Evaluation and measurement of tropospheric glyoxal retrieved from MAX-DOAS in Shenzhen, China

Abstract

Glyoxal is one of the representative oxygenated volatile organic compounds in the atmosphere. Its accurate measurement has high significance for the determination of VOC emission sources and the calculation of the global budget of secondary organic aerosol. We investigated the spatio-temporal variation characteristics of glyoxal through observations over a 23-day period. Sensitivity analysis of simulated and actual observed spectra revealed that the accuracy of glyoxal fitting is primarily controlled by the wavelength range selected. Within the range of 420–459 nm, the value calculated using the simulated spectra was 12.3 × 1014 molecules/cm2 lower than the actual value, and the results obtained using the actual spectra included a large number of negative values. Overall, the wavelength range has a far stronger influence than other parameters. The wavelength range of 420–459 nm (excluding 442–450 nm) is the most suitable because it ensures minimal influence from interference components in the same wavelength. Within this range, the calculated value of the simulated spectra is the closest to the actual value, with a deviation of only 0.89 × 1014 molecules/cm2. Therefore, the 420–459 nm range (excluding 442–450 nm) was selected for further observation experiments. The fourth polynomial order was used in DOAS fitting, and constant terms were used to correct the actual spectral offset. In the experiments, the glyoxal slant column density primarily ranged from −4 × 1015 molecules/cm2 to 8 × 1015 molecules/cm2, and the near-ground glyoxal concentration ranged from 0.02 to 0.71 ppb. Regarding the average daily variation cycle, high values of glyoxal were concentrated around noon, which was similar with UVB. This indicates that the formation of CHOCHO was related to the emission of biological VOCs. Glyoxal was concentrated below 500 m and the pollution height began to rise around 09:00 and reached the maximum value around 12:00, after which they declined.