ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-13-2635-2013 Sulfate-nitrate-ammonium aerosols over China: response to 2000–2015 emission changes of sulfur dioxide, nitrogen oxides, and ammonia Wang Y. 1 Zhang Q. Q. 1 He K. 2 Zhang Q. 1 Chai L. 1 Ministry of Education Key Laboratory for Earth System Modeling, Center for Earth System Science, Institute for Global Change Studies, Tsinghua University, Beijing, China School of Environment, Tsinghua University, Beijing, 100084, China 05 03 2013 13 5 2635 2652 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/13/2635/2013/acp-13-2635-2013.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/13/2635/2013/acp-13-2635-2013.pdf

We use a chemical transport model to examine the change of sulfate-nitrate-ammonium (SNA) aerosols over China due to anthropogenic emission changes of their precursors (SO<sub>2</sub>, NO<sub>x</sub> and NH<sub>3</sub>) from 2000 to 2015. From 2000 to 2006, annual mean SNA concentrations increased by about 60% over China as a result of the 60% and 80% increases in SO<sub>2</sub> and NO<sub>x</sub> emissions. During this period, sulfate is the dominant component of SNA over South China (SC) and Sichuan Basin (SCB), while nitrate and sulfate contribute equally over North China (NC). Based on emission reduction targets in the 12th (2011–2015) Five-Year Plan (FYP), China's total SO<sub>2</sub> and NO<sub>x</sub> emissions are projected to change by −16% and +16% from 2006 to 2015, respectively. The amount of NH<sub>3</sub> emissions in 2015 is uncertain, given the lack of sufficient information on the past and present levels of NH<sub>3</sub> emissions in China. With no change in NH<sub>3</sub> emissions, SNA mass concentrations in 2015 will decrease over SCB and SC compared to their 2006 levels, but increase over NC where the magnitude of nitrate increase exceeds that of sulfate reduction. This suggests that the SO<sub>2</sub> emission reduction target set by the 12th FYP, although effective in reducing SNA over SC and SCB, will not be successful over NC, for which NO<sub>x</sub> emission control needs to be strengthened. If NH<sub>3</sub> emissions are allowed to keep their recent growth rate and increase by +16% from 2006 to 2015, the benefit of SO<sub>2</sub> reduction will be completely offset over all of China due to the significant increase of nitrate, demonstrating the critical role of NH<sub>3</sub> in regulating nitrate. The effective strategy to control SNA and hence PM<sub>2.5</sub> pollution over China should thus be based on improving understanding of current NH<sub>3</sub> emissions and putting more emphasis on controlling NH<sub>3</sub> emissions in the future.

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