The air quality in Delhi on Wednesday continued to be in the “very poor” category for the fifth consecutive day, according to the Central Pollution Control Board. A thick haze hung over the Indian capital due to farm fires in neighbouring states and unfavourable wind speed.

According to the agency’s air quality index or AQI, any reading above 100 on the scale of 500 is progressively unsafe for health. At 5.30 pm, the AQI was 359 in Delhi. An index reading between 0 and 50 puts the air quality in “good” category. A reading between 51 and 100 puts it in the “satisfactory” category, between 101 and 200 in the “moderate” category, and between 201 and 300 in the “poor category”. The air quality is said to be “very poor” when the index value falls between 300 and 400. An index value between 400 and 500 puts the quality in the “severe” category.

While the pollution control board uses 24-hour average data, the Ministry of Earth Sciences’ SAFAR, or System of Air Quality and Weather Forecasting And Research reports real-time figures. The government-run monitoring agency said the overall AQI struck 333 at 5.30 pm. It also said the air quality is likely to deteriorate in the next days.

“The SAFAR synergized stubble fire counts over Punjab, Haryana, Uttar Pradesh, Uttarakhand, and neighboring areas are marginally decreased, but still significant and stood at 1949 yesterday,” it added. “The boundary layer wind direction is not favorable (south-westerly today morning) for efficient direct fire-related transport; stubble burning share in PM2.5 in Delhi’s air is estimated as 5% for today.”

The Central Pollution Control Board index is typically lower than that of SAFAR in cases of extreme pollution because it averages values for 24 hours, and caps hourly indices at 500 even if they are of a higher value.

Deteriorating air quality in Delhi has already led to an increase in respiratory infections, amid the coronavirus pandemic. On Monday, Delhi Chief Minister Arvind Kejriwal announced that no manufacturing industry would be allowed in the Capital in new industrial areas as part of the plan to control air pollution. Only hi-tech and service industries will be permitted to operate in new industrial areas in the city.

According to the chief minister, the move is aimed towards getting rid of polluting industries such as iron, steel and plastic in Delhi.