Air quality and trace metal chemistry of different size fractions of aerosols in N–NW India—implications for source diversity

Three different size fractions of aerosols free fall (FF), suspended particulate matter (SPM) and particles less than 10 μm (PM10) as well as surface sediments were collected from four different locations situated along a dust transport path of nearly 600 km in NW India starting from Bikaner in the Thar to Garhmuktesar through Jhunjhunu and Delhi and were studied for their heavy-metal chemistry. NW India is characterized by hot arid to semiarid climate with prevailing S–SW winds causing dust storms in summer and low intensity N–NW winds during winter months. The aerosol load in the atmosphere increased to several orders of magnitude for all size ranges (FF=21 g m−2 day−1; SPM=10,702 μg m−3 and PM10=2907 μg m−3) during the summer dust storm period compared to national air quality standards as well as to the aerosol load in winter. Aerosol sources are dominantly crustal with a significant anthropogenic contribution during the winter. We also note multiplicity of sources for the heavy metals studied here. Sr, V and Cr are dominantly crustal. Ba and Pb are added largely by fossil fuel burning; Cu, Ni and Zn are contributed by various industries. Anthropogenically added heavy metals show maximum enrichment relative to the upper continental crustal component in finer fractions and especially in winter. We suggest that the aerosol loading in the atmosphere and its heavy-metal chemistry is strongly influenced by the climatic regime and the presence of desert and industrialization in this area.