Aerosol pollution in Maharashtra anticipated to move from ‘orange’ to highly vulnerable ‘red’ zone: Study

Aerosol pollution in Maharashtra is anticipated to move from its current ‘vulnerable’ orange zone to the ‘highly vulnerable’ red zone, a new study said.

Published recently in the Atmospheric Environment Journal, the study `A deep insight into state-level aerosol pollution in India’, by researchers Dr Abhijit Chatterjee, associate professor and his PhD scholar Monami Dutta from Bose Institute, Kolkata, have provided a national scenario of aerosol pollution with the long-term (2005–2019) trend, source apportionment and future scenario (2023) for various Indian states.

High aerosol amounts include particulate matter (PM2.5 and PM10) consisting of sea salt, dust, sulphate, black and organic carbon. If inhaled, they can be harmful for people’s health. The most serious threat to Indians in the current scenario is probably air pollution. It is estimated from the data that in the year 2019, around 1⋅7 million deaths (~18% of the total deaths) in India were due to air pollution out of which almost 1 million deaths were related to particulate matter or atmospheric aerosol pollution as per the Global Burden of Disease – India data (Dec 11,2020).

Dr Chatterjee, when contacted, told The Indian Express that Aerosol optical depth (AOD) is the quantitative estimate of the aerosol present in the atmosphere and it can be used as a proxy measurement of PM2.5. Researchers have investigated the long-term (2005–2019) trend and mean in aerosol optical depth (AOD) for each grid over India from which state-wise trends were obtained. “This is a first-of-its-kind study and shows how air pollution sources are different for each state,” Dr Chatterjee said.

Maharashtra currently falls under the orange category which is a vulnerable zone with AOD between 0.4-0.5. However, rising aerosol pollution is expected to push the AOD higher than 0.5 to enter into the most vulnerable (red) zone. The values of AOD range from 0 to 1.0. While 0 indicates a crystal-clear sky with maximum visibility, a value of 1 indicates very hazy conditions. AOD values less than 0.3 fall under the green zone (safe), 0.3-0.4 is blue zone (less vulnerable), 0.4-0.5 is orange (vulnerable) while over 0.5 is the red zone (highly vulnerable).

In the paper, the threshold for aerosol pollution (AOD) vulnerability has been considered as a value of 0.4, and the states above this threshold are considered vulnerable.

Chatterjee who is the lead author of the study and Associate Professor of Environmental Sciences at Bose Institute said, “According to our study, air pollution in Maharashtra has mostly been influenced by coal-based thermal power plants (TPP) in the past. Its capacity is increasing with the increase in demand for electricity. However, if the state continues to install the TPP capacity as observed in past it would enter into the most vulnerable zone (mean AOD of the state will be higher than 0.5) which could result in an increase in morbidity rate, decrease in life expectancy along with other health issues of the people of Maharashtra.”

Researchers have anticipated that Maharashtra can witness an AOD rise of about 7% between 2019-2023. The study identified the main sources of aerosol pollution in Maharashtra to be thermal power plants, solid fuel burning and vehicular emissions. The sources were assessed through three phases — phase I being 2005 to 2009, phase II 2010 to 2014, and phase III 2015-2019.

The contribution of emissions from TPPs increased from 31% to 39% between phase I and phase III (2005 – 2019), mainly due to the increase in capacity and dependence on coal-based power generation, the study said. Over the years the contribution of solid fuel burning to aerosol pollution has been declining from 24% to 18% while vehicular emissions have remained consistent throughout the three phases (14-15%).

Maharashtra needs to turn down its TPP capacity by 41% (10 GW) to move to the Blue Safe Zone, the study recommended. The researchers said in the report that Aerosol Optical Thickness is the degree to which “aerosols attenuate the solar radiation” in the atmosphere. Small size particles (less than 10 micrometres) in the atmosphere alter how Infrared and Visible light is reflected, scattered, and absorbed.

“AOD is measured on the basis of how much light is getting attenuated due to the presence of particulate matter. More particulates present means more light will be absorbed and hence more will be the AOD. It is measured with the help of remote sensing using satellites,” the authors explained.

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