In Los Angeles, New York and Tokyo, in contrast, the effects of air pollution have long since ceased to be so drastic. Here, the number of additional deaths is less than 500 per year. “The analysis shows a clear trend: the health risk presented by air pollution is greater in the megacities of the developing world than in the industrialized countries,” says Bhola Ram Gurjar.
The researchers admit that the figures do not reflect any absolute certainties. The current model assumes that the entire population of a megacity is exposed to the same degree of airborne pollution. Furthermore, the model also uses annual averages of individual pollutants. In the future, however, the researchers intend to take account of monthly, weekly or even daily fluctuations in the concentrations of contaminants, as well as the number of people who are directly exposed to these substances.
“The estimates of risk may not be perfect, but we believe that they can be helpful in establishing guidelines for pollution control,” says Gurjar. The model breaks down the health risks in order of pollutants: it considers the relative risk – that is, the probability of disease or death – if the concentration of one contaminant rises by one point on the Ri-MAP scale. The resulting figures show for each contaminant how steeply it increases the mortality rate due to respiratory or cardiovascular diseases, or how many hospitalizations it prompts due to chronic obstructive pulmonary disease. In both Karachi and Dhaka, around 2,100 deaths are attributable to respiratory diseases. “The city authorities could even use such approximate values as a basis for decisions on which pollutant to reduce first.”
New Delhi became a test city for the Ri-MAP model. Analysis revealed that the number of additional deaths due to air pollution rose steeply between 1998 and 2002. Then, in 2003, the rate suddenly declined, remained constant for a few years, and is now once again rising steadily.
“The steep decline in 2003 could be attributable to the fact that that was the year in which the city authorities converted all of their public transport service buses from diesel to run on compressed natural gas,” Gurjar explains. “Since then, however, the steep growth in the overall number of vehicles has cancelled out this improvement.” Gurjar and Lelieveld are now keen to broaden their research to include other pollutants, such as heavy metals, ozone and minute particulates that can penetrate the human lung. At some point, Gurjar continues, the estimates of risk generated by the model should be compared against epidemiological data from the megacities. “Correlating the Ri-MAP figures directly like that with actual death statistics is the toughest test of such a model,” says Gurjar.
If the model’s predictions were to be confirmed by such a comparison, it is likely that city administrators would have faith in the forecasts. The results of the model calculations would then demonstrably offer a reliable basis on which to plan the measures needed to make the air healthier to breathe. Not only would there be health benefits the fantastic views of these megacities, seen from above from an approaching aircraft, would also be less clouded by smog – perhaps even to the point where they could be enjoyed in aweinspiring clarity.