Aerosol and trace gas vehicle emission factors measured in a tunnel using an Aerosol Mass Spectrometer and other on-line instrumentation

In this study we present measurements of gas and aerosol phase composition for a mixed vehicle fleet in the Gubrist tunnel (Switzerland) in June 2008. PM1 composition measurements were made with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS) and a Multi Angle Absorption Photometer (MAAP). Gas-phase measurements of CO, CO2, NOx and total hydrocarbons (THC) were performed with standard instrumentation. Weekdays had a characteristic diurnal pattern with 2 peaks in concentrations for all traffic related species corresponding to high vehicle density (similar to 300 +/- 30 vehicles per 5 min) in the morning rush hour between 06:00 and 09:00 and in the afternoon rush hours from approximately 15:30 to 18:30. The emission factors (EF) of OA were heavily influenced by the OA mass loading. To exclude this partitioning effect, only organic aerosol mass concentrations from 60 mu g m(-3) to 90 mu g m(-3) were considered and for these conditions the EF(OA) value for HDV was 33.7 +/- 2.3 mg km(-1) for a temperature inside the tunnel of 20-25 degrees C. This value is not directly applicable to ambient conditions because it is derived from OA mass concentrations that are roughly a factor of 10 higher than typical ambient concentrations. An even higher EF(OA)(HDV) value of 47.4 +/- 1.6 mg km(-1) was obtained when the linear fit was applied to all data points including OA concentrations up to 120 mu g m(-3). Similar to the increasing EF, the OA/BC ratio in the tunnel was also affected by the organic loading and it increased by a factor of similar to 3 over the OA range 10-120 mu g m(-3). This means that also the OA emission factors at ambient concentrations of around 5-10 mu g m(-3) would be 2-3 times lower than the emission factor given above. For OA concentrations lower than 40 mu g m(-3) the OA/BC mass ratio was below 1, while at an OA concentration of 100-120 mu g m(-3) the OA/BC ratio was similar to 1.5. The AMS mass spectra (MS) acquired in the tunnel were highly correlated with the primary organic aerosol (POA) MS from a EURO 3 diesel vehicle with a speed similar to the average tunnel speed. (C) 2011 Elsevier Ltd. All rights reserved.