A chemical analysis of air samples taken from California's San Joaquin Valley and an Oakland traffic tunnel show that diesel fuel emissions are more polluting than previously thought, according to researchers.
The study, which appeared Monday in the journal PNAS, focuses on a specific form of pollutant known as secondary organic aerosol, or SOA. The pollutant is a major element of smog and can contribute to heart and respiratory problems.
The study authors examined air samples taken in Bakersfield and Oakland's Caldecott Tunnel during a 2010 air quality field study conducted by the National Oceanic and Atmospheric Administration and the California Air Resources Board. Researchers concluded that diesel exhaust is responsible for 65% to 90% of a region's vehicle-related SOA emissions, depending on the mix of traffic.
"We can now say that, while both motor vehicle sources are important for these 'secondary' particles, diesel is responsible for a larger proportion, especially in regions such as the San Joaquin Valley with a lot of diesel use," said senior author Allen Goldstein, an environmental scientist at UC Berkeley.