Improving Air Quality to Slow Global Warming

The mechanic who smogs your car has already made major gains in mitigating global warming maybe without even knowing it, according to a new study by researchers at Scripps Institution of Oceanography, UC San Diego.

A team led by climate and atmospheric scientist Veerabhadran Ramanathan found that California achieved dramatic reductions of soot and other forms of black carbon, heat-absorbing particles that have been shown to be a significant cause of atmospheric warming.

The researchers released the results of their analysis of 20 years of California air pollution data in the Dec. 14 issue of the journal Atmospheric Environment. They found that near-surface black carbon concentrations in the state have decreased by about 50 percent from 1990 to 2008, though levels of other atmospheric smog particles such as sulfates and nitrates changed very little.

The scientists concluded that state air quality laws restricting particle emissions from diesel vehicles are a primary factor for this decrease. Using other surface and satellite data, they inferred that the decrease reduced the human-induced warming effect, though the initial purpose of the laws was to cut risks of respiratory diseases and other negative public health effects of smog.

“The fundamental inference from the California data is that reducing

emissions of short-lived climate-warming pollutants is an effective way to reduce the effects of global warming in addition to reducing the damaging health effects of air pollutants,” said Ramanathan.

Carbon dioxide remains the most significant human-created greenhouse gas, but Ramanathan has recently researched the efficacy of efforts to control emissions of other atmospheric warming agents such as black carbon and methane. Because particulate pollution remains in the atmosphere only for weeks to months as opposed to carbon dioxide, which remains for more than a century, controlling it offers a near-term means of providing quick global warming mitigation, he argues.The biggest gains in black carbon reduction came through state air pollution laws governing the emissions of diesel-burning trucks, tractors, and other large vehicles. These laws led to the introduction of diesel particulate filters in non-road vehicles such as farm equipment in 1980 and in 1987, state laws placed a cap on particulate emissions from heavy trucks. Meeting emissions requirements has required new cars and trucks to be equipped with filters and older vehicles to be retrofitted with them.

The scientists took advantage of 20 years worth of particulate pollution measurements made throughout California. Information from 22 sites within the Interagency Monitoring of Protected Visual Environments (IMPROVE) network allowed them to measure elemental carbon, organic carbon, sulfate, and nitrate aerosols smaller than 2.5 microns.

“California should be congratulated for its forward-looking air pollution laws and for maintaining an excellent network of black carbon data,” Ramanathan said.

Robert Monroe