title: High molecular weight organic compounds (HMW-OCs) in severe winter haze: Direct observation and insights on the formation mechanism.
abstract: High molecular weight organic compounds (HMW-OCs), formed as secondary organic aerosols (SOA), have been reported in many laboratory studies. However, little evidence of HMW-OCs formation, in particular during winter season in the real atmosphere, has been reported. In January 2013, Beijing faced historically severe haze pollution, in which the hourly PM2.5concentration reached as high as 974 μg m-3. Four typical haze events (HE1 to HE4) were identified, and HE2 (Jan. 9-16) was the most serious of these. Based on the hourly observed chemical composition of PM2.5and the daily organic composition analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), we found that abundant ion peaks in m/z 200-850 appeared on heavy haze days, whereas these were negligible on a clear day, indicating the existence of HMW-OCs in the wintertime haze. A negative nonlinear correlation between HMW-OCs and O3suggested that gas oxidation was not likely to be the dominant mechanism for HMW-OCs formation. During the heavy haze events, the relative humidity and mass ratio of H2O/PM2.5reached as high as 80% and 0.2, respectively. The high water content and its good positive correlation with HMW-OCs indicated that an aqueous-phase process may be a significant pathway in wintertime. The evidence that acidity was much higher during HE2 (0.37 μg m-3) than on other days, as well as its strong correlation with HMW-OCs, indicated that acid-catalyzed reactions likely resulted in HMW-OCs formation during the heavy winter haze in Beijing.
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China; State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Tsinghua University, Beijing, 100084, China; Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, 100084, China. Electronic address: duanfk@tsinghua.edu.cn.
authors.forename: F K
authors.initials: FK
authors.lastname: Duan
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China; State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Tsinghua University, Beijing, 100084, China; Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, 100084, China. Electronic address: hekb@tsinghua.edu.cn.
authors.forename: K B
authors.initials: KB
authors.lastname: He
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China; State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Tsinghua University, Beijing, 100084, China; Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, Tsinghua University, Beijing, 100084, China.
authors.forename: Y L
authors.initials: YL
authors.lastname: Ma
authors.affiliation: Department of Chemistry and Materials Engineering, Kansai University, Suita, 564-8680, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ihozaki
authors.affiliation: Department of Chemistry and Materials Engineering, Kansai University, Suita, 564-8680, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kawasaki
authors.affiliation: Department of Chemistry and Materials Engineering, Kansai University, Suita, 564-8680, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Arakawa
authors.affiliation: Kimoto Electric Co. Ltd, Funahashi-Cho, Tennouji-Ku, Osaka, 543-0024, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kitayama
authors.affiliation: Kimoto Electric Co. Ltd, Funahashi-Cho, Tennouji-Ku, Osaka, 543-0024, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tujimoto
authors.affiliation: Kimoto Electric Co. Ltd, Funahashi-Cho, Tennouji-Ku, Osaka, 543-0024, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Huang
authors.affiliation: Kimoto Electric Co. Ltd, Funahashi-Cho, Tennouji-Ku, Osaka, 543-0024, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kimoto
authors.affiliation: Project Research Center for Fundamental Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan; Center for Scientific Instrument Renovation and Manufacturing Support, Osaka University, 1-2 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Furutani
authors.affiliation: Project Research Center for Fundamental Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Toyoda
mesh_terms: D000336:Aerosols / Q000032:analysis; D000393:Air Pollutants / Q000737:chemistry*; D001272:Atmosphere / Q000032:analysis; D004784:Environmental Monitoring; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D009930:Organic Chemicals / Q000032:analysis*; D010126:Ozone / Q000737:chemistry; D052638:Particulate Matter / Q000737:chemistry*; D012621:Seasons; D014867:Water / Q000737:chemistry
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D009930:Organic Chemicals; D052638:Particulate Matter; D014867:Water; D010126:Ozone
keywords: Aerosol acidity; Aqueous phase process; Haze pollution; High molecular weight organic compounds; Secondary organic aerosols