The air quality in Delhi deteriorated on Tuesday, with eight areas in the national Capital recording severe pollution levels. Dwarka Sector 8, Jahangirpuri, Mundaka, Narela, Nehru Nagar, Rohini, Anand Vihar and Wazirpur recorded “severe” air quality while 23 localities recorded “very poor” air quality, said the Central Pollution Control Board.

Severe air quality affects healthy people and seriously impacts those with existing diseases while air quality categorised as very poor can cause respiratory illnesses on prolonged exposure, according to the pollution monitoring agency.

The amount of PM2.5 – particles in the air with a diameter of less than 2.5 microns – recorded in the city was 211, PTI reported. In the National Capital Region, Ghaziabad had the worst air with an Air Quality Index reading of 407. Greater Noida, Gurgaon, Faridabad and Noida recorded “very poor” air quality, according to the Central Pollution Control Board.

The Centre-run System of Air Quality and Weather Forecasting and Research, or SAFAR, said pollution levels will gradually increase in the next two days, PTI reported. “The increase in pollution can be attributed to decline in wind speed as compared to past two days,” the agency said in a statement. “All other meteorological factors were already unfavourable.”

The Indian Institute of Tropical Meteorology said wind speed and the ventilation index – which determines how fast pollutants get dispersed – are “extremely unfavourable”. A ventilation index of around 6,000 square metre/second gets rid of pollutants, but it came down to 1,500 square metre/second on Tuesday.