Abstract
From 18 February to 13 March 2014 and from 17 December 2016 to 27 January 2017, an online analyzer for monitoring aerosols and gases (MARGA) and an online single particle aerosol mass spectrometer (SPAMS) were used to measure and analyze the concentrations and sources of water-soluble (WS) ions in PM10, PM2.5, and gases (NH3, HNO3, HCl), in Shenyang City, China. During the field campaign, nine haze episodes (or smog episodes, total 582 h) were identified, with 960 identified as non-haze periods. The average mass concentrations of PM2.5 and total water-soluble ions (TWSIs) in PM2.5 during haze episodes were 131 μg·m−3 and 77.2 μg·m−3, 2.3 times and 1.9 times the values in non-haze periods, respectively. The average mass concentration of TWSIs in PM2.5 was 55.9 μg·m−3 (accounting for 55.9% of PM2.5 mass loading), 37.6% of which was sulfate, 31.7% nitrate, 20.0% ammonium, 6.6% chloride, 1.9% potassium, 1.4% calcium, and 0.8% magnesium throughout the campaign. Concentrations of sulfate, nitrate, and ammonium (SNA) secondary pollution ions increased rapidly during haze episodes to as much as 2.2 times, 3.0 times, and 2.4 times higher than during non-haze periods, respectively. Diurnal variations during non-haze periods were significant, while complex pollution was insignificant. Based on changes in the backward trajectories and concentrations of WS ions, the hazy episodes were divided into three types: complex, coal-burning, and automobile exhaust pollution. All complex episodes had high concentrations and greater contributions of ammonium nitrate from complex and automobile exhaust pollution, while the contribution of ammonium sulfate from coal-burning pollution was greater than that of ammonium nitrate. The correlation coefficients among SNA species were very high in complex pollution, with nitrate and sulfate the main forms present. The results of principal component analysis (PCA) were related to emissions from burning coal for heating and from long-range transmission in winter. In the case of exhaust pollution, NO3− accounted for the highest percentage of PM2.5, and NH4+ was more closely related to NO3− than to SO42−. Coal-burning pollution was the most common type of pollution in Shenyang. The contribution of sulfate was higher than that of nitrate. Based on PCA, the contribution of coal-burning emissions varied from 36.7% to 53.6% due to industry, soil sources, and other factors.
Highlights
In recent years, Northeast China has suffered from serious atmospheric particulate pollution.In autumn and winter especially, the northeastern region exhibits the earliest and most serious haze pollution of all areas of China, which causes major harm to the health of local residents
According to “Haze of PM10, PM2.5, and total water-soluble ions (TWSIs) measured over the ambient observation period
The SNA fractions in PM2.5 were 52.1, 44.6, 61.5, 61.2, 67.6, 70.3, 39.8, 52.0, and 63.7% during the nine haze episodes, respectively; 49.9% over the whole period, and 41.6% in non-haze intervals. These results show that SNA were the principal components of PM2.5 during haze episodes
Summary
Northeast China has suffered from serious atmospheric particulate pollution. In autumn and winter especially, the northeastern region exhibits the earliest and most serious haze pollution of all areas of China, which causes major harm to the health of local residents. During periods characterized by complex pollution caused by biomass burning and secondary aerosols in Shanghai, concentrations of ions (e.g., sulfate and nitrate) rose significantly due to heterogeneous reactions between SO2 and NO2 on the surface of pre-existing KCl particles [18]. Nitrate formation in Lanzhou and Guangzhou is mainly completed by gas-phase reactions under NH3 -rich conditions [19] Such studies have rarely been performed in northeastern China. Online observations and source apportionment were used to analyze the physical and chemical features of WS ions in Shenyang, as well as their correlations, on days with various levels of haze pollution. The formation of these ions with respect to pollution formation is discussed, and an analysis of the pollution sources is presented
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