Size-segregated particulate matter and health effects in air pollution in India: a review

India has recently experienced severe air quality problems and related mortality compared to other countries. Particulate matter (PM) is identified as a major health risk factor. Aerodynamic diameter of PM less than 2.5 mu m (PM2.5) and that of PM less than 10 mu m (PM10) are the two regulatory sizes in India. Nonetheless, size-segregated PM measurements are also crucial for understanding the formation, size distribution, sources, deposition in the human respiratory tract, and health effects. Size-segregated PM is commonly referred to simultaneous measurement of PM in multiple size ranges using cascade impactors or aerosol monitors. Here, we review 106 investigations on size-segregated PM in India. We found that bimodal distribution was common among size-segregated PM and chemical components. Secondary inorganic anions were dominant in all ions analysed. Enrichment factor analysis indicated a strong contribution from anthropogenic sources. Source apportionment data from 33 fine size fractions and 26 coarse size fractions revealed that the major source was vehicular followed by crustal origin, biomass or refuse burning, industrial, coal burning, mixed, and secondary sources. Coarse and fine PM sizes were deposited mainly in the head and alveolar regions of the human respiratory tract, respectively. Bioaerosols contained more fungi than bacteria. Episodic events significantly altered the characteristics of size-segregated PM. Overall, rural areas and indoor environments were less explored.