The airborne contaminants that people breathe in with their city air and how these affect their health is a natural extension of what Bhola Ram Gurjar focused on during his three-year stay in Mainz. During this period, he compiled an emissions inventory for the Indian capital of New Delhi, where the number of vehicles on the roads has burgeoned in recent decades, while the city’s infrastructure has failed to keep pace. Between 1971 and 2001, the overall length of the road network grew by a factor of 3.5, from 8,380 kilometers to 28,508 kilometers. Yet over the same timescale, the number of vehicles on the roads increased 20-fold: from 180,000 to almost 3.5 million.
“The inventory helped us to eliminate some false interpretations regarding the sources of the air pollution,” says Gurjar. In the 1990s, public transportation and private traffic were regarded as the main cause of the contaminants in Delhi’s air. However, Gurjar’s analysis showed that up to 80 percent of sulfur dioxide and particulate emissions in the city were contributed by coal-fired power stations.
The results made it clear that what the megacities needed was an emissions inventory. In an article in the journal ATMOSPHERIC ENVIRONMENT, Gurjar and Lelieveld thus called for an international program to gather data on air pollution emissions and estimate their local and global effects.
The two researchers also practiced what they preached: Shortly after the article was published, Bhola Ram Gurjar returned to India and took up a position at the Indian Institute of Technology in Roorkee. There, he and Lelieveld established a Max Planck Partner Group to study air quality in megacities. Such Partner Groups enable scientists from abroad, when they return home, to continue with the joint research and existing projects first initiated at a Max Planck institute.
The scientists first studied the emissions in the world’s 18 largest megacities and ranked them in order of air quality. The figures measured in 2000 showed that Tokyo, Beijing, and Shanghai had the highest emissions of carbon monoxide, while Beijing, Shanghai and Los Angeles recorded the highest emissions per inhabitant.
The highest concentration of sulfur dioxide was found in Dhaka, followed by Beijing and Shanghai. The levels in each of these three megacities exceeded the standards recommended by the World Health Organization (WHO). Moscow, Beijing and Jakarta claimed the dubious record for the highest concentrations of nitrogen dioxide, while the inhabitants of Karachi, Cairo, Dhaka and Delhi suffered the worst particulate pollution.
But Gurjar and Lelieveld were not satisfied simply with drawing up a pollution ranking table. They wanted to rank these megacities by the actual impact of these contaminants on the health of their populations. Ri-MAP is the result of their continuous research collaboration – a model that combines various data: the population of a megacity, the air quality and the risk to human health presented by each hazardous substance in the air. Based on a set of ratios of concentration to effect, the model predicts the number of additional deaths in each city that can be attributed to individual airborne contaminants.
The resulting table for the 18 megacities in which the researchers analyzed the quality of the air shows where the air is most dangerous to breathe. Karachi has the highest number of additional deaths due to air pollution, almost 15,000 per year. Some 14,700 people die each year as a consequence of Dhaka’s polluted air, 14,100 in Cairo, 11,500 in Beijing and 10,500 in New Delhi.