Refined Source Apportionment of Atmospheric PM2.5 in a Typical City in Northwest China

The Xixian New District (XXND), established in 2014, is the seventh national-level new district in China, but research on air pollution there has been limited. This study focused on the characteristics and sources of PM2.5 in XXND from 2017 to 2018. The average annual PM2.5 mass was 67 mu g m(-3); loadings were high in winter and low in summer. Organic carbon (18.2%), nitrate (17.0%), and sulfate (13.1%) were the main chemical components of PM2.s. A refined statistical assessment of sources was conducted using the CAS-HERM receptor model, and it showed that primary sources accounted for similar to 58.5% of the PM2.5 annual mass, of which dust accounted for 23.3% (road, construction, and soil dust accounted for 11.4%, 8.0% and 3.9%, respectively) while motor vehicles contributed 10.1% (diesels 8.7% and gasoline vehicles 1.4%). Secondary sources for sulfates, nitrates, and organic aerosols accounted for similar to 41.5% of the PM2.5 mass. A complementary analysis using the WRF-CHEM model showed that regional transport accounted for 60.8% of the PM2.5 during the winter high-pollution period, which also implies the importance of secondary aerosols.