Chemical characterization and source identification of PM2.5 in the Huaxi urban area of Guiyang

In 2020, 123 PM_2.5 samples were collected across different seasons in Huaxi District, Guiyang. The primary chemical components of PM_2.5, including water-soluble ions (WSIIs), metallic elements, organic carbon (OC), and elemental carbon (EC), were analyzed. During the sampling period, the average PM_2.5 concentration was 39.7 ± 22.3 µg/m². Chemical mass closure (CMC) was used to reconstruct PM_2.5 mass, yielding a reconstructed concentration of 29.1 ± 16.5 µg/m². The major components were organic matter (OM), sulfate + nitrate + ammonium (SNA), and mineral dust (MD), with mean concentrations of 12.2 ± 6.3 µg/m², 8.2 ± 4.0 µg/m², and 6.3 ± 4.6 µg/m², respectively. From clean days (CD) to lightly-moderately polluted days (LMPD), nitrate oxidation ratio (NOR) increased from 0.09 to 0.16, while sulfate oxidation ratio (SOR) and OC/EC ratio rose by 21.7% and 13.5%, indicating stronger secondary reactions on polluted days. The study also examined changes in chemical components under different atmospheric oxidizing and humidity conditions, revealing that sulfate and nitrate concentrations increased with relative humidity (RH) between 60 and 80%, while other components, especially MD, showed a declining trend due to hygroscopic growth and subsequent gravitational settling and precipitation. The average NO₃^-/SO₄^2- ratio was 0.67, indicating that fixed sources such as industrial and coal emissions were the main contributors to PM_2.5. This study provides insights into the chemical composition, pollution processes, and formation mechanisms of PM_2.5, which are crucial for developing effective air pollution control strategies. Furthermore, source apportionment was conducted with the positive matrix factorization (PMF) model. The Coal combustion, secondary, traffic, Industrial and dust source contributions to the PM_2.5 mass were approximately 30.5%, 20.0%, 18.3%,16.7% and 14.5%, respectively.