title: PM2.5pollution is substantially affected by ammonia emissions in China.
abstract: Urban air quality in China has been declining substantially in recent years due to severe haze episodes. The reduction of sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions since 2013 does not yet appear to yield substantial benefits for haze mitigation. As the reductions of those key precursors to secondary aerosol formation appears not to sufficient, other crucial factors need to be considered for the design of effective air pollution control strategies. Here we argue that ammonia (NH3) plays a - so far - underestimated role in the formation of secondary inorganic aerosols, a main component of urban fine particulate matter (PM2.5) concentrations in China. By analyzing in situ concentration data observed in major cities alongside gridded emission data obtained from remote sensing and inventories, we find that emissions of NH3have a more robust association with the spatiotemporal variation of PM2.5levels than emissions of SO2and NOx. As a consequence, we argue that urban PM2.5pollution in China in many locations is substantially affected by NH3emissions. We highlight that more efforts should be directed to the reduction of NH3emissions that help mitigate PM2.5pollution more efficiently than other PM2.5precursors. Such efforts will yield substantial co-benefits by improving nitrogen use efficiency in farming systems. As a consequence, such integrated strategies would not only improve urban air quality, but also contribute to China's food-security goals, prevent further biodiversity loss, reduce greenhouse gas emissions and lead to economic savings.
authors.affiliation: Policy Simulation Laboratory, Zhejiang University, Hangzhou, 310058, PR China.
authors.forename: Yiyun
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Policy Simulation Laboratory, Zhejiang University, Hangzhou, 310058, PR China; Department of Land Management, Zhejiang University, Hangzhou, 310058, PR China. Electronic address: bjgu@zju.edu.cn.
authors.forename: Baojing
authors.initials: B
authors.lastname: Gu
authors.affiliation: Louis Bolk Institute, Hoofdstraat 24, 3972 LA, Driebergen, The Netherlands; VU Amsterdam, De Boelelaan 1091, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Erisman
authors.affiliation: NERC Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian, EH26 0QB, United Kingdom; University of Exeter Medical School, Knowledge Spa, Truro, TR1 3HD, United Kingdom.
authors.forename: Stefan
authors.initials: S
authors.lastname: Reis
authors.affiliation: Deparment of Global Ecology, Carnegie Institution for Science, Stanford, 94305, CA, USA.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Fang
authors.affiliation: Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology, International Institute for Earth System Science, Nanjing University, Nanjing, 210023, PR China.
authors.forename: Xuehe
authors.initials: X
authors.lastname: Lu
authors.affiliation: Policy Simulation Laboratory, Zhejiang University, Hangzhou, 310058, PR China; College of Life Sciences, Zhejiang University, Hangzhou, 310058, PR China.
authors.forename: Xiuming
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000336:Aerosols / Q000032:analysis; D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D000397:Air Pollution / Q000032:analysis*; D000641:Ammonia / Q000032:analysis* / Q000737:chemistry; D002681:China; D002947:Cities; D004784:Environmental Monitoring / Q000379:methods*; D004787:Environmental Pollution; D006801:Humans; D009589:Nitrogen Oxides / Q000032:analysis; D010126:Ozone; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis; D012905:Smog / Q000032:analysis*; D013458:Sulfur Dioxide / Q000032:analysis; D055549:Volatile Organic Compounds / Q000032:analysis* / Q000737:chemistry
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D009589:Nitrogen Oxides; D052638:Particulate Matter; D012905:Smog; D055549:Volatile Organic Compounds; D013458:Sulfur Dioxide; D010126:Ozone; D000641:Ammonia
keywords: Air pollution; Ammonia emissions; Food security; Haze formation; Nitrogen; Panel model