The odd-even period has seen a marginal dip in the quantity of PM 1, the tiniest and the most harmful of all the respirable pollutants, according to data shared by the Centre’s System of Air Quality and Weather Forecasting and Research.
However, a clear trend of pollution levels has not emerged as other pollutants like PM 2.5, PM 10 and surface-level ozone have fluctuated since the curb on vehicles came into force on April 15.
The city’s air quality was in the ‘very poor’ category on Thursday with the average levels of PM 2.5 and PM 10 recorded at 166 and 334 micrograms per cubic metre (ug/m3). The prescribed limits are 60 and 100.
As per System of Air Quality and Weather Forecasting and Research (Safar), the peak level of PM 1 has been lower and it has seen steeper falls in the intervening period as against the 15-day period from April 1. There are no official safe standards for PM 1 in India as of now.
It hovered around 30-35 ug/m3 from the first day of the scheme’s second phase and even fell to around 20 ug/m3 on April 23. However, it crossed the 60 threshold on Wednesday, first time since April 3.
PM 1 particles measure less than 1 micron, considerably smaller than PM 2.5 and PM 10, and are major byproducts of emissions from fossil fuels like petrol and diesel.
Importantly, unlike the latter, these particles do not get dispersed by wind and are extremely dangerous as they can embed themselves deep into the bloodstream and affect foetal development as well.
The Delhi government had announced that it would measure PM 1 during the first phase of the odd-even scheme, a plan that was later shelved. Safar, which is also measuring ozone, is likely to release a comprehensive report after April 30.