Ambient PM2.5 Exposure in India: Burden, Source-Apportionment and Projection Under Climate Change

Air pollution has been identified as one of the leading factors of premature death in India. Absence of adequate in-situ monitors led us to use satellite retrieved aerosol optical depth (AOD) data to infer surface fine particulate matter (PM2.5). Annual premature mortality burden due to ambient PM2.5 exposure is estimated to be 1.17 (0.42-2.7) million for India. A chemical transport model WRF-Chem is utilized to estimate source-apportioned PM2.5 exposure. We estimate the exposure for four major sources - transport, residential, energy and industrial and found that the largest contribution to ambient PM2.5 exposure in India is contributed by residential sources. We estimate that if all the solid fuel use at households is replaced by clean fuel, ambient PM2.5 exposure would reduce by 30-45%, leading to 170,000 (14.5% of total burden) averted premature deaths annually. To understand how the air quality is projected to change under climate change scenarios, we analyze 13 CMIP5 models. We calculate the relative changes in PM2.5 (ensemble mean) in future relative to the baseline period (2001-2005) and apply the factor to satellite-derived PM2.5 exposure in baseline period to project future PM2.5 exposure. Ambient PM2.5 is expected to reach a maxima in 2030 under RCP4.5 (15.5% rise from baseline period) and in 2040 (25.5% rise) under RCP8.5 scenario. The projected exposure under RCP4.5 and RCP8.5 scenarios are further used to estimate premature mortality burden till the end of the century by considering population distribution projections from five shared socio-economic pathways (SSP) scenarios. We separate the burden due to ambient PM2.5 exposure in future attributable to change in meteorology due to climate change and change in demographic and epidemiological transitions. If all-India average PM2.5 exposure meets WHO interim target 1 (35 µg/m3) by 2031-40, 28000-38000 and 41100-60100 premature deaths can be averted every year under RCP4.5 and RCP8.5 respectively. Even if India fails to meet various standards, any progress towards achieving better air quality will have substantial health benefits.