| Abstract |
This research is one of the few studies concerning the chemical composition of the atmosphere in the Western Mediterranean, in a long term scale. Specifically the concentrations for the main gases (NH3, HNO3, SO2) and ions (Na, NH4+, K+, Mg2+, Ca2+, Cl-, Br-, NO3-, HPO42-, SO42-, C2O42-) as well as organic nitrogen (WSON) were determined, in a total of 773 atmospheric samples collected in the coastal area on the island of Corsica (Ile Rouse), in the Western Mediterranean, during the period of January 2004 to September 2012. The goal of this study was the determination of the concentrations of these chemical species, the identification of their source and the process governing their presence in the atmosphere as well as the interpretation of their spatial and temporal distribution. Moreover, the influence of the long range transport in the formation of the concentration of species was examined for the given period.
The results indicate that the concentrations of the gases NH3, HNO3 and SO2 have higher values during summer because of high temperatures, photochemistry, the absence of wet deposition and enhanced transport from distant sources, phenomena favoured this period. In the same way, secondary ionic species NH4+, NO3-and nss-SO42-, arising from the above precursor gases, follow the same seasonal cycle.
On the other hand, crustal ions nss-Ca2+ enhanced concentration during the summer, largely depends on the dry soil and the dust outbreaks from Africa.
The annual variation for gaseous SO2 and HNO3 followed a typical trend, with apparent decrease in their levels from 2008 and after. This obviously reflects the dynamics of their anthropogenic sources to the atmosphere and probably coincides with the beginning of the economic crisis in Europe, which led to the reduction of anthropogenic emissions worldwide. This fact highlights the importance of air mass circulation in the chemical composition of the atmosphere, given the similar behaviour observed for the levels of these gases in Spain.
A highly significant correlation between ions Na+ and NO3- is showed, demonstrating the presence of NaNO3 salt, by the reaction of HNO3 gas with the NaCl marine salt. This explains the observed deficit in Cl- ions (Cl-Na+ in sea water), due to the evaporation of HCl gas from the above reaction. This process actually seems to be the unique source of gaseous HCl in the atmosphere of Ile Rousse. The deficit of Cl- ions is also proved by the ionic balance, which shows that some anions are not included compared to the cations.
The results obtained from the statistical method of Factor Analysis, suggest the presence of four main sources, in the atmosphere of Ile Rousse: soil, sea salt, anthropogenic emissions and photochemistry, which interpret the 83% of variability.
The water soluble organic nitrogen (WSON) was also determined in the atmospheric particles, and seems to occupy 15% of the total nitrogen fraction, with NO3-and NH4+ as the predominant inorganic species. Finally, a temporal stability in its concentration was obtained, while the fairly good correlation of WSON ions with NH4+ ions confirms that its presence in the atmosphere of Ile Rousse is more likely due to anthropogenic emission.
|
Διαχρονική μεταβολή της χημικής σύστασης των αιρούμενων σωματιδίων στην Κορσική (Δυτική Μεσόγειος)
