Abstract. Satellite observations of the tropospheric NO 2 vertical column density (VCD) are closely correlated to, and thus can be used to estimate, surface NO x emissions. In this study, the NO 2 VCD simulated by a regional chemical transport model with emissions data from the updated Regional Emission inventory in ASia (REAS) version 2.1 were validated through comparison with multisatellite observations during the period 2000-2010. Rapid growth in NO 2 VCD (∼ 11 % year −1 ) driven by the expansion of anthropogenic NO x emissions was identified above the central eastern China (CEC) region, except for the period during the economic downturn. In contrast, slightly decreasing trends (∼ 2 % year −1 ) were identified above Japan accompanied by a decline in anthropogenic emissions. To systematically compare the modeled NO 2 VCD, we estimated sampling bias and the effect of applying the averaging kernel information, with particular focus on the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) data. Using the updated REAS, the modeled NO 2 VCD reasonably reproduced annual trends observed by multisatellites, suggesting that the rate of increase of NO x emissions estimated by the updated REAS inventory would be robust. Province-scale revision of emissions above CEC is needed to further refine emission inventories. Based on the close linear relationship between modeled and observed NO 2 VCD and anthropogenic NO x emissions, NO x emissions in 2009 and 2010, which were not covered by the updated REAS inventory, were estimated. NO x emissions from anthropogenic sources in China in 2009 and 2010 were determined to be 26.4 and 28.5 Tg year −1 , respectively, indicating that NO x emissions increased more than twofold between 2000 and 2010. This increase reflected the strong growth of anthropogenic emissions in China following the rapid recovery from the economic downturn from late 2008 until mid-2009. Our method consists of simple estimations from satellite observations and provides results that are consistent with the most recent inventory of emissions data for China.
Abstract. Anthropogenic SO 2 emissions increased alongside economic development in China at a rate of 12.7 % yr −1 from 2000 to 2005. However, under new Chinese government policy, SO 2 emissions declined by 3.9 % yr −1 between 2005 and 2009. Between 2000 and 2010, we found that the variability in the fine-mode (submicron) aerosol optical depth (AOD) over the oceans adjacent to East Asia increased by 3-8 % yr −1 to a peak around [2005][2006] and subsequently decreased by 2-7 % yr −1 , based on observations by the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA's Terra satellite and simulations by a chemical transport model. This trend is consistent with ground-based observations of aerosol particles at a mountainous background observation site in central Japan. These fluctuations in SO 2 emission intensity and fine-mode AOD are thought to reflect the widespread installation of fuel-gas desulfurization (FGD) devices in power plants in China, because aerosol sulfate is a major determinant of the fine-mode AOD in East Asia. Using a chemical transport model, we confirmed that the contribution of particulate sulfate to the fine-mode AOD is more than 70 % of the annual mean and that the abovementioned fluctuation in fine-mode AOD is caused mainly by changes in SO 2 emission rather than by other factors such as varying meteorological conditions in East Asia. A strong correlation was also found between satellite-retrieved SO 2 vertical column density and bottom-up SO 2 emissions, both of which were also consistent with observed fine-mode AOD trends. We propose a simplified approach for evaluating changes in SO 2 emissions in China, combining the use of modeled sensitivity coefficients that describe the variation of fine-mode AOD with changes in SO 2 emissions and satellite retrieval. Satellite measurements of fine-mode AOD above the Sea of Japan marked a 4.1 % yr −1 decline between 2007 and 2010, which corresponded to the 9 % yr −1 decline in SO 2 emissions from China during the same period.
A 15-year record (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) of the ratio of nitrate to non-sea-salt sulfate in precipitation over East Asia
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