Secondary organic aerosol formation from the photooxidation of isoprene, 1,3-butadiene, and 2,3-dimethyl-1,3-butadiene under high NOsubx/sub conditions

摘要

Secondary organic aerosol (SOA) formation from atmospheric oxidation ofisoprene has been the subject of multiple studies in recent years; however,reactions of other conjugated dienes emitted from anthropogenic sourcesremain poorly understood. SOA formation from the photooxidation of isoprene,isoprene-1-13C, 1,3-butadiene, and 2,3-dimethyl-1,3-butadiene isinvestigated for high NO_x conditions. The SOA yield measured in the1,3-butadiene/NO_x/H₂O₂ irradiation system (0.089–0.178) wasclose to or slightly higher than that measured with isoprene under similarNO_x conditions (0.077–0.103), suggesting that the photooxidation of1,3-butadiene is a possible source of SOA in urban air. In contrast, a verysmall amount of SOA particles was produced in experiments with2,3-dimethyl-1,3-butadiene. Off-line liquid chromatography – massspectrometry analysis revealed that the signals of oligoesters comprise amajor fraction (0.10–0.33) of the signals of the SOA products observed fromall dienes investigated. The oligoesters originate from the unsaturatedaldehyde gas phase diene reaction products; namely, semi-volatile compounds producedby the oxidation of the unsaturated aldehyde undergo particle-phaseoligoester formation. Oligoesters produced by the dehydration reactionbetween nitrooxypolyol and 2-methylglyceric acid monomer or its oligomerwere also characterized in these experiments with isoprene as the startingdiene. These oligomers are possible sources of the 2-methyltetrols found inambient aerosol samples collected under high NO_x conditions.Furthermore, in low-temperature experiments also conducted in this study,the SOA yield measured with isoprene at 278 K was 2–3 times as high as thatmeasured at 300 K under similar concentration conditions. Althougholigomerization plays an important role in SOA formation from isoprenephotooxidation, the observed temperature dependence of SOA yield is largelyexplained by gas/particle partitioning of semi-volatile compounds.