Multiphase chemistry of NO2 and alkaline matter in aerosol water explains rapid sulfate formation and severe haze in China.
Abstract.With the rapid development of the economy, the sulfur dioxide (SO 2 ) emission from China since 2000 is of increasing concern. In this study, we estimate the annual SO 2 emission in China after 2000 using a technology-based methodology specifically for China. From 2000 to 2006, total SO 2 emission in China increased by 53%, from 21.7 Tg to 33.2 Tg, at an annual growth rate of 7.3%. Emissions from power plants are the main sources of SO 2 in China and they increased from 10.6 Tg to 18.6 Tg in the same period. Geographically, emission from north China increased by 85%, whereas that from the south increased by only 28%. The emission growth rate slowed around 2005, and emissions began to decrease after 2006 mainly due to the wide application of flue-gas desulfurization (FGD) devices in power plants in response to a new policy of China's government. This paper shows that the trend of estimated SO 2 emission in China is consistent with the trends of SO 2 concentration and acid rain pH and frequency in China, as well as with the increasing trends of background SO 2 and sulfate concentration in East Asia. A longitudinal gradient in the percentage change of urban SO 2 concentration in Japan is found during 2000-2007, indicating that the decrease of urban SO 2 is lower in areas close to the Asian continent. This implies that the transport of increasing SO 2 from the Asian continent partially counteracts the local reduction of SO 2 emission downwind. The aerosol optical depth (AOD) products of Moderate ResoluCorrespondence to: Z. Lu (zlu@anl.gov) tion Imaging Spectroradiometer (MODIS) are found to be highly correlated with the surface solar radiation (SSR) measurements in East Asia. Using MODIS AOD data as a surrogate of SSR, we found that China and East Asia excluding Japan underwent a continuous dimming after 2000, which is in line with the dramatic increase in SO 2 emission in East Asia. The trends of AOD from both satellite retrievals and model over East Asia are also consistent with the trend of SO 2 emission in China, especially during the second half of the year, when sulfur contributes the largest fraction of AOD. The arrested growth in SO 2 emissions since 2006 is also reflected in the decreasing trends of SO 2 and SO 2− 4 concentrations, acid rain pH values and frequencies, and AOD over East Asia.
An accurate description of emissions is crucial for model simulations to reproduce and interpret observed phenomena over extended time periods. In this study, we used an approach based on activity data to develop a consistent series of spatially resolved emissions in the United States from 1990 to 2010. The state-level anthropogenic emissions of SO2, NOx, CO, NMVOC (non-methane volatile organic compounds), NH3, PM10 and PM2.5 for a total of 49 sectors were estimated based on several long-term databases containing information about activities and emission controls. Activity data for energy-related stationary sources were derived from the State Energy Data System. Corresponding emission factors reflecting implemented emission controls were calculated back from the National Emissions Inventory (NEI) for seven years (i.e., 1990, 1995, 1996, 1999, 2001, 2002 and 2005), and constrained by the AP-42 (US EPA's Compilation of Air Pollutant Emissions Factors) dataset. Activity data for mobile sources including different types of highway vehicles and non-highway equipment were obtained from highway statistics reported by the Federal Highway Administration. The trends in emission factors for highway mobile source were informed by the 2011 National Transportation Statistics. Emissions for all non-energy-related sources were either scaled by the growth ratio of activity indicators or adjusted based on the NEI trends report.
Because of the strengthened control efforts, particularly for the power sector and mobile sources, emissions of all pollutants except NH3 were reduced by half over the last two decades. The emission trends developed in this study are comparable with the NEI trend report and EDGAR (Emissions Database for Global Atmospheric Research) data, but better constrained by trends in activity data. Reductions in SO2, NOx, CO and EC (speciation of PM2.5 by SMOKE, Sparse Matrix Operator Kernel Emissions) emissions agree well with the observed changes in ambient SO2, NO2, CO and EC concentrations, suggesting that the various controls on emissions implemented over the last two decades are well represented in the emission inventories developed in this study. These inventories were processed by SMOKE and are now ready to be used for regional chemistry transport model simulations over the 1990–2010 period
Abstract.Trends in air quality across the Northern Hemisphere over a 21-year period were simulated using the Community Multiscale Air Quality (CMAQ) multiscale chemical transport model driven by meteorology from Weather Research and Forecasting (WRF) simulations and internally consistent historical emission inventories obtained from EDGAR. Thorough comparison with several ground observation networks mostly over Europe and North America was conducted to evaluate the model performance as well as the ability of CMAQ to reproduce the observed trends in air quality over the past 2 decades in three regions: eastern China, the continental United States and Europe.The model successfully reproduced the observed decreasing trends in SO 2 , NO 2 , 8 h O 3 maxima, SO 2− 4 and elemental carbon (EC) in the US and Europe. However, the model fails to reproduce the decreasing trends in NO − 3 in the US, potentially pointing to uncertainties of NH 3 emissions. The model failed to capture the 6-year trends of SO 2 and NO 2 in CN-API (China -Air Pollution Index) from 2005 to 2010, but reproduced the observed pattern of O 3 trends shown in three World Data Centre for Greenhouse Gases (WDCGG) sites over eastern Asia. Due to the coarse spatial resolution employed in these calculations, predicted SO 2 and NO 2 concentrations are underestimated relative to all urban networks, i.e., US-AQS (US -Air Quality System; normalized mean bias (NMB) = −38 % and −48 %), EU-AIRBASE (European Air quality data Base; NMB = −18 and −54 %) and CN-API (NMB = −36 and −68 %). Conversely, at the rural network EU-EMEP (European Monitoring and Evaluation Programme), SO 2 is overestimated (NMB from 4 to 150 %) while NO 2 is simulated well (NMB within ±15 %) in all seasons. Correlations between simulated and observed O 3 wintertime daily 8 h maxima (DM8) are poor compared to other seasons for all networks. Better correlation between simulated and observed SO 2− 4 was found compared to that for SO 2 . Underestimation of summer SO 2− 4 in the US may be associated with the uncertainty in precipitation and associated wet scavenging representation in the model. The model exhibits worse performance for NO − 3 predictions, particularly in summer, due to high uncertainties in the gas/particle partitioning of NO − 3 as well as seasonal variations of NH 3 emissions. There are high correlations (R > 0.5) between observed and simulated EC, although the model underestimates the EC concentration by 65 % due to the coarse grid resolution as well as uncertainties in the PM speciation profile associated with EC emissions.The almost linear response seen in the trajectory of modeled O 3 changes in eastern China over the past 2 decades suggests that control strategies that focus on combined control of NO x and volatile organic compound (VOC) emissions with a ratio of 0.46 may provide the most effective means for O 3 reductions for the region devoid of nonlinear response potentially associated with NO x or VOC limitation resulting from alternate strategies. The response of O 3 is ...
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