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Papers by Youhua Tang

Research paper thumbnail of The Performance and Issues of a Regional Chemical Transport Model During Discover-AQ 2014 Aircraft Measurements Over Colorado

Springer Proceedings in Complexity, 2016

The National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Pre... more The National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction operates the U.S. Air Quality Forecasting Capability (NAQFC) which uses primarily the U.S Environmental Protection Agency’s Community Multi-Scale Air Quality (CMAQ) model. NAQFC focuses on surface ozone and PM2.5 (particle matter with diameter <2.5 µm), which impacts human-health. Near surface ozone mainly comes from photochemical reactions of NOx and volatile organic compounds (VOCs). Its sources in upper layers could come from either long-range transport or stratospheric ozone. Most PM2.5 comes from near-surface primary emissions or secondary generation from photochemical reactions. During the summer 2014 NASA Discover-AQ-Colorado program, the NOAA Air Resources Laboratory (ARL) provided a real-time forecast in support of aircraft measurements with 12 km CONUS (Contiguous United States) and 4 km nested domains. Here we compare the model results with the aircraft data to investigate our predictions.

Research paper thumbnail of Comparison of emission data and the backward trajectory analysis from airborne observation for East Asia

Proceedings of the Symposium on Global Environment, 2003

Long-range transport of the pollutants influenced by both anthropogenic and natural emission sour... more Long-range transport of the pollutants influenced by both anthropogenic and natural emission source in East Asia including the biomass burning emission in Southeast Asia was investigated by using the backward trajectory analysis from NASA TRACE-P airborne observation and a numerical simulation with three-dimensional chemical transport model (STEM-2k1). As a result, we found systematic regional bias between observed and calculated concentration. The ratios between CO and some NHMCs, such as ethane/CO and ethane/propane, were highly associated with the distribution of emission

Research paper thumbnail of Study of atmospheric mercury budget in East Asia using STEM-Hg modeling system

Science of the Total Environment, 2010

East Asia is the largest source region of global anthropogenic mercury emissions, and contributes... more East Asia is the largest source region of global anthropogenic mercury emissions, and contributes to atmospheric mercury concentration and deposition in other regions. Similarly, mercury from the global pool also plays a role in the chemical transport of mercury in East Asia. Annual simulations of atmospheric mercury in East Asia were performed using the STEM-Hg modeling system to study the mass budgets of mercury in the region. The model results showed strong seasonal variation in mercury concentration and deposition, with signals from large point sources. The annual mean concentrations for gaseous elemental mercury, reactive gaseous mercury and particulate mercury in central China and eastern coastal areas were 1.8 ng m(-3), 100 pg m(-3) and 150 pg m(-3), respectively. Boundary conditions had a strong influence on the simulated mercury concentration and deposition, contributing to 80% of the concentration and 70% of the deposition predicted by the model. The rest was caused by the regional emissions before they were transported out of the model domain. Using different oxidation rates reported for the Hg(0)-O(3) reaction (i.e., by Hall, 1995 vs. by Pal and Ariya, 2004) led to a 9% difference in the predicted mean concentration and a 40% difference in the predicted mean deposition. The estimated annual dry and wet deposition for East Asia in 2001 was in the range of 590-735 Mg and 482-696 Mg, respectively. The mercury mass outflow caused by the emissions in the domain was estimated to be 681-714 Mg yr(-1). This constituted 70% of the total mercury emission in the domain. The greatest outflow occurred in spring and early summer.

Research paper thumbnail of Predicting Air Quality: Current Status and Future Directions

NATO Science for Peace and Security Series

Air quality prediction plays an important role in the management of our environment. Computationa... more Air quality prediction plays an important role in the management of our environment. Computational power and efficiencies have advanced to the point where chemical transport models can predict pollution in an urban air shed with spatial resolution less than a kilometer, and cover the globe with a horizontal resolution of less than 50 km. Predicting air quality remains a challenge due to the complexity of the governing processes and the strong coupling across scales. While air quality prediction is closely aligned with weather prediction, there are important differences, including the role of pollution emissions and their associated large uncertainties. As more atmospheric chemical observations become available chemical data assimilation is expected to play an essential role in air quality forecasting. In this paper the current status of air quality forecasting is discussed and illustrated by comparison of predictions with observations. The future directions are also discussed, with an emphasis on data assimilation. Applications of the four dimensional variational method (4D-Var) and the ensemble Kalman filter (EnKF) approach are presented and discussed.

Research paper thumbnail of A Modeling Study on Regional Air Pollutions Transport Patterns Over the Pearl River Delta in the Fall Season

Modern Physics Letters B, 2005

This paper presents the preliminary results of a modeling study on regional air pollutants transp... more This paper presents the preliminary results of a modeling study on regional air pollutants transport over the Pearl River Delta (PRD) region of China in fall season (Nov. 2002) on the basis of compiled emission inventories. The advanced regional chemical transport model, STEM-2K1, driven by meso-scale meteorological model MM5, was employed with a nesting technique. Three weather patterns were found in the fall season. Numerical sensitive study indicated that external influence on air quality in PRD was significant and dependent on the transport pattern determined by weather situations.

Research paper thumbnail of Chemical data assimilation of Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft measurements

Journal of Geophysical Research, 2006

In this paper, the four-dimensional variational (4D-Var) technique is applied to assimilate aircr... more In this paper, the four-dimensional variational (4D-Var) technique is applied to assimilate aircraft measurements during the Transport and Chemical Evolution over the Pacific (TRACE-P) field experiment into a chemical transport model, Sulfur Transport Eulerian Model, version 2K1 (STEM-2K1). Whether data assimilation would produce better analyzed fields is examined. It is found that assimilating ozone observations from one of two independent flights improves model prediction of the other flight ozone measurements, which are withheld as validation data. The adjusted initial fields after only assimilating the total reactive nitrogen (NO y) observations lead to better predictions of NO, NO 2 , and PAN, based on their agreement with the withheld measurements. One experiment simultaneously assimilating the observations of O 3 , NO, NO 2 , HNO 3 , PAN, and RNO 3 demonstrates that the model is able to match those measurements well by changing the initial fields. In addition, the model predictions of NO y improve significantly after assimilating the aforementioned multiple observation species, which are independent of the withheld NO y measurements. In the paper, we also show that the key species whose initial mixing ratios would significantly affect the agreement between model and measurements can be identified using adjoint sensitivity analysis. Such information can be used to reduce the number of control variables in the 4D-Var data assimilation. To speed up the optimization process in the 4D-Var, we enforce the concentration upper bounds through the limited memory-Broyden-Fletcher-Goldfarb-Shanno-B (L-BFGS-B) algorithm, and this proves to be effective.

Research paper thumbnail of Four-dimensional data assimilation experiments with International Consortium for Atmospheric Research on Transport and Transformation ozone measurements

Journal of Geophysical Research, 2007

Ozone measurements by various platforms during the International Consortium for Atmospheric Resea... more Ozone measurements by various platforms during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) operations in the summer of 2004 are assimilated into the STEM regional chemical transport model (CTM). Under the four-dimensional variational data assimilation (4D-Var) framework, the model forecast (background) error covariance matrix is constructed using both the so-called NMC (National Meteorological Center, now National Centers for Environmental Prediction) method and the observational (Hollingworth-Lönnberg) method. The inversion of the covariance matrix is implemented using truncated singular value decomposition (TSVD) approach. The TSVD approach is numerically stable even with severely ill conditioned vertical correlation covariance matrix and large horizontal correlation distances. Ozone observations by different platforms (aircraft, surface, and ozonesondes) are first assimilated separately. The impacts of the various measurements are evaluated on their ability to improve the predictions, defined as the information content of the observations under the current framework. In the end, all observations are assimilated into the CTM. The final analysis matches well with observations from all platforms. Assessed with all the observations throughout the boundary layer and midtroposphere, the model bias is reduced from 11.3 ppbv for the base case to À1.5 ppbv. A reduction of 10.3 ppbv in root mean square error is also seen. In addition, the potential of improving air quality forecasts by chemical data assimilation is demonstrated. The effect of assimilating ozone observations on model predictions of other species is also shown.

Research paper thumbnail of Regional distribution and emissions of mercury in east Asia: A modeling analysis of Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) observations

Journal of Geophysical Research, 2006

Mercury tracer model simulations are performed to support the analysis of the total gas phase mer... more Mercury tracer model simulations are performed to support the analysis of the total gas phase mercury (TGM) observations on 15 flights of the NSF/NCAR C-130 aircraft during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) campaign conducted during April 2001. Ninety-seven percent of the observed mercury concentrations are greater than 1.2 ng/m 3. The mean value of the observations is 1.9 ng/m 3. No simple relationships between Hg-CO and Hg-total sulfur are found; however, strong correlations are observed in individual flight segments. Backward trajectory analysis is used to help characterize regional of Hg/CO ratios, and these are compared with emission-based ratios from the various sectors. Model predictions using new Hg emission estimates are presented and compared to the observations. Under the condition of a mercury background level of 1.2 ng/m 3 the tracer model underestimates the observations when the flights were over the Yellow Sea but is consistent with the observations when the flights were over the Japan Sea. Further analysis suggests that Hg emissions are underestimated in north central China and the eastern coastal areas of China. Model sensitivity studies indicate that the emissions of China may be underestimated by 80-200%.

Research paper thumbnail of Revisiting China's CO emissions after the Transport and Chemical Evolution over the Pacific (TRACE-P) mission: Synthesis of inventories, atmospheric modeling, and observations

Journal of Geophysical Research, 2006

A new inventory of CO emissions in China is presented for the year 2001. This inventory improves ... more A new inventory of CO emissions in China is presented for the year 2001. This inventory improves and updates the a priori CO emission inventory prepared in support of NASA&amp;amp;amp;amp;amp;#x27;s TRACE-P mission in the spring of 2001. Analysis of CO observations using chemical transport models in ...

Research paper thumbnail of Characterization of the seasonal cycle of south Asian aerosols: A regional-scale modeling analysis

Journal of Geophysical Research, 2007

The sulfur transport and deposition model (STEM) is used to study the aerosol seasonality, distri... more The sulfur transport and deposition model (STEM) is used to study the aerosol seasonality, distribution, and composition over south Asia from September 2004 to August 2005. Model predictions of sulfate, black carbon, primary organic carbon, other anthropogenic particulate matter, windblown mineral dusts, and sea salt are compared at two sites in south Asia where yearlong experimental observations are available from the Atmospheric Brown Cloud (ABC) project. The model predictions are able to capture both the magnitude and seasonality of aerosols over Hanimaadhoo Observatory, Maldives. However, the model is not able to explain the seasonality at the Kathmandu Observatory; but the model does capture Kathmandu's observed annual mean concentration. The absence of seasonal brick kiln emissions within Kathmandu valley in the current inventory is a probable reason for this problem. This model study reveals high-anthropogenic aerosol loading over the Ganges valley even in the monsoonal months, which needs to be corroborated by experimental observations. Modeling results also show a high dust loading over south Asia with a distinct seasonality. Model results of aerosol monthly composition are also presented at five cities in south Asia. Total and fine-mode monthly aerosol optical depth along with contribution from each aerosol species is presented; the results show that the anthropogenic fraction dominates in the postmonsoon and the early dry season with major contributions from sulfate and absorbing aerosols. Model sensitivity studies of dry deposition velocity and wet scavenging efficiency show that model improvements are needed in the treatment of carbonaceous aerosol dry and wet removal processes. Modeled SO 2 conversion rate constrained with sulfate observations at Hanimaadhoo suggests the need to increase model sulfate production rate during the dry season to account for probable sulfate production via heterogeneous pathways.

Research paper thumbnail of Impacts of aerosols and clouds on photolysis frequencies and photochemistry during TRACE-P: 2. Three-dimensional study using a regional chemical transport model

Journal of Geophysical Research: Atmospheres, 2003

A three-dimensional regional chemical transport model, STEM 2K1, coupled with a detailed radiatio... more A three-dimensional regional chemical transport model, STEM 2K1, coupled with a detailed radiation model is used to study the influences of aerosols and clouds on photolysis rates and photochemical processes over East Asia-Western Pacific during the TRACE-P period. Measured J-values are compared with those calculated using threedimensional modeled fields of clouds and aerosols. The model is shown to accurately represent observed J-values over a broad range of conditions. Model studies with and without aerosols and clouds are performed and compared with clear-sky conditions to isolate the various influences. Clouds are shown to have a large impact on photolysis rates during the observation periods of TRACE-P, with J[NO 2 ] decreased by 20% below clouds and enhanced by 3030% from 1 km to 8 km. Clouds also exert a dominant influence on short-lived radicals, like OH and HO 2. For March, clouds reduce OH by 23% at altitudes below 1 km and increase OH by 3025% above 1 km. Asian aerosols contain large amounts of carbonaceous material, inorganic components such as sulfates, and mineral oxides. These aerosols significantly influence J-values and photochemical processes. When averaged over all TRACE-P DC-8 and P-3 flights, the aerosol influence via affecting J-values reduces OH by 4040% below 1 km, and by 4024% above 1 km. Aerosols have a stronger impact on longer-lived chemical species than clouds do because aerosols tend to be coemitted with precursors and have a longer contact time with the polluted air masses. The accumulated aerosol impact generally is to reduce O 3 concentrations by about 6 ppbv in the biomass burning plumes emitted from Southeast Asia. In megacity plumes, aerosols can increase NO x concentration by 40% via reducing its photolytic loss and reduce NO z concentration by a similar amount. A detailed case study of the DC-8 and P-3 flights on 27 March is used to make comparisons for cloud and aerosol influences. During these flights, the cloud impact on J-values is stronger than the aerosol impact, but aerosols are shown to exert a much stronger accumulated influence on O 3 production.

Research paper thumbnail of Multiscale simulations of tropospheric chemistry in the eastern Pacific and on the U.S. West Coast during spring 2002

Journal of Geophysical Research: Atmospheres, 2004

Regional modeling analysis for the Intercontinental Transport and Chemical Transformation 2002 (I... more Regional modeling analysis for the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) experiment over the eastern Pacific and U.S. West Coast is performed using a multiscale modeling system, including the regional tracer model Chemical Weather Forecasting System (CFORS), the Sulfur Transport and Emissions Model 2003 (STEM-2K3) regional chemical transport model, and an off-line coupling with the Model of Ozone and Related Chemical Tracers (MOZART) global chemical transport model. CO regional tracers calculated online in the CFORS model are used to identify aircraft measurement periods with Asian influences. Asian-influenced air masses measured by the National Oceanic and Atmospheric Administration (NOAA) WP-3 aircraft in this experiment are found to have lower DAcetone/DCO, DMethanol/DCO, and DPropane/DEthyne ratios than air masses influenced by U.S. emissions, reflecting differences in regional emission signals. The Asian air masses in the eastern Pacific are found to usually be well aged (>5 days), to be highly diffused, and to have low NO y levels. Chemical budget analysis is performed for two flights, and the O 3 net chemical budgets are found to be negative (net destructive) in the places dominated by Asian influences or clear sites and positive in polluted American air masses. During the trans-Pacific transport, part of gaseous HNO 3 was converted to nitrate particle, and this conversion was attributed to NO y decline. Without the aerosol consideration, the model tends to overestimate HNO 3 background concentration along the coast region. At the measurement site of Trinidad Head, northern California, high-concentration pollutants are usually associated with calm wind scenarios, implying that the accumulation of local pollutants leads to the high concentration. Seasonal variations are also discussed from April to May for this site. A high-resolution nesting simulation with 12-km horizontal resolution is used to study the WP-3 flight over Los Angeles and surrounding areas. This nested simulation significantly improved the predictions for emitted and secondary generated species. The difference of photochemical behavior between the coarse (60-km) and nesting simulations is discussed and compared with the observation.

Research paper thumbnail of Influences of biomass burning during the Transport and Chemical Evolution Over the Pacific (TRACE-P) experiment identified by the regional chemical transport model

Journal of Geophysical Research: Atmospheres, 2003

Using a regional chemical transport model, STEM 2K1, and the emission inventory for the Transport... more Using a regional chemical transport model, STEM 2K1, and the emission inventory for the Transport and Chemical Evolution Over the Pacific (TRACE-P) period [Woo et al., 2003 Streets et al., 2003], we successfully simulated important features of the biomass burning (BB) CO outflow. Simulated results agree well with the TRACE-P aircraft measurements and Thailand surface observations. On the basis of sensitivity studies with and without biomass emissions, we identified nine flight segments that are affected by biomass plumes during the TRACE-P period and compared the characteristics of the BB air masses with the other air masses. The BB air masses emitted from Southeast Asia contain relatively high HCN (ÁHCN/ÁCO $ 0.0015) and potassium (ÁK + /ÁCO $ 0.0038) but very low NO y (ÁNO y / ÁCO $ 0.005) mixing ratios, which may be associated with the special burning condition in this region. The biomass burning air masses have high ozone production efficiency. The observed ÁO 3 /ÁNO z values were $17 in biomass events and 1.7 in other events. The BB influence on the trace gas distributions can be divided into two categories: the influence through direct reactions and the influence caused by BB aerosols changing J values. These two influences are discussed for the BB-affected TRACE-P flights and for east Asia. The BB influences on chemical species are not only determined by the BB plume intensity but also by the ambient environment caused by other emissions. In Southeast Asia, where the biogenic emissions are very strong, the OH background concentration is low, and the BB gas-phase compounds mainly contribute to OH production. Arranged in the sensitivity to the J value change caused by BB aerosols, we have OH > HO 2 > HCHO > O 3 when evaluated on a regional average. Averaged over March, the biomass burning net influence is as high as 50% for OH, 40% for HO 2 , 60% for HCHO, and 10 ppbv for O 3 for the layers below 1 km.

Research paper thumbnail of Large-scale structure of trace gas and aerosol distributions over the western Pacific Ocean during the Transport and Chemical Evolution Over the Pacific (TRACE-P) experiment

Journal of Geophysical Research: Atmospheres, 2003

The Models-3 Community Multiscale Air Quality modeling system (CMAQ) coupled with the Regional At... more The Models-3 Community Multiscale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to analyze the Asian continental outflow of carbon monoxide (CO), ozone (O 3), and aerosol sulfate (SO 4 2À) to the western Pacific Ocean during the period 17-24 March 2001. In this time period eight airborne observations (DC-8 flights 11-14 and P-3B flights 13-16) of the NASA Transport and Chemical Evolution Over the Pacific (TRACE-P) mission were being conducted over a broad area covering Hong Kong, Okinawa, the East China Sea, and southern Japan. Comparison of model results with observations shows that the model reproduces the main observed features of CO, O 3 , and SO 4 2À , including horizontal and vertical gradients, of the Asian pollution outflow over the western Pacific. Model results show that the fast boundary outflow from Asia to the western Pacific is largely restricted to the middle latitudes, and the maximum outflow fluxes are in the lower free atmosphere (3-6 km) north of 25°N. Simulations with and without biomass burning emissions are conducted to quantify the impacts of biomass burning on tropospheric concentrations of CO and O 3. Biomass burning is found to contribute more than 50% of the CO concentrations and up to 40% of the O 3 concentrations in the boundary layer over the major source regions. The largest percentage contributions to CO and O 3 levels (up to 40% and 30%, respectively) over the western Pacific are in the lower free troposphere (2-6 km).

Research paper thumbnail of Predicting air quality: Improvements through advanced methods to integrate models and measurements

Journal of Computational Physics, 2008

This article was published in an Elsevier journal. The attached copy is furnished to the author f... more This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author's institution, sharing with colleagues and providing to institution administration. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Research paper thumbnail of Adjoint Sensitivity Analysis of Ozone Nonattainment over the Continental United States

Environmental Science & Technology, 2006

An application of the adjoint method in air quality management is demonstrated. In the adjoint ap... more An application of the adjoint method in air quality management is demonstrated. In the adjoint applications (e.g., variational data assimilation), sensitivities of a receptor-based metric to a variety of parameters can be efficiently calculated. Here, we calculate the sensitivities of a nationwide U.S. ozone National Ambient Air Quality Standard (NAAQS) non-attainment metric to precursor emissions during the month of July 2004. We use the adjoint version of a continental scale chemical transport model (STEM) with 60 km horizontal grid resolution. The model shows low bias and error (3, and 21 percent, respectively), particularly for areas with high ozone concentrations that are subject of this study. The non-attainment metric is integrated over the month and entire domain, and accounts for both 1-hour and 8-hour ozone standards. The metric is quadratic, and therefore, higher concentrations are given larger overall weights in the calculations. The non-attainment metric for the month of July is heavily dominated by the 8-hour standard (98% of the combined metric). Using these spatial distributions of sensitivities we identify the regions and source categories with significant contribution/effect on the overall non-attainment metric. Largest values of sensitivities are found to be with respect to emissions in the southeast U.S. and in the Ohio River Valley. When non-attainment sensitivities are integrated over the entire U.S., NO x emissions account for the largest contribution (64% of the total), followed by the biogenic and anthropogenic VOCs (23% and 13%, respectively). For NO x emissions, point/area, mobile, and non-road mobile sources account for 51, 39, and 10 percent of the total sensitivities, respectively. Point/area sources also have the largest effect among the VOC source categories (62%). No significant difference is seen between weekday and weekend emission contribution patterns. We also provide a state-by-state comparison for the non-attainment magnitude, non-attainment sensitivity, and emission magnitudes to explore the influence of interstate transport of ozone and its precursors, and policy implications of the results. Our analysis of the nationwide ozone non-attainment metric suggests that simple cap-and-trade programs may prove inadequate in achieving the sought-after air quality objectives.

Research paper thumbnail of Mineral dust is a sink for chlorine in the marine boundary layer

Atmospheric Environment, 2007

Dust particles affect the budgets of important traces gases by providing a surface on which heter... more Dust particles affect the budgets of important traces gases by providing a surface on which heterogeneous reactions can occur. The uptake of soluble species on dust alters the physical, chemical, and optical properties and the overall ability of dust to act as cloud condensation and ice nuclei. It is commonly assumed that all measured chloride in particulate filter samples is associated with sea-salt particles and any chloride in dust occurs as the result of internal mixtures of sea-salt and dust particles, formed by cloud processing. Here we show high temporal resolution data demonstrating the direct uptake of chlorine by dust via heterogeneous reaction with HCl(g). This reaction added significant amounts of chlorine to the dust particles during a major dust storm, representing 4-9% of the individual dust particle mass. Up to 6574% of the dust particles contained chlorine due to this heterogeneous reaction during the dust front. Ignoring this process leads to an overestimation of sea-salt concentrations from bulk measurements, and an underestimation of the degree of sea-salt aging. The uptake of chloride will change the pH and hygroscopic properties of the dust and thus can influence the budgets of other reactive gases. Including this heterogeneous process in atmospheric measurements and chemical transport models will improve our ability to predict the atmosphere's composition and radiation budget with greater accuracy.

Research paper thumbnail of A regional scale chemical transport modeling of Asian aerosols with data assimilation of AOD observations using optimal interpolation technique

Atmospheric Environment, 2008

aerosols are presented at these two sites. Positive Matrix Factorization (PMF), a factor analytic... more aerosols are presented at these two sites. Positive Matrix Factorization (PMF), a factor analytic method was also used to characterize the source profile and source contribution at these two locations. A three-factor solution was able to explain more than 80% of the variation in the individual species at Hanimaadhoo and 90% variation of aerosol loadings at Gosan. The four-year averaged PMF model results were able to capture the seasonality of anthropogenic and dust loadings at both these locations. In addition, the PMF model identified the differences in the composition of anthropogenic aerosols over Hanimaadhoo and Gosan reflecting the differences in regional emissions. The PMF derived factors could be used as additional constraints for future assimilation studies.

Research paper thumbnail of A communication library for the parallelization of air quality models on structured grids

Atmospheric Environment, 2002

PAQMSG is an MPI-based, Fortran 90 communication library for the parallelization of air quality m... more PAQMSG is an MPI-based, Fortran 90 communication library for the parallelization of air quality models (AQMs) on structured grids. It consists of distribution, gathering and repartitioning routines for different domain decompositions implementing a master-worker strategy. The library is architecture and application independent and includes optimization strategies for different architectures. This paper presents the library from a user perspective. Results are shown from the parallelization of STEM-III on Beowulf clusters. The PAQMSG library is available on the web. The communication routines are easy to use, and should allow for an immediate parallelization of existing AQMs. PAQMSG can also be used for constructing new models.

Research paper thumbnail of Improving regional ozone modeling through systematic evaluation of errors using the aircraft observations during the International Consortium for Atmospheric Research on Transport and Transformation

Journal of Geophysical Research, 2007

During the operational phase of the ICARTT field experiment in 2004, the regional air quality mod... more During the operational phase of the ICARTT field experiment in 2004, the regional air quality model STEM showed a strong positive surface bias and a negative upper troposphere bias (compared to observed DC-8 and WP-3 observations) with respect to ozone. After updating emissions from NEI 1999 to NEI 2001 (with a 2004 large point sources inventory update), and modifying boundary conditions, low-level model bias decreases from 11.21 to 1.45 ppbv for the NASA DC-8 observations and from 8.26 to À0.34 for the NOAA WP-3. Improvements in boundary conditions provided by global models decrease the upper troposphere negative ozone bias, while accounting for biomass burning emissions improved model performance for CO. The covariances of ozone bias were highly correlated to NO z , NO y , and HNO 3 biases. Interpolation of bias information through kriging showed that decreasing emissions in SE United States would reduce regional ozone model bias and improve model correlation coefficients. The spatial distribution of forecast errors was analyzed using kriging, which identified distinct features, which when compared to errors in postanalysis simulations, helped document improvements. Changes in dry deposition to crops were shown to reduce substantially high bias in the forecasts in the Midwest, while updated emissions were shown to account for decreases in bias in the eastern United States. Observed and modeled ozone production efficiencies for the DC-8 were calculated and shown to be very similar (7.8) suggesting that recurring ozone bias is due to overestimation of NO x emissions. Sensitivity studies showed that ozone formation in the United States is most sensitive to NO x emissions, followed by VOCs and CO. PAN as a reservoir of NO x can contribute to a significant amount of surface ozone through thermal decomposition.

Research paper thumbnail of The Performance and Issues of a Regional Chemical Transport Model During Discover-AQ 2014 Aircraft Measurements Over Colorado

Springer Proceedings in Complexity, 2016

The National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Pre... more The National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction operates the U.S. Air Quality Forecasting Capability (NAQFC) which uses primarily the U.S Environmental Protection Agency’s Community Multi-Scale Air Quality (CMAQ) model. NAQFC focuses on surface ozone and PM2.5 (particle matter with diameter <2.5 µm), which impacts human-health. Near surface ozone mainly comes from photochemical reactions of NOx and volatile organic compounds (VOCs). Its sources in upper layers could come from either long-range transport or stratospheric ozone. Most PM2.5 comes from near-surface primary emissions or secondary generation from photochemical reactions. During the summer 2014 NASA Discover-AQ-Colorado program, the NOAA Air Resources Laboratory (ARL) provided a real-time forecast in support of aircraft measurements with 12 km CONUS (Contiguous United States) and 4 km nested domains. Here we compare the model results with the aircraft data to investigate our predictions.

Research paper thumbnail of Comparison of emission data and the backward trajectory analysis from airborne observation for East Asia

Proceedings of the Symposium on Global Environment, 2003

Long-range transport of the pollutants influenced by both anthropogenic and natural emission sour... more Long-range transport of the pollutants influenced by both anthropogenic and natural emission source in East Asia including the biomass burning emission in Southeast Asia was investigated by using the backward trajectory analysis from NASA TRACE-P airborne observation and a numerical simulation with three-dimensional chemical transport model (STEM-2k1). As a result, we found systematic regional bias between observed and calculated concentration. The ratios between CO and some NHMCs, such as ethane/CO and ethane/propane, were highly associated with the distribution of emission

Research paper thumbnail of Study of atmospheric mercury budget in East Asia using STEM-Hg modeling system

Science of the Total Environment, 2010

East Asia is the largest source region of global anthropogenic mercury emissions, and contributes... more East Asia is the largest source region of global anthropogenic mercury emissions, and contributes to atmospheric mercury concentration and deposition in other regions. Similarly, mercury from the global pool also plays a role in the chemical transport of mercury in East Asia. Annual simulations of atmospheric mercury in East Asia were performed using the STEM-Hg modeling system to study the mass budgets of mercury in the region. The model results showed strong seasonal variation in mercury concentration and deposition, with signals from large point sources. The annual mean concentrations for gaseous elemental mercury, reactive gaseous mercury and particulate mercury in central China and eastern coastal areas were 1.8 ng m(-3), 100 pg m(-3) and 150 pg m(-3), respectively. Boundary conditions had a strong influence on the simulated mercury concentration and deposition, contributing to 80% of the concentration and 70% of the deposition predicted by the model. The rest was caused by the regional emissions before they were transported out of the model domain. Using different oxidation rates reported for the Hg(0)-O(3) reaction (i.e., by Hall, 1995 vs. by Pal and Ariya, 2004) led to a 9% difference in the predicted mean concentration and a 40% difference in the predicted mean deposition. The estimated annual dry and wet deposition for East Asia in 2001 was in the range of 590-735 Mg and 482-696 Mg, respectively. The mercury mass outflow caused by the emissions in the domain was estimated to be 681-714 Mg yr(-1). This constituted 70% of the total mercury emission in the domain. The greatest outflow occurred in spring and early summer.

Research paper thumbnail of Predicting Air Quality: Current Status and Future Directions

NATO Science for Peace and Security Series

Air quality prediction plays an important role in the management of our environment. Computationa... more Air quality prediction plays an important role in the management of our environment. Computational power and efficiencies have advanced to the point where chemical transport models can predict pollution in an urban air shed with spatial resolution less than a kilometer, and cover the globe with a horizontal resolution of less than 50 km. Predicting air quality remains a challenge due to the complexity of the governing processes and the strong coupling across scales. While air quality prediction is closely aligned with weather prediction, there are important differences, including the role of pollution emissions and their associated large uncertainties. As more atmospheric chemical observations become available chemical data assimilation is expected to play an essential role in air quality forecasting. In this paper the current status of air quality forecasting is discussed and illustrated by comparison of predictions with observations. The future directions are also discussed, with an emphasis on data assimilation. Applications of the four dimensional variational method (4D-Var) and the ensemble Kalman filter (EnKF) approach are presented and discussed.

Research paper thumbnail of A Modeling Study on Regional Air Pollutions Transport Patterns Over the Pearl River Delta in the Fall Season

Modern Physics Letters B, 2005

This paper presents the preliminary results of a modeling study on regional air pollutants transp... more This paper presents the preliminary results of a modeling study on regional air pollutants transport over the Pearl River Delta (PRD) region of China in fall season (Nov. 2002) on the basis of compiled emission inventories. The advanced regional chemical transport model, STEM-2K1, driven by meso-scale meteorological model MM5, was employed with a nesting technique. Three weather patterns were found in the fall season. Numerical sensitive study indicated that external influence on air quality in PRD was significant and dependent on the transport pattern determined by weather situations.

Research paper thumbnail of Chemical data assimilation of Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft measurements

Journal of Geophysical Research, 2006

In this paper, the four-dimensional variational (4D-Var) technique is applied to assimilate aircr... more In this paper, the four-dimensional variational (4D-Var) technique is applied to assimilate aircraft measurements during the Transport and Chemical Evolution over the Pacific (TRACE-P) field experiment into a chemical transport model, Sulfur Transport Eulerian Model, version 2K1 (STEM-2K1). Whether data assimilation would produce better analyzed fields is examined. It is found that assimilating ozone observations from one of two independent flights improves model prediction of the other flight ozone measurements, which are withheld as validation data. The adjusted initial fields after only assimilating the total reactive nitrogen (NO y) observations lead to better predictions of NO, NO 2 , and PAN, based on their agreement with the withheld measurements. One experiment simultaneously assimilating the observations of O 3 , NO, NO 2 , HNO 3 , PAN, and RNO 3 demonstrates that the model is able to match those measurements well by changing the initial fields. In addition, the model predictions of NO y improve significantly after assimilating the aforementioned multiple observation species, which are independent of the withheld NO y measurements. In the paper, we also show that the key species whose initial mixing ratios would significantly affect the agreement between model and measurements can be identified using adjoint sensitivity analysis. Such information can be used to reduce the number of control variables in the 4D-Var data assimilation. To speed up the optimization process in the 4D-Var, we enforce the concentration upper bounds through the limited memory-Broyden-Fletcher-Goldfarb-Shanno-B (L-BFGS-B) algorithm, and this proves to be effective.

Research paper thumbnail of Four-dimensional data assimilation experiments with International Consortium for Atmospheric Research on Transport and Transformation ozone measurements

Journal of Geophysical Research, 2007

Ozone measurements by various platforms during the International Consortium for Atmospheric Resea... more Ozone measurements by various platforms during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) operations in the summer of 2004 are assimilated into the STEM regional chemical transport model (CTM). Under the four-dimensional variational data assimilation (4D-Var) framework, the model forecast (background) error covariance matrix is constructed using both the so-called NMC (National Meteorological Center, now National Centers for Environmental Prediction) method and the observational (Hollingworth-Lönnberg) method. The inversion of the covariance matrix is implemented using truncated singular value decomposition (TSVD) approach. The TSVD approach is numerically stable even with severely ill conditioned vertical correlation covariance matrix and large horizontal correlation distances. Ozone observations by different platforms (aircraft, surface, and ozonesondes) are first assimilated separately. The impacts of the various measurements are evaluated on their ability to improve the predictions, defined as the information content of the observations under the current framework. In the end, all observations are assimilated into the CTM. The final analysis matches well with observations from all platforms. Assessed with all the observations throughout the boundary layer and midtroposphere, the model bias is reduced from 11.3 ppbv for the base case to À1.5 ppbv. A reduction of 10.3 ppbv in root mean square error is also seen. In addition, the potential of improving air quality forecasts by chemical data assimilation is demonstrated. The effect of assimilating ozone observations on model predictions of other species is also shown.

Research paper thumbnail of Regional distribution and emissions of mercury in east Asia: A modeling analysis of Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) observations

Journal of Geophysical Research, 2006

Mercury tracer model simulations are performed to support the analysis of the total gas phase mer... more Mercury tracer model simulations are performed to support the analysis of the total gas phase mercury (TGM) observations on 15 flights of the NSF/NCAR C-130 aircraft during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) campaign conducted during April 2001. Ninety-seven percent of the observed mercury concentrations are greater than 1.2 ng/m 3. The mean value of the observations is 1.9 ng/m 3. No simple relationships between Hg-CO and Hg-total sulfur are found; however, strong correlations are observed in individual flight segments. Backward trajectory analysis is used to help characterize regional of Hg/CO ratios, and these are compared with emission-based ratios from the various sectors. Model predictions using new Hg emission estimates are presented and compared to the observations. Under the condition of a mercury background level of 1.2 ng/m 3 the tracer model underestimates the observations when the flights were over the Yellow Sea but is consistent with the observations when the flights were over the Japan Sea. Further analysis suggests that Hg emissions are underestimated in north central China and the eastern coastal areas of China. Model sensitivity studies indicate that the emissions of China may be underestimated by 80-200%.

Research paper thumbnail of Revisiting China's CO emissions after the Transport and Chemical Evolution over the Pacific (TRACE-P) mission: Synthesis of inventories, atmospheric modeling, and observations

Journal of Geophysical Research, 2006

A new inventory of CO emissions in China is presented for the year 2001. This inventory improves ... more A new inventory of CO emissions in China is presented for the year 2001. This inventory improves and updates the a priori CO emission inventory prepared in support of NASA&amp;amp;amp;amp;amp;#x27;s TRACE-P mission in the spring of 2001. Analysis of CO observations using chemical transport models in ...

Research paper thumbnail of Characterization of the seasonal cycle of south Asian aerosols: A regional-scale modeling analysis

Journal of Geophysical Research, 2007

The sulfur transport and deposition model (STEM) is used to study the aerosol seasonality, distri... more The sulfur transport and deposition model (STEM) is used to study the aerosol seasonality, distribution, and composition over south Asia from September 2004 to August 2005. Model predictions of sulfate, black carbon, primary organic carbon, other anthropogenic particulate matter, windblown mineral dusts, and sea salt are compared at two sites in south Asia where yearlong experimental observations are available from the Atmospheric Brown Cloud (ABC) project. The model predictions are able to capture both the magnitude and seasonality of aerosols over Hanimaadhoo Observatory, Maldives. However, the model is not able to explain the seasonality at the Kathmandu Observatory; but the model does capture Kathmandu's observed annual mean concentration. The absence of seasonal brick kiln emissions within Kathmandu valley in the current inventory is a probable reason for this problem. This model study reveals high-anthropogenic aerosol loading over the Ganges valley even in the monsoonal months, which needs to be corroborated by experimental observations. Modeling results also show a high dust loading over south Asia with a distinct seasonality. Model results of aerosol monthly composition are also presented at five cities in south Asia. Total and fine-mode monthly aerosol optical depth along with contribution from each aerosol species is presented; the results show that the anthropogenic fraction dominates in the postmonsoon and the early dry season with major contributions from sulfate and absorbing aerosols. Model sensitivity studies of dry deposition velocity and wet scavenging efficiency show that model improvements are needed in the treatment of carbonaceous aerosol dry and wet removal processes. Modeled SO 2 conversion rate constrained with sulfate observations at Hanimaadhoo suggests the need to increase model sulfate production rate during the dry season to account for probable sulfate production via heterogeneous pathways.

Research paper thumbnail of Impacts of aerosols and clouds on photolysis frequencies and photochemistry during TRACE-P: 2. Three-dimensional study using a regional chemical transport model

Journal of Geophysical Research: Atmospheres, 2003

A three-dimensional regional chemical transport model, STEM 2K1, coupled with a detailed radiatio... more A three-dimensional regional chemical transport model, STEM 2K1, coupled with a detailed radiation model is used to study the influences of aerosols and clouds on photolysis rates and photochemical processes over East Asia-Western Pacific during the TRACE-P period. Measured J-values are compared with those calculated using threedimensional modeled fields of clouds and aerosols. The model is shown to accurately represent observed J-values over a broad range of conditions. Model studies with and without aerosols and clouds are performed and compared with clear-sky conditions to isolate the various influences. Clouds are shown to have a large impact on photolysis rates during the observation periods of TRACE-P, with J[NO 2 ] decreased by 20% below clouds and enhanced by 3030% from 1 km to 8 km. Clouds also exert a dominant influence on short-lived radicals, like OH and HO 2. For March, clouds reduce OH by 23% at altitudes below 1 km and increase OH by 3025% above 1 km. Asian aerosols contain large amounts of carbonaceous material, inorganic components such as sulfates, and mineral oxides. These aerosols significantly influence J-values and photochemical processes. When averaged over all TRACE-P DC-8 and P-3 flights, the aerosol influence via affecting J-values reduces OH by 4040% below 1 km, and by 4024% above 1 km. Aerosols have a stronger impact on longer-lived chemical species than clouds do because aerosols tend to be coemitted with precursors and have a longer contact time with the polluted air masses. The accumulated aerosol impact generally is to reduce O 3 concentrations by about 6 ppbv in the biomass burning plumes emitted from Southeast Asia. In megacity plumes, aerosols can increase NO x concentration by 40% via reducing its photolytic loss and reduce NO z concentration by a similar amount. A detailed case study of the DC-8 and P-3 flights on 27 March is used to make comparisons for cloud and aerosol influences. During these flights, the cloud impact on J-values is stronger than the aerosol impact, but aerosols are shown to exert a much stronger accumulated influence on O 3 production.

Research paper thumbnail of Multiscale simulations of tropospheric chemistry in the eastern Pacific and on the U.S. West Coast during spring 2002

Journal of Geophysical Research: Atmospheres, 2004

Regional modeling analysis for the Intercontinental Transport and Chemical Transformation 2002 (I... more Regional modeling analysis for the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) experiment over the eastern Pacific and U.S. West Coast is performed using a multiscale modeling system, including the regional tracer model Chemical Weather Forecasting System (CFORS), the Sulfur Transport and Emissions Model 2003 (STEM-2K3) regional chemical transport model, and an off-line coupling with the Model of Ozone and Related Chemical Tracers (MOZART) global chemical transport model. CO regional tracers calculated online in the CFORS model are used to identify aircraft measurement periods with Asian influences. Asian-influenced air masses measured by the National Oceanic and Atmospheric Administration (NOAA) WP-3 aircraft in this experiment are found to have lower DAcetone/DCO, DMethanol/DCO, and DPropane/DEthyne ratios than air masses influenced by U.S. emissions, reflecting differences in regional emission signals. The Asian air masses in the eastern Pacific are found to usually be well aged (>5 days), to be highly diffused, and to have low NO y levels. Chemical budget analysis is performed for two flights, and the O 3 net chemical budgets are found to be negative (net destructive) in the places dominated by Asian influences or clear sites and positive in polluted American air masses. During the trans-Pacific transport, part of gaseous HNO 3 was converted to nitrate particle, and this conversion was attributed to NO y decline. Without the aerosol consideration, the model tends to overestimate HNO 3 background concentration along the coast region. At the measurement site of Trinidad Head, northern California, high-concentration pollutants are usually associated with calm wind scenarios, implying that the accumulation of local pollutants leads to the high concentration. Seasonal variations are also discussed from April to May for this site. A high-resolution nesting simulation with 12-km horizontal resolution is used to study the WP-3 flight over Los Angeles and surrounding areas. This nested simulation significantly improved the predictions for emitted and secondary generated species. The difference of photochemical behavior between the coarse (60-km) and nesting simulations is discussed and compared with the observation.

Research paper thumbnail of Influences of biomass burning during the Transport and Chemical Evolution Over the Pacific (TRACE-P) experiment identified by the regional chemical transport model

Journal of Geophysical Research: Atmospheres, 2003

Using a regional chemical transport model, STEM 2K1, and the emission inventory for the Transport... more Using a regional chemical transport model, STEM 2K1, and the emission inventory for the Transport and Chemical Evolution Over the Pacific (TRACE-P) period [Woo et al., 2003 Streets et al., 2003], we successfully simulated important features of the biomass burning (BB) CO outflow. Simulated results agree well with the TRACE-P aircraft measurements and Thailand surface observations. On the basis of sensitivity studies with and without biomass emissions, we identified nine flight segments that are affected by biomass plumes during the TRACE-P period and compared the characteristics of the BB air masses with the other air masses. The BB air masses emitted from Southeast Asia contain relatively high HCN (ÁHCN/ÁCO $ 0.0015) and potassium (ÁK + /ÁCO $ 0.0038) but very low NO y (ÁNO y / ÁCO $ 0.005) mixing ratios, which may be associated with the special burning condition in this region. The biomass burning air masses have high ozone production efficiency. The observed ÁO 3 /ÁNO z values were $17 in biomass events and 1.7 in other events. The BB influence on the trace gas distributions can be divided into two categories: the influence through direct reactions and the influence caused by BB aerosols changing J values. These two influences are discussed for the BB-affected TRACE-P flights and for east Asia. The BB influences on chemical species are not only determined by the BB plume intensity but also by the ambient environment caused by other emissions. In Southeast Asia, where the biogenic emissions are very strong, the OH background concentration is low, and the BB gas-phase compounds mainly contribute to OH production. Arranged in the sensitivity to the J value change caused by BB aerosols, we have OH > HO 2 > HCHO > O 3 when evaluated on a regional average. Averaged over March, the biomass burning net influence is as high as 50% for OH, 40% for HO 2 , 60% for HCHO, and 10 ppbv for O 3 for the layers below 1 km.

Research paper thumbnail of Large-scale structure of trace gas and aerosol distributions over the western Pacific Ocean during the Transport and Chemical Evolution Over the Pacific (TRACE-P) experiment

Journal of Geophysical Research: Atmospheres, 2003

The Models-3 Community Multiscale Air Quality modeling system (CMAQ) coupled with the Regional At... more The Models-3 Community Multiscale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to analyze the Asian continental outflow of carbon monoxide (CO), ozone (O 3), and aerosol sulfate (SO 4 2À) to the western Pacific Ocean during the period 17-24 March 2001. In this time period eight airborne observations (DC-8 flights 11-14 and P-3B flights 13-16) of the NASA Transport and Chemical Evolution Over the Pacific (TRACE-P) mission were being conducted over a broad area covering Hong Kong, Okinawa, the East China Sea, and southern Japan. Comparison of model results with observations shows that the model reproduces the main observed features of CO, O 3 , and SO 4 2À , including horizontal and vertical gradients, of the Asian pollution outflow over the western Pacific. Model results show that the fast boundary outflow from Asia to the western Pacific is largely restricted to the middle latitudes, and the maximum outflow fluxes are in the lower free atmosphere (3-6 km) north of 25°N. Simulations with and without biomass burning emissions are conducted to quantify the impacts of biomass burning on tropospheric concentrations of CO and O 3. Biomass burning is found to contribute more than 50% of the CO concentrations and up to 40% of the O 3 concentrations in the boundary layer over the major source regions. The largest percentage contributions to CO and O 3 levels (up to 40% and 30%, respectively) over the western Pacific are in the lower free troposphere (2-6 km).

Research paper thumbnail of Predicting air quality: Improvements through advanced methods to integrate models and measurements

Journal of Computational Physics, 2008

This article was published in an Elsevier journal. The attached copy is furnished to the author f... more This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author's institution, sharing with colleagues and providing to institution administration. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

Research paper thumbnail of Adjoint Sensitivity Analysis of Ozone Nonattainment over the Continental United States

Environmental Science & Technology, 2006

An application of the adjoint method in air quality management is demonstrated. In the adjoint ap... more An application of the adjoint method in air quality management is demonstrated. In the adjoint applications (e.g., variational data assimilation), sensitivities of a receptor-based metric to a variety of parameters can be efficiently calculated. Here, we calculate the sensitivities of a nationwide U.S. ozone National Ambient Air Quality Standard (NAAQS) non-attainment metric to precursor emissions during the month of July 2004. We use the adjoint version of a continental scale chemical transport model (STEM) with 60 km horizontal grid resolution. The model shows low bias and error (3, and 21 percent, respectively), particularly for areas with high ozone concentrations that are subject of this study. The non-attainment metric is integrated over the month and entire domain, and accounts for both 1-hour and 8-hour ozone standards. The metric is quadratic, and therefore, higher concentrations are given larger overall weights in the calculations. The non-attainment metric for the month of July is heavily dominated by the 8-hour standard (98% of the combined metric). Using these spatial distributions of sensitivities we identify the regions and source categories with significant contribution/effect on the overall non-attainment metric. Largest values of sensitivities are found to be with respect to emissions in the southeast U.S. and in the Ohio River Valley. When non-attainment sensitivities are integrated over the entire U.S., NO x emissions account for the largest contribution (64% of the total), followed by the biogenic and anthropogenic VOCs (23% and 13%, respectively). For NO x emissions, point/area, mobile, and non-road mobile sources account for 51, 39, and 10 percent of the total sensitivities, respectively. Point/area sources also have the largest effect among the VOC source categories (62%). No significant difference is seen between weekday and weekend emission contribution patterns. We also provide a state-by-state comparison for the non-attainment magnitude, non-attainment sensitivity, and emission magnitudes to explore the influence of interstate transport of ozone and its precursors, and policy implications of the results. Our analysis of the nationwide ozone non-attainment metric suggests that simple cap-and-trade programs may prove inadequate in achieving the sought-after air quality objectives.

Research paper thumbnail of Mineral dust is a sink for chlorine in the marine boundary layer

Atmospheric Environment, 2007

Dust particles affect the budgets of important traces gases by providing a surface on which heter... more Dust particles affect the budgets of important traces gases by providing a surface on which heterogeneous reactions can occur. The uptake of soluble species on dust alters the physical, chemical, and optical properties and the overall ability of dust to act as cloud condensation and ice nuclei. It is commonly assumed that all measured chloride in particulate filter samples is associated with sea-salt particles and any chloride in dust occurs as the result of internal mixtures of sea-salt and dust particles, formed by cloud processing. Here we show high temporal resolution data demonstrating the direct uptake of chlorine by dust via heterogeneous reaction with HCl(g). This reaction added significant amounts of chlorine to the dust particles during a major dust storm, representing 4-9% of the individual dust particle mass. Up to 6574% of the dust particles contained chlorine due to this heterogeneous reaction during the dust front. Ignoring this process leads to an overestimation of sea-salt concentrations from bulk measurements, and an underestimation of the degree of sea-salt aging. The uptake of chloride will change the pH and hygroscopic properties of the dust and thus can influence the budgets of other reactive gases. Including this heterogeneous process in atmospheric measurements and chemical transport models will improve our ability to predict the atmosphere's composition and radiation budget with greater accuracy.

Research paper thumbnail of A regional scale chemical transport modeling of Asian aerosols with data assimilation of AOD observations using optimal interpolation technique

Atmospheric Environment, 2008

aerosols are presented at these two sites. Positive Matrix Factorization (PMF), a factor analytic... more aerosols are presented at these two sites. Positive Matrix Factorization (PMF), a factor analytic method was also used to characterize the source profile and source contribution at these two locations. A three-factor solution was able to explain more than 80% of the variation in the individual species at Hanimaadhoo and 90% variation of aerosol loadings at Gosan. The four-year averaged PMF model results were able to capture the seasonality of anthropogenic and dust loadings at both these locations. In addition, the PMF model identified the differences in the composition of anthropogenic aerosols over Hanimaadhoo and Gosan reflecting the differences in regional emissions. The PMF derived factors could be used as additional constraints for future assimilation studies.

Research paper thumbnail of A communication library for the parallelization of air quality models on structured grids

Atmospheric Environment, 2002

PAQMSG is an MPI-based, Fortran 90 communication library for the parallelization of air quality m... more PAQMSG is an MPI-based, Fortran 90 communication library for the parallelization of air quality models (AQMs) on structured grids. It consists of distribution, gathering and repartitioning routines for different domain decompositions implementing a master-worker strategy. The library is architecture and application independent and includes optimization strategies for different architectures. This paper presents the library from a user perspective. Results are shown from the parallelization of STEM-III on Beowulf clusters. The PAQMSG library is available on the web. The communication routines are easy to use, and should allow for an immediate parallelization of existing AQMs. PAQMSG can also be used for constructing new models.

Research paper thumbnail of Improving regional ozone modeling through systematic evaluation of errors using the aircraft observations during the International Consortium for Atmospheric Research on Transport and Transformation

Journal of Geophysical Research, 2007

During the operational phase of the ICARTT field experiment in 2004, the regional air quality mod... more During the operational phase of the ICARTT field experiment in 2004, the regional air quality model STEM showed a strong positive surface bias and a negative upper troposphere bias (compared to observed DC-8 and WP-3 observations) with respect to ozone. After updating emissions from NEI 1999 to NEI 2001 (with a 2004 large point sources inventory update), and modifying boundary conditions, low-level model bias decreases from 11.21 to 1.45 ppbv for the NASA DC-8 observations and from 8.26 to À0.34 for the NOAA WP-3. Improvements in boundary conditions provided by global models decrease the upper troposphere negative ozone bias, while accounting for biomass burning emissions improved model performance for CO. The covariances of ozone bias were highly correlated to NO z , NO y , and HNO 3 biases. Interpolation of bias information through kriging showed that decreasing emissions in SE United States would reduce regional ozone model bias and improve model correlation coefficients. The spatial distribution of forecast errors was analyzed using kriging, which identified distinct features, which when compared to errors in postanalysis simulations, helped document improvements. Changes in dry deposition to crops were shown to reduce substantially high bias in the forecasts in the Midwest, while updated emissions were shown to account for decreases in bias in the eastern United States. Observed and modeled ozone production efficiencies for the DC-8 were calculated and shown to be very similar (7.8) suggesting that recurring ozone bias is due to overestimation of NO x emissions. Sensitivity studies showed that ozone formation in the United States is most sensitive to NO x emissions, followed by VOCs and CO. PAN as a reservoir of NO x can contribute to a significant amount of surface ozone through thermal decomposition.