How high temperatures and strong winds helped Delhi breathe a bit easier this Diwali

Clearer skies, above-normal temperatures in October and strong winds saved Delhi’s air quality from deteriorating into the ‘severe’ category, despite the relentless bursting of firecrackers during the celebrations the previous day.

On Friday morning, the pollution level was the lowest since 2015, with the exception of 2022, even though the 24-hour average air quality on the days before Diwali and on Diwali — Wednesday and Thursday, respectively — was worse than in the previous two years.

Let’s take a closer look.

Delhi air quality

A thick layer of haze blanketed the National Capital, with the air quality index (AQI) recorded at 362 at 9 am as people defied a citywide ban on firecrackers on Diwali. However, the condition improved and the city’s 24-hour average AQI at 4 pm was 339, according to the Central Pollution Control Board (CPCB).

An AQI between zero and 50 is considered ‘good’, 51 and 100 ‘satisfactory’, 101 and 200 ‘moderate’, 201 and 300 ‘poor’, 301 and 400 ‘very poor’, 401 and 450 ‘severe’ and above 450 ‘severe-plus’.

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It was anticipated that the city’s air quality would enter the ‘severe’ category due to the bursting of firecrackers, but it remained ‘very poor’.

Of the 40 weather-monitoring stations in the city, 32 recorded ‘very poor’ air quality, the data showed.

Areas including Alipur (335), Anand Vihar (385), Ashok Vihar (365), Aaya Nagar (316), Bawana (364), Burari (345), Mathura Road (332), IGI Airport, Dwarka (367), Jahangirpuri (361), Mundka (340), Patparganj (339), Rohini (367), Sonia Vihar (370) and Wazirpur (366) recorded ”very poor” air quality, according to the Sameer app that provides hourly updates of the National AQI published by the CPCB.

Friday’s post-Diwali 24-hour average air quality index was 339, just 11 points higher than Thursday’s reading of 328. The post-Diwali air quality this year was better than 358 on November 13, 2023, the day after Diwali. With an AQI of 462, Delhi had the worst post-Diwali air quality day in 2021.

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As the air quality remained in ‘very poor’ category, Environment Minister Gopal Rai expressed gratitude to Delhiites for ‘largely refraining from bursting firecrackers’ on Diwali.

”Thanks to the responsible actions of many residents who avoided using firecrackers, we managed to avoid a severe AQI reading,” he said.

Also read:  Why is the Delhi air quality so poor despite firecracker ban?

Low pollution levels

The report said the PM2.5 levels decreased by four per cent as compared to last year’s Diwali, while the PM10 levels increased by 11 per cent. The acceptable annual standard for PM2.5 is 40 micrograms per cubic metre.

PM2.5 are fine inhalable particles with a diameter that is generally 2.5 micrometre or smaller and are hazardous for health conditions. PM10 are particulate matters that are 10 micrometre or less in diameter.

The Capital also saw an increase in noise pollution levels between 6 pm and midnight on Diwali, data from the Delhi Pollution Control Committee (DPCC) showed.

The reason

This year’s favourable post-Diwali air quality was maintained by a number of variables, including the National Capital’s warm temperatures and strong winds.

“Despite the ban, firecrackers were burst in Delhi-NCR. However, the air quality did not reach the severe category as the winds helped improve the situation,” environmentalist Vimalendu Jha told PTI. However, he added that in the coming days, there is a possibility of a spike in pollution levels in the capital due to unfavourable weather conditions.

Higher temperatures cause the atmosphere’s mixing height—an imperceptible layer that allows particles to travel freely—to rise. This mixing height is lowered by low temperatures, which also slow down the flow of these pollutants and particles.

Temperatures were significantly lower last year when Diwali was celebrated on November 13, with a monthly average lowest of 13 degrees Celsius and a maximum of 27.8 degrees Celsius.

According to the India Meteorological Department (IMD), this year’s October was the warmest in 73 years. The monthly maximum and minimum averages recorded at the city’s Safdarjung weather station in October were 35.1 degrees Celsius and 21.2 degrees Celsius, respectively.

Another factor of the weather that improved the air quality was the wind speed, which until Friday morning was only three to seven kilometres per hour. From midday onwards, the wind speed gradually increased to 15 km/h.

An average wind speed of 10 kilometres per hour is considered favourable for the dispersal of pollutants.

Tiny pollutants like PM2.5 and PM10, which had increased on Thursday probably as a result of crackers popping and stubble burning in Punjab and Haryana, decreased the following day as a result of the stronger winds.

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Record number of emergency calls

The Delhi Fire Services (DFS) reported a surge in fire-related calls on Diwali, with more than 300 such incidents — the highest in 13 years — reported from across the city.

According to a DFS official, the increase in the number of such calls this year was due to the extensive use of firecrackers.

Delhi hospitals reported more than 280 cases of burn injuries, largely caused by firecrackers, on Diwali.

The Safdarjung Hospital, which has the largest burn unit in the country, recorded the highest number of 117 such cases on Thursday, followed by 48 at the All India Institute of Medical Sciences (AIIMS) and 19 at the LNJP Hospital.

Of the patients, 102 suffered minor burns and were treated in the outpatient departments, while 15 with major burns were admitted, according to hospital authorities.

Although the Delhi government had set up 377 enforcement teams and spread awareness through local associations to ensure compliance with the firecracker ban, neighbourhoods across the eastern and western parts of the city reported large-scale flouting of the restrictions.

Gaps in enforcement, limited monitoring and easy access to firecrackers at places in the National Capital Region (NCR) where restrictions were slack were largely responsible for the widespread flouting of the firecracker ban, experts said.

With inputs from PTI