On the wet and dry deposition of ionic species in the vicinity of coal-fired power plants, northwestern Greece

摘要

Rainwater and deposited particle samples were collected for 1 year (October 2000-October 2001), at two sites in the area of "Eordaia Basin", northwestern Greece, where four lignite-burning power units (total capacity 4000 MW) are operated. The samples were collected on a monthly basis and analyzed for Cl~-, NO_3~-, SO_4~(2-), Na~+, K~+, NH_4~+, Ca~(2+) and Mg~(2+). pH and conductivity measurements were conducted only for rain samples. The lowest rain pH values measured at the two sites (S1 and S2) were 4.15 and 5.20 respectively. 40-50% of rain samples at both sites showed pH values in the acidic area (mean values: 5.13 and 5.99 respectively). The quantification of the neutralization effect of the alkaline ions showed the prevalence role of Ca, followed by NH_4, Na and Mg. Wet and dry ionic concentrations and deposition fluxes showed considerable variability between the sites with higher values for Ca and SO_4 for both sites. This could be partly attributed to the strong influence of the local emissions. Fly ash, produced in huge amounts, is the major source for Ca and SO_4 in the area even at the site of Vegoritida (S2), which is a pure remote site located out of the main wind flow of the basin. The relative contribution of wet and dry to the total annual deposition for the site of Petrana (S1) is 45% and 55% respectively for SO_4, 41% and 59% for NO_3 and 41% and 59% for Ca. Contrary, for Vegoritida site (S2) the wet deposition is the main contributor to the total, by 60-80%, for the majority of the species. The difference between the two site environments could be explained by the different local source effect, which is more obvious to dry deposition of the nearest to power plants site of Petrana. Additionally, the application of principal component analysis confirmed the different formation patterns for rain and dust and considerable difference in source emission impact between the sites.