Estimating Secondary Organic Aerosol Production from Toluene Photochemistry in a Megacity of China

Abstract

The production of secondary organic aerosols (SOA) from toluene photochemistry in Shanghai, a megacity of China, was estimated by two approaches, the parametrization method and the tracer-based method. The temporal profiles of toluene, together with other fifty-six volatile organic compounds (VOCs), were characterized. Combing with the vapor wall loss corrected SOA yields derived from chamber experiments, the estimated toluene SOA by the parametrization method as embodied in the two-product model contributes up to ∼40% of the total SOA budget during summertime. 2,3-Dihydroxy-4-oxopentanoic acid (DHOPA), a unique product from the OH-initiated oxidation of toluene in the presence of elevated NO x , was used as a tracer to back calculate the toluene SOA concentrations. By taking account for the effect of gas-particle partitioning processes on the fraction of DHOPA in the particle phase, the estimated toluene SOA concentrations agree within ∼33% with the estimates by the parametrization method. The agreement between these two independent approaches highlight the need to update current model frameworks with recent laboratory advances for a more accurate representation of SOA formation in regions with substantial anthropogenic emissions.

Estimation of Secondary Organic Aerosol Formation During a Photochemical Smog Episode in Shanghai, China

“…Correlations of benzene to toluene, benzene to ethylbenzene, and benzene to toluene with ozone were relatively bad, suggesting the sources of each couple of VOC species were not very similar in Shanghai. The photochemical age (∆ t ) of the air mass was estimated from the measured concentration ratios of ethylbenzene ( E ) to m,p‐xylene ( X ) in this study, and the diurnal pattern of E / X reflected the evolution of photochemistry in the present study as shown in Figure 2a, which has been proved to be suitable in Shanghai in our previous studies (Gao et al, 2019; Wang et al, 2013 ) according to equation below. …”

“…These two values are comparable. SOCvoc (3.9 ± 1.0 μg/m 3 ) determined from the yield method in section 3.2 could explain 67.2% of total SOC, which was much higher than that (29%) of clean period in Shanghai in summer (Gao et al, 2019). It suggested that the photochemical oxidation of VOCs, especially aromatics, by OH radicals played important roles in SOC formation during the photochemical pollution episode in summer in Shanghai.…”

“…One important reason was due to the high SOA yield of toluene in the calculation. We corrected the yield of toluene SOA by a factor of 10 owing to vapor wall losses, but applied a wall‐loss correction factor in the range of 1.16–1.25 for all the other alkanes and aromatic compounds (Gao et al, 2019; Zhang et al, 2014). There has been some evidence showing that toluene photochemistry that leads to SOA formation is unique.…”

Observation Constrained Aromatic Emissions in Shanghai, China

“…Aromatics have been reported as the most important anthropogenic VOC precursors of ozone and SOA in most of eastern China (Gao et al, 2019; Wang, Chen, et al, 2013). With stronger solar radiation in summer, aromatic photochemistry was more active to enhance the formation of ozone and SOA than expected due to more emissions in summer.…”

Supplementary material to "Measurement report: Characteristics and sources of non-methane VOCs and their roles in SOA formation during autumn in a central Chinese city"

“…10 in the current condition, and the Rwall of dodecane, benzene and xylene are 1.16, 1.25, and 1.2, respectively. The other species in a and b are corrected With a Rwall of 1.16, as a recent study performed (Gao et al, 2019).…”