Revealing the Influencing Factors of an Oxygenated Volatile Organic Compounds (OVOCs) Source Apportionment Model: A Case Study of a Dense Urban Agglomeration in the Winter

Understanding sources of oxygenated volatile organic compounds (OVOCs) in the atmosphere still has large uncertainties. In this study, an improved OVOC source apportionment model was developed by principal component analysis and multiple linear regression based on the online monitoring of nonmethane hydrocarbons (NMHCs) and OVOCs in a dense urban agglomeration in the winter. The modeled concentrations were in good agreement with the measured concentrations (R2 = 0.56-0.97). The concentrations of major OVOCs, except for 2-methylacrolein, were greatly affected by anthropogenic sources (15.8%-76.8%) and secondary generation (0.0%-51.7%), while transport and natural sources contributed to 0.0%-26.8% and 0.0%-32.0%, respectively. The selection of isoprene as the natural tracer led to an underestimation of the OVOC species from primary emission and an overestimation from natural sources. In addition, photochemical reactions significantly reduced the simulation accuracy of the model for NMHCs in the afternoon, with the R2 of 0.60 +/- 0.23, which was lower than the overall value of 0.82 +/- 0.11. However, the R2 for OVOCs (0.83 +/- 0.14) did not decrease significantly in the afternoon due to the compensation of secondary oxidation. Furthermore, the concentration gradient distribution of the species gradually changes from a normal distribution to an exponential normal distribution with a decrease in concentration, the accuracy of the model was influenced by the degree of matching between tracer and species concentration gradient as species concentration change. Developing models with additional tracers at different concentration levels may enhance the robustness of the OVOC source apportionment model without increasing its complexity. The precision of oxygenated volatile organic compound (OVOC) source apportionment models is subject to external factors that affect the accuracy of the analysis. Thus, understanding their sources in the atmosphere still has large uncertainties. In this study by measuring the full spectrum of VOCs, we developed a source apportionment model. The model had good agreement with the measured concentrations (R2 = 0.56-0.97) and quantified main sources of OVOCs, except for 2-methylacrolein, as follows: (a) anthropogenic sources (15.8%-76.8%), (b) secondary generation (0.0%-51.7%), (c) regional transport (0.0%-26.8%), and (d) natural sources (0.0%-32.0%). However, due to the selection of isoprene as the natural source tracer, the concentrations of OVOCs were higher in the natural source category and lower in the anthropogenic source category. In addition, the photochemical reaction can reduce the simulation accuracy of NMHCs with the R2 of 0.60 +/- 0.23, but has little effect on the simulation accuracy of OVOCs (R2 = 0.83 +/- 0.14). A downside of the model is that the predicted concentrations are higher at low concentration gradients and lower at high concentration gradients. Thus, we recommend implementing a model with more tracers at different concentration levels in order to improve the source apportionment results. image