1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA
2Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA
3Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
4Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
5Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA
*now at: Department of Chemistry, University of Montreal, Montreal, Quebec, Canada
Abstract. The underprediction of ambient secondary organic aerosol (SOA) levels by atmospheric models in urban areas is well established, yet the cause of this underprediction remains elusive. Likewise, the relative contribution of emissions from gasoline- and diesel-fueled vehicles to the formation of SOA is generally unresolved. Here we address these two issues using data from the 2010 CalNex experiment carried out in the Los Angeles basin (Ryerson et al., 2013). We use gas-phase organic mass (GPOM) and CO emission factors in conjunction with measured enhancements in oxygenated organic aerosol (OOA) relative to CO to investigate the relative importance of gasoline vs. diesel emissions to organic aerosol formation. Two possible conclusions emerge from the analysis to yield consistency with the ambient data: (1) vehicular emissions are not a dominant source of anthropogenic fossil SOA in the Los Angeles basin, or (2) ambient SOA mass yields are substantially higher than those derived from laboratory chamber studies.