Chemical composition of atmospheric aerosol (PM10) at a semi-arid urban site: influence of terrestrial sources.

Atmospheric aerosol (PM(10)) measurements were made at a regional representative semi-arid urban site, Tirupati, India over one-year period i.e. from October, 2001 to September, 2002. The samples were collected on polyflex filters, and analyzed for the major water-soluble ions - F, Cl, NO(3), SO(4), Na, NH(4), K, Ca and Mg, employing ion chromatograph. The average mass of PM(10) is found to be 32.75 mug/m(3) with a total water-soluble aerosol load (total anion + total cation) of 13.56 mug/m(3). Composition of aerosol showed higher concentration of SO(4) followed by Na, Ca and NO(3). Very good correlation is observed between crustal ions Ca and Mg (r=0.82) as well as between crustal and acidic ions; Ca and SO(4) (r=0.75) and NO(3) (r=0.67) and Mg and NO(3) (r=0.78) and SO(4) (r=0.73), suggest that the ionic composition was influenced by local terrestrial sources. The presence of SO(4) and NO(3) may be due to re-suspension of soil particles (formation by heterogeneous oxidation). Ca, Mg and Na are mainly soil derived ones. Correlation matrix with meteorological factors, as well as seasonal distribution of PM(10) and its ionic components present a clear trend of higher concentrations during summer due to greater particle release and lowering atmospheric levels during the rainy season due to washout effect. ANOVA results showed the significant variation of composition from season to season. Paired comparisons (DMRT) revealed the occurrence of significant difference in pairs of mean concentration from season to season except within monsoon i.e. between S-W and N-E monsoon.