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

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/m 3 whilst that of WSII was 51.63 µg/m 3 , 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.