Central India sees annual rise of 2.6 hazy days in winters

Central India is witnessing an annual increase of 2.6 days of hazy days( high aerosol loading) during the dry winter season of November to February.

This is higher than the change over the Indo-Gangetic Plain (~1.7 days/year), a well known global hotspot of particulate pollution.

This rise in the number of hazy days over Central India is associated with the relatively higher increase in biomass burning over the region, according to a research study published in the Nature magazine.

“Moreover, the trend in aerosol loading over the Arabian Sea, which is located downwind to Central India, is also higher than that over the Bay of Bengal during the same season,” the study done by Abin Thomas, Chandan Sarangi and Vijay Kanawade observes.

“Our findings not only draw attention to the rapid deteriorating air quality over Central India, but also underline the significance of increasing biomass burning under the recent climate change”, say the authors.

It’s pertinent to note in this context that the capital city New Delhi and most parts of north India were in a grip of thick smog and air pollution that raised a furore. Biomass (Stubble) burning was the top cause cited, in addition to vehicular and other pollutants.

The researchers used 15 years (2003–2017) of satellite and model reanalysis datasets over India and adjoining Seas to estimate the trend in hazy days.

Role of aerosols

Aerosols are ubiquitous in the atmosphere. While natural aerosols constitute the largest fraction of global aerosol burden, regional ‘hotspots’ coincide with regions of high population density, urbanization and industrialization, or biomass burning.

The observational campaigns (e.g. Indian Space Research Organization-Geosphere Biosphere Programme, ISRO-GBP; Indian Ocean Experiment, INDOEX; Arabian Sea Monsoon Experiment, ARMEX) have shown large aerosol negative radiative forcing at the surface and relatively large atmospheric warming than top of the atmosphere (TOA).

Along with the obvious health impacts, studies have shown that the high aerosol loading in winter can reduce radiation reaching to the surface by about 25 per cent, thereby decreasing crop yield.

Aerosols act as cloud condensation nuclei and affect cloud formation and rainfall. A good understanding is extremely essential for reducing uncertainty in future climate, health, and economic predictions, the researchers say.

Rapid urbanisation is a primary source of the overall aerosol burden in India. Out of the ten most populous metropolitan, five of them lie within CI region (Bangalore, Hyderabad, Mumbai, Nagpur and Pune) and these cities are known for rapid change in the land use and land cover over the last decade.

It should be noted that forests, shrubs, and cropland contributes to a large fraction of the land cover. As a result, the biomass burning activities peak within the two central states (Madhya Pradesh and Maharashtra), accounting for about 36 per cent of the total fire counts in India.

Besides, the Eastern Ghats in Central Eastern India is a dense active fire hotspot, owing to shifting cultivation practices and clearing of mixed deciduous forest in the late winter season.

Therefore, biomass burning (e.g. forest fires, crop residue burning, trash/wood burning), which is a major sources of aerosol loading over India, can contribute significantly to this anomalous enhancement in aerosol overloading in the recent decades, the Study done done by Abin Thomas and Vijay Kanawade of the Centre for Earth, Ocean and Atmospheric Sciences, University of Hyderabad and Chandan Sarangi of the Pacific Northwest National Laboratory, Richland, Washington.