Most air quality monitoring stations in Delhi continued to show “very poor” or “severe” readings on Monday. The overall air quality index reading for the national capital was 354 at noon – better than 381 on Sunday afternoon, but still “very poor”, data from the Central Pollution Control Board showed.

A thick haze has remained in the city since Sunday, when the air quality was at its worst of the season so far.

The air quality index is a scale from 0 to 500 – the higher the value, the worse is the air for public health. An index value from 301 to 400, categorised “very poor”, poses a risk of respiratory illness, while an even higher value – “severe” – can affect even healthy people and “seriously impacts those with existing diseases”, according to the pollution control board.

Six of the 33 monitoring stations where readings were available had an index value of over 400 at noon on Monday. The worst among them was Mundaka, with a reading of 424. Among nearby cities, a monitoring station at Ghaziabad had a reading of 409 and another in Noida recorded an index value of 362.

The decline in air quality has been attributed to vehicular pollution, construction dust as well as stubble burning in the neighbouring states of Haryana and Punjab, authorities said. The Centre-run System of Air Quality Forecasting and Research on Saturday issued a report indicating that stubble burning caused 32% of the pollution in Delhi. The organisation said the pollution is likely to worsen but will not become “severe” for the next two days, PTI reported.

“This is owing to stagnation conditions forced by calm winds with low ventilation and moderate stubble injection,” SAFAR said. Less stubble burning took place in the last two days compared to Thursday and Friday.

The organisation has also issued a health advisory for the capital city, specifically for people suffering from heart or lung disease, older adults and children, asking them to avoid prolonged or heavy exertion. The advisory also recommended that people go for short walks instead of jogs, keep windows closed, and wear masks while stepping outside.