Interannual variation in the fine-mode MODIS aerosol optical depth and its relationship to the changes in sulfur dioxide emissions in China between 2000 and 2010

摘要

Anthropogenic SO₂ emissions increased alongside economic development inChina at a rate of 12.7% yr?1 from 2000 to 2005. However, under new Chinesegovernment policy, SO₂ emissions declined by 3.9% yr?1 between 2005 and2009. Between 2000 and 2010, we found that the variability in the fine-mode(submicron) aerosol optical depth (AOD) over the oceans adjacent to East Asiaincreased by 3–8% yr?1 to a peak around 2005–2006 and subsequently decreasedby 2–7% yr?1, based on observations by the Moderate Resolution ImagingSpectroradiometer (MODIS) on board NASA's Terra satellite and simulations bya chemical transport model. This trend is consistent with ground-basedobservations of aerosol particles at a mountainous background observationsite in central Japan. These fluctuations in SO₂ emission intensity andfine-mode AOD are thought to reflect the widespread installation of fuel-gasdesulfurization (FGD) devices in power plants in China, because aerosolsulfate is a major determinant of the fine-mode AOD in East Asia. Using achemical transport model, we confirmed that the contribution of particulatesulfate to the fine-mode AOD is more than 70% of the annual mean and thatthe abovementioned fluctuation in fine-mode AOD is caused mainly by changesin SO₂ emission rather than by other factors such as varyingmeteorological conditions in East Asia. A strong correlation was also foundbetween satellite-retrieved SO₂ vertical column density and bottom-upSO₂ emissions, both of which were also consistent with observed fine-modeAOD trends. We propose a simplified approach for evaluating changes in SO₂emissions in China, combining the use of modeled sensitivity coefficientsthat describe the variation of fine-mode AOD with changes in SO₂ emissionsand satellite retrieval. Satellite measurements of fine-mode AOD above theSea of Japan marked a 4.1% yr?1 decline between 2007 and 2010, whichcorresponded to the 9% yr?1 decline in SO₂ emissions from China during thesame period.