Mineral aerosols from Western India: temporal variability of coarse and fine atmospheric dust and elemental characteristics

Abstract

Size-segregated aerosol samples (PM_2.5 and PM₁₀) were collected during Jan-Dec-2007 from a high-altitude site located in a semi-arid region (Mt. Abu, 24.6°N, 72.7°E, 1680 m asl) in order to asses the temporal variability in the abundance of atmospheric mineral dust and its elemental composition over western India. The mass concentrations of fine (PM_2.5) and coarse (PM_10-2.5) mode aerosols varied from 1.6 to 46.1 and 2.3 to 102 µg m^-3respectively over the annual seasonal cycle; with dominant and uniform contribution of mineral dust (60-80%) in the coarse mode relative to large temporal variability (11-75%) observed in the fine mode. The coarse mass fraction shows a characteristic increase with the wind speed during summer months (Mar to Jun); whereas fine aerosol mass and its elemental composition exhibit conspicuous temporal pattern associated with north-easterlies during wintertime (Oct-Feb). The Fe/Al weight ratio in PM_2.5 ranges from 0.5 to 1.0 during winter months. The relative enrichment of Fe in fine mode, compared to the crustal ratio of 0.44, is attributed to the down-wind advective transport of combustion products derived from large-scale biomass burning, industrial and automobile emission sources located in the Indo-Gangetic Plain (northern India). In contrast, Ca/Al and Mg/Al weight ratios show relative enrichment of Ca and Mg in the coarse mode; indicating their dominant contribution from carbonate minerals. This has implication to efficient neutralization of atmospheric acidic species (SO₄^2- and NO₃^-) by mineral dust over western India.