Secondary organic aerosol formation from transportation emissions

Transportation emissions can be a significant source of secondary organic aerosol (SOA) both in urban areas and regionally. Aromatic hydrocarbons and large alkanes are expected to be the major SOA precursors. However, there are still major uncertainties in understanding SOA from vehicle exhaust in different timescales.

To address these uncertainties, this study focuses on measuring SOA formation from vehicle emissions in a real-world environment. The SOA formation from vehicle emissions in a large underground parking structure was investigated using an oxidation flow reactor (OFR). The organic vapors in the study were dominated by cold start emissions. The air in the parking structure was continuously fed to the OFR. The OH exposure was controlled by varying combinations of the OFR’s UV lamps. Α scanning mobility particle sizer (SMPS) was used to continuously measure the SOA formation inside the OFR. A high-resolution aerosol mass spectrometer and a high-resolution proton-transfer-reaction time-of-flight mass spectrometer coupled to a CHARON inlet were used to characterize the particulate phase alternating sampling between the parking garage and the OFR every 20 minutes. The PTR-MS also monitored the gas phase, while quartz filters were collected for offline analysis. Trace gases (NO, NO₂, CO, CO₂, O₃, and SO₂) and black carbon were quantified using dedicated instruments that continuously sampled air from the parking garage.

Significant SOA formation was observed increasing the organic aerosol levels several times. The SOA increased with the intensity of UV lamp exposure in the OFR. The results of the measurements can be used for the parameterization of SOA formation from the vehicle emissions at both intermediate and longer timescales.