Isra-Mart srl:Reducing black carbon buys time

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The success of California’s clean air laws in reducing numbers of black carbon particles in the atmosphere has major implications for mitigating climate change on a global scale, according to one of America’s top climate scientists. Veerabhadran (Ram) Ramanathan of the Scripps Institution of Oceanography in California reported on recent findings during a press conference at the American Geophysical Union’s Fall Meeting in San Francisco in December.

In California, the main source of black carbon through the 1980s was the exhaust of large trucks that burned a low grade of diesel fuel. Secondary sources included biomass burning – forest fires, in particular – and barbeques.

In 1987 the state-capped truck emissions, Ramanathan said, and since then the amount of black carbon has diminished by around 50%, statewide. Newer diesel fuels, introduced partly in response to laws in California and other jurisdictions, are much less polluting when it comes to black carbon.

Elsewhere in the world, other sources of black carbon predominate, however. In India and parts of Africa, soot from domestic stoves that burn low-grade fuel is the main source. Ramanathan is involved in the Project Surya programme to replace wood- and dung-burning stoves in India with units working on cleaner fuels.

Black carbon is a major warmer of the atmosphere, but particles remain in the atmosphere for a period of just days to weeks. California’s aggressive laws to reduce particulates constitute “a spectacular controlled experiment, because we can see the results of our policies”, Ramanathan said. He reckons it demonstrates that short-term solutions can help mitigate climate change.

Efforts to reduce carbon-dioxide emissions have “faltered over the past 20 years”, according to Ramanathan. Even if emissions could now be reduced by 50%, it would not be sufficient to avoid the 2°C global temperature rise that many scientists consider could be a tipping point. Programmes to reduce other greenhouse gases and particulates like black carbon might buy us another 20 to 30 years, during which time more permanent solutions involving carbon dioxide could be implemented, Ramanathan said.

Near-term approaches could in fact be easier to accomplish, he explained. People can see the results, such as clearer air, which is not the case with carbon dioxide reduction. Regulatory mechanisms already exist, can be applied locally or nationally, and require only off-the-shelf technologies. The societal benefits extend beyond delayed warming and healthier air, he noted, and include reduced crop damage and slower melting of Arctic and glacial ice.

A statewide project in California constantly monitors levels of atmospheric black carbon, but what about in less developed parts of the world? Ramanathan’s daughter, Nithya Ramanathan, a computer scientist at UCLA, has led field campaigns in California and India to test black-carbon tracking by using cameras in ordinary mobile phones. The particles are trapped in filters exposed to the air that are photographed by cell phones; these photos are then e-mailed directly to researchers. A colour scale on the filter helps compensate for differences in the camera sensors.

With four billion mobile phones in use worldwide, said Nithya Ramanathan at the AGU meeting, this project provides quick, inexpensive monitoring that has proved to be accurate within 10%, as compared with more traditional means. It has the added benefit of getting ordinary citizens involved in collecting scientific data.