Trends and Regional Heterogeneity in the Pollution Cycle in India

Abstract:

Exposure to air pollution has been identified as the leading environmental health risk in India. Given inadequate ground-based monitoring in India (that is only confined to the major cities/towns), a satellite-based PM_2.5 database for India has been developed at a 1-km resolution for 20+ years. Satellite-PM_2.5 show R²=0.89 and 0.98 for 24-hr and annual scale concentration with the measurements under the Central Pollution Control Board network. The trends in air quality and the regional pollution build-up are examined using this data over the urban and rural India for the period 2000-2019. The seasonal trends are analysed in terms of meteorology and other factors. A statistically significant increasing trend is observed over most parts of India (except the high-altitude states and the desert area) in the dry season (October-February). Considerable regional heterogeneity is observed in the pollution cycle in India with two major peaks – one in post-monsoon (October-November) affected by a combined influence of open biomass burning and meteorology and one in winter (December-January) affected mostly by highly stable boundary layer trapping the regional and local emissions, and a minor peak in summer (April-May) affected by dust transport from the arid regions. However, declining dust transport over the years is reflected in the decreasing trend in PM_2.5 over western India during this season. Urban and rural PM_2.5 exposure is almost identical in the Indo-Gangetic Plain and other major air sheds.

Spatial patterns and trends in PM_2.5 exposure over 20 years suggest that urban-centric approach alone will not work. India must consider a regional approach targeting mitigation efforts within major air sheds, linking the National Clean Air Program with other major programs such as the Prime Minister’s clean household fuel scheme (primarily in the rural regions), rural electrification scheme and the program to stop open biomass burning. A balance in policies targeting the extreme episodic pollution and sustained regional pollution must be restored to achieve maximum benefit. In the present scenario, meeting the annual national ambient air quality standard (which itself is four times higher than the WHO air quality guideline) seems to be challenging. India, therefore, must act aggressively before it’s too late.