The air quality in Delhi remained in the “very poor” category on Monday, according to data shared by the Ministry of Earth Sciences’ System of Air Quality and Weather Forecasting And Research, or SAFAR.

The overall air quality index in the national capital was 309 as of 10.15 am, according to real-time figures shared by SAFAR.

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 AQI in the “very poor” category can lead to respiratory illness on prolonged exposure.

On Sunday, Delhi’s air quality turned “very poor” for the first time since May 17 due to unfavourable meteorological conditions, PTI reported quoting monitoring agencies. The 24-hour average air quality index worsened to 313 on Sunday from 248 on Saturday.

Meanwhile, the PM10 index, which measures the concentration of particulate matter of 10 microns in diameter or less in the air, was 228 on Monday, according to SAFAR.

Levels of PM2.5 climbed to around 132 micrograms per cubic meter. This falls under the “very poor” category. Particulate matter smaller than 2.5 microns, or about a ten-thousandth of an inch, is particularly dangerous to human health as these particles are small enough to travel deep into the respiratory system, potentially impairing lung function.

The National Ambient Air Quality Standards prescribed by the Central Pollution Control Board require PM2.5 concentration to be less than 60 micrograms per cubic metre of air in any given 24-hour period to be considered safe.

The air quality in nearly all areas of the national capital region was in the “very poor” category. The PM10 index for Noida was 322 on Monday.

Action plan’s second phase implemented

On Monday, Delhi’s Environment Minister Gopal Rai announced that the second phase of the Graded Response Action Plan has been implemented in the national capital to reduce the effect of increased pollution, ANI reported.

The action plan is a set of emergency measures that are triggered when air pollution in the national capital region reaches a certain level to prevent further worsening of air quality.

“The cold has started increasing in Delhi and the speed of the wind has decreased, this may result in an increase in pollution...” Rai told the news agency. “The particulate matter is staying near the ground.”

Under the Graded Response Action Plan’s second phase, the frequency of buses and trains, along with parking charges, will be increased to encourage people to use vehicles less, Rai said. “Since winter is increasing, people will be burning bonfires, so Resident Welfare Associations would be guided to provide heaters to their people,” the environment minister added.

Air quality plunges in the winter months in Delhi, which is often ranked the world’s most polluted capital. Stubble burning in Punjab and Haryana, along with falling temperatures, low wind speed and emissions from industries and coal-fired plants contribute to air pollution in the region.

On Friday, the National Green Tribunal sought reports from the Delhi and Punjab governments on steps they intend to take to control air pollution.