PANAJI
A first-of-its-kind study from a coastal site in India to classify aerosol types has found that Goa's air pollution is at its worst during winter and post-monsoon, while southwest monsoon rains and marine winds significantly improve air quality by clearing pollutants from the atmosphere.
A comprehensive study by the School of Earth, Ocean and Atmospheric Sciences, Goa University, co-authored by Goa University Vice-Chancellor Prof Harilal Menon along with researchers Avirup Sen and Atiba Anis Ahmed Shaikh, also found the highest concentrations of airborne pollutants during two daily peaks-8 am to 9 am and 8 pm to 10 pm
The researchers examined the optical properties of near-surface aerosols over Goa between December 2019 and November 2020. It is the first study from a coastal site in India to classify aerosol types using the relationship between scattering and absorption characteristics.
The researchers observed that winter and post-monsoon seasons recorded significantly higher concentrations of airborne particles due to the combined effect of pollution transported from inland regions, local emissions and stagnant atmospheric conditions.
"Distinct seasonal variability was observed, with elevated aerosol concentrations during winter and post-monsoon attributable to the influence of continental air masses and stagnant meteorological conditions," the study noted. In contrast, the monsoon season recorded the lowest aerosol concentrations.
The study attributed this to "wet scavenging and marine air intrusion", explaining that rainfall effectively removes suspended particles from the atmosphere while clean marine air from the Arabian Sea replaces pollution-laden continental air. The study suggests that morning and evening human activity, coupled with atmospheric conditions, causes pollutants to accumulate near the surface. The nature of airborne particles was also found to change markedly with the seasons. Winter and post-monsoon were dominated by fine, pollution-related aerosols, including black carbon, while the monsoon season saw larger sea-salt particles becoming predominant. The study found that fine, pollution-related aerosol types accounted for 922 per cent of aerosols during the post-monsoon season and 65.6 per cent during winter. During the monsoon, however, coarse marine aerosol types made up 89.3 per cent of the total aerosol population.
"Their seasonal distributions reflected a shift from continental to marine influence," the researchers observed, highlighting how the onset of the monsoon transforms the composition of the air over Goa. The study also reported that black carbon-dominated aerosols were most prevalent during winter and exhibited the lowest single scattering albedo, indicating they absorbed the greatest amount of sunlight. Conversely, low-absorbing large marine particles recorded the highest albedo during the monsoon.
The researchers concluded that Goa's aerosol environment is governed by a complex interaction between local emissions, pollution transported from inland regions, seasonal weather systems and coastal atmospheric circulation.
