Fine and coarse ionic aerosol components in relation to wet and dry deposition

The distribution of acidic and alkaline constituents (SO42-, NO3-, Cl-, NH4+, Na+, K+, Ca2+) between the fine and coarse particle range has been examined in an urban location in Thessaloniki, N. Greece over an 8-month period. The chemistry of wet and dry deposition collected over the same period was also examined. Statistical associations between species within each environmental phase were investigated using correlation analysis. Use of principal component analysis was made to investigate compositional similarities between aerosol, deposited dust and rain. It was found that SO4 followed by NO3, NH4 and Ca prevailed in fine aerosol. Sulphates and Ca were also the prevailing ions in the coarse particle fraction. Wet deposition was found to be the dominant deposition mechanism for all species. The high dry deposition rates observed for Ca and SO4 suggest that most of the dry deposited sulphate is in the form of CaSO4. Scavenging ratios of ionic species associated with coarse aerosol were higher than the corresponding ratios for fine particles. Principal component analysis suggested that variations in ionic composition of fine aerosol could be interpreted primarily by gas-to-particle neutralization reactions involving atmospheric ammonia. In contrast, the interaction between SO2 and HNO3 with Ca compounds seems to be the most likely factor that can explain variations in wet and dry deposition ionic contents.