High time-resolved measurements of water-soluble sulfate, nitrate and ammonium in PM2.5 and their precursor gases over the Eastern Mediterranean

Abstract

High time-resolved measurements of aerosol SO42−, NO3−, NH4+ and their precursor gases HNO3, SO2, NH3 between 27 and 02 January/February and 19–01 August/September 2015 were carried out by applying AIM-IC at a rural site located on the coast of the Eastern Mediterranean, Erdemli, Turkey. The comparison between online and offline techniques revealed better correlation coefficients for SO42− and NH4+ (r > 0.90) than that of NO3− (0.63). Mean concentrations of water-soluble species were found in decreasing order SO42− (2814 ng m−3) > NH4+ (1371 ng m−3) > NO3− (495 ng m−3). NH3 (3390 ng m−3) concentration was more than enough to neutralize SO2 (879 ng m−3) and HNO3 (346 ng m−3). The gas-to-particle conversion ratios (>0.3) implied that SO42−, NO3− and NH4+ were mainly influenced by non-local sources. SO42−, NO3−, NH4+, HNO3, SO2 exhibited remarkable decrease (leastways 40%) in the atmosphere over the Eastern Mediterranean throughout fifteen years. In winter, day time NH3 concentrations illustrated significant relationship with temperature (positive) and humidity (negative), implying evaporation of dew or emission from plant stoma. Whereas, diurnal cycle of SO42− and SO2 was considerably influenced by populated City of Mersin in winter. During summer, HNO3 and SO2 (r = 0.74) demonstrated similar diurnal cycle, suggesting a common source for these precursor gases whilst NH3 was considerably affected by biomass burning emissions. Variability of all species was governed by local or nearly mesoscale transport in winter possibly due to frequent rain events. In summer, air flow from Eastern Mediterranean denoted aged air masses (GPC > 0.65) containing rather uniform concentrations of SO42− (~65 nmol m−3) and NH4+ (~140 nmol m−3). The highest NH3 along with the greatest % KBB contribution to PM2.5 mass was observed under the influence of Northerly airflow, exhibiting significance of biomass burning emissions as a source of NH3 in summer.