Variability of outdoor fine particulate (PM2.5) concentration in the Indian Subcontinent: A remote sensing approach

The rapid increase of aerosols over the Indian Subcontinent over the last decade has the potential for severe health implications. However, the lack of a dense network to measure PM2.5 (particles with aerodynamic diameter b 2.5 μm) hinders health risk assessments at regional scale. Here, we utilize Multiangle Imaging SpectroRadiometer (MISR)-retrieved columnar aerosol optical depths to estimate surface PM2.5 based on recently published conversion factors that account for the composition and vertical distribution of aerosols. We examine the space–time variability of bias-corrected (utilizing coincident in-situ observations) PM2.5 over the Indian Subcontinent for the period Mar 2000–Feb 2010. We show that 51% of the subcontinent's 1.4 billion people are exposed to pollution that exceed the World Health Organization's highest annual air quality threshold of 35 μg m −3, while another 13% and 18% are exposed in the ranges 25–35 and 15–25 μg m−3 respectively. Of the remaining population who breathe clean air, only 25% live in urban areas. In many regions, the high-levels of pollution are persistent rather than episodic. PM2.5 concentrations in the rural areas of the Indo-Gangetic Basin are higher than many urban centers in peninsular India. Five hotspots (where PM2.5 increases by > 15 μg m −3 over the ten-year period) are identified, which cover parts of the eleven Indian states and Bangladesh affecting ~23% of the population. Our results highlight the urgent need to carry out local cohort studies at these hotspots to better understand the health impacts under local conditions.