Met factors like temperature influence spikes in PM 2.5 pollution in summer: Study

While the PM 2.5 levels exceeded national ambient air quality standards in all cities, the study revealed that higher temperatures caused occasional spikes in PM 2.5 levels. These spikes are caused when during higher temperatures, volatile organic compounds and nitrogen oxide react to form secondary pollutants. VOCs and nitrogen oxide are emitted in vehicular pollution, industrial activities and through vehicle fuels and solvents.

The analysis of temperatures and PM 2.5 levels for Delhi showed that air quality was better during the summer of 2023 when average temperatures were cooler in comparison to that of 2022 and 2023 for the same period.

“PM 2.5 levels decreased by 28.4% from 93.81 µg/m³ (microgram/per metre cube) in April and May 2022 to 67.19 µg/m³ during the same period in 2023. However, in 2024, PM2.5 levels increased by 21.3% to 81.53 µg/m³ in the same months,” the study noted.

Delhi had recorded its coolest May in 2023 in 36 years as the city had received several spells of rain whereas it saw record long heat waves during the recent peak summer season. The data for April and May 2024 showed that PM 2.5 levels were in the range of 53.66 ug/m3 at the beginning of the month. As the summer progressed, it touched a high of 141.13 ug/m3 on May 5.

In Patna, the analysis showed that on April 12, 2023 PM 2.5 levels was as high as 123.95 ug/m3 when temperature was 31.27 degree Celsius and had dipped to 71.6 ug/m3 at the end of the month when the temperature was 27.02 degree Celsius. Similarly, PM 2.5 levels were as high as 128.97 ug/m3 in April 2024, when temperature was in the range of 34-35 degree Celsius.

The National Ambient Air Quality Standards prescribe that PM 2.5 levels should be 60 ug/m3 (microgram/cubic metre) for a 24-hour period. PM 2.5 particles are fine particles that are smaller than 2.5 micrometres in diameter, which is smaller than human hair. These particles can cause harmful health effects such as decreased lung function, irritable airways as they go deep in the respiratory organs and can even enter our bloodstream.

“Extreme temperatures can enhance the photochemical reactions that can lead to the formation of various secondary pollutants, while also influencing atmospheric stability and pollutant dispersion. Understanding the interplay between PM 2.5 levels and temperature is crucial for developing effective air quality management and public health protection strategies,” said Palak Balyan, Research Lead, Climate Trends.