Abstract
PM2.5 samples were collected in Beijing between February 24 and March 12 of 2014, and analyzed to examine chemical compositions and origins of the PM2.5 at pollution levels of clean (PM2.5 < 75 µg m–3), light-medium (75–150 µg m–3), heavy (150–250 µg m–3) and severe (> 250 µg m–3). The mean PM2.5 concentration was 137.7 ± 124.8 µg m–3 during the observation period, accounting for 66% of PM10. As all aerosol species concentrations increased with the pollution level, the contributions of secondary inorganic aerosols (SIA) to PM2.5 continuously increased while the contributions of OC and EC decreased, indicating a substantial contribution from secondary formation to the elevation of PM2.5 pollution. The acidity of PM2.5, the ratio of anion microequivalent concentration to cation, increased from 0.96 to 1.08 as pollution levels increased. Using a PMF model, secondary inorganic aerosols, industrial emissions, soil dust, traffic emissions, and coal combustion and biomass burning were identified as contributors to the PM2.5, and on average accounted 46%, 20%, 10%, 6% and 18% of the PM2.5, respectively, in the observation period. Industrial emissions were the dominant PM2.5 source during the clean period (60%). Except for traffic emission, sources of PM2.5 at the light-medium level were consistent, accounting for 17%–29%. Secondary inorganic aerosols were the largest origin of PM2.5 at heavy and severe pollution levels, accounting for 40% and 78%, respectively. In addition, the 48 h transport distances of air masses decreased from 2000 km (clean) to 300 km (severe level) and the proportion of air masses from south pollution areas in the total air masses at each pollution level increased from 0% to 97%, indicating that the stability of near surface air and the northerly transport of pollutants from the south at local and regional scales played a the key role in the PM2.5 elevation.
Highlights
Due to rapid industrialization and urbanization in recent decades, China has become one of the most significant source regions of anthropogenic atmospheric pollutants (Guo et al, 2014; Sun et al, 2015a; Lin et al, 2016)
As all aerosol species concentrations increased with the pollution level, the contributions of secondary inorganic aerosols (SIA) to PM2.5 continuously increased while the contributions of organic carbon (OC) and elemental carbon (EC) decreased, indicating a substantial contribution from secondary formation to the elevation of PM2.5 pollution
The 48 h transport distances of air masses decreased from 2000 km to 300 km and the proportion of air masses from south pollution areas in the total air masses at each pollution level increased from 0% to 97%, indicating that the stability of near surface air and the northerly transport of pollutants from the south at local and regional scales played a the key role in the PM2.5 elevation
Summary
Due to rapid industrialization and urbanization in recent decades, China has become one of the most significant source regions of anthropogenic atmospheric pollutants (Guo et al, 2014; Sun et al, 2015a; Lin et al, 2016). Zhao et al, 2016); and (3) aerosol optical properties, hygroscopic properties, size distribution of haze particles (Zhang et al, 2012; Jing et al, 2014; Tao et al, 2015; Wang et al, 2015; Zhang et al, 2015a; Fajardo et al, 2016; Liu et al, 2016; Wu et al, 2016, 2017) These studies were based on observations in haze episodes and have shown that aerosol properties and aerosol sources in the pollution and even at different altitudes. We applied the chemical mass balance, the ISORROPIA II thermodynamic equilibrium model, the positive matrix factorization (PMF) and the trajectory clustering to both characterize chemical species and explore potential origins of PM2.5 at different haze pollution levels, as well as provide aids for controlling emission and reducing particle pollution
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