Chemical Composition and Deposition Fluxes of Water-Soluble Inorganic Ions on Dry and Wet Deposition Samples in...

Measurement of PM_2.5 concentration, dry and wet deposition of water-soluble inorganic ions (WSII) and their deposition flux was carried out. During sampling, a total number of 31 samples of PM_2.5, five wet deposition samples and seven dry deposition samples were collected. The analyses results showed that the average concentration of PM_2.5 was 122.95 µg/m³ whilst that of WSII was 51.63 µg/m³, equivalent to 42% of the total mass of PM_2.5. The correlation coefficients between WSII in samples of PM_2.5 was significant (r = 0.50 and p-value of 0.0019). Ions of   SO 4 2 - , NO 3 - , Cl - , and   NH 4 + were dominant in the entire samples (PM_2.5, dry and wet depositions), nevertheless, the average concentration of both SO 4 2 - and Cl - were below the China environmental quality standard for surface water. The ratio of dominant anions in wet deposition ( SO 4 2 - / NO 3 - ) was 1.59, whilst that for dry deposition ( SO 4 2 - / Cl - ) was 1.4, indicating that acidity was mainly derived from sulphate. In the case of dominant cations, the dry and wet deposition ratios ( Ca 2 + / NH 4 + ) were 1.36 and 1.37, respectively, suggesting the alkaline substances were mainly dominated by calcium salts. Days with higher recorded concentrations of PM_2.5 were accompanied by dry and warm boundary layer structure, weak low-level wind and strong inversion layer.