Black Carbon Declines With Diesel Emissions

A study of the pollutant black carbon shows that stricter pollutant emission regulations in California over the past 20 years have led to a 50% reduction in concentrations of the substance. The reduction correlates directly with a reduction in emissions from burning diesel fuel, V. Ramanathan, a climate and atmospheric science professor at Scripps Institution of Oceanography, said at the American Geophysical Union meeting in San Francisco on Dec. 14. The study is being published in the journal Atmospheric Environment and was funded by the California Air Resources Board. Black carbon, a sooty particulate material produced from burning heavy hydrocarbons and solid biofuels, has recently been recognized as a major pollutant and global-warming agent in its own right, alongside nitrogen oxides, sulfur, and CO₂. For example, scientists have found that black carbon deposited on snowpacks can cause increased warming and melting in areas such as the Sierra Mountains. Ramanathan said he was surprised and delighted that the California regulations resulted in such a strong and swift reduction in the levels of black carbon. “It’s what a [climate change] mitigation person’s dream would be,” he said at the meeting.