Reduction in black carbon level in Varanasi since '12: BHU study

Varanasi, July 9 (IANS) Varanasi and central Indo-Gangetic plains have recorded an annual average decrease of 0.47 micrograms per cubic metre in carbon level, according to a study led by Manoj Kumar Srivastava, a meteorologist in the Geophysics department at the Banaras Hindu University (BHU).

The research paper was recently published in the prestigious journal of earth and environmental science, the Journal of Geophysical Research—Atmosphere.

The study was conducted using black carbon data generated by co-author RS Singh and his group at IIT (BHU) in the Chemical Engineering department under the Aerosol Radiative Forcing over India (ARFI) programme of the Indian Space Research Organisation.

For the first time, analysis of a decade long measurement of black carbon mass concentration was carried out at a representative location in central Indo-Gangetic plain, Varanasi, from 2009 to 2021 to understand its physical, optical, and radiative impact.

A consistent post-monsoon average decline of 1.86 micrograms per cubic metre and a pre-monsoon average decline of 0.31 micrograms per cubic metre have been found in the study.

The study considered relevant data of a span of 13 years and is aimed at measuring changes in the atmosphere caused by polluted and hazardous black carbon in Varanasi and the central Indo-Gangetic plains.

Varying effects on the summer, winter, and monsoon seasons were also noticed.

The study observed a reduction in the increase of atmospheric temperature due to black carbon.

"From 2009 to 2012, black carbon mass concentration was found to be increasing from an annual mean of about nine micrograms per metre of air during 2009 to an annual mean of about 18 microgram per metre cube volume of air in 2012. The highest value was recorded in 2012, followed by a smooth decline till 2021, when the mean black carbon mass concentration was about 5.5 microgram per metre cube volume of air. In 2020, the lowest mean value of about 4.5 microgram per metre cube volume of air was recorded," Srivastava said.

Black carbon levels averaged 14.67 micrograms per cubic metre during the winter, while during the monsoon, the levels dropped to an average of 4.4 micrograms per cubic metre.

Higher black carbon levels were recorded in winter due to local factors like biomass burning, fossil fuel usage, and adverse dispersion.

Seasonal black carbon levels also showed a consistent decline, with a post-monsoon average decrease of 1.86 micrograms per cubic metre and a pre-monsoon average decrease of 0.31 micrograms per cubic metre.

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