Acid-extractable heavy metals in PM2.5 over Xi’an, China: seasonal distribution and meteorological influence
2019
Liu, Pingping | Zhang, Yiling | Wu, Tiantian | Shen, Zhenxing | Xu, Hongmei
To investigate the acid-extractable heavy metals in fine particulate matter (PM₂.₅) over Xi’an, China, 24-h PM₂.₅ samples were collected every 3 days from December 2015 through November 2016. The bioavailable fraction, termed here the bioavailability index (BI), of PM₂.₅-bound metal (As, Ba, Cd, Co, Cu, Mn, Ni, Pb, Ti, V, and Zn) and potential influencing factors, including relative humidity, temperature, air pressure, wind speed, visibility, PM₂.₅, and SO₂ concentrations, were assessed in this study. The annual average PM₂.₅ concentration was 50.6 ± 35.6 μg m⁻³, 1.5 times higher than the Chinese national secondary standard. Zn, Ti, and As were the most abundant elements of those analyzed in the PM₂.₅ samples, accounting for 72.1% of total quantity. The seasonal variations and enrichment factor analysis of heavy metals revealed that coal combustion in winter was a crucial source of Pb, Co, Cu, and Zn; and dust resuspension in spring contributed considerable Mn, Ti, and V. The acid-extractable fractions of the measured metals varied. Pb, Cu, Mn, and Zn exhibited relatively high acid-extractable concentrations and BI values. Pb was mostly in the acid-extractable fraction in PM₂.₅, with a mean BI value of 66.7%, the highest in summer (69.8%) and lowest in winter (63.7%). Moreover, the BIs of PM₂.₅-bound heavy metals were inversely related to temperature and wind speed, whereas positively correlated with relative humidity, SO₂, and PM₂.₅ concentration in this study. This study assessed the seasonal distribution and meteorological influence of acid-extractable heavy metals, providing a deeper understanding of atmospheric heavy metal pollution in Xi’an, China.
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