Delhi saw about 7 mm of rainfall till 8.30 a.m. on Wednesday, improving air quality by settling the particle pollutants.
However, rains have also increased the moisture in the air, which according to the System of Air Quality and Weather Forecasting And Research (SAFAR), will trap the pollutants and worsen the air quality.
"After the isolated shower in part of Delhi, a lot of moisture is introduced in the air, making it heavy and increased the holding capacity which will force AQI to go to the 'severe' category from evening until late night as the ventilation is also reduced," SAFAR forecast said.
However, it adds that the air quality will recover in the next two days as the wind is likely to pick up by Friday.
The Air Quality Index (AQI) of Delhi at 4 p.m. on Wednesday was 312, considered 'very poor,' against 409 or 'severe' at this time on Tuesday. Gurugram saw "poor" air quality with AQI of 254. The AQI was 339 in Faridabad, 352 in Ghaziabad, 348 in Greater Noida and 332 in Noida, all measured on a scale of 0 to 500 and falling under 'very poor' category.
The major pollutant, PM2.5 or particles with a diameter less than 2.5 mm, dropped from 'severe' category on Tuesday to 'very poor' category in Delhi on Wednesday.
The average presence of PM2.5 was 160 microgrammes per cubic meters at 5 p.m., against 182 units at 12 p.m. Meanwhile, the same across Delhi on Tuesday was 271 units.
Known to impact health severely by entering the bloodstream, the safe limit for PM2.5 is 25 units by international standards and 60 units by national standards.
Due to the rains, the larger suspended particles PM10 or particles with a diameter less than 10 mm, dropped from the "severe" to the "moderate" category on Wednesday morning, according to SAFAR.
"Weather has improved in Delhi, but since the system has moved, the region may see a slight increase in pollutants on Thursday due to calm winds. But after that, north-westerly winds will improve the air quality," Mahesh Palawat, Director of private weather forecast group Skymet said.