What is polluting India’s air?
The study has been authored by Tanushree Ganguly, Adeel Khan, and Karthik Ganesan
India has one of the highest burdens of emissions of particulate matter (PM), sulphur dioxide (SO2), and carbon monoxide (CO) in the world; second only to China. Multiple sources suggest that India’s PM2.5 emissions have grown significantly in the last three decades. In response to India’s rising air pollution, the Indian government has taken numerous interventions including the introduction of the Swachh Bharat Mission (SBM) to improve solid waste management, the Pradhan Mantri Ujjwala Yojana (PMUY) and Unnat Chulha Abhiyan (UCA) to promote improved cook stoves and clean fuel, the National Electric Mobility Mission Plan (NEMMP) to scale up the adoption of zero-emission vehicles, and the accelerated introduction of Bharat Stage (BS) VI fuel in the country (Swachh Bharat Urban 2021; PMUY 2021). The ministry of environment, forest and climate change (MoEFCC) launched the National Clean Air Programme (NCAP) with the goal to ensure that India meets its National Ambient Air Quality Standards (NAAQS) within a stipulated time frame.
While numerous estimates have modelled pollutant emissions from India, there is a dearth of studies that capture the impact of the aforementioned interventions on India’s emission burden. This could, in part, be attributed to the absence of an official air pollution emission inventory for India. While estimates for India’s emissions exist, they vary significantly at both the aggregate level and for sectoral contributions. Notwithstanding the variations in estimates, the different assessments agree on the leading emitters and highlight the need for priority action on point sources like industries and power plants, while also highlighting the significant burden that households face by way of emissions originating from solid fuel use. The variability does not affect our ability to plan for achieving the National Clean Air Programme (NCAP) target for reducing particulate concentrations by 20 to 30% by 2024. However, it increases the uncertainty in assessing impacts of various interventions and prioritising action for various parts of the country.
One of the major criticisms of the NCAP has been its failure to specify sectoral emission reduction targets. To set sectoral emission reduction targets it is crucial to understand the extent to which the different polluting sectors contribute to ambient air pollution. Given the variations in the existing estimates, it is difficult to conclusively determine the relative share of sources to India’s emission burden. To illustrate the extent of variations across these estimates, we compared criteria pollutants (PM2.5, PM10, NOx , SO2 and CO) emission estimates from three global emission inventories, including EDGAR, ECLIPSE, REAS and two domestic inventories - SMoG and TERI. EDGAR, ECLIPSE, REAS and SMoG are multi-year inventories and 2015 is the latest year for which all of them provide estimates. The TERI inventory estimates emissions for 2016. Here’s what we find in our study.
Total emissions vary within 25% for all pollutants except PM10
The relative standard deviation (RSD)1 for total emissions for all pollutants, except PM10, fall within 25%. For PM10, the RSD was found to be 37%, owing largely to the higher PM10 estimates in TERI’s inventory. TERI’s PM10 emissions are higher than the other inventories as it takes urban fugitive dust into account, while others do not. SMoG includes dust as a sector but does not report PM10 emissions.
Sectoral emission estimates are noticeably different
While the variations at an aggregate level are not too large, we observe significant variations in emission estimates across sectors and pollutants. This level of variation can impact modelled concentration of pollutants through the use of chemical transport models, as the transformation and transport of pollutants from different sources will vary. Therefore, the observed variations in emission estimates call for a closer look at the underlying activity data and emission factors that were used to arrive at these estimates.
Sectoral contributions differ greatly
Across the different inventories, the residential sector is seen to be the leading emitter of PM2.5 emissions, with contributions ranging from 27 to 50%. The power sector is the leading emitter of SO2 emissions across the five inventories, with contributions ranging from 44 to 62%. This is on account of the significant share of coal that is consumed in power generation. The power sector is also the leading emitter of NOx emissions, with its contribution ranging from 24 to 43 per cent. While the contribution of households to primary PM2.5 emissions is highest, it must be noted that large point sources such as such as coalbased power plants and industrial units contribute a large share of PM2.5 through secondary particulate matter, which is a result of the transformation of SOx and NOx emissions from gas form to particle form.
A recent study estimates that the contribution of secondary particulate matter from coal-based power plants could be as high as 80% of total particulate matter attributable to power plants. Industrial production stands as the second largest source of most of the criteria pollutants that were assessed and when combined with power plants, represent a possibly the largest and most easily targeted source of emissions for policy makers and regulators to address. They are large point sources and finite in number. Particulate pollution arising from solid fuel use in households is distributed across the length and breadth of the country and much harder to abate, as it involves interventions that target both affordability of cleaner fuels and affecting behaviour change to move populations away from the use of free of cost biomass in many pockets.
(The study has been authored by Tanushree Ganguly, Adeel Khan, and Karthik Ganesan)