Secondary organic aerosol formed by Euro 5 gasoline vehicle emissions: chemical composition and gas-to-particle phase partitioning

In this study we investigated the photo-oxidation of Euro 5 gasoline vehicle emissions during cold urban, hot urban and motorway Artemis cycles. The experiments were conducted in an environmental chamber with average OH concentrations ranging between 6.6 x 10 5 -2.3 x 10 6 molec. cm - 3 , relative humidity (RH) between 40 %-55 % and temperatures between 22-26 degrees C. A proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) and the CHemical Analysis of aeRosol ON-line (CHARON) inlet coupled with a PTR-ToF-MS were used for the gas- and particle-phase measurements respectively. This is the first time that the CHARON inlet has been used for the identification of the secondary organic aerosol (SOA) produced from vehicle emissions. The secondary organic gas-phase products ranged between C 1 and C 9 with one to four atoms of oxygen and were mainly composed of small oxygenated C 1 -C 3 species. The SOA formed contained compounds from C 1 to C 14 , having one to six atoms of oxygen, and the products' distribution was centered at C 5 . Organonitrites and organonitrates contributed 6 %-7 % of the SOA concentration. Relatively high concentrations of ammonium nitrate (35-160 mu g m - 3 ) were formed. The nitrate fraction related to organic nitrate compounds was 0.12-0.20, while ammonium linked to organic ammonium compounds was estimated only during one experiment, reaching a fraction of 0.19. The SOA produced exhibited log C * values between 2 and 5. Comparing our results to theoretical estimations for saturation concentrations, we observed differences of 1-3 orders of magnitude, indicating that additional parameters such as RH, particulate water content, aerosol hygroscopicity, and possible reactions in the particulate phase may affect the gas-to-particle partitioning.