Nisarga cleans air, Mumbai AQI at 17

NEW DELHI: Cyclone Nisarga cleaned up the air in its trail as it dwindled to a low-pressure area near central India on Thursday evening.
Mumbai saw an air quality index (AQI) of 17 on Thursday evening, the lowest figure in 2020, reflecting the cleanest air since July last year. Pune saw a one-year low at an AQI of 23, as per data from the System of Air Quality and Weather Forecasting and Research (SAFAR).

On Friday, Mumbai’s AQI climbed to 28 while Pune’s was at 30.

The PM 2.5 level in Mumbai on Thursday was 9 while the figure for Pune was 14. PM 10 levels in Mumbai and Pune were 17 and 23 respectively. These firmly remain in the “good” category, which notes AQIs of 50 or lower.

The two factors helping the air clear out were the rain and high wind speed, said Gufran Beig, programme director at SAFAR. “The rain helped wash away the pollutants, while the wind cleaned the air,” he said.

However, Beig said the AQI levels were down before the cyclone as well due to the lockdown. “We were already observing better air due to the lockdown, and the cyclone’s influence has helped bring the pollutants down this low,” he said.

This effect has also been observed in New Delhi, which has saw an AQI of 117 on Thursday. Over the past two months, the AQI has remained between moderate (50 to 100) and satisfactory (100 to 200) categories. However, with the lockdown easing in the capital, the levels are expected to rise, especially due to vehicular pollutants, which are a major cause of pollution in the national capital.

This purple patch of clean air is expected to continue in the coming days. SAFAR’s model suggests that Mumbai will see a further drop in the PM 2.5 and PM 10 levels before rising a little due to restoration of normalcy in the coming days. The same trend is expected in Pune, although the rise will be slower. Both cities are likely to remain in the “good” category, the highest classification according to SAFAR.

PM 2.5 (particulate matter of diameter 2.5 micrometres) comprises dust and other matter from construction sites while PM 10 (of 10 micrometres) comes from vehicular emissions and burning of waste.

Both Mumbai and Pune last saw such clean air during the Prime Minister’s “janata curfew” on March 22, with AQIs of 63 and 58 respectively.