Secondary organic aerosol formation from the irradiation of simulated automobile exhaust

Abstract

A laboratory study was conducted to evaluate the potential for secondary organic aerosol formation from emissions from automotive exhaust. The goal was to determine to what extent photochemical oxidation products of these hydrocarbons contribute to secondary organic aerosol (SOA) and how well their formation is described by recently developed models for SOA formation. The quality of a surrogate was tested by comparing its reactivity with that from irradiations of authentic automobile exhaust. Experiments for secondary particle formation using the surrogate were conducted in a fixed volume reactor operated in a dynamic mode. The mass concentration of the aerosol was determined from measurements of organic carbon collected on quartz filters and was corrected for the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. A functional group analysis of the aerosol made by Fourier transform infrared (FTIR) spectroscopy indicated that carbonyl groups dominated the aerosol with relatively little aliphatic or aromatic C-H functionality. This result is consistent with the presence of polycarbonyl compounds measured in the aerosol. The hygroscopic potential of the aerosol was determined with the use of a liquid water content analyzer, and the analysis indicated that the aerosol uptake of water was minor at relative humidities less than 70%. The yield for the formation of SOA was found to be 1.8% when measured for an aerosol mass of 7.38 μg/m3. These results were compared to an aerosol model developed by Odum and coworkers and suggested that 75-85% of the fine particulate matter was due to reaction products of aromatic precursors. Organic analysis of the collected aerosol from this complex system indicates that the identified oxidation products were identical to those found in the toluene oxidation system.