US satellites show Delhi's air has been getting dirtier since 2000

NEW DELHI: Air pollution has been increasing in and around Delhi since the year 2000 with just two blips between 2004 and 2006, a new analysis has revealed. This contradicts government agencies' claim that there is no definite trend of deteriorating air quality.

Using satellite measurements, an American scientist has found a steady increase in both PM2.5 (fine, respirable particles) and PM10 (coarse particles) in Delhi's air between 2000 and 2015, with the annual averages ranging from 74 to 92 micrograms per cubic metre.

Naresh Kumar, associate professor of environmental health at the University of Miami, USA, analysed satellite-based aerosol optical depth (AOD) in and around Delhi 2000 onwards, using data from Moderate Resolution Imaging Spectroradiometer (MODIS), on board the NASA satellites Terra and Aqua. AOD measures the concentration of aerosols or solid and liquid particles suspended in air that can arise from human activities, such as driving and construction, or natural factors like dust and water vapour.

His analysis shows the worst air quality in a 50km radius around Connaught Place and the cleanest in a range of 150-200km, showing how urbanization causes pollution. The AOD around Connaught Place ranged from 0.6 to 0.7, whereas in the US it was less than 0.2.

Kumar says industries and burning of garbage and plant matter could also be driving up air pollution, especially in winter when a blanket of cold air makes the dispersion of pollutants difficult. About vehicles, he says, they are among the main sources of PM2.5 and reactive gases, such as nitrogen oxides and carbon monoxide, and volatile organic compounds. "If the city wants to cope with air pollution, it needs a multi-sectoral approach."

Kumar is also tracking the impact of the odd-even experiment in Delhi but hasn't drawn any conclusions yet. "Weather plays an important role in dispersion and transport of air pollution. The 1952 London smog was caused by high levels of air pollution and cold air masses." But he says halving the number of diesel vehicles on the road will certainly reduce people's local exposure to pollutants.

Kumar is running a map: precise.ccs.miami.edu/delhi that shows air pollution data in real-time. Each place, he says, has a more or less fixed capacity to disperse air pollution. "The capacity will remain the same in the future unless artificial filters are installed to check the increasing pollution in the city. The problem is that the pollution from anthropogenic (human) activities has been increasing dramatically without any effective mechanism to clean the air pollution, assuming it will disperse automatically."