Application of VUV-PIMS coupled with GC-MS in chemical characterization, identification and comparative analysis of organic components in both vehicular-derived SOA and haze particles

Abstract

Gasoline vehicle exhaust is a significant source of volatile organic compounds (VOCs) in megacities. In this study, chemical characterization of secondary aerosol particles from the oxidation of gasoline vehicular exhaust by O3, OH, and NO3 radicals and the airborne aerosol particles collected during a heavy haze episode (23–25 December 2015) in Beijing were elaborately investigated. The secondary organic aerosols (SOAs) collected from the exhaust and airborne aerosol particles were characterized with a newly built vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) after thermal desorption, and identified by gas chromatography mass spectrometry (GC-MS). The obtained photoionization mass spectra revealed that the SOAs from the oxidation of gasoline vehicular exhaust and airborne aerosol particles possess a series of common characteristic mass peaks at m/z 98, 112, 126, and 140. The components at m/z 98, 112, 126, 140 were further identified to be carbonyl species after PFBHA derivatization followed by GC-MS analyses. The carbonyl species from exhaust SOAs were found to be responsible for 51.7%, 57.5%, 36.3%, and 27.9% of the chemical components in haze particles at m/z 98, 112, 126, and 140, respectively, which indicates that these SOA components from the oxidation of gasoline vehicular exhaust are a major factor that affects the air quality in Beijing. Among the exhaust SOAs, the carbonyl species detected simultaneously in two (P(O3/OH)) or three kinds of exhaust oxidation reactions (P(O3/NO3/OH)) make a significant contributions to these carbonyl species in haze particles (10.6% for m/z 98, 18.3% for m/z 112, 23.4% for m/z 126, and 20.5% for m/z 140). These results implies that the unsaturated VOCs (i.e. alkenes) from exhaust may be one kind of important SOA precursor and that their chemical degradation in the atmosphere may have an important impact on urban air quality in heavy polluted cities such as Beijing, especially during severe winter haze weather.