doi:10.1038/nindia.2014.118 Published online 28 August 2014
Every day millions of Indians walk on city pavements or wade through smoke-belching cars to cross roads, unknowingly inhaling a lethal dose of harmful pollutants. A new study by US-based Lawrence Berkeley National Laboratory has found high levels of three pollutants — fine particles, black carbon and ultra-fine particles on Delhi roads during morning and evening rush hours.They found that the fine particles are most harmful to human health. These particles are invisible to the naked eye and can easily make their way into the lungs. The Global Burden of Disease 2010 study had shown that exposure to such air pollutants might be killing more Indians than AIDS and malaria put together.
“We found that air quality inside auto-rickshaws and cars in Delhi is substantially worse than the air that one would measure at a typical rooftop monitoring site,” said Joshua Apte who led the Berkeley team. Poor urban air quality is a large and growing health hazard in Delhi and many other cities in India, he told Nature India.
Air pollution is the number five risk factor for premature death in India, causing three times as many deaths as AIDS and malaria together. This prompted Apte and his colleagues to assess the air pollution-related health risks in an urban set-up like Delhi. To measure the amount of pollutants that people breathe on the streets, they used three different portable instruments and traveled on the roads and highways of Delhi on an auto-rickshaw for four months.
The researchers found that the level of fine particles was 50% higher on the road than in the ambient air. The level of black carbon and ultra-fine particles was 3.6 and 8.4 times higher in Delhi vehicles than in the ambient air. The fine particles' level dropped in the evening rush hours but that of black carbon increased. These results corroborate a previous study in which Apte and his teammates estimated that urban commuters in Delhi traveling by an auto-rickshaw were exposed to what residents in many high income countries would be in a full day1.
According to US-based Environmental Protection Agency, an annual average concentration in excess of 12 micrograms per cubic metre of fine particles is considered to be a health concern. It is alarming that average annual levels of fine particles in India are between 50 and 150 micrograms, Apte says. “Vehicles account for 20-40% of ambient concentration of fine particles. Various industries and electric power generation also contributes to the load of pollutants in metro cities like Delhi,” he says.
A separate study carried out in Agra and Delhi has also detected very high levels of secondary organic aerosols, a type of fine particles formed by the chemical transformation of atmospheric organic compounds such as volatile organic compounds2.
“Fine particles are really harmful as they can remain suspended in the atmosphere for several days to weeks and can be transported to distant locations through atmospheric circulations. These particles can even infiltrate homes contributing to indoor pollution,” says Ajay Taneja of Dr. B R Ambedkar University, Agra. The study results indicate that immediate measures should be taken to lower the vehicular emissions in Indian cities, Taneja adds.
However, Gufran Beig, joint director at Indian Institute of Tropical Meteorology, Pune is a bit skeptical about the results of this study. Measurement of pollutant levels in a moving car is highly affected by aerodynamic flow of air, says Beig. The instruments measure pollutant levels close to the exhaust pipes and people do not breathe in pollutants from there directly, he points out. According to him, an ideal study model is to get an average of all kinds of environments and then identify the hot spots.