Changes in PM<sub>2.5</sub> sensitivity to NO<i> <sub>x</sub> </i> and NH<sub>3</sub> emissions due to a large decrease in SO<sub>2</sub> emissions from 2013 to 2018
Guangyi Xu, Qianqian Zhang, Yu Yao, Xingying Zhang
Abstract
The authors evaluated and compared the behavior of PM<sub>2.5</sub> with respect to NO<i><sub>x</sub></i> and NH<sub>3</sub> emission changes in high (the year 2013) and low (the year 2018) SO<sub>2</sub> emission cases. Two groups of simulations were conducted based on anthropogenic emissions from China in 2013 and 2018, respectively. In each group of simulations, a respective 25% reduction in NO<i><sub>x</sub></i> and NH<sub>3</sub> emissions were assumed. A sensitivity factor (<i>β</i>) was defined as the relative change in PM<sub>2.5</sub> concentration due to 1% change in NO<i><sub>x</sub></i> or NH<sub>3</sub> emissions. In the high SO<sub>2</sub> emissions case, PM<sub>2.5</sub> was more sensitive to NH<sub>3</sub> (0.31) emissions change than NO<i><sub>x</sub></i> (0.21). Due to the significant decrease in SO<sub>2</sub> emissions from the high to low SO<sub>2</sub> emissions case, the sensitivity of PM<sub>2.5</sub> to NO<i><sub>x</sub></i> increased to 0.33, while its sensitivity to NH<sub>3</sub> decreased to 0.22. The result implies that now and in the future, PM<sub>2.5</sub> is/will be less sensitive to NH<sub>3</sub> emissions change, while NO<i><sub>x</sub></i> emissions control is more effective in reducing the surface PM<sub>2.5</sub> concentration. Seasonally, in the low SO<sub>2</sub> emissions case, the sensitivities of PM<sub>2.5</sub> to NO<i><sub>x</sub></i> and NH<sub>3</sub> in winter were higher than those in summer, indicating that to deal with severe winter haze more attention should be paid to the emissions control of inorganic PM<sub>2.5</sub> precursors, especially NO<i><sub>x</sub></i>.