Delhi’s good air quality spell likely to be short-lived

“The impact of widespread rainfall could last for another three to four days if there is no further rain. Thereafter, the anticyclonic circulation could mean that stagnation conditions will prevail. Calm wind conditions may begin. So once the washout effect of the rain ends, the accumulation of emissions will begin again, and could push the air quality towards deterioration. In general, due to the local weather becoming more hostile with calm winds, and local emissions, air quality could deteriorate,” said Gufran Beig, founder project director, SAFAR (System of Air Quality and Weather Forecasting and Research).

Calm winds with average speed of less than 10 kmph prevent pollutants from dispersing. In contrast, the rainfall helps to wash pollutants away.

“During this time (once calm conditions set in), if stubble burning is not curbed and wind direction is favourable, it will begin to contribute…but this depends on wind direction and wind speed. If the stubble burning contribution starts, then air quality may slip to the poor category by the beginning of next week,” Beig said. Winds from the northwest usually help bring smoke from stubble burning closer to the NCR.

With parts of Punjab and Haryana also receiving rainfall recently, paddy residue burning events had fallen. The number of burning events was 130 in Punjab on October 5, according to the Indian Agricultural Research Institute’s (IARI) Consortium for Research on Agroecosystem Monitoring and Modelling from Space. Thereafter, it fell to 19 on October 8 and three on October 9. On October 11, it rose again to 45 in Punjab. Haryana recorded no burning events on October 11.

Delhi has recorded two ‘good’ air quality days over the past one week.