Source identification of volatile organic compounds precursors from glyoxal and secondary formaldehyde utilizing MAX-DOAS observations in guangzhou, China

Glyoxal (CHOCHO) and formaldehyde (HCHO) are vital oxidization intermediates of volatile organic compounds (VOCs) and play a significant role in studying VOC precursor sources. This research utilizes multi-axis differential optical absorption spectroscopy (MAX-DOAS) to measure vertical column densities (VCDs) of CHOCHO, HCHO, and NO₂ in Guangzhou, China, from June 2019 to June 2020. A sensitivity analysis for DOAS fitting was performed to accurately retrieve CHOCHO due to its low atmospheric concentration. Increased CHOCHO and HCHO levels from June to October 2019 were attributed to heightened photochemical oxidation, while higher CHOCHO levels in November and December 2019 were linked to increased anthropogenic emissions. CHOCHO and HCHO VCDs were lowest in the mornings, increasing with light intensity, whereas NO₂ peaked in the mornings and evenings. Additionally, we utilized the CO-O_x trace pair to distinguish between primary and secondary HCHO sources, finding that 79.32 % of HCHO originated from secondary formation via photochemical processes. We employed four indicators (R_GF, R_GF-1, R_GF-2, and R_GF-3) to identify the sources of VOC precursors. R_GF-1, R_GF-2 and R_GF-3, corresponding to different model scenarios with increased HCHO_pri contributions, were greater than the traditional R_GF, emphasizing the influence of AVOC while minimizing BVOC effects. These findings emphasize the importance of considering primary HCHO contributions for accurate VOC source identification and effective air pollution control strategies. Additionally, R_GF values derived from MAX-DOAS were found to be 1.29 times higher than those from TROPOMI, suggesting a greater tendency of TROPOMI R_GF to identify BVOC sources.