After morning rain spell, Delhi breathes best air since Sept ’23

New Delhi: Intermittent spells of pre-monsoon showers cleared Delhi’s air of sooty pollutants, as the Capital logged its first “satisfactory” reading of the 24-hour average air quality (AQI) in 282 days, according to the Central Pollution Control Board.

The AQI was 79 (satisfactory) at 4pm on Thursday, a drop of 59 points compared to Wednesday’s reading of 136 (moderate). The last time Delhi’s air was in the “satisfactory” zone was on September 19, 2023, when it was 73. The main pollutants mitigated by the rain were PM2.5 and PM10.

Coarse dust particles from construction sites and other sources had caused the air quality to remain in the moderate range. Along with this, a highly volatile gas, ozone, has also been a major pollutant.

System (EWS) for Delhi – a forecasting model under the ministry of earth sciences – said Delhi’s air quality should remain “satisfactory to moderate” for the next few days.

“The air quality is likely to be in moderate category on June 28... satisfactory category from June 29 to June 30. The outlook for subsequent six days is that the air quality is likely to be in satisfactory to moderate category,” said the EWS bulletin on Thursday.

According to experts, the trend of better air days will continue for a few weeks.

“The prolonged heat during summer increases dust in the air, which primarily affects the AQI. Rain has a washout effect and brings the dust particles down, which makes the AQI improve,” said Anumita Roychowdhury, executive director at the Centre for Science and Environment (CSE).

“This year, there was a continuous spell of heatwave which brought up pollution. This relief is temporary, but the pollution levels should remain considerably low for the next two to three months,” she added.

CPCB classifies an AQI of 0-50 as “good”, 51-100 as “satisfactory”, 101-200 as “moderate”, 201-300 as “poor”, 301-400 as “very poor” and 401-500 as “severe”. Forecasts by the Early Warning

Unlike winter months, when PM2.5 and PM10 levels remain high, the main pollutant in summer is ozone.

Experts have pointed out that ground-level ozone levels remain fairly high throughout the year but its concentration starts to rise in March with levels breaching the safe limit on most days between March and June. Though ozone is present in winter as well, the levels are lower owing to low temperatures, as it needs sharp sun to aid its formation.

HT had reported in March that ozone had emerged as the lead pollutant, impacting the city’s air even as summer had only begun. The latest data, however, has not been released. In 2023, parts of Delhi-NCR reported ozone levels exceeding its national standards on 87 out of 92 days between March 1 and May 30.

Mukesh Khare, an air pollution expert at the Indian Institute of Technology (IIT), Delhi, said that scattered rains and winds dispersed pollution. “The effect results in dilution. High heat increases the buoyancy of the pollutants, making them suspended in the atmosphere. Rain brings this layer of dust down and clears the air