Project at a Glance

Title: Characterization of the atmospheric chemistry in the southern San Joaquin Valley

Principal Investigator / Author(s): Goldstein, Allen & Ronald Cohen

Contractor: UC Berkeley

Contract Number: 08-316

Research Program Area: Atmospheric Processes

Topic Areas: Chemistry & Reactivity


While air quality in the San Joaquin Valley Air Basin (SJVAB) was never as poor as it was in the South Coast Air Basin (SOCAB), reductions in ozone (O3) and particulate matter (PM2.5) in the SJVAB have been slow compared to those in the SoCAB. These different responses in ambient air quality to similar regulatory control strategies are likely a result of different atmospheric chemistry regimes occurring in the two air basins. To improve our understanding of the chemistry in the southern SJV, and thus assess one part of the comparative question, we organized a field site in Bakersfield, CA. Here we measured a wide suite of organic molecules (hydrocarbons, oxygenates, peroxides, organic acids, aldehydes; including primary emissions and secondary oxidation products), nitrogen oxides (NO, NO2, total and speciated peroxynitrates, total organic nitrates (RONO2), HNO3), hydrogen oxides (OH, HO2), O3, CO, CO2, H2O, and meteorological parameters during CalNex 2010. We also measured aerosol organic nitrate, ozone production rates, and total OH loss rates. Collaborators at the site measured a wide suite of additional gas and aerosol properties. The data are posted in a publically accessible website: The measurements were made from May 18–June 29, 2010 providing a statistical sampling of atmospheric variation in response to fluctuations in winds and temperature and to systematic variations in emissions with day-of-week and time-of-day. The observations form the basis for analyses aimed at understanding the photochemistry controlling ozone and PM2.5 production in the study region. Here we describe the measurements made under this contract and briefly list the additional observations at the site. We then present several analyses of these and earlier measurements. These analyses indicate that volatile organic compound (VOC) controls have been effective in all areas of the SJV at moderate temperatures and in the central and northern locations of the SJV at high temperatures but they have been minimally effective at high temperatures in the southern SJV. Controls on oxides of nitrogen (NOx) have recently become effective at reducing the frequency of high ozone days in some cases in the SJV and they are poised to be even more effective in the future. The observations also provide insight into the sources of VOCs and the extent to which those sources might be controllable. In this work, we present assessments of several prominent sources in the SJV, which include motor vehicles and petroleum operations, and include their potential to produce secondary pollutants. Observations of aerosol supported by this contract were limited. Those observations we did make show that nitrate radical (NO3) chemistry is an important source of aerosol growth at night. Further, in combination with aerosol mass spectrometry (AMS) these observations demonstrate that about 20% of the individual molecules in secondary organic aerosol (SOA) are chemicals of the form RONO2. Additional results will no doubt emerge with further analyses that are ongoing with continuing support from other funding sources.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

Stay involved, sign up with CARB's Research Email Distribution List