The air quality level in Delhi plummeted to 450 on Sunday, the second-worst pollution level recorded so far this year, according to the Central Pollution Control Board. The worst pollution level in the city was recorded on November 8, the day after Diwali.

An Air Quality Index between zero 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”. The pollution control agency advised people to keep outdoor activities to a minimum for the next few days and avoid private vehicles, PTI reported.

The overall reading of PM 2.5 – particulate matter with a diameter of 2.5 microns – was 460, according to the System of Air Quality and Weather Forecasting and Research, while it was 434 in Gurugram and 517 in Noida. The PM 2.5 levels in Lodhi Road and Chandni Chowk were 429 and 458.

Officials said weather conditions would cause the air quality levels to remain in the severe category for a few more days. Sunday was the coldest day in December in the national Capital in 12 years. “The air quality is likely to improve on December 25, but it will remain in the upper end of the poor to severe [air quality] category,” the pollution control board added.