Delhi's air quality is predicted to deteriorate to the "moderate" category by October 5

The air quality in the national capital was recorded in the "satisfactory" level on Wednesday but it is predicted to slip into the "moderate" category by Friday as wind direction changes to northwesterly.

These winds bring dust from western regions and smoke caused by burning of crop residue in neighbouring Punjab and Haryana to Delhi-NCR.

However, the centre-run System of Air Quality and Weather Forecasting And Research (SAFAR) said even a change in wind direction won't drastically impact Delhi's AQI for at least a week.

The Central Pollution Control Board (CPCB) and SAFAR on Wednesday recorded the city's air quality index in the "satisfactory" category -- at 90 and 71, respectively.

An AQI between 0 and 50 is considered ''good'', 51 and 100 ''satisfactory'', 101 and 200 ''moderate'', 201 and 300 ''poor'', 301 and 400 ''very poor'', and 401 and 500 ''severe''.

Delhi's air quality is predicted to deteriorate to the "moderate" category by October 5 as a result of change in wind direction from easterly to north and northwesterly, SAFAR said, adding satellite data has indicated sporadic biomass burning signatures in north India over the last week but no increasing trend in fires counts has been noticed.

"Delhi air quality is very unlikely to be influenced by this for the next two-three days. However, the transport of relatively dusty air form western regions is expected by October 5," it said.

SAFAR said it is not expecting any "drastic" deterioration in air quality until the second week of October. This is mainly because strong, moist easterly winds are opposing any flow of polluted biomass plume from the north of the NCR region.

However, the condition is likely to change from the second week of October as models indicate development of a weak anticyclone over the region as part of monsoon withdrawal which can lead to the accumulation of pollutants over the Delhi-NCR region, the SAFAR said.