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Diesel particulate matter (DPM) is a significant source of aerosol in urbanareas and has been linked to adverse health effects. Although newer Europeandirectives have introduced increasingly stringent standards for primary PMemissions, gaseous organics emitted from diesel cars can still lead to largeamounts of secondary organic aerosol (SOA) in the atmosphere. Here wepresent results from smog chamber investigations characterizing the primaryorganic aerosol (POA) and the corresponding SOA formation at atmosphericallyrelevant concentrations for three in-use diesel vehicles with differentexhaust aftertreatment systems. One vehicle lacked exhaust aftertreatmentdevices, one vehicle was equipped with a diesel oxidation catalyst (DOC) andthe third vehicle used both a DOC and diesel particulate filter (DPF). Theexperiments presented here were obtained from the vehicles at conditionsrepresentative of idle mode, and for one car in addition at a speed of 60 km/h.An Aerodyne high-resolution time-of-flight aerosol mass spectrometer(HR-ToF-AMS) was used to measure the organic aerosol (OA) concentration andto obtain information on the chemical composition. For the conditionsexplored in this paper, primary aerosols from vehicles without a particulatefilter consisted mainly of black carbon (BC) with a low fraction of organicmatter (OM, OM/BC < 0.5), while the subsequent aging by photooxidationresulted in a consistent production of SOA only for the vehicles without aDOC and with a deactivated DOC. After 5 h of aging ~80% of thetotal organic aerosol was on average secondary and the estimated "emissionfactor" for SOA was 0.23–0.56 g/kg fuel burned. In presence of both a DOCand a DPF, only 0.01 g SOA per kg fuel burned was produced within 5 hafter lights on. The mass spectra indicate that POA was mostly anon-oxidized OA with an oxygen to carbon atomic ratio (O/C) ranging from0.10 to 0.19. Five hours of oxidation led to a more oxidized OA with an O/Crange of 0.21 to 0.37

atmospheric chemistry and physics

Impact of aftertreatment devices on primary emissions and secondary organic aerosol formation potential from in-use diesel vehicles: results from smog chamber experiments