Warmer, windier: why post-Diwali Delhi air was cleaner this year

Why were contamination levels debased connected Friday?

Several factors played a role, but meteorological conditions had the biggest impact.

WARMER TEMPERATURES: Last year, Diwali was successful November, erstwhile the somesthesia conditions were overmuch cooler — the monthly mean minimum was 13 degrees Celsius and the maximum was 27.8 degrees Celsius.

This year, however, the festival was celebrated successful precocious October, erstwhile temperatures were overmuch warmer. In fact, this October was the warmest successful 73 years, according to the India Meteorological Department (IMD). The monthly maximum and minimum averages recorded astatine the city’s Safdarjung upwind presumption successful October were 35.1 degrees Celsius and 21.2 degrees Celsius respectively. This was the fourth-highest monthly time somesthesia and the sixth-highest monthly nighttime somesthesia successful the period recorded since 1901.

This is significant, arsenic cooler temperatures mean accrued contamination levels. As somesthesia dips, the inversion tallness — which is the furniture beyond which pollutants cannot disperse into the precocious furniture of the ambiance — is lowered. The attraction of aerial pollutants increases erstwhile this happens. STRONG WINDS: Another origin was precocious upwind speeds, which led to a amended dispersal of the contamination post-Diwali.

According to IMD, westerly winds of velocity arsenic debased arsenic 3 to 7 kmph were observed until Friday aboriginal morning, and they touched 10 kmph by 9 am. The upwind velocity accrued to 15 kmph from noon onward. An mean upwind velocity of 10 kmph is considered favourable for the dispersal of pollutants.

Due to the stronger winds, levels of tiny pollutants specified arsenic PM2.5 and PM10, which had spiked connected Thursday apt owed to the bursting of crackers and stubble burning successful Punjab and Haryana, dropped the adjacent day. For instance, the 24-hour mean PM2.5 level was 144.3 micrograms per cubic metre (µg/m3) connected Diwali astatine 8 pm, but had accrued sharply to 168.4 µg/m3 by midnight. It gradually accrued further until 7 americium connected Friday  to 209.1µg/m3, arsenic recorded by the CPCB, and past reduced to 198.1 µg/m3 astatine 4 pm.

The mean PM10 level was recorded astatine 288.6µg/m3 connected Thursday astatine midnight, and jumped to 322.6 µg/m3 connected Friday astatine 6 am. However, it dropped to 308.1µg/m3 by noon.

Anumita Roychowdury, Executive Director, Research and Advocacy astatine the Centre for Science and Environment, told The Indian Express,  “This time, Diwali was successful October, erstwhile cooler meteorological conditions had not settled successful yet. The upwind velocity was besides favourable to assistance dissipate the contamination build-up aft Diwali midnight. Till day connected Diwali day, the aerial prime remained ‘poor’ and past worsened to ‘very poor’ successful the evening. Severe AQI levels were observed astatine midnight and persisted till 7 americium successful galore stations. The night-time contamination related to Diwali caused a precocious buildup successful PM2.5 levels. Though we cannot quantify the publication of firecrackers specifically, respective sources came into play.”