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.