Abstract
Abstract. The North China Plain has been identified as a significant hotspot of ammonia (NH3) due to extensive agricultural activities. Satellite observations suggest a significant increase of about 30 % in tropospheric gas-phase NH3 concentrations in this area during 2008–2016. However, the estimated NH3 emissions decreased slightly by 7 % because of changes in Chinese agricultural practices, i.e., the transition in fertilizer types from ammonium carbonate fertilizer to urea, and in the livestock rearing system from free-range to intensive farming. We note that the emissions of sulfur dioxide (SO2) have rapidly declined by about 60 % over the recent few years. By integrating measurements from ground and satellite, a long-term anthropogenic NH3 emission inventory, and chemical transport model simulations, we find that this large SO2 emission reduction is responsible for the NH3 increase over the North China Plain. The simulations for the period 2008–2016 demonstrate that the annual average sulfate concentrations decreased by about 50 %, which significantly weakens the formation of ammonium sulfate and increases the average proportions of gas-phase NH3 within the total NH3 column concentrations from 26 % (2008) to 37 % (2016). By fixing SO2 emissions of 2008 in those multi-year simulations, the increasing trend of the tropospheric NH3 concentrations is not observed. Both the decreases in sulfate and increases in NH3 concentrations show highest values in summer, possibly because the formation of sulfate aerosols is more sensitive to SO2 emission reductions in summer than in other seasons. Besides, the changes in NOx emissions and meteorological conditions both decreased the NH3 column concentrations by about 3 % in the study period. Our simulations suggest that the moderate reduction in NOx emissions (16 %) favors the formation of particulate nitrate by elevating ozone concentrations in the lower troposphere.
Highlights
Ammonia (NH3) is considered the most important alkaline gas in the atmosphere
By integrating measurements from ground and satellite, a long-term anthropogenic NH3 emission inventory, and chemical transport model simulations, we find that this large SO2 emission reduction is responsible for the NH3 increase over the North China Plain
By integrating chemical model simulations and ground and satellite observations, this study investigates an increase (∼ 30 %) in tropospheric NH3 column concentrations that was observed from the space over the North China Plain during 2008–2016
Summary
Ammonia (NH3) is considered the most important alkaline gas in the atmosphere. On both a global and regional scale, NH3 is mostly emitted from agricultural activities, mainly including the fertilization and livestock industry (Bouwman et al, 1997). As a major agricultural country, China is one of the world’s largest emitters of NH3, the amount of which (∼ 10 Tg yr−1) exceeds the sum of those in Europe (∼ 4.0 Tg yr−1) and North America (∼ 4.0 Tg yr−1) (Huang et al, 2012; Bouwman et al, 1997; Paulot et al, 2014). Fertilizer application and livestock manure management contribute to nearly 90 % of China’s NH3 emissions (Huang et al, 2012; Zhang et al, 2018). NH3 emissions have not been regulated by the Chinese government, they serve as an important contributor to haze pollution in China
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