title: Heavy haze episodes in Beijing during January 2013: Inorganic ion chemistry and source analysis using highly time-resolved measurements from an urban site.
abstract: The heavy air pollution that occurred in Beijing in January of 2013 attracted intense attention around the world. During this period, we conducted highly time-resolved measurements of inorganic ions associated with PM2.5 at an urban site of Beijing, and investigated ion chemistry and potential sources. Hourly concentrations of Cl(-), NO3(-), SO4(2-), Na(+), NH4(+), K(+), Mg(2+), and Ca(2+) were measured. Peak concentrations of SO4(2-) and NO3(-) were observed on the 10th-15th, 21st-24th, and the 26th-30th during this monitoring campaign. The percentages of SO4(2-) and NH4(+) in total ion concentration increased with the enhancement of PM2.5 concentrations, indicating that high concentrations of SO4(2-) and NH4(+) may play important roles in the formation of haze episodes. The ratio of [NO3(-)]/[SO4(2-)] was calculated, revealing that the sources of SO4(2-) would contribute more to the formation of PM2.5 than mobile sources. Diurnal variations of SO4(2-), NO3(-), NH4(+) (SNA) exhibited a similar pattern, with high concentrations at night and low levels during the day, revealing that meteorological conditions, such as mixing layer height, relative humidity, were likely to be responsible for high levels of SNA at night. The roles of meteorological conditions were further discussed in the formation of secondary inorganic ions. Relative humidity and temperature played key roles and exhibited positive correlations with secondary inorganic ions. An aerosol inorganics simulation model showed that SNA existed mainly in the aqueous phase during the sampling period. Furthermore, potential sources were identified by applying positive matrix factorization model. Secondary nitrate, secondary sulfate, coal combustion and biomass burning, as well as fugitive dust, were considered to be major contributors to total ions.
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Han
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China; Beijing Municipal Research Institute of Environmental Protection, Beijing, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China.
authors.forename: Wen
authors.initials: W
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China.
authors.forename: Zhipeng
authors.initials: Z
authors.lastname: Bai
authors.affiliation: Institute of Urban Meteorology, China Meteorological Administration, Beijing, China.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Ma
authors.affiliation: State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China.
authors.forename: Wenjie
authors.initials: W
authors.lastname: Zhang
mesh_terms: D000336:Aerosols / Q000032:analysis; D000393:Air Pollutants / Q000032:analysis; D000397:Air Pollution / Q000706:statistics & numerical data*; D000068476:Beijing; D004784:Environmental Monitoring; D055904:Meteorology; D009566:Nitrates / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis*; D013431:Sulfates / Q000032:analysis
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D009566:Nitrates; D052638:Particulate Matter; D013431:Sulfates
keywords: Beijing; Heavy haze episode; Highly time-resolved; Meteorological factors; Water soluble inorganic ions in PM(2.5)