The chemical characteristics and sources of formaldehyde on O3 and non-O3 polluted days in Wuhan, central China

In August 2023, a detailed investigation of formaldehyde (HCHO) chemical characteristics on ozone (O₃) polluted days and non-O₃ polluted days in Wuhan was undertaken. The mean value of HCHO on O₃ polluted days (3.02 ± 1.15 ppbv) was 122% higher than that on non-O₃ polluted days (1.35 ± 0.41 ppbv). Utilizing Positive Matrix Factorization (PMF) model revealed secondary formation as the dominant HCHO source (58.3% on non-O₃ polluted days and 66.2% on O₃ polluted days). On O₃ polluted days, the contribution of liquefied petroleum gas (LPG)/solvent usage and industrial emissions to HCHO were 13.7% and 8.2%, respectively, whereas on non-O₃ polluted days, LPG/solvent use and diesel exhaust contributed 15.4% and 14.7%, respectively. The top ten species, with the highest Relative Incremental Reactivity (RIR) to HCHO, were mainly alkenes and aromatics, which remained consistent on both O₃ and non-O₃ polluted days. It is noteworthy that the RIR of isobutane to HCHO is significant in this study. Further reapportionment of secondary HCHO by a photochemical box model indicated that LPG/solvent usage (33.2%) contributed the most to HCHO on O₃ polluted days, while diesel exhaust (31.9%) dominated on non-O₃ polluted days. This research enhances understanding of HCHO in Wuhan, providing a theoretical basis for targeted pollution reduction and supporting efforts to improve air quality and public health.