title: Role of secondary aerosols in haze formation in summer in the Megacity Beijing.
abstract: A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility<l0 km and RH (relative humidity)<90%. Four haze episodes, which accounted for ~60% of the time during the whole campaign, were characterized by increases of SNA (sulfate, nitrate, and ammonium) and SOA (secondary organic aerosol) concentrations. The average values with standard deviation of SO4(2-), NO3-, NH4+ and SOA were 49.8 (±31.6), 31.4 (±22.3), 25.8 (±16.6) and 8.9 (±4.1)μg/m3, respectively, during the haze episodes, which were 4.3, 3.4, 4.1, and 1.7 times those in the non-haze days. The SO4(2-), NO3-, NH4+, and SOA accounted for 15.8%, 8.8%, 7.3%, and 6.0% of the total mass concentration of PM10 during the non-haze days. The respective contributions of SNA species to PM10 rose to about 27.2%, 15.9%, and 13.9% during the haze days, while the contributions of SOA maintained the same level with a slight decrease to about 4.9%. The observed mass concentrations of SNA and SOA increased with the increase of PM10 mass concentration, however, the rate of increase of SNA was much faster than that of the SOA. The SOR (sulfur oxidation ratio) and NOR (nitrogen oxidation ratio) increased from non-haze days to hazy days, and increased with the increase of RH. High concentrations of aerosols and water vapor favored the conversion of SO2 to SO4(2-) and NO2 to NO3-, which accelerated the accumulation of the aerosols and resulted in the formation of haze in Beijing.
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Han
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China. Electronic address: liuxingang@bnu.edu.cn.
authors.forename: Xingang
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China. Electronic address: yhzhang@pku.edu.cn.
authors.forename: Yuanhang
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Qu
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
authors.forename: Limin
authors.initials: L
authors.lastname: Zeng
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
authors.forename: Min
authors.initials: M
authors.lastname: Hu
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
authors.forename: Tong
authors.initials: T
authors.lastname: Zhu
mesh_terms: D000336:Aerosols / Q000737:chemistry*; D000393:Air Pollutants / Q000737:chemistry*; D000397:Air Pollution / Q000032:analysis*; D002681:China; D012621:Seasons; D013997:Time Factors
chemical_list: D000336:Aerosols; D000393:Air Pollutants
keywords: Haze formation; Nitrogen oxidation ratio; Secondary inorganic aerosols; Secondary organic aerosols; Sulfur oxidation ratio