The air quality of Delhi deteriorated on Friday as the dispersion of pollutants slowed, PTI reported. The pollution level in the National Capital Region had improved in the last two days after rain washed away pollutants.

The surface wind speeds are better now but the air holding capacity is also high, which is not favourable to the dispersion of pollutants, said the System of Air Quality and Weather Forecasting And Research, or SAFAR. The air pollution is on “the path of reversal” and has increased after the impact of rain is over, the agency said.

The overall air quality index was recorded at 285 at 4 pm, worse than the reading of 217 at the same time on Thursday, according to the Central Pollution Control Board. Both values lie in the “poor” category. The index had “very poor” readings earlier in the day, when the level of PM2.5 (pollutants with a diameter of less than 2.5 micrometres) was recorded at 139, while that for PM10 particles was recorded at 210.

The burning of crop stubble contributed to 8% of the air pollution in the city, as compared with just 1% the previous day, said SAFAR. The concentration of PM2.5 particles is likely to improve in the next two days, though the air quality will remain in the “poor” or “very poor” category.