gases; their impact is more regional, and the extent of their cooling and heating effects is still quite uncertain. When the Supreme Court of InBut the new fleet produced far “The people who discuss climate dia ordered the city of New Delhi lower amounts of aerosolssblack and the people who discuss air to switch its mass-transit system carbon, which warms air by abquality operate really in different to a cleaner-burning fuel, the sorbing light, and organic carbon realms,” says Tami Bond, an atmocourt was responding to citizens’ and sulfates, which reflect radiation spheric chemist at the University of concerns about air pollution. The and cool the atmospheresthan Illinois Urbana-Champaign. government of New Delhi comdiesel vehicles did. When the scienBut the new study “clearly shows plied and enforced regulations, tists analyzed the change in aerosol that the distinction between which by 2003 turned the the air pollution policies city’s diesel and gasolineand climate change policies dependent public transbecomes more and more port fleetsbuses, taxis, artificial,” adds Frank Raes, and auto rickshawssinto head of the European Comone that runs on commission’s Joint Research pressed natural gas Centre’s Climate Change (CNG). Unit. Contributions to local Bringing both air-quallevels of air pollutants like ity and climate change carbon monoxide, sulpolicies under one umfates, and PM10 emitted brella is important befrom these vehicles decause, unlike in the New creased, as shown by an earlier study. New Delhi’s air quality has improved since the city switched Delhi case, a policy that benefits one may hinder But the switch to CNG its mass-transit system to natural gas, but air pollution remains a problem, partly because of a rapidly rising number the other, says Hadi also had an unexpected Dowlatabadi, who is the global benefit, according to of diesel private vehicles. Canada Research Chair at a new study published in IRES and is Kandlikar’s longemissions between the new and ES&T (DOI 10.1021/es702863p). It term collaborator. The new study old fleet, they found that the led to a 10% reduction in the global is “an unusual case of the benefits of changes in sulfates and organic warming effect of the greenhouse the air-quality and the greenhouse carbon emissions had no signifigases and aerosols emitted by the gas [policies] pointing in the same cant impact, but the reduction in fleet. direction rather than tugging at one the amounts of black carbon more The results emphasize the need another.” than offset the increase in warming to integrate air-quality and global For example, in the U.K., a from methane and CO2. warming policies and to evaluate 2001 policy to mitigate climate the climate impacts of aerosols in Thus the overall impact was a change led to a rapid replacethe process. lowering of atmospheric warming ment of gasoline vehicles with When lead author Conor Reyby emissions from the mass-transit diesel ones. Greenhouse gas nolds, a graduate student at the fleet. emissions dropped as a result, Institute for Resources, Environ“There is no substitute for mitibut the diesel vehicles emitted ment, and Sustainability (IRES) of gating greenhouse gases,” says more particulate pollutants, the University of British Columbia Chandra Venkataraman, an airwhich increased the number of (Canada), and his adviser, Milind quality and climate expert at Bomdeaths by 90 per year, according Kandlikar, looked at the effects the bay’s Indian Institute of to a 2006 study by Dowlatabadi. fuel switch had on the levels of the Technology. “However, mitigating “Any policy aimed at either air greenhouse gases CO2 and methaerosols, which have especially imquality or climate is likely to have portant regional effects, could yield ane, they found an increase in consequences for both,” says Kandadditional climate benefits.” emissions leading to a 30% rise in likar. The challenge will be to deThis approach is not being acted atmospheric warming caused by sign the policies “in such a way as on by governments, largely because these gases. This is because the veto make them beneficial from both particulate matter is not included hicles, most of which were retrofitperspectives,” he adds. in the voluntary international ted with CNG engines and fueling agreements designed to mitigate systems, were less efficient, thus —RHITU CHATTERJEE climate change. Aerosols are shortemitting more methane and CO2 ES801744P lived compared with greenhouse than they did before. RHITU CHATTERJEE
New Delhi: integrating air and climate policies
10.1021/es801744p
2008 American Chemical Society
Published on Web 07/02/2008
August 15, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5835
