted for nearly half of the total CO, PM 2.5 , and UFP emissions, and 15% of the vehicles were responsible for more than half of the total NO X and BC emissions from the vehicles sampled during the study. Implications: This study evaluated the real-world emission behavior and super-emitter distribution of light-duty gasoline vehicles in California, and investigated the relationship of on-road vehicle emissions with local socioeconomic conditions. The study observed a significant reduction in vehicle emissions for all measured pollutants when compared to an earlier study in Wilmington, CA, and found a higher prevalence of high-emitting vehicles in low-socioeconomic-status communities. As overall fleet emissions decrease from stringent vehicle emission regulations, a small fraction of the fleet may contribute to a disproportionate share of the overall on-road vehicle emissions. Therefore, this work will have important implications for improving air quality and public health, especially in low-SES communities.

Science of The Total Environment, Mar 1, 2019

Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings th... more Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings the pollution plume can extend hundreds of meters into surrounding neighborhoods. Solid sound walls and vegetation barriers are commonly used to mitigate noise, but they also help mitigate near-road air pollution. Here we assess the effectiveness of barriers consisting of vegetation only and of a combination of vegetation and a solid sound wall (combination barrier) in reducing pollution concentrations downwind of roads, under stable atmospheric stability and calm to light wind conditions. Because there was no practical (no barrier) control site in the area, we primarily compare the two barrier types to each other and explore the importance of atmospheric conditions. Using measurements collected with a mobile platform, we develop concentration decay profiles of ultrafine and fine particles, oxides of nitrogen (NO and NO 2) and carbon monoxide downwind of a freeway in California with different barrier configurations and meteorological conditions. Diurnally averaged data collected with passive samplers indicate that pollution from morning rush hour has about equal impact as the entire remainder of the day, because of differences in atmospheric dispersion as the day progresses. Under calm and stable atmospheric conditions (wind speed < 0.6 m/s); a vegetation-only barrier was more effective than a combination barrier with a total height that was somewhat lower than the vegetation-only barrier, by 10-24 % in the first 160 m downwind. Under light winds (above ~ 0.6 but below 3 m/s) and stable conditions, the combination barrier was more effective the vegetation barrier alone, by 6-33%, in the first 160 m from the barrier. The average particle size downwind of the vegetation-only barrier was larger than downwind of the combination barrier, indicating that particle deposition plays an important role in the reductions observed downwind of vegetation. Our results are consistent with the notion that at low wind speeds, vegetation acts as an effective barrier. Overall, adding vegetation alone or to an *

Atmospheric Environment, Dec 1, 2012

h i g h l i g h t s < Pollutant plumes from major roadways extend up to 2 km under stable conditi... more h i g h l i g h t s < Pollutant plumes from major roadways extend up to 2 km under stable conditions. < Wide area impacts of freeway plumes are commonly observed in the SoCAB. < Dilution rate coefficients in stable atmospheres are less than a tenth of daytime. < Decay rates of UFP vary with size, changing size distributions. < Mixed fleet emissions of UFP for a given traffic flow have decreased over time.

AGU Fall Meeting Abstracts, Dec 1, 2019

AGU Fall Meeting Abstracts, Dec 1, 2019

The statement and conclusion in the Report are those of the contractor and not necessarily those ... more The statement and conclusion in the Report are those of the contractor and not necessarily those of the California Air Resource Board. The mention of commercial products, their source, or their use in connection with material reported herein is not to be construed as actual or implied endorsement of such products. ACKKNOWLEGEMENTS

Atmospheric Environment, 2022

Air Pollution and Health, 2010

Science of The Total Environment, 2018

Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings th... more Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings the pollution plume can extend hundreds of meters into surrounding neighborhoods. Solid sound walls and vegetation barriers are commonly used to mitigate noise, but they also help mitigate near-road air pollution. Here we assess the effectiveness of barriers consisting of vegetation only and of a combination of vegetation and a solid sound wall (combination barrier) in reducing pollution concentrations downwind of roads, under stable atmospheric stability and calm to light wind conditions. Because there was no practical (no barrier) control site in the area, we primarily compare the two barrier types to each other and explore the importance of atmospheric conditions. Using measurements collected with a mobile platform, we develop concentration decay profiles of ultrafine and fine particles, oxides of nitrogen (NO and NO 2) and carbon monoxide downwind of a freeway in California with different barrier configurations and meteorological conditions. Diurnally averaged data collected with passive samplers indicate that pollution from morning rush hour has about equal impact as the entire remainder of the day, because of differences in atmospheric dispersion as the day progresses. Under calm and stable atmospheric conditions (wind speed < 0.6 m/s); a vegetation-only barrier was more effective than a combination barrier with a total height that was somewhat lower than the vegetation-only barrier, by 10-24 % in the first 160 m downwind. Under light winds (above ~ 0.6 but below 3 m/s) and stable conditions, the combination barrier was more effective the vegetation barrier alone, by 6-33%, in the first 160 m from the barrier. The average particle size downwind of the vegetation-only barrier was larger than downwind of the combination barrier, indicating that particle deposition plays an important role in the reductions observed downwind of vegetation. Our results are consistent with the notion that at low wind speeds, vegetation acts as an effective barrier. Overall, adding vegetation alone or to an *

Journal of the Air & Waste Management Association (1995), Oct 7, 2016

This paper discusses results from a vehicular emissions research study of over 350 vehicles condu... more This paper discusses results from a vehicular emissions research study of over 350 vehicles conducted in three communities in Los Angeles, California in 2010 using vehicle chase measurements. The study expounds the real-world emission behavior of light-duty gasoline vehicles, characterizes real-world super-emitters in the different regions, and investigates the relationship of on-road vehicle emissions with the socioeconomic status (SES) of the region. The study found that in comparison to a 2007 earlier study in a neighboring community (Park et al., 2011), vehicle emissions for all measured pollutants had experienced a significant reduction over the years, with oxides of nitrogen (NOX) and black carbon (BC) emissions showing the largest reductions. Mean emission factors of the sampled vehicles in low-SES communities were roughly 2-3 times higher for NOX, BC, carbon monoxide, and ultrafine particles, and 4-11 times greater for fine particulate matter (PM2.5) than vehicles in the hig...

Journal of the Air & Waste Management Association, 2014

Measuring greenhouse gas (GHG) source emissions provides data for validation of GHG inventories, ... more Measuring greenhouse gas (GHG) source emissions provides data for validation of GHG inventories, which provide the foundation for climate change mitigation. Two Toyota RAV4 electric vehicles were outfitted with high-precision instrumentation to determine spatial and temporal resolution of GHGs (e.g., nitrous oxide, methane [CH 4 ], and carbon dioxide [CO 2 ]), and other gaseous species and particulate metrics found near emission sources. Mobile measurement platform (MMP) analytical performance was determined over relevant measurement time scales. Pollutant residence times through the sampling configuration were measured, ranging from 3 to 11 sec, enabling proper time alignment for spatial measurement of each respective analyte. Linear response range for GHG analytes was assessed across expected mixing ratio ranges, showing minimal regression and standard error differences between 5, 10, 30, and 60 sec sampling intervals and negligible differences between the two MMPs. GHG instrument drift shows deviation of less than 0.8% over a 24-hr measurement period. These MMPs were utilized in tracer-dilution experiments at a California landfill and natural gas compressor station (NGCS) to quantify CH 4 emissions. Replicate landfill measurements during October 2009 yielded annual CH 4 emissions estimates of 0.10 ± 0.01, 0.11 ± 0.01, and 0.12 ± 0.02 million tonnes of CO 2 equivalent (MTCO 2 E). These values compare favorably to California GHG Emissions Inventory figures for 2007, 2008, and 2009 of 0.123, 0.125, and 0.126 MTCO 2 E/yr, respectively, for this facility. Measurements to quantify NGCS boosting facility-wide emissions, during June 2010 yielded an equivalent of 5400 ± 100 TCO 2 E/yr under steady-state operation. However, measurements during condensate transfer without operational vapor recovery yield an instantaneous emission rate of 2-4 times greater, but was estimated to only add 12 TCO 2 E/yr overall. This work displays the utility for mobile GHG measurements to validate existing measurement and modeling approaches, so emission inventory values can be confirmed and associated uncertainties reduced. Implications: Measuring greenhouse gas (GHG) source emissions provides data and validation for GHG inventories, the foundation for climate change mitigation. Mobile measurement platforms with robust analytical instrumentation completed tracerdilution experiments in California at a landfill and natural gas compressor station (NGCS) to quantify CH 4 emissions. Data collected for landfill CH 4 agree with the current California emissions inventory, while NGCS data show the possible variability from this type of facility. This work displays the utility of mobile GHG measurements to validate existing measurement and modeling approaches, such that emission inventory values can be confirmed, associated uncertainties reduced, and mitigation efforts quantified.

Environmental Science & Technology, 2009

Real time air pollutant concentrations were measured downwind of Santa Monica Airport (SMA), usin... more Real time air pollutant concentrations were measured downwind of Santa Monica Airport (SMA), using an electric vehicle mobile platform equipped with fast response instruments in spring and summer of 2008. SMA is a general aviation airport operated for private aircraft and corporate jets in Los Angeles County, California. An impact area of elevated ultrafine particle (UFP) concentrations was observed extending beyond 660 m downwind and 250 m perpendicular to the wind on the downwind side of SMA. Aircraft operations resulted in average UFP concentrations elevated by factors of 10 and 2.5 at 100 and 660 m downwind, respectively, over background levels. The long downwind impact distance (i.e., compared to nearby freeways at the same time of day) is likely primarily due to the large volumes of aircraft emissions containing higher initial concentrations of UFP than on-road vehicles. Aircraft did not appreciably elevate average levels of black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (PB-PAH), although spikes in concentration of these pollutants were observed associated with jet takeoffs. Jet departures resulted in peak 60-s average concentrations of up to 2.2 × 10 6 cm-3 , 440 ng m-3 , and 30 µg m-3 for UFP, PB-PAH, and BC, respectively, 100 m downwind of the takeoff area. These peak levels were elevated by factors of 440, 90, and 100 compared to background concentrations. Peak UFP concentrations were reasonably correlated (r 2) 0.62) with fuel consumption rates associated with aircraft departures, estimated from aircraft weights and acceleration rates. UFP concentrations remained elevated for extended periods associated particularly with jet departures, but also with jet taxi and idle, and operations of propeller aircraft. UFP measured downwind of SMA had a median mode of about 11 nm (electric mobility diameter), which was about half of the 22 nm median mode associated with UFP from heavy duty diesel trucks. The observation of highly elevated ultrafine particle concentrations in a large residential area downwind of this local airport has potential health implications for persons living near general aviation airports.

Environmental Science & Technology, 2014

Measurements on truck-dominated freeways in southern California have offered a unique opportunity... more Measurements on truck-dominated freeways in southern California have offered a unique opportunity to track emission changes that have occurred due to the implementation of local and state regulations affecting heavy-duty diesel trucks. These regulations have accelerated fleet turnover to cleaner and newer trucks. In this study, a mobile platform was used to measure nitrogen oxides (NO X), black carbon (BC), and ultrafine particles (UFPs) on diesel-dominated southern California freeways. Fleet-averaged fuel-based emission factors were calculated for diesel trucks and the results showed NO X and BC emissions were reduced by 40% or more between 2009 and 2011, but there were no statistically significant reductions for UFP. Technologies associated with these new trucks, mainly diesel particulate filters, have changed the physical characteristics of diesel particulate, shifting the size distribution of such particles to smaller modes (10−20 nm). In addition, integration of 2007 MY trucks into the fleet was also observed in on-road ratios of nitrogen dioxide (NO 2) and NO X. NO 2 /NO X ratios steadily increased from 0.23 ± 0.06 in 2009 to 0.30 ± 0.03 in 2010 but plateaued and declined in 2011.

Atmospheric Environment, 2010

Increasing epidemiological evidence has established an association between a host of adverse heal... more Increasing epidemiological evidence has established an association between a host of adverse health effects and exposure to ambient particulate matter (PM) and co-pollutants, especially those emitted from motor vehicles. Although PM and their co-pollutants dispersion profiles near the open freeway have been extensively characterized by means of both experimental measurements and numerical simulations in recent years, such investigations near freeways with roadside barriers have not been well documented in the literature. A few previous studies suggested that the presence of roadside structures, such as noise barriers and vegetation, may impact the decay of pollutant concentrations downwind of the freeway by limiting the initial dispersion of traffic emissions and increasing their vertical mixing due to the upward deflection of airflow. Since the noise barriers are now common roadside features of the freeways, particularly those running through populated urban areas, it is pertinent to investigate the impact of their presence on the particles and co-pollutants concentrations in areas adjacent to busy roadways. This study investigated two highly trafficked freeways (I-710 and I-5) in Southern California, with two sampling sites for each freeway, one with and the other without the roadside noise barriers. Particle size distributions and co-pollutants concentrations were measured in the immediate proximity of freeways and at different distances downwind of the freeways. The results showed the formation of a "concentration deficit" zone in the immediate vicinity of the freeway with the presence of roadside noise barrier, followed by a surge of pollutant concentrations further downwind at 80e100 m away from freeway. The particle and co-pollutants concentrations reach background levels at farther distances of 250e400 m compared to 150e200 m at the sites without roadside noise barriers.

Atmospheric Environment, 2012

We observed elevated air pollutant concentrations, especially of ultrafine particles (UFP), black... more We observed elevated air pollutant concentrations, especially of ultrafine particles (UFP), black carbon (BC) and NO, across the residential neighborhood of the Boyle Heights Community (BH) of Los Angeles, California. Using an electric vehicle mobile platform equipped with fast response instruments, real-time air pollutant concentrations were measured in BH in spring and summer of 2008. Pollutant concentrations varied significantly in the two seasons, on different days, and by time of day, with an overall average UFP concentration in the residential areas of w33 000 cm À3. The averaged UFP, BC, and NO concentrations measured on Soto St, a major surface street in BH, were 57 000 cm À3 , 5.1 mg m À3 , and 67 ppb, respectively. Concentrations of UFP across the residential areas in BH were nearly uniform spatially, in contrast to other areas in the greater metropolitan area of Los Angeles where UFP concentrations exhibit strong gradients downwind of roadways. We attribute this "UFP cloud" to high traffic volumes, including heavy duty diesel trucks on the freeways which surround and traverse BH, and substantial numbers of high-emitting vehicles (HEVs) on the surface streets traversing BH. Additionally, the high density of stop signs and lights and short block lengths, requiring frequent accelerations of vehicles, may contribute. The data also support a role for photochemical production of UFP in the afternoon. UFP concentration peaks (5 s average) of up to 9 million particles cm À3 were also observed immediately behind HEVs when they accelerated from stop lights in the BH neighborhood and areas immediately adjacent. Although encounters with HEV during mornings accounted for only about 6% and 17% of time spent monitoring residential areas and major surface streets, HEV contributed to about 28% and 53% of total ultrafine particles measured on the route, respectively. The observation of elevated pollutant concentrations across the Boyle Heights community highlights how multiple factors combine to create high pollutant levels, and has important human exposure assessment implications, including the potential utility of our data as inputs to epidemiological studies.

Atmospheric Environment, 2013

ABSTRACT A mobile monitoring platform (MMP) was used to measure real-time air pollutant concentra... more ABSTRACT A mobile monitoring platform (MMP) was used to measure real-time air pollutant concentrations in different built environments of Boyle Heights (BH, a lower-income community enclosed by several freeways); Downtown Los Angeles (DTLA, adjacent to BH with taller buildings and surrounded by several freeways); and West Los Angeles (WLA, an affluent community traversed by two freeways) in summer afternoons of 2008 and 2011 (only for WLA). Significant inter-community and less significant but observable intra-community differences in traffic-related pollutant concentrations were observed both in the residential neighborhoods studied and on their arterial roadways between BH, DTLA, and WLA, particularly for ultrafine particles (UFP). HEV, defined as vehicles creating plumes with concentrations more than three standard deviations from the adjusted local baseline, were encountered during 6-13% of sampling time, during which they accounted for 17-55% of total UFP concentrations both on arterial roadways and in residential neighborhoods. If instead a single threshold value is used to define HEVs in all areas, HEV&amp;#39;s were calculated to make larger contributions to UFP concentrations in BH than other communities by factors of 2-10 or more. Santa Monica Airport located in WLA appears to be a significant source for elevated UFP concentrations in nearby residential neighborhoods 80-400 m downwind. In the WLA area, we also showed, on a neighborhood scale, striking and immediate reductions in particulate pollution (˜70% reductions in both UFP and, somewhat surprisingly, PM2.5), corresponding to dramatic decreases in traffic densities during an I-405 closure event (&amp;quot;Carmageddon&amp;quot;) compared to non-closure Saturday levels. Although pollution reduction due to decreased traffic is not unexpected, this dramatic improvement in particulate pollution provides clear evidence air quality can be improved through strategies such as heavy-duty-diesel vehicle retrofits, earlier retirement of HEV, and transition to electric vehicles and alternative fuels, with corresponding benefits for public health.

Aaar 28th Annual Conference, Oct 26, 2009

AAAR 28th Annual Conference., Oct 26, 2009

AGU Fall Meeting Abstracts, Dec 1, 2019

AGU Fall Meeting Abstracts, Dec 1, 2019

Journal of the Air & Waste Management Association, Jun 7, 2016

This paper discusses results from a vehicular emissions research study of over 350 vehicles condu... more This paper discusses results from a vehicular emissions research study of over 350 vehicles conducted in three communities in Los Angeles, CA, in 2010 using vehicle chase measurements. The study explores the real-world emission behavior of light-duty gasoline vehicles, characterizes real-world super-emitters in the different regions, and investigates the relationship of on-road vehicle emissions with the socioeconomic status (SES) of the region. The study found that in comparison to a 2007 earlier study in a neighboring community, vehicle emissions for all measured pollutants had experienced a significant reduction over the years, with oxides of nitrogen (NO X) and black carbon (BC) emissions showing the largest reductions. Mean emission factors of the sampled vehicles in low-SES communities were roughly 2-3 times higher for NO X , BC, carbon monoxide, and ultrafine particles, and 4-11 times greater for fine particulate matter (PM 2.5) than for vehicles in the high-SES neighborhood. Further analysis indicated that the emission factors of vehicles within a technology group were also higher in low-SES communities compared to similar vehicles in the high-SES community, suggesting that vehicle age alone did not explain the higher vehicular emission in low-SES communities. Evaluation of the emission factor distribution found that emissions from 12% of the sampled vehicles were greater than five times the mean from all of the sampled fleet, and these vehicles were consequently categorized as "real-world super-emitters." Low-SES communities had approximately twice as many super-emitters for most of the pollutants as compared to the high-SES community. Vehicle emissions calculated using model-year-specific average fuel consumption assumptions suggested that approximately 5% of the sampled vehicles accounted for nearly half of the total CO, PM 2.5 , and UFP emissions, and 15% of the vehicles were responsible for more than half of the total NO X and BC emissions from the vehicles sampled during the study. Implications: This study evaluated the real-world emission behavior and super-emitter distribution of light-duty gasoline vehicles in California, and investigated the relationship of on-road vehicle emissions with local socioeconomic conditions. The study observed a significant reduction in vehicle emissions for all measured pollutants when compared to an earlier study in Wilmington, CA, and found a higher prevalence of high-emitting vehicles in low-socioeconomic-status communities. As overall fleet emissions decrease from stringent vehicle emission regulations, a small fraction of the fleet may contribute to a disproportionate share of the overall on-road vehicle emissions. Therefore, this work will have important implications for improving air quality and public health, especially in low-SES communities.

Science of The Total Environment, Mar 1, 2019

Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings th... more Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings the pollution plume can extend hundreds of meters into surrounding neighborhoods. Solid sound walls and vegetation barriers are commonly used to mitigate noise, but they also help mitigate near-road air pollution. Here we assess the effectiveness of barriers consisting of vegetation only and of a combination of vegetation and a solid sound wall (combination barrier) in reducing pollution concentrations downwind of roads, under stable atmospheric stability and calm to light wind conditions. Because there was no practical (no barrier) control site in the area, we primarily compare the two barrier types to each other and explore the importance of atmospheric conditions. Using measurements collected with a mobile platform, we develop concentration decay profiles of ultrafine and fine particles, oxides of nitrogen (NO and NO 2) and carbon monoxide downwind of a freeway in California with different barrier configurations and meteorological conditions. Diurnally averaged data collected with passive samplers indicate that pollution from morning rush hour has about equal impact as the entire remainder of the day, because of differences in atmospheric dispersion as the day progresses. Under calm and stable atmospheric conditions (wind speed < 0.6 m/s); a vegetation-only barrier was more effective than a combination barrier with a total height that was somewhat lower than the vegetation-only barrier, by 10-24 % in the first 160 m downwind. Under light winds (above ~ 0.6 but below 3 m/s) and stable conditions, the combination barrier was more effective the vegetation barrier alone, by 6-33%, in the first 160 m from the barrier. The average particle size downwind of the vegetation-only barrier was larger than downwind of the combination barrier, indicating that particle deposition plays an important role in the reductions observed downwind of vegetation. Our results are consistent with the notion that at low wind speeds, vegetation acts as an effective barrier. Overall, adding vegetation alone or to an *

Atmospheric Environment, Dec 1, 2012

h i g h l i g h t s < Pollutant plumes from major roadways extend up to 2 km under stable conditi... more h i g h l i g h t s < Pollutant plumes from major roadways extend up to 2 km under stable conditions. < Wide area impacts of freeway plumes are commonly observed in the SoCAB. < Dilution rate coefficients in stable atmospheres are less than a tenth of daytime. < Decay rates of UFP vary with size, changing size distributions. < Mixed fleet emissions of UFP for a given traffic flow have decreased over time.

AGU Fall Meeting Abstracts, Dec 1, 2019

AGU Fall Meeting Abstracts, Dec 1, 2019

The statement and conclusion in the Report are those of the contractor and not necessarily those ... more The statement and conclusion in the Report are those of the contractor and not necessarily those of the California Air Resource Board. The mention of commercial products, their source, or their use in connection with material reported herein is not to be construed as actual or implied endorsement of such products. ACKKNOWLEGEMENTS

Atmospheric Environment, 2022

Air Pollution and Health, 2010

Science of The Total Environment, 2018

Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings th... more Pollutants in tailpipe emissions can be highly elevated around roadways, and in early mornings the pollution plume can extend hundreds of meters into surrounding neighborhoods. Solid sound walls and vegetation barriers are commonly used to mitigate noise, but they also help mitigate near-road air pollution. Here we assess the effectiveness of barriers consisting of vegetation only and of a combination of vegetation and a solid sound wall (combination barrier) in reducing pollution concentrations downwind of roads, under stable atmospheric stability and calm to light wind conditions. Because there was no practical (no barrier) control site in the area, we primarily compare the two barrier types to each other and explore the importance of atmospheric conditions. Using measurements collected with a mobile platform, we develop concentration decay profiles of ultrafine and fine particles, oxides of nitrogen (NO and NO 2) and carbon monoxide downwind of a freeway in California with different barrier configurations and meteorological conditions. Diurnally averaged data collected with passive samplers indicate that pollution from morning rush hour has about equal impact as the entire remainder of the day, because of differences in atmospheric dispersion as the day progresses. Under calm and stable atmospheric conditions (wind speed < 0.6 m/s); a vegetation-only barrier was more effective than a combination barrier with a total height that was somewhat lower than the vegetation-only barrier, by 10-24 % in the first 160 m downwind. Under light winds (above ~ 0.6 but below 3 m/s) and stable conditions, the combination barrier was more effective the vegetation barrier alone, by 6-33%, in the first 160 m from the barrier. The average particle size downwind of the vegetation-only barrier was larger than downwind of the combination barrier, indicating that particle deposition plays an important role in the reductions observed downwind of vegetation. Our results are consistent with the notion that at low wind speeds, vegetation acts as an effective barrier. Overall, adding vegetation alone or to an *

Journal of the Air & Waste Management Association (1995), Oct 7, 2016

This paper discusses results from a vehicular emissions research study of over 350 vehicles condu... more This paper discusses results from a vehicular emissions research study of over 350 vehicles conducted in three communities in Los Angeles, California in 2010 using vehicle chase measurements. The study expounds the real-world emission behavior of light-duty gasoline vehicles, characterizes real-world super-emitters in the different regions, and investigates the relationship of on-road vehicle emissions with the socioeconomic status (SES) of the region. The study found that in comparison to a 2007 earlier study in a neighboring community (Park et al., 2011), vehicle emissions for all measured pollutants had experienced a significant reduction over the years, with oxides of nitrogen (NOX) and black carbon (BC) emissions showing the largest reductions. Mean emission factors of the sampled vehicles in low-SES communities were roughly 2-3 times higher for NOX, BC, carbon monoxide, and ultrafine particles, and 4-11 times greater for fine particulate matter (PM2.5) than vehicles in the hig...

Journal of the Air & Waste Management Association, 2014

Measuring greenhouse gas (GHG) source emissions provides data for validation of GHG inventories, ... more Measuring greenhouse gas (GHG) source emissions provides data for validation of GHG inventories, which provide the foundation for climate change mitigation. Two Toyota RAV4 electric vehicles were outfitted with high-precision instrumentation to determine spatial and temporal resolution of GHGs (e.g., nitrous oxide, methane [CH 4 ], and carbon dioxide [CO 2 ]), and other gaseous species and particulate metrics found near emission sources. Mobile measurement platform (MMP) analytical performance was determined over relevant measurement time scales. Pollutant residence times through the sampling configuration were measured, ranging from 3 to 11 sec, enabling proper time alignment for spatial measurement of each respective analyte. Linear response range for GHG analytes was assessed across expected mixing ratio ranges, showing minimal regression and standard error differences between 5, 10, 30, and 60 sec sampling intervals and negligible differences between the two MMPs. GHG instrument drift shows deviation of less than 0.8% over a 24-hr measurement period. These MMPs were utilized in tracer-dilution experiments at a California landfill and natural gas compressor station (NGCS) to quantify CH 4 emissions. Replicate landfill measurements during October 2009 yielded annual CH 4 emissions estimates of 0.10 ± 0.01, 0.11 ± 0.01, and 0.12 ± 0.02 million tonnes of CO 2 equivalent (MTCO 2 E). These values compare favorably to California GHG Emissions Inventory figures for 2007, 2008, and 2009 of 0.123, 0.125, and 0.126 MTCO 2 E/yr, respectively, for this facility. Measurements to quantify NGCS boosting facility-wide emissions, during June 2010 yielded an equivalent of 5400 ± 100 TCO 2 E/yr under steady-state operation. However, measurements during condensate transfer without operational vapor recovery yield an instantaneous emission rate of 2-4 times greater, but was estimated to only add 12 TCO 2 E/yr overall. This work displays the utility for mobile GHG measurements to validate existing measurement and modeling approaches, so emission inventory values can be confirmed and associated uncertainties reduced. Implications: Measuring greenhouse gas (GHG) source emissions provides data and validation for GHG inventories, the foundation for climate change mitigation. Mobile measurement platforms with robust analytical instrumentation completed tracerdilution experiments in California at a landfill and natural gas compressor station (NGCS) to quantify CH 4 emissions. Data collected for landfill CH 4 agree with the current California emissions inventory, while NGCS data show the possible variability from this type of facility. This work displays the utility of mobile GHG measurements to validate existing measurement and modeling approaches, such that emission inventory values can be confirmed, associated uncertainties reduced, and mitigation efforts quantified.

Environmental Science & Technology, 2009

Real time air pollutant concentrations were measured downwind of Santa Monica Airport (SMA), usin... more Real time air pollutant concentrations were measured downwind of Santa Monica Airport (SMA), using an electric vehicle mobile platform equipped with fast response instruments in spring and summer of 2008. SMA is a general aviation airport operated for private aircraft and corporate jets in Los Angeles County, California. An impact area of elevated ultrafine particle (UFP) concentrations was observed extending beyond 660 m downwind and 250 m perpendicular to the wind on the downwind side of SMA. Aircraft operations resulted in average UFP concentrations elevated by factors of 10 and 2.5 at 100 and 660 m downwind, respectively, over background levels. The long downwind impact distance (i.e., compared to nearby freeways at the same time of day) is likely primarily due to the large volumes of aircraft emissions containing higher initial concentrations of UFP than on-road vehicles. Aircraft did not appreciably elevate average levels of black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (PB-PAH), although spikes in concentration of these pollutants were observed associated with jet takeoffs. Jet departures resulted in peak 60-s average concentrations of up to 2.2 × 10 6 cm-3 , 440 ng m-3 , and 30 µg m-3 for UFP, PB-PAH, and BC, respectively, 100 m downwind of the takeoff area. These peak levels were elevated by factors of 440, 90, and 100 compared to background concentrations. Peak UFP concentrations were reasonably correlated (r 2) 0.62) with fuel consumption rates associated with aircraft departures, estimated from aircraft weights and acceleration rates. UFP concentrations remained elevated for extended periods associated particularly with jet departures, but also with jet taxi and idle, and operations of propeller aircraft. UFP measured downwind of SMA had a median mode of about 11 nm (electric mobility diameter), which was about half of the 22 nm median mode associated with UFP from heavy duty diesel trucks. The observation of highly elevated ultrafine particle concentrations in a large residential area downwind of this local airport has potential health implications for persons living near general aviation airports.

Environmental Science & Technology, 2014

Measurements on truck-dominated freeways in southern California have offered a unique opportunity... more Measurements on truck-dominated freeways in southern California have offered a unique opportunity to track emission changes that have occurred due to the implementation of local and state regulations affecting heavy-duty diesel trucks. These regulations have accelerated fleet turnover to cleaner and newer trucks. In this study, a mobile platform was used to measure nitrogen oxides (NO X), black carbon (BC), and ultrafine particles (UFPs) on diesel-dominated southern California freeways. Fleet-averaged fuel-based emission factors were calculated for diesel trucks and the results showed NO X and BC emissions were reduced by 40% or more between 2009 and 2011, but there were no statistically significant reductions for UFP. Technologies associated with these new trucks, mainly diesel particulate filters, have changed the physical characteristics of diesel particulate, shifting the size distribution of such particles to smaller modes (10−20 nm). In addition, integration of 2007 MY trucks into the fleet was also observed in on-road ratios of nitrogen dioxide (NO 2) and NO X. NO 2 /NO X ratios steadily increased from 0.23 ± 0.06 in 2009 to 0.30 ± 0.03 in 2010 but plateaued and declined in 2011.

Atmospheric Environment, 2010

Increasing epidemiological evidence has established an association between a host of adverse heal... more Increasing epidemiological evidence has established an association between a host of adverse health effects and exposure to ambient particulate matter (PM) and co-pollutants, especially those emitted from motor vehicles. Although PM and their co-pollutants dispersion profiles near the open freeway have been extensively characterized by means of both experimental measurements and numerical simulations in recent years, such investigations near freeways with roadside barriers have not been well documented in the literature. A few previous studies suggested that the presence of roadside structures, such as noise barriers and vegetation, may impact the decay of pollutant concentrations downwind of the freeway by limiting the initial dispersion of traffic emissions and increasing their vertical mixing due to the upward deflection of airflow. Since the noise barriers are now common roadside features of the freeways, particularly those running through populated urban areas, it is pertinent to investigate the impact of their presence on the particles and co-pollutants concentrations in areas adjacent to busy roadways. This study investigated two highly trafficked freeways (I-710 and I-5) in Southern California, with two sampling sites for each freeway, one with and the other without the roadside noise barriers. Particle size distributions and co-pollutants concentrations were measured in the immediate proximity of freeways and at different distances downwind of the freeways. The results showed the formation of a "concentration deficit" zone in the immediate vicinity of the freeway with the presence of roadside noise barrier, followed by a surge of pollutant concentrations further downwind at 80e100 m away from freeway. The particle and co-pollutants concentrations reach background levels at farther distances of 250e400 m compared to 150e200 m at the sites without roadside noise barriers.

Atmospheric Environment, 2012

We observed elevated air pollutant concentrations, especially of ultrafine particles (UFP), black... more We observed elevated air pollutant concentrations, especially of ultrafine particles (UFP), black carbon (BC) and NO, across the residential neighborhood of the Boyle Heights Community (BH) of Los Angeles, California. Using an electric vehicle mobile platform equipped with fast response instruments, real-time air pollutant concentrations were measured in BH in spring and summer of 2008. Pollutant concentrations varied significantly in the two seasons, on different days, and by time of day, with an overall average UFP concentration in the residential areas of w33 000 cm À3. The averaged UFP, BC, and NO concentrations measured on Soto St, a major surface street in BH, were 57 000 cm À3 , 5.1 mg m À3 , and 67 ppb, respectively. Concentrations of UFP across the residential areas in BH were nearly uniform spatially, in contrast to other areas in the greater metropolitan area of Los Angeles where UFP concentrations exhibit strong gradients downwind of roadways. We attribute this "UFP cloud" to high traffic volumes, including heavy duty diesel trucks on the freeways which surround and traverse BH, and substantial numbers of high-emitting vehicles (HEVs) on the surface streets traversing BH. Additionally, the high density of stop signs and lights and short block lengths, requiring frequent accelerations of vehicles, may contribute. The data also support a role for photochemical production of UFP in the afternoon. UFP concentration peaks (5 s average) of up to 9 million particles cm À3 were also observed immediately behind HEVs when they accelerated from stop lights in the BH neighborhood and areas immediately adjacent. Although encounters with HEV during mornings accounted for only about 6% and 17% of time spent monitoring residential areas and major surface streets, HEV contributed to about 28% and 53% of total ultrafine particles measured on the route, respectively. The observation of elevated pollutant concentrations across the Boyle Heights community highlights how multiple factors combine to create high pollutant levels, and has important human exposure assessment implications, including the potential utility of our data as inputs to epidemiological studies.

Atmospheric Environment, 2013

ABSTRACT A mobile monitoring platform (MMP) was used to measure real-time air pollutant concentra... more ABSTRACT A mobile monitoring platform (MMP) was used to measure real-time air pollutant concentrations in different built environments of Boyle Heights (BH, a lower-income community enclosed by several freeways); Downtown Los Angeles (DTLA, adjacent to BH with taller buildings and surrounded by several freeways); and West Los Angeles (WLA, an affluent community traversed by two freeways) in summer afternoons of 2008 and 2011 (only for WLA). Significant inter-community and less significant but observable intra-community differences in traffic-related pollutant concentrations were observed both in the residential neighborhoods studied and on their arterial roadways between BH, DTLA, and WLA, particularly for ultrafine particles (UFP). HEV, defined as vehicles creating plumes with concentrations more than three standard deviations from the adjusted local baseline, were encountered during 6-13% of sampling time, during which they accounted for 17-55% of total UFP concentrations both on arterial roadways and in residential neighborhoods. If instead a single threshold value is used to define HEVs in all areas, HEV&amp;#39;s were calculated to make larger contributions to UFP concentrations in BH than other communities by factors of 2-10 or more. Santa Monica Airport located in WLA appears to be a significant source for elevated UFP concentrations in nearby residential neighborhoods 80-400 m downwind. In the WLA area, we also showed, on a neighborhood scale, striking and immediate reductions in particulate pollution (˜70% reductions in both UFP and, somewhat surprisingly, PM2.5), corresponding to dramatic decreases in traffic densities during an I-405 closure event (&amp;quot;Carmageddon&amp;quot;) compared to non-closure Saturday levels. Although pollution reduction due to decreased traffic is not unexpected, this dramatic improvement in particulate pollution provides clear evidence air quality can be improved through strategies such as heavy-duty-diesel vehicle retrofits, earlier retirement of HEV, and transition to electric vehicles and alternative fuels, with corresponding benefits for public health.

Aaar 28th Annual Conference, Oct 26, 2009