Transport And Chemical Evolution Over The Pacific Research Articles

Development of the CREATE Inventory in Support of Integrated Climate and Air Quality Modeling for Asia

A bottom-up emissions inventory is one of the most important data sets needed to understand air quality (AQ) and climate change (CC). Several emission inventories have been developed for Asia, including Transport and Chemical Evolution over the Pacific (TRACE-P), Regional Emission Inventory in Asia (REAS), and Inter-Continental Chemical Transport Experiment (INTEX) and, while these have been used successfully for many international studies, they have limitations including restricted amounts of information on pollutant types and low levels of transparency with respect to the polluting sectors or fuel types involved. To address these shortcomings, we developed: (1) a base-year, bottom-up anthropogenic emissions inventory for Asia, using the most current parameters and international frameworks (i.e., the Greenhouse gas—Air pollution INteractions and Synergies (GAINS) model); and (2) a base-year, natural emissions inventory for biogenic and biomass burning. For (1), we focused mainly on China, South Korea, and Japan; however, we also covered emission inventories for other regions in Asia using data covering recent energy/industry statistics, emission factors, and control technology penetration. The emissions inventory (Comprehensive Regional Emissions inventory for Atmospheric Transport Experiment (CREATE)) covers 54 fuel classes, 201 subsectors, and 13 pollutants, namely SO2, NOx, CO, non-methane volatile organic compounds (NMVOC), NH3, OC, BC, PM10, PM2.5, CO2, CH4, N2O, and Hg. For the base-year natural emissions inventory, the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and BlueSky-Asia frameworks were used to estimate biogenic and biomass burning emissions, respectively. Since the CREATE emission inventory was designed/developed using international climate change/air quality (CC/AQ) assessment frameworks, such as GAINS, and has been fully connected with the most comprehensive emissions modeling systems—such as the US Environmental Protection Agency (EPA) Chemical Manufacturing Area Source (CMAS) system—it can be used to support various climate and AQ integrated modeling studies, both now and in the future.

REGIONAL-SCALE MODELING OZONE AIR QUALITY OVER THE CONTINENTAL SOUTH EAST ASIA

Long range transport of ozone and its precursors can significantly impact the air quality in downwind regions. The problem of regional transport of ozone has been studied for more than three decades in Europe and U.S but not yet in Southeast Asia. This study investigated the regional scale distribution of tropospheric ozone over the Continental South East Asia Region (CSEA) of Thailand, Burma, Cambodia, Lao and Vietnam. The Models-3 Community Multi-scale Air Quality (CMAQ modeling system, driven by the NCAR/Penn State Fifth-Generation Mesoscale Model (MM5), is used for the purpose. The model domain covers the longitude range from 91'E to 111°E and the latitude range from 5°N to 25°N. Two most recent ozone episodes of March 24-26, 2004 and January 2-4, 2005 were selected which represent the typical meteorological conditions for high ozone concentrations periods of a year. The episode analysis was made based on available data from 10 and 4 monitoring stations located in Bangkok of Thailand and Ho Chi Minh City (HCMC) of Vietnam, respectively. The episodes were characterized with hourly ozone levels above the National Ambient Air Quality Standards of Thailand and Vietnam of 100 ppb at a number of the monitoring stations. The maximum ground level concentrations of ozone for March 2004 and January 2005 episodes reached 173 ppb and 157 ppb, respectively, in the urban plume of the Bangkok Metropolitan Region (BMR). The simulations were performed with 0.5o 0.5° emission input data which was prepared from the regional anthropogenic emission inventory used in the Transport and Chemical Evolution over the Pacific (TRACE-P), and the biogenic emissions obtained from the Global Emissions Inventory Activity (GEIA). The simulated overall picture of ground level ozone concentrations over CSEA domain shows that the concentrations were high at the downwind areas at a considerable distance from large urban areas such as BMR and HCMC. During March 2004 episode the ozone plume moved northeastward following the Southwesterly monsoon and the maximum width of the modeled plume with the ozone above 100 ppb was about 70 km from BMR. For HCMC the ozone plume moved northward and the concentration in the city plume was lower with the width of isopleth of 50ppb of around 40 km. During the Jan 2005 episode the ozone plume moved southwestward following the Northeasterly monsoon and the width of the modeled plume with the ozone concentration above 100 ppb in BMR was 50 km while for HCMC the width of the 40ppb isopleth was about 30 km. The model performance was evaluated on the available observed hourly ozone concentrations. The model system was shown to be able to reproduce the peak ozone levels that occurred during the episodes at these two large urban areas, and capture the day by day variations during the selected episodes. The performance statistics MNBE, NGE, and UPA for the simulated ozone concentrations are within U.S. EPA guidance criteria and are comparable to those reported previous for other regional ozone simulations. It is shown that the MM5/CMAQ system is the suitable modeling tools for ozone prediction over the CSEA.

Modeling Regional/Urban Ozone and Particulate Matter in Beijing, China

This paper examines Beijing air quality in the winter and summer of 2001 using an integrated air quality modeling system (Fifth Generation Mesoscale Meteorological Model [MM5]/Community Multiscale Air Quality [CMAQ]) in nested mode. The National Aeronautics and Space Administration (NASA) Transport and Chemical Evolution over the Pacific (TRACE-P) emission inventory is used in the 36- (East Asia), 12- (East China), and 4-km (greater Beijing area) domains. Furthermore, we develop a local Beijing emission inventory that is used in the 4-km domain. We also construct a corroborated mapping of chemical species between the TRACE-P inventory and the Carbon Bond IV (CB-IV) chemical mechanism before the integrated modeling system is applied to study ozone (O3) and particulate matter (PM) in Beijing. Meteorological data for the integrated modeling runs are extracted from MM5. Model results show O3 hourly concentrations in the range of 80–159 parts per billion (ppb) during summer in the urban areas and up to 189 ppb downwind of the city. High fine PM (PM2.5) concentrations (monthly average of 75 μg · m-3 in summer and 150 μg · m-3 in winter) are simulated over the metropolitan and down-wind areas with significant secondary constituents. A comparison against available O3 and PM measurement data in Beijing is described. We recommend refinements to the developed local Beijing emission inventory to improve the simulation of Beijing’s air quality. The 4-km modeling configuration is also recommended for the development of air pollution control strategies

Characterizing the long-range transport of black carbon aerosols during Transport and Chemical Evolution over the Pacific (TRACE-P) experiment

A major aircraft experiment Transport and Chemical Evolution over the Pacific (TRACE-P) mission over the NW Pacific in March-April 2001 was conducted to better understand how outflow from the Asian continent affects the composition of the global atmosphere. In this paper, a global climate model, GEOS-Chem is used to investigate possible black carbon aerosol contributions from TRACE-P region. Our result depicts that absorbing black carbon ("soot") significantly outflow during lifting to the free troposphere through warm conveyor belt and convection associated with this lifting. The GEOS-Chem simulation results show significant transport of black carbon aerosols from Asian regions to the Western Pacific region during the spring season. As estimated by GEOS-Chem simulations, approximately 25% of the black carbon concentrations over the western pacific originate from SE Asia in the spring.

Estimate of radiative forcing of Asian biomass‐burning aerosols during the period of TRACE‐P

The regional radiative impact of biomass‐burning aerosols in Asia is estimated using the new and detailed emission data during the experimental period of Transport and Chemical Evolution over the Pacific (TRACE‐P) in March 2001. Integration of the USA National Oceanic and Atmospheric Administration (NOAA) Hybrid Single‐Particle Lagrangian Integrated Transport model (HYSPLIT) and a solar radiative transfer model (CLIRAD‐SW) allow us to simulate the spatial and temporal distributions of black carbon (BC) and organic carbon (OC) aerosols from biomass burning in the South Asian region. It also allows us to estimate further their aerosol optical properties and radiative forcing. We find that an anticyclone over Bay of Bengal dominates the transport of pollutants of the South Asian region. The monthly mean surface concentration of OC and BC is 1.1 μg m−3 in this region. Western Myanmar has the maximum value, with the concentration reaching 12.5 μg m−3. The monthly mean clear‐sky direct shortwave radiative forcing ranges from −1.9 to 0.4 W m−2 at the top of the atmosphere and from −0.5 to −12.0 W m−2 at surface, resulting in an increase of the atmospheric heating rate from 0.01 to 0.3°C day−1. Owing to the spatial distributions of the aerosol optical depth ratio (OC/BC) and the surface albedo, there is a strong gradient of heating rate near the source regions, which may modify local circulations.

Source characteristics of oxygenated volatile organic compounds and hydrogen cyanide

Airborne trace gas measurements from Transport and Chemical Evolution over the Pacific (TRACE‐P), Pacific Exploratory Mission (PEM)‐Tropics B, and Intercontinental Chemical Transport Experiment‐North America (INTEX‐NA) experiments are analyzed to examine the major source factors contributing to the observed variabilities of oxygenated volatile organic compounds and cyanides. The positive matrix factorization method is applied to coincident measurements of 11 chemicals including CH3OH, CH3COCH3, CH3CHO, C2H2, C2H6, i‐C5H12, CO, CH3Cl, and CHBr3. Measurements of HCN and CH3CN are available for TRACE‐P and INTEX‐NA. We identify major source contributions from the terrestrial biosphere, biomass burning, industry/urban regions, and oceans. Spatial and back trajectory characteristics of these factors are examined. On the basis of TRACE‐P and PEM‐Tropics B data, we find a factor that explains 80–88% of the CH3OH variability, 20–40% of CH3COCH3, 7–35% of CH3CHO, and 41% of HCN, most likely representing the emissions from terrestrial biosphere. Our analysis suggested that biogenic emissions of HCN may be significant. Cyanogenesis in plants is likely a major emission process for HCN, which was not fully accounted for previously. Larger contributions than previous global estimations to CH3COCH3 and CH3CHO by biomass burning and industry/urban sources likely reflect significant secondary production from volatile organic compound oxidation. No evidence was found for large emissions of CH3COCH3 from the ocean. The oceanic CH3CHO contribution implies large regional variations.

Long‐range transport of the April 2001 dust clouds over the subtropical East Asia and the North Pacific and its impacts on ground‐level air pollution: A Lagrangian simulation

One of the most remarkable Asian dust storms occurred in April 2001, during the periods of the Aerosol Characterization Experiment (ACE)‐Asia and the Transport and Chemical Evolution Over the Pacific (TRACE‐P) field experiments. Our high‐resolution Lagrangian simulations and the detailed comparisons with the Total Ozone Mapping Spectrometer (TOMS)‐Aerosol Index (AI) data, the Geostationary Meteorological Satellite (GMS)‐5 derived dust distribution, and the ground‐level ambient air particulate matter measurements over Taiwan in the subtropical East Asia reveal several features which were not reported before. We found that (1) the trans‐Pacific long‐range transport was dominated by the dust emissions from the natural source over the Gobi desert and the anthropogenic source over east China before 6–7 April, while the southward long‐range transport to the subtropical East Asia were mainly contributed by the dust emissions from natural source over the Taklamakan and the Gobi, and the anthropogenic source over east China after 6–7 April; (2) the southward long‐range transport implies that the anthropogenic pollution is ahead of the cold front (where the precipitation washes out the particulate matter), while the dust is behind the cold front. (3) The dust emissions from the Gobi during 7–9 April, anthropogenic emissions from east China during 9–10 April, and dust emissions from the Taklamakan during 1–4 April appear to have the most significant impacts on the ground‐level particulate matter concentrations over Taiwan. The simulated particle emitted from desert regions before 6–7 April mainly confined to the Gobi and the Taklamakan regions until 6 April when they became highly mobile for the long‐range transport by the large‐scale cyclonic activity and its associated cold air outbreak. The southward transport characteristics simulated here are consistent with the aerosol characterization observed at Taiwan during this period. Our simulations reveal that the rapid trans‐Pacific transport processes occurred on 12 April contribute to the extensive areas of elevated AI values prevail over the North Pacific during this day.

A regional air quality model: Evaluation and simulation of O 3 and relevant gaseous species in East Asia during spring 2001

A regional air quality model (RAQM) has been introduced, evaluated and applied to investigate the behaviors of tropospheric O 3 and relevant species in East Asia. Model simulation is performed with an up-to-date monthly emission inventory [Streets, D.G., Bond, T.C., Carmichael, G.R., Fernandes, S.D., Fu, Q., He, D., Klimont, Z., Nelson, S.M., Tsai, N.Y., Wang, M.Q., Woo, J.-H. and Yarber, K.F., 2003. An inventory of gaseous and primary emissions in Asia in the year 2000. Journal of Geophysical Research 108 (D21), 8809. doi:10.1029/2002JD003093] for March 2001 when extensive experimental data sets were available, including ground-level observations and the TRACE-P (TRAnsport and Chemical Evolution over the Pacific) aircraft experiments, which allow a comprehensive evaluation for this model system. Model validation demonstrates that RAQM is able to represent most of the major processes of chemical species in the troposphere, with model results agreeing with observations reasonably well. Statistical analysis has been conducted for both meteorological parameters (wind speed, temperature and humidity) and chemical components (10 key gaseous species) by comparing with the TRACE-P data sets. At altitudes <5 km, the correlations ( R) for meteorological parameters are all above 0.8, with temperature the highest (0.97). The model produces the highest R for O 3 (around 0.75), followed by CO (0.66–0.72) and HO 2 (0.7), and the lowest R for NO x (0.1–0.2), with R = 0.4–0.7 for the remaining species. The model successfully reproduces the major features in chemical transport associated with the Asian outflow and reasonably explains the observed fluctuation in species concentrations at downwind monitoring sites over the western Pacific.

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

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's TRACE‐P mission in the spring of 2001. Analysis of CO observations using chemical transport models in inverse and forward modes suggested that China's emissions were underestimated by about 50%. We have reexamined the source characteristics and conclude that emissions from cement kilns, brick kilns, and the iron and steel industry were underestimated. Our new estimate for China's CO emissions in 2001 is 157 Tg, 36% higher than the TRACE‐P estimate for the year 2000 of 116 Tg. Bottom‐up and modeled emission estimates are now in good agreement, which represents a major success story for the TRACE‐P mission. The new inventory has been gridded at 30 min × 30 min resolution and tested with the CFORS/STEM‐2K1 model, considerably improving the correlation between model predictions and observations (bias reduced from 27% to 9%). Propagation‐of‐error estimates in the new inventory yield an uncertainty of ±68% (95% confidence intervals), lower than the TRACE‐P value of ±156%; however, the good agreement with results from inverse and forward models implies a greater level of confidence than this. The largest remaining uncertainties concern (1) characterization of open vegetation burning, which cannot be resolved without new field studies; (2) emission factors for small combustion devices, for which emissions testing is urgently needed; and (3) residential fuel consumption, which may require a reassessment of China's official statistics.

A Three-Dimensional Simulation of HO x Concentrations Over East Asia During TRACE-P

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is used to simulate three-dimensional concentration distributions of hydroxyl (OH) and hydroperoxyl (HO2) radicals over the western Pacific Ocean during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) field campaign. Modeled values of OH and HO2 and their closely related chemical species and photolysis rates are compared with observational data collected onboard the DC-8 aircraft. Comparison shows that the model reasonably reproduced these observed values over a broad range of conditions with an overall tendency to overestimate the measured OH and HO2 by a factor of 1.56 and 1.24, respectively. A case study of OH, HO2 and their closely related chemical species and photolysis rates along the DC-8 flights 11 and 12 conducted on 17–18 March 2001 shows that the model reproduces the temporal and spatial variations reasonable well, and produces more reliable OH and HO2 concentrations in the polluted environment than in the clean marine boundary layer.

Evaluation of the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with observations obtained during the TRACE-P experiment: Comparison of ozone and its related species

The Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS) was applied to East Asia to investigate the transport and photochemical transformation of tropospheric ozone during the Transport and Chemical Evolution over the Pacific (TRACE-P) field campaign. Modeled concentrations of hydroxyl radical, hydroperoxyl radical, nitric oxide, nitrogen dioxide, ethene, ethane, carbon monoxide, and ozone were compared with observations obtained onboard of two aircrafts in order to evaluate the model performance. Comparison indicates that the model reproduced the tempo-spatial distributions of ozone and its related chemical species reasonably well, and most model results were within a factor of 2 of the observations.

On the determination of a cloud condensation nuclei from satellite: Challenges and possibilities

We use aerosol size distributions measured in the size range from 0.01 to 10+ μm during Transport and Chemical Evolution over the Pacific (TRACE‐P) and Aerosol Characterization Experiment–Asia (ACE‐Asia), results of chemical analysis, measured/modeled humidity growth, and stratification by air mass types to explore correlations between aerosol optical parameters and aerosol number concentration. Size distributions allow us to integrate aerosol number over any size range expected to be effective cloud condensation nuclei (CCN) and to provide definition of a proxy for CCN (CCNproxy). Because of the internally mixed nature of most accumulation mode aerosol and the relationship between their measured volatility and solubility, this CCNproxy can be linked to the optical properties of these size distributions at ambient conditions. This allows examination of the relationship between CCNproxy and the aerosol spectral radiances detected by satellites. Relative increases in coarse aerosol (e.g., dust) generally add only a few particles to effective CCN but significantly increase the scattering detected by satellite and drive the Angstrom exponent (α) toward zero. This has prompted the use of a so‐called aerosol index (AI) on the basis of the product of the aerosol optical depth and the nondimensional α, both of which can be inferred from satellite observations. This approach biases the AI to be closer to scattering values generated by particles in the accumulation mode that dominate particle number and is therefore dominated by sizes commonly effective as CCN. Our measurements demonstrate that AI does not generally relate well to a measured proxy for CCN unless the data are suitably stratified. Multiple layers, complex humidity profiles, dust with very low α mixed with pollution, and size distribution differences in pollution and biomass emissions appear to contribute most to method limitations. However, we demonstrate that these characteristic differences result in predictable influences on AI. These results suggest that inference of CCN from satellites will be challenging, but new satellite and model capabilities could possibly be integrated to improve this retrieval.

Chemical data assimilation of Transport and Chemical Evolution over the Pacific (TRACE‐P) aircraft measurements

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 (NOy) observations lead to better predictions of NO, NO2, and PAN, based on their agreement with the withheld measurements. One experiment simultaneously assimilating the observations of O3, NO, NO2, HNO3, PAN, and RNO3 demonstrates that the model is able to match those measurements well by changing the initial fields. In addition, the model predictions of NOy improve significantly after assimilating the aforementioned multiple observation species, which are independent of the withheld NOy 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.

Comparison of model-simulated tropospheric NO 2 over China with GOME-satellite data

Tropospheric NO 2 column densities over China simulated with a regional model using different emission inventory input are compared with Global Ozone Monitoring Experiment (GOME) satellite data. These emission inventories include (i) emission estimates for the year 1995 from the Emission Database for Global Atmospheric Research (EDGAR), (ii) regional emission inventory used in the Transport and Chemical Evolution over the Pacific (TRACE-P) program with emission estimates for the year 2000 and (iii) national emission inventory used in the Chinese Ozone Research Programme (CORP) with emission estimates for the year 1995. Model simulations were performed for a summertime period and the results under clear-sky conditions were selected for comparison with GOME data of the years 1996 and 2000. The model generally reproduces high tropospheric NO 2 column densities in polluted areas of China that have been observed by GOME. However, the model simulations do not agree with the GOME measurements in a quantitative sense for some regions. Region-to-region comparisons show that with all the emission inventories the model underestimates the tropospheric NO 2 column density in remote and rural areas of China. It is found that TRACE-P underestimates the tropospheric NO 2 column density in all the regions with respect to the GOME measurements (by more than 50%). CORP and EDGAR appear to behave well for the model simulations in the North of China (within 15% deviations), but poorer for the model simulations in other regions (within 30–80% deviations). Linear regressions were performed with the NO 2 column densities available from GOME, Y, and the model, X, of each grid cell in selected regions. For all the region of China, comparison statistics are Y = 0.3 6 1 × X + 0.9 3 5 with r 2 = 0.3 6 0 and bias=−41% for EDGAR, Y = 1.1 2 4 × X + 0.9 2 0 with r 2 = 0.4 7 2 and bias=−67% for TRACE-P, and Y = 0.4 3 1 × X + 0.8 3 5 with r 2 = 0.5 0 9 and bias=−31% for CORP.

Impacts of Asian megacity emissions on regional air quality during spring 2001

Measurements from the Transport and Chemical Evolution over the Pacific (TRACE‐P) and Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) field experiments obtained during the period of March–April 2001 are used to evaluate the impact of megacity emissions on regional air quality in east Asia. A classification method built upon back trajectory analysis and sensitivity runs using the Sulfur Transport and Emissions Model 2001 (STEM‐2K1) regional chemical transport model are used to identify the aircraft observations that were influenced by megacity emissions. More than 30% of measurement points are classified as urban points, with a significant number of plumes found to have originated from Shanghai, Qingdao, Beijing, Taiyuan, Tianjin and Guiyang, Seoul, and Pusan. These data are then analyzed, and chemical characteristics of these megacities are compared. Emission estimates for the megacities are also presented and discussed in the context of expected similarities and differences in the chemical signals in the ambient air impacted by these cities. Comparisons of the observation‐based ratios with emission‐based estimates are presented and provide a means to test for the consistency of the emission estimates. The observation‐based ratios are shown to be generally consistent with the emissions ratios. The megacity emissions are used in the STEM‐2K1 model to study the effects of these emissions on criteria and photochemical species in the region. Over large portions of the Japan Sea, Yellow Sea, western Pacific Ocean, and the Bay of Bengal, megacity emissions contribute in excess of 10% of the near‐surface ambient levels of O3, CO, SO2, H2SO4, HCHO, and NOz. The megacity emissions are also used to study ozone levels in Asia under a scenario where all cities evolve their emissions in a manner such that they end up with the same VOC/NOx emission ratio as that for Tokyo. Monthly mean ozone levels are found to increase by at least 5%.

Numerical simulation with a comprehensive chemical transport model of nitrate, sulfate, and ammonium aerosol distributions over east asia

The transport and chemical production processes of nitrate, sulfate, and ammonium aerosols over East Asia were investigated by use of the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system coupled with the Regional Atmospheric Modeling System (RAMS). For the evaluation of the model's ability in depicting their 3-dimensional concentration distributions and temporal variations, modeled concentrations of nitrate, sulfate, and ammonium aerosols are compared with the observations obtained at a ground station in Japan in March 2001 and onboard of an aircraft DC-8 on 18 and 21 March 2001 during the Transport and Chemical Evolution over the Pacific (TRACE-P) field campaign. Comparison shows that simulated values of nitrate, sulfate, and ammonium aerosols are generally in good agreement with their observed data, and the model captures most important observed features, and reproduces temporal and spatial variations of nitrate, sulfate, and ammonium aerosol concentrations reasonably well, e.g., the timing and locations of the concentration spikes of nitrate, sulfate, and ammonium aerosols are well reproduced, but large discrepancies between observed and simulated values are also clearly seen at some points and some times due to the coarse grid resolution and uncertainties of the emissions used in this study. This comparison results indicate that CMAQ is able to simulate the distributions of nitrate, sulfate, and ammonium aerosols and their related species in the troposphere over East Asia reasonably well.

Contribution of particulate nitrate to airborne measurements of total reactive nitrogen

Simultaneous measurements of speciated, total reactive nitrogen (NOy) and particulate NO3− (particle diameter &lt;1.3 μm) were made on board the NASA P‐3B aircraft over the western Pacific in February–April 2001 during the Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment. Gas‐phase and particulate NOy was measured using a gold tube catalytic converter. For the interpretation of particulate NOy, conversion efficiencies of particulate NH4NO3, KNO3, NaNO3, and Ca(NO3)2 were measured in the laboratory. Only NH4NO3 showed quantitative conversion, and its conversion efficiency was as high as that for HNO3. NOy measured on board the aircraft was found to be systematically higher by 10–30% than the sum of the individual NOy gas components (∑(NOy)i) at 0–4 km. Particulate NO3− concentrations measured by a particle‐into‐liquid sampler (PILS) were nearly equal to NOy − ∑(NOy)i under low‐dust‐loading conditions. The PILS data showed that the majority of the particulate NO3− was in the form of NH4NO3 under these conditions, suggesting that NH4NO3 particles were quantitatively converted to detectable NO by the NOy converter, consistent with the laboratory experiments. The contribution of particulate NO3− to NOy was most important at 0–2 km, where NO3− constituted 10–30% of NOy during TRACE‐P. On average, the amounts of particulate NO3− and gas‐phase HNO3 were comparable in this region.

Export efficiency of black carbon aerosol in continental outflow: Global implications

We use aircraft observations of Asian outflow from the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) mission over the NW Pacific in March–April 2001 to estimate the export efficiency of black carbon (BC) aerosol during lifting to the free troposphere, as limited by scavenging from the wet processes (warm conveyor belts and convection) associated with this lifting. Our estimate is based on the enhancement ratio of BC relative to CO in Asian outflow observed at different altitudes and is normalized to the enhancement ratio observed in boundary layer outflow (0–1 km). We similarly estimate export efficiencies of sulfur oxides (SOx = SO2(g) + fine SO42−) and total inorganic nitrate (HNO3T = HNO3(g) + fine NO3−) for comparison to BC. Normalized export efficiencies for BC are 0.63–0.74 at 2–4 km altitude and 0.27–0.38 at 4–6 km. Values at 2–4 km altitude are higher than for SOx (0.48–0.66) and HNO3T (0.29–0.62), implying that BC is scavenged in wet updrafts but not as efficiently as sulfate or nitrate. Simulation of the TRACE‐P period with a global three‐dimensional model (GEOS‐CHEM) indicates that a model timescale of 1 ± 1 days for conversion of fresh hydrophobic to hydrophilic BC provides a successful fit to the export efficiencies observed in TRACE‐P. The resulting mean atmospheric lifetime of BC is 5.8 ± 1.8 days, the global burden is 0.11 ± 0.03 Tg C, and the decrease in Arctic snow albedo due to BC deposition is 3.1 ± 2.5%.

Biomass burning emission inventory from burnt area data given by the SPOT‐VEGETATION system in the frame of TRACE‐P and ACE‐Asia campaigns

One of the main uncertainties in the estimation of the climatic impact of aerosols is linked to our knowledge of gas and aerosol emissions. This is particularly crucial over Asia, where a strong regional fingerprint is observed, with different emission types, depending on the various vegetation and climate conditions (biomass burning emissions) and on the very fast changes of the population and industrialization (biofuel and fossil fuel emissions). The main contribution of this work is to derive a biomass burning inventory of 1° × 1° over Asia (the Asian biomass burning inventory (ABBI)) for gases and particles for the Aerosol Characterization Experiment‐Asia (ACE‐Asia) and Transport and Chemical Evolution Over the Pacific (TRACE‐P) campaign period (March to May 2001) in 2001. In this paper we apply new estimates of burnt biomass area to estimate emissions. The method is based on burnt areas (GBA2000 project; Tansey et al. (2002) and Grégoire et al. (2003)) obtained from 1 km resolution SPOT‐VEGETATION satellite data. Regional‐scale maps of burnt areas are produced, and then spatial and temporal emission distribution are obtained from biomass density and emission factors. Strength and weaknesses associated with the use of satellite products are discussed, including the problem of subpixel classification and the lack of validation data for the accuracy assessment of the products for the studied area. Estimated emissions are compared with ACE‐Asia and TRACE‐P Modeling and Emission Support System (ACESS) climatological estimates. In addition, interannual variability is estimated by preparing inventories for the years 2000 and 2001.

Simulation of sulfur transport and transformation in East Asia with a comprehensive chemical transport model

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is applied to East Asia to analyze the production and transport processes of sulfur compounds in the springtime of 2001, when two large field campaigns TRACE-P (TRAnsport and Chemical Evolution over the Pacific) and ACE-Asia (Aerosol Characterization Experiment – Asia) were being conducted over a broad area covering northeastern Asia and the western pacific. Simulated concentrations of sulfur dioxide (SO 2) and sulfate aerosol (SO 4 2−) were compared with observed data obtained on the ground level at three remote sites in South Korea and China and onboard aircraft C130, and it was found that the modeling system reproduced many of the important features in the observations, including horizontal and vertical gradients, of the Asian pollution outflow over the western Pacific. Analysis of model results shows that the SO 2 and SO 4 2− concentrations exhibited pronounced variations in time and space, with SO 2 and SO 4 2− behaving differently due to the interplay of chemical conversion, removal and transport processes.