Μελέτη της παρουσίας ιοντικών συστατικών στην αέρια και σωματιδιακή φάση στην ατμόσφαιρα και της απομάκρυνσής τους με υγρή και ξηρή απόθεση

Abstract

The aim of this research was to investigate the presence of acidic and alkaline constituents in the gas and particulate phase of the atmosphere at an urban environment, Thessaloniki (Greece), and their removal mechanisms, in the prevailing weather conditions, by wet and dry deposition. More precisely, the concentrations of 8 ionic constituents (Cl-, NO3 -, SO4 2-, NH4 +, Na+, K+, Ca2+ and Mg2+) were determined in every phase (gases, particles, rainwater and dust). In addition, the concentrations of 8 trace metals (Al, Cd, Cr, Fe, Mn, Ni, Pb and Zn) were also determined in the case of rain and dust samples. The gas phase compounds (HCl, HNO3, SO2 and NH3) were measured (24hrs samples) by an annular denuder system equipped with a back up filter for the collection of particles with diameter # 5 μm (PM5), while the sampling of wet and dry deposits was performed by using a conventional wet/dry collector. The gas phase compounds and the particles were collected for a period of 16 months, the rainwater and the dust deposits were sampled for 27 and 24 months respectively. The distribution of the common constituents’ concentration of the gaseous and particulate phase and their seasonal variation was evaluated. Furthermore, the presence of several volatile or non-volatile compounds (for example: NH4NO3, NH4Cl and (NH4)2SO4/NH4HSO4) in the particulate phase was investigated. This investigation revealed the formation of NH4NO3 under cold conditions (T < 15 ° C), while NH4Cl is not expected to be formed neither in the warm nor in the cold period. On the other hand, both forms of ammonium sulfate ((NH4)2SO4/NH4HSO4) are probably present in the atmosphere, depending on the atmospheric concentration levels of ammonia. Possible emissions sources were evaluated using statistical methods for particles, rain and dust data. ##3 and CaCO3 were found to be the main neutralizing agents of the atmospheric acidity, by calculating the Neutralization Factors (NF) and applying the Multiple Linear Regression Analysis (MLR). The study of the air masses’ origin, by using the HYSPLIT model, in the case of rainwater and particle samples, showed a possible contribution of long range transported pollutants. In order to investigate the atmospheric scavenging mechanisms of ionic constituents and trace elements we determined the wet and dry deposition fluxes (dry deposition represents the sum of gaseous and particle fluxes), their relative contribution to the total atmospheric deposition, as well as the influence of the precipitation amount to the prevailing mechanism. The contribution of gases to the total dry deposition was significant, while the prevailing removal process for the majority of the constituents was found to be wet deposition. Finally, it was feasible to calculate the dry deposition velocities of major particles (NO3 -, SO4 2-, NH4 + and Cl-) by using the dust fluxes. Their seasonal variation was evaluated, while the comparison of these results with literature data (obtained by models or using direct measurement of dry deposition with several surrogate techniques) showed a good agreement with values estimated by models.