Chemical Characteristics of Fine Particles (PM ₁ ) from Xi'an, China

Abstract

Daily mass concentrations of water-soluble inorganic (WS-i) ions, organic carbon (OC), and elemental carbon (EC) were determined for fine particulate matter (PM1, particles < 1.0 μm in diameter) collected at Xi'an, China. The annual mean PM1 mass concentration was 127.3 ± 62.1 μg m–3: WS-i ions accounted for ∼38% of the PM1 mass; carbonaceous aerosol was ∼30%; and an unidentified fraction, probably mostly mineral dust, was ∼32%. WS-i ions and carbonaceous aerosol were the dominant species in winter and autumn, whereas the unidentified fraction had stronger influences in spring and summer. Ion balance calculations indicate that PM1 was more acidic than PM2.5 from the same site. PM1 mass, sulfate and nitrate concentrations followed the order winter > spring > autumn > summer, but OC and EC levels were higher in autumn than spring. Annual mean OC and EC concentrations were 21.0 ± 12.0 μg m−3 and 5.1 ± 2.7 μg m–3 with high OC/EC ratios, presumably reflecting emissions from coal combustion and biomass burning. Secondary organic carbon, estimated from the minimum OC/EC ratios, comprised 28.9% of the OC. Positive matrix factorization (PMF) analysis indicates that secondary aerosol and combustion emissions were the major sources for PM1.