Delhi’s baseline pollution level, the minimum pollution when major sources of pollution are shut down, is about one-tenth of the maximum pollution the capital witnesses, especially during the October-January period, a new study based on data from real-time contamination during Covid -19 lockdown this April, has found.
The air quality of a place depends on the total pollution load from sources such as industries and vehicles and on local climatic conditions, which impact the dispersion of pollutants.
Scientists from the Delhi Pollution Control Committee (DPCC) and the Indian Institute of Tropical Meteorology (IITM) have published an article in the scientific journal Current Science, which provides the reference pollution level for six different pollutants for Delhi, after to study air quality levels in 34 cities in the capital, where pollution is monitored in real time.
“These are the first baseline pollution level data from Delhi. While background pollution is pollution that comes from outside or that would have been naturally present, baseline pollution is the lowest level of pollution to which the population is chronically exposed and is therefore of great importance to epidemiological research. Such an emission scenario was almost impractical in a densely populated megacity like Delhi, ”said Deputy George, a scientist with the Delhi Pollution Control Committee and one of the team members that conducted the research.
The study is based on the city’s average pollution levels before and during the Covid-19 shutdown that began across India as of March 25, halting factories, construction sites, nearly all vehicle movement, and some other local sources that pollute the air of Delhi.
While the emission sources were reduced by 85-90%, causing a sharp decline in pollution levels, the weather also favored Delhi and pushed the city’s pollution to the bottom.
“The reference levels of PM10 and PM2.5 were found to be 38μg / m3 (± 8) and 22μg / m3 (± 6) respectively. The reference value for NO2 was 8 ppb (± 3), which is considered very high, ”states the research article, published on October 10.
The research was led by Gufran Beig, a senior scientist at the Indian Institute of Tropical Meteorology, in Pune. Eleven researchers from IITM, DPCC, Utkal University, and the Indian Meteorological Department (IMD) analyzed data from 34 automatic air quality monitoring stations in Delhi from February 20 to April 14 and prepared the baseline level of seven pollutants, including PM10, PM2.5, NO2 and SO2 among others.
The data was compared to 2019 pollution levels during the same period for reference purposes. The PM10 level was found to occasionally spike in May despite the shutdown due to dust storms bringing pollutants from the sandy western parts of India.
Findings show that although PM10 levels remained mostly above the allowable limit of 100 μg / m3 during the pre-closure period, occasionally touching and crossing the 200 μg / m3 mark, in the post-closure period they remained well below the 100 μg / m3 mark. On Saturday at 5 p.m., it was 232 μg / m3, almost six times the baseline contamination level.
The PM2.5 level remained mostly above the allowable limit of 60 µg / m3 in the run-up to closure and on one occasion shot up to almost 140 µg / m3. Compared to this, in the closure period it remained below the 40 μg / m3 mark most days and even reached 20 μg / m3. On Saturday at 5 p.m. it was 95 μg / m3, almost five times the baseline.
In winter, PM2.5 and PM10 exceed their respective severe + marks of 300ug / m3 and 500ug / m3, mainly due to poor dispersion and higher pollution load due to stubble burning in the farm-rich states of Punjab and Haryana. It starts to go down from February when the weather starts to get warmer and burning is also reduced.
“The level of contamination was drastically reduced immediately after the closure and the concentration of contaminants reached the saturation level within a few days, beyond which no further decrease was possible. In the present case, each pollutant in Delhi reached the saturation level between 4 and 6 days after closure, beyond which a stable level was maintained, ”the authors said in the article.
Experts have welcomed the study saying that it is this baseline contamination that the population is chronically exposed to and is therefore of great importance for epidemiological research.
“These are the first reference data. There will always be some pollution due to pollution from the kitchen and pollution brought on to operate emergency services, let’s say an ambulance on the road or a thermal power plant. Such a baseline pollution scenario is practically impossible to achieve in a megacity like Delhi, but the closure helped us prepare the first baseline pollution dataset. Now we should use this to redefine our air quality standards and also plan our pollution mitigation strategies, ”said D Saha, former head of the air quality laboratory at the Central Pollution Control Board.
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