Secondary PM_(2.5) in Zhengzhou, China: Chemical Species Based on Three Years of Observations

10.4209/aaqr.2015.01.0007

Jia Wang；Xiao Li；Wen-Kai Zhang；Nan Jiang；Rui-Qin Zhang；Xiao-Yan Tang

PM_(2.5) ； Water-soluble ionic species ； Carbonaceous components ； Secondary aerosols ； Light extinction coefficient

Aerosol and Air Quality Research

16卷1期（2016 / 01 / 01）

91 - 104

英文

The chemical properties and secondary components of PM_(2.5) were investigated in the city of Zhengzhou, China. Watersoluble ionic species (Na^+, NH_4^+, K^+, Mg^(2+), Ca^(2+), F^–, Cl^–, NO_3^– and SO_4^(2–)) contents, carbonaceous components (organic carbon (OC) and elemental carbon (EC)) in PM_(2.5) were measured for three years. The EC tracer method was used to estimate the secondary organic carbon (SOC) content, and the Interagency Monitoring of Protected Visual Environments formula was used to estimate light extinction due to the chemical composition of PM_(2.5). The annual mean concentrations of PM_(2.5) were 186, 180 and 218 μg m^(–3) in 2011, 2012 and 2013, respectively. These concentrations were 5–6 times greater than the National Ambient Air Quality Standards of China (annual value of 35 μg m^(–3)) and indicated the presence of severe PM_(2.5) pollution in Zhengzhou. Particulate organic matter (OM) contributed the most (18–26%) to the annual average PM_(2.5), followed by SO_4^(2–) (14–19%), NO_3^– (10–11%), NH_4^+ (8–9%) and EC (3%). From 2011 to 2013, the contributions of OM and SO_4^(2–) increased by 8% and 3%, respectively. The higher sulfur oxidation ratio indicated the formation of significant amounts of secondary inorganic aerosols (SIA), particularly during the summer and spring. Obvious SOC enrichment occurred during the winter and autumn. In addition, SIA and secondary organic aerosols accounted for 26–50% and 4–21% of the PM2.5 by mass, respectively. An investigation of the secondary species revealed that secondary aerosols played a dominant role in the total PM2.5 mass and the decrease in visibility. The secondary aerosols ((NH_4)_2SO_4 + NH_4NO_3 + SOC) accounted for 80% of b_(ext). The main secondary aerosols that led to poor visibility in Zhengzhou were (NH_4)_2SO_4 and NH_4NO_3.