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Study: Gasoline emissions dominate over diesel in secondary organic aerosol formation

13 March 2012

Emissions from gasoline vehicles contribute more to the formation of secondary organic aerosols (SOA) than those from diesel vehicles, according to a new study by scientists from the University of Colorado Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES), NOAA’s Earth System Research Laboratory and other colleagues.

“The surprising result we found was that it wasn’t diesel engines that were contributing the most to the organic aerosols in L.A.,” said CIRES research scientist Roya Bahreini who led the study. “This was contrary to what the scientific community expected.”

SOAs are particles formed in air that make up typically 40-60% of the aerosol mass in urban environments. They are suspected to cause human health effects, such as heart or respiratory problems. They can also impact the climate and can reduce visibility. SOAs could be formed from gases released by gasoline engines, diesel engines and natural sources—biogenic agents from plants and trees—but the relative significance of these sources has been poorly known.

In the study, researchers conducted airborne and ground-based measurements of organic aerosol in the Los Angeles Basin, California during May and June 2010 to assess the amount of SOA formed from diesel emissions. The scientists made three weekday and three weekend flights with the NOAA P3 research aircraft, instrumented to measure different aspects of air pollution. Diesel emissions in the LA Basin have been known to vary between weekdays and weekends, with diesel emissions 54% lower on weekends.

The measurements confirmed that diesel trucks were used less during weekends, while the use of gasoline vehicles remained nearly constant throughout the week. Despite this difference in source contributions, formation of SOAs was found to be the same on weekends and weekdays. This result indicates that the contribution from diesel emissions to SOA formation is zero, within the measurement uncertainties. Therefore, substantial reductions of SOA mass can be achieved by reducing gasoline vehicle emissions, concluded the study.

The study, to be published in Geophysical Research Letters, was funded by NOAA’s Climate Change and Air Quality Programs, the California Air Resources Board and the National Science Foundation.

Source: University of Colorado Boulder