Extreme haze episodes repeatedly shrouded Beijing during the winter of 2012-2013, causing major environmental and health problems. To better understand these extreme events, we performed a model-assisted analysis of the hourly observation data of PM2.5 and its major chemical compositions. The synthetic analysis shows that (1) the severe winter haze was driven by stable synoptic meteorological conditions over northeastern China, and not by an abrupt increase in anthropogenic emissions. (2) Secondary species, including organics, sulfate, nitrate, and ammonium, were the major constituents of PM2.5 during this period. (3) Due to the dimming effect of high loading of aerosol particles, gaseous oxidant concentrations decreased significantly, suggesting a reduced production of secondary aerosols through gas-phase reactions. Surprisingly, the observational data reveals an enhanced production rate of secondary aerosols, suggesting an important contribution from other formation pathways, most likely heterogeneous reactions. These reactions appeared to be more efficient in producing secondary inorganics aerosols than organic aerosols resulting in a strongly elevated fraction of inorganics during heavily polluted periods. (4) Moreover, we found that high aerosol concentration was a regional phenomenon. The accumulation process of aerosol particles occurred successively from cities southeast of Beijing. The apparent sharp increase in PM2.5 concentration of up to several hundred mu g m(-3) per hour recorded in Beijing represented rapid recovery from an interruption to the continuous pollution accumulation over the region, rather than purely local chemical production. This suggests that regional transport of pollutants played an important role during these severe pollution events

Abstract. Severe regional haze pollution events occurred in eastern and central China in January 2013, which had adverse effects on the environment and public health. Extremely high levels of particulate matter with aerodynamic diameter of 2.5 µm or less (PM 2.5 ) with dominant components of sulfate and nitrate are responsible for the haze pollution. Although heterogeneous chemistry is thought to play an important role in the production of sulfate and nitrate during haze episodes, few studies have comprehensively evaluated the effect of heterogeneous chemistry on haze formation in China by using the 3-D models due to of a lack of treatments for heterogeneous reactions in most climate and chemical transport models. In this work, the WRF-CMAQ model with newly added heterogeneous reactions is applied to East Asia to evaluate the impacts of heterogeneous chemistry and the meteorological anomaly during January 2013 on regional haze formation. As the parameterization of heterogeneous reactions on different types of particles is not well established yet, we arbitrarily selected the uptake coefficients from reactions on dust particles and then conducted several sensitivity runs to find the value that can best match observations. The revised CMAQ with heterogeneous chemistry not only captures the magnitude and temporal variation of sulfate and nitrate, but also reproduces the enhancement of relative contribution of sulfate and nitrate to PM 2.5 mass from clean days to polluted haze days. These results indicate the significant role of heterogeneous chemistry in regional haze formation and improve the understanding of the haze formation mechanisms during the January 2013 episode.

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 speciation mapping of non-methane volatile organic compounds (NMVOC) emissions has an important impact on the performance of chemical transport models (CTMs) in simulating ozone mixing ratios and secondary organic aerosols. Taking the INTEX-B Asian NMVOC emission inventory as the case, we developed an improved speciation framework to generate model-ready anthropogenic NMVOC emissions for various gas-phase chemical mechanisms commonly used in CTMs in this work, by using an explicit assignment approach and updated NMVOC profiles. NMVOC profiles were selected and aggregated from a wide range of new measurements and the SPECIATE database v.4.2. To reduce potential uncertainty from individual measurements, composite profiles were developed by grouping and averaging source profiles from the same category. The fractions of oxygenated volatile organic compounds (OVOC) were corrected during the compositing process for those profiles which used improper sampling and analyzing methods. Emissions of individual species were then lumped into species in different chemical mechanisms used in CTMs by applying mechanism-dependent species mapping tables, which overcomes the weakness of inaccurate mapping in previous studies. Emission estimates for individual NMVOC species differ between one and three orders of magnitude for some species when different sets of profiles are used, indicating that source profile is the most important source of uncertainties of individual species emissions. However, those differences are diminished in lumped species as a result of the lumping in the chemical mechanisms. Gridded emissions for eight chemical mechanisms at 30 min x 30 min resolution as well as the auxiliary data are available at < a href='http://mic.greenresource.cn/intex-b2006'target='_blank'> http://mic.greenresource.cn/intex-b2006 . The framework proposed in this work can be also used to develop speciated NMVOC emissions for other regions

With the rapid development of the economy, the sulfur dioxide (SO₂) emission from China since 2000 is of increasing concern. In this study, we estimate the annual SO₂ emission in China after 2000 using a technology-based methodology specifically for China. From 2000 to 2006, total SO₂ 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 SO₂ 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 SO₂ emission in China is consistent with the trends of SO₂ concentration and acid rain pH and frequency in China, as well as with the increasing trends of background SO₂ and sulfate concentration in East Asia. A longitudinal gradient in the percentage change of urban SO₂ concentration in Japan is found during 2000–2007, indicating that the decrease of urban SO₂ is lower in areas close to the Asian continent. This implies that the transport of increasing SO₂ from the Asian continent partially counteracts the local reduction of SO₂ emission downwind. The Aerosol Optical Depth (AOD) products of Moderate Resolution 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 SO₂ emission in East Asia. The trends of AOD from both satellite retrievals and model over East Asia are also consistent with the trend of SO₂ emission in China, especially during the second half of the year, when sulfur contributes the largest fraction of AOD. The arrested growth in SO₂ emissions since 2006 is also reflected in the decreasing trends of SO₂ and SO₄^2&minus; concentrations, acid rain pH values and frequencies, and AOD over East Asia