Interannual variation of reactive nitrogen emissions and their impacts on PM2.5 air pollution in China during 2005–2015

Abstract

Emissions of reactive nitrogen as ammonia (NH _3 ) and nitrogen oxides (NO _x ), together with sulfur dioxide (SO _2 ), contribute to formation of secondary PM _2.5 in the atmosphere. Satellite observations of atmospheric NH _3 , NO _2 , and SO _2 levels since the 2000s provide valuable information to constrain the spatial and temporal variability of their emissions. Here we present a bottom-up Chinese NH _3 emission inventory combined with top-down estimates of Chinese NO _x and SO _2 emissions using ozone monitoring instrument satellite observations, aiming to quantify the interannual variations of reactive nitrogen emissions in China and their contributions to PM _2.5 air pollution over 2005–2015. We find small interannual changes in the total Chinese anthropogenic NH _3 emissions during 2005–2016 (12.0–13.3 Tg with over 85% from agricultural sources), but large interannual change in top-down Chinese NO _x and SO _2 emissions. Chinese NO _x emissions peaked around 2011 and declined by 22% during 2011–2015, and Chinese SO _2 emissions declined by 55% in 2015 relative to that in 2007. Using the GEOS-Chem chemical transport model simulations, we find that rising atmospheric NH _3 levels in eastern China since 2011 as observed by infrared atmospheric sounding interferometer and atmospheric infrared sounder satellites are mainly driven by rapid reductions in SO _2 emissions. The 2011–2015 Chinese NO _x emission reductions have decreased regional annual mean PM _2.5 by 2.3–3.8 μ g m ^−3 . Interannual PM _2.5 changes due to NH _3 emission changes are relatively small, but further control of agricultural NH _3 emissions can be effective for PM _2.5 pollution mitigation in eastern China.

Keywords

• reactive nitrogen
• ammonia
• air pollution
• satellite observations
• fine particulate matter
• emission inversion