title: High secondary aerosol contribution to particulate pollution during haze events in China.
abstract: Rapid industrialization and urbanization in developing countries has led to an increase in air pollution, along a similar trajectory to that previously experienced by the developed nations. In China, particulate pollution is a serious environmental problem that is influencing air quality, regional and global climates, and human health. In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 (refs 4, 5), the Chinese State Council announced its aim to reduce concentrations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 micrometres) by up to 25 per cent relative to 2012 levels by 2017 (ref. 6). Such efforts however require elucidation of the factors governing the abundance and composition of PM2.5, which remain poorly constrained in China. Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing, Shanghai, Guangzhou and Xi'an during January 2013. We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation, which contributed 30-77 per cent and 44-71 per cent (average for all four cities) of PM2.5 and of organic aerosol, respectively. On average, the contribution of secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) are found to be of similar importance (SOA/SIA ratios range from 0.6 to 1.4). Our results suggest that, in addition to mitigating primary particulate emissions, reducing the emissions of secondary aerosol precursors from, for example, fossil fuel combustion and biomass burning is likely to be important for controlling China's PM2.5 levels and for reducing the environmental, economic and health impacts resulting from particulate pollution.
authors.affiliation: 1] Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland [2] State Key Laboratory of Loess and Quaternary Geology (SKLLQG), and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China [3].
authors.forename: Ru-Jin
authors.initials: RJ
authors.lastname: Huang
authors.affiliation: 1] Department of Chemistry and Biochemistry, and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, Switzerland [2] Laboratory of Radiochemistry and Environmental Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Yanlin
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Carlo
authors.initials: C
authors.lastname: Bozzetti
authors.affiliation: The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Kin-Fai
authors.initials: KF
authors.lastname: Ho
authors.affiliation: State Key Laboratory of Loess and Quaternary Geology (SKLLQG), and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China.
authors.forename: Jun-Ji
authors.initials: JJ
authors.lastname: Cao
authors.affiliation: State Key Laboratory of Loess and Quaternary Geology (SKLLQG), and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China.
authors.forename: Yongming
authors.initials: Y
authors.lastname: Han
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Kaspar R
authors.initials: KR
authors.lastname: Daellenbach
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Jay G
authors.initials: JG
authors.lastname: Slowik
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Platt
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Francesco
authors.initials: F
authors.lastname: Canonaco
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Zotter
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Robert
authors.initials: R
authors.lastname: Wolf
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Simone M
authors.initials: SM
authors.lastname: Pieber
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Emily A
authors.initials: EA
authors.lastname: Bruns
authors.affiliation: 1] Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland [2] European Commission, Joint Research Centre, Institute for Environment and Sustainability, Air and Climate Unit, Via Fermi, 2749, 21027 Ispra, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Crippa
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Ciarelli
authors.affiliation: Department of Earth and Environmental Sciences, University of Milano Bicocca, Piazza della Scienza 1, Milan 20126, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Piazzalunga
authors.affiliation: 1] Department of Chemistry and Biochemistry, and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, Switzerland [2] Laboratory of Radiochemistry and Environmental Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Margit
authors.initials: M
authors.lastname: Schwikowski
authors.affiliation: Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Joint Mass Spectrometry Centre, Cooperation Group Comprehensive Molecular Analytics and Helmholtz Virtual Institute of Complex Molecular Systems in Environmental Health - Aerosol and Health (HICE), 85764 Neuherberg, Germany.
authors.forename: Gülcin
authors.initials: G
authors.lastname: Abbaszade
authors.affiliation: Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Joint Mass Spectrometry Centre, Cooperation Group Comprehensive Molecular Analytics and Helmholtz Virtual Institute of Complex Molecular Systems in Environmental Health - Aerosol and Health (HICE), 85764 Neuherberg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schnelle-Kreis
authors.affiliation: 1] Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Joint Mass Spectrometry Centre, Cooperation Group Comprehensive Molecular Analytics and Helmholtz Virtual Institute of Complex Molecular Systems in Environmental Health - Aerosol and Health (HICE), 85764 Neuherberg, Germany [2] University of Rostock, Joint Mass Spectrometry Centre, Institute of Chemistry, Analytical Chemistry, 18015 Rostock, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Zimmermann
authors.affiliation: State Key Laboratory of Loess and Quaternary Geology (SKLLQG), and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China.
authors.forename: Zhisheng
authors.initials: Z
authors.lastname: An
authors.affiliation: Department of Chemistry and Biochemistry, and Oeschger Centre for Climate Change Research, University of Bern, 3012 Bern, Switzerland.
authors.forename: Sönke
authors.initials: S
authors.lastname: Szidat
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: Urs
authors.initials: U
authors.lastname: Baltensperger
authors.affiliation: 1] Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland [2].
authors.forename: Imad
authors.initials: I
authors.lastname: El  Haddad
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland.
authors.forename: André S H
authors.initials: AS
authors.lastname: Prévôt
mesh_terms: D000336:Aerosols / Q000032:analysis* / Q000737:chemistry; D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry*; D000397:Air Pollution / Q000032:analysis*; D018533:Biomass; D002681:China; D002947:Cities; D004784:Environmental Monitoring; D005579:Fossil Fuels; D006801:Humans; D009930:Organic Chemicals / Q000032:analysis / Q000737:chemistry; D052638:Particulate Matter / Q000032:analysis* / Q000737:chemistry*; D011634:Public Health; D055549:Volatile Organic Compounds / Q000032:analysis / Q000737:chemistry
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D005579:Fossil Fuels; D009930:Organic Chemicals; D052638:Particulate Matter; D055549:Volatile Organic Compounds