title: Evolutionary processes and sources of high-nitrate haze episodes over Beijing, Spring.
abstract: Rare and consecutive high-nitrate haze pollution episodes were observed in Beijing in spring 2012. We present detailed characterization of the sources and evolutionary mechanisms of this haze pollution, and focus on an episode that occurred between 15 and 26 April. Submicron aerosol species were found to be substantially elevated during haze episodes, and nitrates showed the largest increase and occupation (average: 32.2%) in non-refractory submicron particles (NR-PM1), which did not occur in other seasons as previously reported. The haze episode (HE) was divided into three sub-episodes, HEa, HEb, and HEc. During HEa and HEc, a shallow boundary layer, stagnant meteorological conditions, and high humidity favored the formation of high-nitrate concentrations, which were mainly produced by three different processes - daytime photochemical production, gas-particle partitioning, and nighttime heterogeneous reactions - and the decline in visibility was mainly induced by NR-PM1.However, unlike HEa and HEc, during HEb, the contribution of high nitrates was partly from the transport of haze from the southeast of Beijing - the transport pathway was observed at ~800-1000m by aerosol Lidar - and the decline in visibility during HEb was primarily caused by PM2.5. Our results provide useful information for air quality improvement strategies in Beijing during Spring.
authors.affiliation: State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China. Electronic address: tingyang@mail.iap.ac.cn.
authors.forename: Ting
authors.initials: T
authors.lastname: Yang
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: Yele
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Aviation Meteorological Center of China, Beijing 100021, China.
authors.forename: Wei
authors.initials: W
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. Electronic address: zifawang@mail.iap.ac.cn.
authors.forename: Zifa
authors.initials: Z
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100089, China.
authors.forename: Xingang
authors.initials: X
authors.lastname: Liu
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: Pingqing
authors.initials: P
authors.lastname: Fu
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: Xiquan
authors.initials: X
authors.lastname: Wang
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data*; D000068476:Beijing; D004784:Environmental Monitoring; D006813:Humidity; D009566:Nitrates / Q000032:analysis*; D052638:Particulate Matter / Q000032:analysis*; D012621:Seasons; D014887:Weather
chemical_list: D000393:Air Pollutants; D009566:Nitrates; D052638:Particulate Matter
keywords: Aerosol Chemical Speciation Monitor; Boundary layer; Haze; Lidar; Nitrate; Sources