The air quality in Delhi turned “severe” on Monday evening with the Air Quality Index touching 407 at 8 pm, according to the Central Pollution Control Board. The pollution level is likely to have increased due to unfavourable meteorological conditions like low wind speed, PTI reported.

The index had “severe” readings between Saturday evening and Sunday afternoon.

The PM 2.5 (particles in the air with a diameter of less than 2.5 micrometres) level on Monday was recorded at 263 while the PM10 (particles in the air with a diameter of less than 10 micrometres) was recorded at 457.

At least 19 localities in Delhi recorded “severe” air quality, while the air in 17 areas was under the “poor” category. The 24-hour average air quality index for Ghaziabad, Faridabad, Greater Noida and Noida was “severe”, while Gurugram’s air quality had improved to “moderate”.

The Centre-run System of Air Quality and Weather Forecasting said the air quality in Delhi is likely to improve further on Tuesday, but will remain in the “very poor” category. “The stubble-related impact continue to remain nominal due to slow transport height winds,” it said.

Meanwhile, the Central Pollution Control Board’s task force recommended the entry of heavy vehicles into the city and carrying out construction activities between 6 am and 6 pm. The Supreme Court-appointed Environment Pollution Control Authority also allowed the entry of those vehicles that are stranded at Delhi’s borders.

Truckers will also be exempt from paying toll or Environment Compensation Charge from 11 pm on Monday to 7 am on Tuesday. This is expected to reduce congestion pollution as trucks can move through the city without halting.

On Sunday, Haryana’s chief secretary said it was unfair to blame the state for Delhi’s poor air quality, as its farmers have a negligible contribution to air pollution in the National Capital Region.