Temporal distribution and source apportionment of PM2.5 chemical composition in Xinjiang, NW-China

Daily fine particulate matter samples were collected in Dushanzi district within four months from September 2015 to August 2016 and represent the four seasons. The samples were determined for major chemical components in PM2.5, including elements, water-soluble ions (WSIs) and the organic/elemental carbon (OC/EC). The results indicated that the annual mean PM2.5 concentration was 62.85 +/- 43.5 mu g m(-3) in the Dushanzi district, with the highest seasonal average in winter (95.47 +/- 61.7 mu g m(-3)) and the lowest in summer (33.22 +/- 17.7 mu g m(-3)). The crustal elements were the most abundant elements and accounted for 96.51% of the total analyzed elements. Carcinogenic metals, such as Cr, Pb, As and Cd, originated from human activity, especially during winter. The highest total WSI concentration was 68.99 mu g m(-3) in winter, followed by autumn (16.32 mu g m(-3)), spring (10.23 mu g m(-3)) and summer (7.06 mu g m(-3)). SO42-, NO3- and NH4+ were the most abundant WSIs in Dushanzi. Ion balance calculations showed that PM2.5 in winter was acidic; in autumn and spring alkaline; and in summer nearly neutral. Total carbonaceous aerosol (TCA) accounted for 34% of the PM2.5. The chemical mass closure (CMC) indicated that minerals and WSIs were the major fraction, accounting for 33.58% and 23.17% of PM2.5 mass concentration, respectively. Dushanzi was controlled by four major air masses, and the relative contributions of these air masses differ by season. Positive matrix factorization (PMF) analysis identified six sources including vehicle emission, biomass burning, coal combustion, industrial pollution, secondary aerosols and soil dust, with annual mean contributions of 9.43%, 10.86%, 18.45%, 12.15%, 18.26% and 30.85%, respectively. Moreover, the relative contributions of these identified sources varied significantly with the changing seasons.