During summer, ozone and dust are among the main sources of pollution. Particulate pollution in the season rises due to arid conditions, high heat and transportation of dust to Delhi. Experts said ozone is produced from complex interaction between nitrogen oxides (NOx) and volatile organic compounds (VOCs) that are emitted from vehicles, power plants, factories and other combustion sources and undergo cyclic reactions in the presence of sunlight to generate ground-level ozone.
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Anumita Roychowdhury, executive director, research and advocacy, Centre for Science and Environment (CSE), said, “Summer strategy will require action to control both particulate matter and gases, including NOx and ozone. During summer, ozone standards are exceeded on more days. This demands stronger action on vehicles, industries and other combustion sources.”
A CSE analysis in 2022 stated that every year, ground-level ozone usually exceeds the safety standard on all days of summer in some locations in Delhi-NCR. In 2022, the spatial spread, i.e., the number of stations exceeding the standard across the city, was much higher. On an average, 16 stations exceeded the standard daily in March and April last year, a 33% increase from the same time period the previous year.
Gufran Beig, founder project director, System of Air Quality and Weather Forecasting and Research (SAFAR), the forecasting body under the Union ministry of earth sciences, said, “As the temperature soars and crosses 39-40 degrees Celsius, ozone pollution will increase significantly in Delhi. It is mainly because the VOC emissions will increase, which helps in ozone production. Particulate matter no longer remains a lead pollutant during this period.”
A national assessment by CSE done on summer pollution in 2022 found that north India suffered the maximum pollution, with Delhi-NCR a hotspot. The PM2.5 average of NCR was almost three times the average of cities in southern India.
The summer average PM2.5 for north India stood at 71 micrograms per cubic metre, the highest among all regions. Within north India, Delhi NCR was found to be the most polluted sub-region. Delhi ranked eighth in the country with a season average of 97 micrograms per cubic metre.