Enhanced SOA formation from mixtures of biogenic and anthropogenic emissions during the CARES campaign

Description

An Aerodyne High Resolution Aerosol Mass Spectrometer (AMS) and an Ionicon Proton Transfer Reaction Mass Spectrometer (PTRMS) were deployed on the G-1 research aircraft during the CARES campaign in Sacramento, California, to investigate aerosol gas- and particle-phase chemical composition. Over the course of the campaign, PTR-MS data showed that biogenic volatile organic compounds (VOCs), particularly isoprene, dominate the region with anthropogenic VOCs, such as benzene and toluene, observed in smaller concentrations. Overall, the AMS showed that the particle phase is dominated by organic material (81% on average) with smaller concentrations of sulfate (10%), nitrate (6%), and ammonium (4%) nitrate observed. Comparison of organic aerosol (OA) concentrations on flight days with different prevailing meteorological conditions will be presented to elucidate the role of anthropogenic and biogenic emissions on OA formation. The data show that airmasses predominantly influenced by only anthropogenic or biogenic emissions contained relatively small concentrations of OA, even when other photochemical conditions were favorable. However, OA levels are dramatically enhanced when isoprene-rich air from the foothills is mixed with the Sacramento urban plume, suggesting both anthropogenic and biogenic emissions are key in producing elevated OA concentrations.