Chemical Characteristics and Source Apportionment by Two Receptor Models of Size-segregated Aerosols in an Emerging Megacity in China

Abstract

PM2.5, PM2.5-10, and PM10 samples were collected in Zhengzhou in 2014 to examine the chemical characteristics and sources of aerosols in this area. The PM concentrations, nine water soluble inorganic ions, organic carbon, elemental carbon, and twenty-two elements were determined, and positive matrix factorization (PMF) and chemical mass balance (CMB) were used for source apportionments. The meteorological impact was also evaluated by back-trajectory cluster analysis. Severe PM pollution was present in the study area, and the aerosol concentrations of PM2.5 samples (92%) and PM10 samples (85%) significantly exceeded the recommended levels of the Chinese National Ambient Air Quality Standard (NAAQS), with the average annual mass concentrations of PM2.5 and PM10 reaching 187 and 281 µg m–3, respectively. Secondary inorganic aerosols were the major ions in PM and accounted for 36%, 10%, and 27% of PM2.5, PM2.5-10, and PM10, respectively. The annual concentration of As (0.029 µg m–3) and Cd (0.010 µg m–3) in PM10 also exceeded the Chinese NAAQS levels, indicating a high health risk. Results from source apportionment by PMF modelling indicated that dust, vehicular traffic, coal combustion, secondary aerosols, and industry were the main pollution sources, accounting for 13.1%, 14.1%, 16.1%, 35.8%, and 14.6% of PM2.5; 25.1%, 20.8%, 21.8%, 10.5%, and 11.6% of PM2.5-10; and 19.8%, 15.8%, 18.5%, 22.5%, and 13.5% of PM10, respectively. Dust sources played an important role in PM pollution, especially coarse particles; however, secondary aerosol sources contributed the most to PM2.5. Both of these observations were consistent with the results of mass reconstruction of the size-segregated aerosols. The CMB results coincided with the PMF results for PM2.5. Cluster analysis showed that air quality in the study area across the four seasons was mainly affected by air masses from the northeast and the east.