Serena Chung - Academia.edu (original) (raw)

Papers by Serena Chung

Global change will clearly have a significant impact on the environment. Among the concerns for f... more Global change will clearly have a significant impact on the environment. Among the concerns for future air quality in the United States, intercontinental transport of pollution has become increasingly important. In this study, we examined the effect of the changes in chemical boundary conditions, including the upper troposphere, and emissions from lightning and wildfires to produce ozone background concentrations within the continental US as the basis for developing an understanding of policy relevant background levels and how they may change in the future. Meteorological fields were downscaled from the results of the ECHAM5 global climate model using the Weather Research Forecast (WRF) model. Two nested domains were employed, one covering most of the Northern Hemisphere from eastern Asia to North America using 200k km grid cells (semi-hemispheric domain) and one covering the continental US using 36 km grid cells (CONUS). Meteorological results from WRF were used to drive the MEGAN ...

Geosci. Model Dev. Discuss., 2013

A pollen model that simulates the timing and production of wind-dispersed allergenic pollen by te... more A pollen model that simulates the timing and production of wind-dispersed allergenic pollen by terrestrial, temperate vegetation has been developed to quantify how pollen occurrence may be affected by climate change and to investigate how pollen can interact with anthropogenic pollutants to affect human health. The Simulator of the Timing and Nevada. Differences in the simulated timing and magnitude of pollen season for the selected allergenic species under current and future climate scenarios are presented. The results suggest that across all of the simulated species, pollen season starts an average of 5-6 days earlier under predicted future climatic conditions with an associated average annual domain-wide temperature increase of about 1 • C compared to 5 simulated current conditions. Differences in the amount of pollen produced under the two scenarios vary by species and are affected by the selected simulation period (1 March-30 June). Uncertainties associated with the STaMPS model and future model development plans are also discussed.

Biogeosciences, 2014

Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway dise... more Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway disease (AAD) in sensitive populations, and thus cause serious public health problems. Assessing these health impacts by linking the airborne pollen levels, concentrations of respirable allergenic material, and human allergenic response under current and future climate conditions is a key step toward developing preventive and adaptive actions. To that end, a regional-scale pollen emission and transport modeling framework was developed that treats allergenic pollens as non-reactive tracers within the WRF/CMAQ air-quality modeling system. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model was used to generate a daily pollen pool that can then be emitted into the atmosphere by wind. The STaMPS is driven by species-specific meteorological (temperature and/or precipitation) threshold conditions and is designed to be flexible with respect to its representation of vegetation species and plant functional types (PFTs). The hourly pollen emission flux was parameterized by considering the pollen pool, friction velocity, and wind threshold values. The dry deposition velocity of each species of pollen was estimated based on pollen grain size and density. An evaluation of the pollen modeling framework was conducted for southern California for the period from March to June 2010. This period coincided with observations by the University of Southern California's Children's Health Study (CHS), which included O3, PM2.5, and pollen count, as well as measurements of exhaled nitric oxide in study participants. Two nesting domains with horizontal resolutions of 12 km and 4 km were constructed, and six representative allergenic pollen genera were included: birch tree, walnut tree, mulberry tree, olive tree, oak tree, and brome grasses. Under the current parameterization scheme, the modeling framework tends to underestimate walnut and peak oak pollen concentrations, and tends to overestimate grass pollen concentrations. The model shows reasonable agreement with observed birch, olive, and mulberry tree pollen concentrations. Sensitivity studies suggest that the estimation of the pollen pool is a major source of uncertainty for simulated pollen concentrations. Achieving agreement between emission modeling and observed pattern of pollen releases is the key for successful pollen concentration simulations.

Acknowledgments This Report was submitted,in fulfillment of ARB contract number 02-322 ti- tled G... more Acknowledgments This Report was submitted,in fulfillment of ARB contract number 02-322 ti- tled Global Radiative Effect of Particulate Black Carbon by California Institute of Technology under the sponsorship,of the California Air Resources Board. Work was completed as of January 25, 2005. ii Contents

International Symposium on Erosion and Landscape Evolution (ISELE), 18-21 September 2011, Anchorage, Alaska, 2011

International Symposium on Erosion and Landscape Evolution (ISELE), 18-21 September 2011, Anchorage, Alaska, 2011

... ISELE Paper No 11023. St. Joseph, Mich.: ASABE. 8. Gillette, DA 1988. Threshold friction velo... more ... ISELE Paper No 11023. St. Joseph, Mich.: ASABE. 8. Gillette, DA 1988. Threshold friction velocities for dust production for agricultural soils. J. Geophys. Res. ... Res. 94: 2197-2206. 10. Gillette, D., and R. Passi.1988. Modeling dust emission caused by wind erosion. J. Geophys. ...

Global change will clearly have a significant impact on the environment. Among the concerns for f... more Global change will clearly have a significant impact on the environment. Among the concerns for future air quality in the United States, intercontinental transport of pollution has become increasingly important. In this study, we examined the effect of the changes in chemical boundary conditions, including the upper troposphere, and emissions from lightning and wildfires to produce ozone background concentrations within the continental US as the basis for developing an understanding of policy relevant background levels and how they may change in the future. Meteorological fields were downscaled from the results of the ECHAM5 global climate model using the Weather Research Forecast (WRF) model. Two nested domains were employed, one covering most of the Northern Hemisphere from eastern Asia to North America using 200k km grid cells (semi-hemispheric domain) and one covering the continental US using 36 km grid cells (CONUS). Meteorological results from WRF were used to drive the MEGAN ...

Transactions of the ASABE, 2013

Journal of the Air & Waste Management Association, 2012

The impact of climate change on surface-level ozone is examined through a multiscale modeling eff... more The impact of climate change on surface-level ozone is examined through a multiscale modeling effort that linked global and regional climate models to drive air quality model simulations. Results are quantified in terms of the relative response factor (RRF(E)), which estimates the relative change in peak ozone concentration for a given change in pollutant emissions (the subscript E is added to RRF to remind the reader that the RRF is due to emission changes only). A matrix of model simulations was conducted to examine the individual and combined effects offuture anthropogenic emissions, biogenic emissions, and climate on the RRF(E). For each member in the matrix of simulations the warmest and coolest summers were modeled for the present-day (1995-2004) and future (2045-2054) decades. A climate adjustment factor (CAF(C) or CAF(CB) when biogenic emissions are allowed to change with the future climate) was defined as the ratio of the average daily maximum 8-hr ozone simulated under a future climate to that simulated under the present-day climate, and a climate-adjusted RRF(EC) was calculated (RRF(EC) = RRF(E) x CAF(C)). In general, RRF(EC) > RRF(E), which suggests additional emission controls will be required to achieve the same reduction in ozone that would have been achieved in the absence of climate change. Changes in biogenic emissions generally have a smaller impact on the RRF(E) than does future climate change itself The direction of the biogenic effect appears closely linked to organic-nitrate chemistry and whether ozone formation is limited by volatile organic compounds (VOC) or oxides of nitrogen (NO(x) = NO + NO2). Regions that are generally NO(x) limited show a decrease in ozone and RRF(EC), while VOC-limited regions show an increase in ozone and RRF(EC). Comparing results to a previous study using different climate assumptions and models showed large variability in the CAF(CB). We present a methodology for adjusting the RRF to account for the influence of climate change on ozone. The findings of this work suggest that in some geographic regions, climate change has the potential to negate decreases in surface ozone concentrations that would otherwise be achieved through ozone mitigation strategies. In regions of high biogenic VOC emissions relative to anthropogenic NO(x) emissions, the impact of climate change is somewhat reduced, while the opposite is true in regions of high anthropogenic NO(x) emissions relative to biogenic VOC emissions. Further, different future climate realizations are shown to impact ozone in different ways.

Journal of Geophysical Research, 2007

JD_description.

Journal of Geophysical Research, 2007

Real-time forecasts of PM2.5 aerosol mass from seven air quality forecast models (AQFMs) are stat... more Real-time forecasts of PM2.5 aerosol mass from seven air quality forecast models (AQFMs) are statistically evaluated against observations collected in the northeastern United States and southeastern Canada from two surface networks and aircraft data during the summer of 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)/New England Air Quality Study (NEAQS) field campaign. The AIRNOW surface network

Journal of Geophysical Research, 2010

1] Soot aerosol particles (also called light-absorbing, black, or elemental carbon) are major con... more 1] Soot aerosol particles (also called light-absorbing, black, or elemental carbon) are major contributors to global warming through their absorption of solar radiation. When embedded in organic matter or sulfate, as is common in polluted areas such as over Mexico City (MC) and other megacities, their optical properties are affected by their shapes and positions within their host particles. However, large uncertainties remain regarding those variables and how they affect warming by soot. Using electron tomography with a transmission electron microscope, three-dimensional (3-D) images of individual soot particles embedded within host particles collected from MC and its surroundings were obtained. From those 3-D images, we calculated the optical properties using a discrete dipole approximation. Many soot particles have open, chainlike shapes even after being surrounded by organic matter and are located in off-center positions within their host materials. Such embedded soot absorbs sunlight less efficiently than if compact and located near the center of its host particle. In the case of our MC samples, their contribution to direct radiative forcing is ∼20% less than if they had a simple core-shell shape, which is the shape assumed in many climate models. This study shows that the shapes and positions of soot within its host particles have an important effect on particle optical properties and should be recognized as potentially important variables when evaluating global climate change.

Journal of Geophysical Research, 2006

Received 12 January 2006; revised 24 April 2006; accepted 16 May 2006; published 29 August 2006. ... more Received 12 January 2006; revised 24 April 2006; accepted 16 May 2006; published 29 August 2006. [1] A single-particle soot photometer (SP2) was flown on a NASA WB-57F high-altitude research aircraft in November 2004 from Houston, Texas. The SP2 uses laser-induced ...

Journal of Geophysical Research, 2005

1] The equilibrium climate effect of direct radiative forcing of anthropogenic black carbon (BC) ... more 1] The equilibrium climate effect of direct radiative forcing of anthropogenic black carbon (BC) is examined by 100-year simulations in the Goddard Institute for Space Studies General Circulation Model II-prime coupled to a mixed-layer ocean model. Anthropogenic BC is predicted to raise globally and annually averaged equilibrium surface air temperature by 0.20 K if BC is assumed to be externally mixed. The predicted increase is significantly greater in the Northern Hemisphere (0.29 K) than in the Southern Hemisphere (0.11 K). If BC is assumed to be internally mixed with the present-day level of sulfate aerosol, the predicted annual mean surface temperature increase rises to 0.37 K globally, 0.54 K for the Northern Hemisphere, and 0.20 K for the Southern Hemisphere. The climate sensitivity of BC direct radiative forcing is calculated to be 0.6 K W À1 m 2 , which is about 70% of that of CO 2 , independent of the assumption of BC mixing state. The largest surface temperature response occurs over the northern high latitudes during winter and early spring. In the tropics and midlatitudes, the largest temperature increase is predicted to occur in the upper troposphere. Direct radiative forcing of anthropogenic BC is also predicted to lead to a change of precipitation patterns in the tropics; precipitation is predicted to increase between 0 and 20°N and decrease between 0 and 20°S, shifting the intertropical convergence zone northward. If BC is assumed to be internally mixed with sulfate instead of externally mixed, the change in precipitation pattern is enhanced. The change in precipitation pattern is not predicted to alter the global burden of BC significantly because the change occurs predominantly in regions removed from BC sources. Citation: Chung, S. H., and J. H. Seinfeld (2005), Climate response of direct radiative forcing of anthropogenic black carbon,

Journal of Geophysical Research, 2002

1] The global distribution of carbonaceous aerosols is simulated online in the Goddard Institute ... more 1] The global distribution of carbonaceous aerosols is simulated online in the Goddard Institute for Space Studies General Circulation Model II-prime (GISS GCM II-prime). Prognostic tracers include black carbon (BC), primary organic aerosol (POA), five groups of biogenic volatile organic compounds (BVOCs), and 14 semivolatile products of BVOC oxidation by O 3 , OH, and NO 3 , which condense to form secondary organic aerosols (SOA) based on an equilibrium partitioning model and experimental observations. Estimated global burdens of BC, organic carbon (OC), and SOA are 0.22, 1.2, and 0.19 Tg with lifetimes of 6.4, 5.3, and 6.2 days, respectively. The predicted global production of SOA is 11.2 Tg yr À1 , with 91% due to O 3 and OH oxidation. Globally averaged, top of the atmosphere (TOA) radiative forcing by anthropogenic BC is predicted as +0.51 to +0.8 W m À2 , the former being for BC in an external mixture and the latter for BC in an internal mixture of sulfate, OC, and BC. Globally averaged, anthropogenic BC, OC, and sulfate are predicted to exert a TOA radiative forcing of À0.39 to À0.78 W m À2 , depending on the exact assumptions of aerosol mixing and water uptake by OC. Forcing estimates are compared with those published previously. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0365 Atmospheric Composition and Structure: Troposphere-composition and chemistry Citation: Chung, S. H., and J. H. Seinfeld, Global distribution and climate forcing of carbonaceous aerosols,

International Journal of Heat and Mass Transfer, 1998

In this paper\ we introduce a methodology to characterize time!dependent soot volume fraction~uct... more In this paper\ we introduce a methodology to characterize time!dependent soot volume fraction~uctuations in turbulent di}usion~ames via chaotic maps[ The approach is based on the hypothesis that~uctuations of properties in turbulent~ames are deterministic in nature\ rather than statistical[ Our objective is to develop models of these~uctuations to be used in comprehensive algorithms to study the nature of turbulent~ames and the interaction of turbulence with radiation[ To this end we measured the time series of soot scattering coe.cient in an ethylene di}usion~ame from light scattering experiments and _t these data to linear combinations of chaotic maps of the unit interval[ Both time series and power spectra can be modeled with reasonable accuracy in this way[ Þ 0887 Elsevier Science Ltd[ All rights reserved[

Geophysical Research Letters, 2009

Geophysical Research Letters, 2005

1] Nanoparticles are ubiquitous in nature. Their large surface areas and consequent chemical reac... more 1] Nanoparticles are ubiquitous in nature. Their large surface areas and consequent chemical reactivity typically result in their aggregation into clusters. Their chemical and physical properties depend on cluster shapes, which are commonly complex and unknown. This is the first application of electron tomography with a transmission electron microscope to quantitatively determine the threedimensional (3D) shapes, volumes, and surface areas of nanoparticle clusters. We use soot (black carbon, BC) nanoparticles as an example because it is a major contributor to environmental degradation and global climate change. To the extent that our samples are representative, we find that quantitative measurements of soot surface areas and volumes derived from electron tomograms differ from geometrically derived values by, respectively, almost one and two orders of magnitude. Global sensitivity studies suggest that the global burden and direct radiative forcing of fractal BC are only about 60% of the value if it is assumed that BC has a spherical shape. (2005), Electron tomography of nanoparticle clusters: Implications for atmospheric lifetimes and radiative forcing of soot, Geophys.

GEOCHEMICAL JOURNAL, 2007

The cored sediments sampled by R/V Marion Dufrense are mostly muds consisting mainly of quartz, f... more The cored sediments sampled by R/V Marion Dufrense are mostly muds consisting mainly of quartz, feldspar, illite, chlorite + kaolinite and calcite. Authigenic carbonates mainly composed of aragonite, calcite, dolomite and associated with Fe-montmorillonite and pyrite occur in core samples collected from station MD-052911 (22°15.6′ N, 119°51.0′ E) at 2137-2140 cm and 2237-2240 cm depth which may be formed via sulfate reduction by CH 4 . In general Illite/Quartz intensity ratios of the sediments show little variation with core depth indicating the relatively constant abundance of illite in the source rock on Taiwan. The cored sediments have higher average Al 2 O 3 , ∑FeO and MgO but lower SiO 2 , Na 2 O, and CaO contents when compared with upper continental crust (UCC). High field strength elements (Zr, Hf, Y, Nb and Ta) are also depleted in the cored sediments. CaO, Sr, Mn and Pb in the core samples collected from station MD-052912 (22°21.5′ N, 119°48.5′ E) tend to decrease with depth which may be essentially related to the decrease of biogenic CaCO 3 with core depth. The La/Th, La/Sc, Th/Sc ratios of the cored sediments are similar to those of UCC, however the (La/Yb) N ratios of the cored sediments are higher. The cored sediments display similar REE patterns with LREE enrichment and negative Eu anomaly reflecting a felsic nature of the source rock which can also be identified in the La-Th-Sc plot. The chemistry of the sediments can be deduced using a mixing model involved four end members i.e., shale, greywacke, quartzite and limestone.

Global change will clearly have a significant impact on the environment. Among the concerns for f... more Global change will clearly have a significant impact on the environment. Among the concerns for future air quality in the United States, intercontinental transport of pollution has become increasingly important. In this study, we examined the effect of the changes in chemical boundary conditions, including the upper troposphere, and emissions from lightning and wildfires to produce ozone background concentrations within the continental US as the basis for developing an understanding of policy relevant background levels and how they may change in the future. Meteorological fields were downscaled from the results of the ECHAM5 global climate model using the Weather Research Forecast (WRF) model. Two nested domains were employed, one covering most of the Northern Hemisphere from eastern Asia to North America using 200k km grid cells (semi-hemispheric domain) and one covering the continental US using 36 km grid cells (CONUS). Meteorological results from WRF were used to drive the MEGAN ...

Geosci. Model Dev. Discuss., 2013

A pollen model that simulates the timing and production of wind-dispersed allergenic pollen by te... more A pollen model that simulates the timing and production of wind-dispersed allergenic pollen by terrestrial, temperate vegetation has been developed to quantify how pollen occurrence may be affected by climate change and to investigate how pollen can interact with anthropogenic pollutants to affect human health. The Simulator of the Timing and Nevada. Differences in the simulated timing and magnitude of pollen season for the selected allergenic species under current and future climate scenarios are presented. The results suggest that across all of the simulated species, pollen season starts an average of 5-6 days earlier under predicted future climatic conditions with an associated average annual domain-wide temperature increase of about 1 • C compared to 5 simulated current conditions. Differences in the amount of pollen produced under the two scenarios vary by species and are affected by the selected simulation period (1 March-30 June). Uncertainties associated with the STaMPS model and future model development plans are also discussed.

Biogeosciences, 2014

Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway dise... more Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway disease (AAD) in sensitive populations, and thus cause serious public health problems. Assessing these health impacts by linking the airborne pollen levels, concentrations of respirable allergenic material, and human allergenic response under current and future climate conditions is a key step toward developing preventive and adaptive actions. To that end, a regional-scale pollen emission and transport modeling framework was developed that treats allergenic pollens as non-reactive tracers within the WRF/CMAQ air-quality modeling system. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model was used to generate a daily pollen pool that can then be emitted into the atmosphere by wind. The STaMPS is driven by species-specific meteorological (temperature and/or precipitation) threshold conditions and is designed to be flexible with respect to its representation of vegetation species and plant functional types (PFTs). The hourly pollen emission flux was parameterized by considering the pollen pool, friction velocity, and wind threshold values. The dry deposition velocity of each species of pollen was estimated based on pollen grain size and density. An evaluation of the pollen modeling framework was conducted for southern California for the period from March to June 2010. This period coincided with observations by the University of Southern California's Children's Health Study (CHS), which included O3, PM2.5, and pollen count, as well as measurements of exhaled nitric oxide in study participants. Two nesting domains with horizontal resolutions of 12 km and 4 km were constructed, and six representative allergenic pollen genera were included: birch tree, walnut tree, mulberry tree, olive tree, oak tree, and brome grasses. Under the current parameterization scheme, the modeling framework tends to underestimate walnut and peak oak pollen concentrations, and tends to overestimate grass pollen concentrations. The model shows reasonable agreement with observed birch, olive, and mulberry tree pollen concentrations. Sensitivity studies suggest that the estimation of the pollen pool is a major source of uncertainty for simulated pollen concentrations. Achieving agreement between emission modeling and observed pattern of pollen releases is the key for successful pollen concentration simulations.

Acknowledgments This Report was submitted,in fulfillment of ARB contract number 02-322 ti- tled G... more Acknowledgments This Report was submitted,in fulfillment of ARB contract number 02-322 ti- tled Global Radiative Effect of Particulate Black Carbon by California Institute of Technology under the sponsorship,of the California Air Resources Board. Work was completed as of January 25, 2005. ii Contents

International Symposium on Erosion and Landscape Evolution (ISELE), 18-21 September 2011, Anchorage, Alaska, 2011

International Symposium on Erosion and Landscape Evolution (ISELE), 18-21 September 2011, Anchorage, Alaska, 2011

... ISELE Paper No 11023. St. Joseph, Mich.: ASABE. 8. Gillette, DA 1988. Threshold friction velo... more ... ISELE Paper No 11023. St. Joseph, Mich.: ASABE. 8. Gillette, DA 1988. Threshold friction velocities for dust production for agricultural soils. J. Geophys. Res. ... Res. 94: 2197-2206. 10. Gillette, D., and R. Passi.1988. Modeling dust emission caused by wind erosion. J. Geophys. ...

Global change will clearly have a significant impact on the environment. Among the concerns for f... more Global change will clearly have a significant impact on the environment. Among the concerns for future air quality in the United States, intercontinental transport of pollution has become increasingly important. In this study, we examined the effect of the changes in chemical boundary conditions, including the upper troposphere, and emissions from lightning and wildfires to produce ozone background concentrations within the continental US as the basis for developing an understanding of policy relevant background levels and how they may change in the future. Meteorological fields were downscaled from the results of the ECHAM5 global climate model using the Weather Research Forecast (WRF) model. Two nested domains were employed, one covering most of the Northern Hemisphere from eastern Asia to North America using 200k km grid cells (semi-hemispheric domain) and one covering the continental US using 36 km grid cells (CONUS). Meteorological results from WRF were used to drive the MEGAN ...

Transactions of the ASABE, 2013

Journal of the Air & Waste Management Association, 2012

The impact of climate change on surface-level ozone is examined through a multiscale modeling eff... more The impact of climate change on surface-level ozone is examined through a multiscale modeling effort that linked global and regional climate models to drive air quality model simulations. Results are quantified in terms of the relative response factor (RRF(E)), which estimates the relative change in peak ozone concentration for a given change in pollutant emissions (the subscript E is added to RRF to remind the reader that the RRF is due to emission changes only). A matrix of model simulations was conducted to examine the individual and combined effects offuture anthropogenic emissions, biogenic emissions, and climate on the RRF(E). For each member in the matrix of simulations the warmest and coolest summers were modeled for the present-day (1995-2004) and future (2045-2054) decades. A climate adjustment factor (CAF(C) or CAF(CB) when biogenic emissions are allowed to change with the future climate) was defined as the ratio of the average daily maximum 8-hr ozone simulated under a future climate to that simulated under the present-day climate, and a climate-adjusted RRF(EC) was calculated (RRF(EC) = RRF(E) x CAF(C)). In general, RRF(EC) > RRF(E), which suggests additional emission controls will be required to achieve the same reduction in ozone that would have been achieved in the absence of climate change. Changes in biogenic emissions generally have a smaller impact on the RRF(E) than does future climate change itself The direction of the biogenic effect appears closely linked to organic-nitrate chemistry and whether ozone formation is limited by volatile organic compounds (VOC) or oxides of nitrogen (NO(x) = NO + NO2). Regions that are generally NO(x) limited show a decrease in ozone and RRF(EC), while VOC-limited regions show an increase in ozone and RRF(EC). Comparing results to a previous study using different climate assumptions and models showed large variability in the CAF(CB). We present a methodology for adjusting the RRF to account for the influence of climate change on ozone. The findings of this work suggest that in some geographic regions, climate change has the potential to negate decreases in surface ozone concentrations that would otherwise be achieved through ozone mitigation strategies. In regions of high biogenic VOC emissions relative to anthropogenic NO(x) emissions, the impact of climate change is somewhat reduced, while the opposite is true in regions of high anthropogenic NO(x) emissions relative to biogenic VOC emissions. Further, different future climate realizations are shown to impact ozone in different ways.

Journal of Geophysical Research, 2007

JD_description.

Journal of Geophysical Research, 2007

Real-time forecasts of PM2.5 aerosol mass from seven air quality forecast models (AQFMs) are stat... more Real-time forecasts of PM2.5 aerosol mass from seven air quality forecast models (AQFMs) are statistically evaluated against observations collected in the northeastern United States and southeastern Canada from two surface networks and aircraft data during the summer of 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)/New England Air Quality Study (NEAQS) field campaign. The AIRNOW surface network

Journal of Geophysical Research, 2010

1] Soot aerosol particles (also called light-absorbing, black, or elemental carbon) are major con... more 1] Soot aerosol particles (also called light-absorbing, black, or elemental carbon) are major contributors to global warming through their absorption of solar radiation. When embedded in organic matter or sulfate, as is common in polluted areas such as over Mexico City (MC) and other megacities, their optical properties are affected by their shapes and positions within their host particles. However, large uncertainties remain regarding those variables and how they affect warming by soot. Using electron tomography with a transmission electron microscope, three-dimensional (3-D) images of individual soot particles embedded within host particles collected from MC and its surroundings were obtained. From those 3-D images, we calculated the optical properties using a discrete dipole approximation. Many soot particles have open, chainlike shapes even after being surrounded by organic matter and are located in off-center positions within their host materials. Such embedded soot absorbs sunlight less efficiently than if compact and located near the center of its host particle. In the case of our MC samples, their contribution to direct radiative forcing is ∼20% less than if they had a simple core-shell shape, which is the shape assumed in many climate models. This study shows that the shapes and positions of soot within its host particles have an important effect on particle optical properties and should be recognized as potentially important variables when evaluating global climate change.

Journal of Geophysical Research, 2006

Received 12 January 2006; revised 24 April 2006; accepted 16 May 2006; published 29 August 2006. ... more Received 12 January 2006; revised 24 April 2006; accepted 16 May 2006; published 29 August 2006. [1] A single-particle soot photometer (SP2) was flown on a NASA WB-57F high-altitude research aircraft in November 2004 from Houston, Texas. The SP2 uses laser-induced ...

Journal of Geophysical Research, 2005

1] The equilibrium climate effect of direct radiative forcing of anthropogenic black carbon (BC) ... more 1] The equilibrium climate effect of direct radiative forcing of anthropogenic black carbon (BC) is examined by 100-year simulations in the Goddard Institute for Space Studies General Circulation Model II-prime coupled to a mixed-layer ocean model. Anthropogenic BC is predicted to raise globally and annually averaged equilibrium surface air temperature by 0.20 K if BC is assumed to be externally mixed. The predicted increase is significantly greater in the Northern Hemisphere (0.29 K) than in the Southern Hemisphere (0.11 K). If BC is assumed to be internally mixed with the present-day level of sulfate aerosol, the predicted annual mean surface temperature increase rises to 0.37 K globally, 0.54 K for the Northern Hemisphere, and 0.20 K for the Southern Hemisphere. The climate sensitivity of BC direct radiative forcing is calculated to be 0.6 K W À1 m 2 , which is about 70% of that of CO 2 , independent of the assumption of BC mixing state. The largest surface temperature response occurs over the northern high latitudes during winter and early spring. In the tropics and midlatitudes, the largest temperature increase is predicted to occur in the upper troposphere. Direct radiative forcing of anthropogenic BC is also predicted to lead to a change of precipitation patterns in the tropics; precipitation is predicted to increase between 0 and 20°N and decrease between 0 and 20°S, shifting the intertropical convergence zone northward. If BC is assumed to be internally mixed with sulfate instead of externally mixed, the change in precipitation pattern is enhanced. The change in precipitation pattern is not predicted to alter the global burden of BC significantly because the change occurs predominantly in regions removed from BC sources. Citation: Chung, S. H., and J. H. Seinfeld (2005), Climate response of direct radiative forcing of anthropogenic black carbon,

Journal of Geophysical Research, 2002

1] The global distribution of carbonaceous aerosols is simulated online in the Goddard Institute ... more 1] The global distribution of carbonaceous aerosols is simulated online in the Goddard Institute for Space Studies General Circulation Model II-prime (GISS GCM II-prime). Prognostic tracers include black carbon (BC), primary organic aerosol (POA), five groups of biogenic volatile organic compounds (BVOCs), and 14 semivolatile products of BVOC oxidation by O 3 , OH, and NO 3 , which condense to form secondary organic aerosols (SOA) based on an equilibrium partitioning model and experimental observations. Estimated global burdens of BC, organic carbon (OC), and SOA are 0.22, 1.2, and 0.19 Tg with lifetimes of 6.4, 5.3, and 6.2 days, respectively. The predicted global production of SOA is 11.2 Tg yr À1 , with 91% due to O 3 and OH oxidation. Globally averaged, top of the atmosphere (TOA) radiative forcing by anthropogenic BC is predicted as +0.51 to +0.8 W m À2 , the former being for BC in an external mixture and the latter for BC in an internal mixture of sulfate, OC, and BC. Globally averaged, anthropogenic BC, OC, and sulfate are predicted to exert a TOA radiative forcing of À0.39 to À0.78 W m À2 , depending on the exact assumptions of aerosol mixing and water uptake by OC. Forcing estimates are compared with those published previously. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0365 Atmospheric Composition and Structure: Troposphere-composition and chemistry Citation: Chung, S. H., and J. H. Seinfeld, Global distribution and climate forcing of carbonaceous aerosols,

International Journal of Heat and Mass Transfer, 1998

In this paper\ we introduce a methodology to characterize time!dependent soot volume fraction~uct... more In this paper\ we introduce a methodology to characterize time!dependent soot volume fraction~uctuations in turbulent di}usion~ames via chaotic maps[ The approach is based on the hypothesis that~uctuations of properties in turbulent~ames are deterministic in nature\ rather than statistical[ Our objective is to develop models of these~uctuations to be used in comprehensive algorithms to study the nature of turbulent~ames and the interaction of turbulence with radiation[ To this end we measured the time series of soot scattering coe.cient in an ethylene di}usion~ame from light scattering experiments and _t these data to linear combinations of chaotic maps of the unit interval[ Both time series and power spectra can be modeled with reasonable accuracy in this way[ Þ 0887 Elsevier Science Ltd[ All rights reserved[

Geophysical Research Letters, 2009

Geophysical Research Letters, 2005

1] Nanoparticles are ubiquitous in nature. Their large surface areas and consequent chemical reac... more 1] Nanoparticles are ubiquitous in nature. Their large surface areas and consequent chemical reactivity typically result in their aggregation into clusters. Their chemical and physical properties depend on cluster shapes, which are commonly complex and unknown. This is the first application of electron tomography with a transmission electron microscope to quantitatively determine the threedimensional (3D) shapes, volumes, and surface areas of nanoparticle clusters. We use soot (black carbon, BC) nanoparticles as an example because it is a major contributor to environmental degradation and global climate change. To the extent that our samples are representative, we find that quantitative measurements of soot surface areas and volumes derived from electron tomograms differ from geometrically derived values by, respectively, almost one and two orders of magnitude. Global sensitivity studies suggest that the global burden and direct radiative forcing of fractal BC are only about 60% of the value if it is assumed that BC has a spherical shape. (2005), Electron tomography of nanoparticle clusters: Implications for atmospheric lifetimes and radiative forcing of soot, Geophys.

GEOCHEMICAL JOURNAL, 2007

The cored sediments sampled by R/V Marion Dufrense are mostly muds consisting mainly of quartz, f... more The cored sediments sampled by R/V Marion Dufrense are mostly muds consisting mainly of quartz, feldspar, illite, chlorite + kaolinite and calcite. Authigenic carbonates mainly composed of aragonite, calcite, dolomite and associated with Fe-montmorillonite and pyrite occur in core samples collected from station MD-052911 (22°15.6′ N, 119°51.0′ E) at 2137-2140 cm and 2237-2240 cm depth which may be formed via sulfate reduction by CH 4 . In general Illite/Quartz intensity ratios of the sediments show little variation with core depth indicating the relatively constant abundance of illite in the source rock on Taiwan. The cored sediments have higher average Al 2 O 3 , ∑FeO and MgO but lower SiO 2 , Na 2 O, and CaO contents when compared with upper continental crust (UCC). High field strength elements (Zr, Hf, Y, Nb and Ta) are also depleted in the cored sediments. CaO, Sr, Mn and Pb in the core samples collected from station MD-052912 (22°21.5′ N, 119°48.5′ E) tend to decrease with depth which may be essentially related to the decrease of biogenic CaCO 3 with core depth. The La/Th, La/Sc, Th/Sc ratios of the cored sediments are similar to those of UCC, however the (La/Yb) N ratios of the cored sediments are higher. The cored sediments display similar REE patterns with LREE enrichment and negative Eu anomaly reflecting a felsic nature of the source rock which can also be identified in the La-Th-Sc plot. The chemistry of the sediments can be deduced using a mixing model involved four end members i.e., shale, greywacke, quartzite and limestone.