After a short breather, pollution levels rise in Delhi

The national capital’s air quality remained in the “poor” category on Thursday morning, the Central Pollution Control Board’s (CPCB) data showed.

Delhi’s Air Quality Index (AQI) reading at 7am stood at 267. Thursday’s AQI reading was higher, as compared to Wednesday, when the 24-hour average stood at 211 based on the data collected from 37 monitoring stations across the city.

An AQI reading between 0 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”.

Delhi’s AQI has fluctuated between poor and severe and moderate from November 13 to 17.

On November 15, the AQI reading was 435, which fell in the “severe” category and improved to poor (221) the following day and further improved to moderate (171) on November 17.

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Rain, good wind speed and low farm fire counts in neighbouring Haryana, Punjab and parts of western Uttar Pradesh (UP) after Diwali, which was celebrated on November 14, led to a significant improvement of the AQI.

An analysis of the AQI data showed that Delhi experienced a moderate air quality day between November 13 and 17 for the first time since 2017.

The System of Air Quality and Weather Forecasting and Research (SAFAR), an initiative of the Union Ministry of Earth Sciences (MoES), said the farm fire count rose to 427 on Wednesday, as compared to 98 on the previous day.

The farm fires contributed to a spike in Delhi’s PM 2.5 levels -- ultrafine particulate matter with diameter less than 2.5 micrometres – and had peaked to around 40% in October, which came down appreciably after Diwali.

“The stubble burning share in PM 2.5 levels in Delhi’s air is estimated at 8%. AQI may further worsen to the higher end of ‘poor’ to the lower end of the ‘very poor’ category on November 21 (Saturday), as the conductive meteorological environment created after rainfall is gradually retreating,” the SAFAR bulletin stated.

V K Soni, the head of the environment monitoring research centre of India Meteorological Department (IMD), said wind speed is likely to remain high over the next two days and no significant deterioration is expected.

“The average wind speed is likely to remain between 12 and 15 kilometres per hour (kmph), which will allow continuous dispersion of pollutants. Wind speed is likely to reduce Saturday, when the AQI may plunge to the lower end of the ‘very poor’ zone,” Soni said.

The temperatures are also likely to dip in the national capital this week and are expected to be in single digits between Saturday and Monday (November 21-23).

According to the IMD forecast, Delhi is likely to have a foggy Thursday morning, which may clear during the course of the day. The minimum and maximum temperatures are likely to be 10 and 26 degrees Celsius (C), respectively.

On Wednesday, Delhi’s minimum temperature, recorded at the Safdarjung observatory, which is considered the official reading for the city, was 10.6 degrees C --- two notches below the season’s average. While the maximum temperature was 25.4 degrees C-- two notches below normal.