Kilometer-level glyoxal retrieval via satellite for anthropogenic volatile organic compound emission source and secondary organic aerosol formation identification

Abstract

Volatile organic compounds (VOCs) are key precursors of PM2.5 and ozone. Glyoxal can be utilized as an indicator of VOC emission sources and secondary organic aerosol (SOA) formation. In this study, the high-resolution satellite observations of glyoxal were utilized to identify anthropogenic VOC sources, which can be utilized to formulate pollution control policies. Glyoxal vertical column densities were firstly retrieved by the TROPOspheric monitoring instrument (TROPOMI) onboard the Copernicus Sentinel-5 Precursor satellite. Glyoxal retrieval is sensitive to wavelength; therefore, four different areas were studied, and the optimum wavelength range of 435–462 nm was determined and applied in the wavelength sensitivity test. Glyoxal slant column density was corrected by utilizing the daily stripe-correction in the Sahara region which reduces the error by approximately 2.2 × 1014 molec/cm2. Glyoxal vertical column densities computed using TROPOMI were validated via multi-axis differential optical absorption spectroscopy measurements obtained at three sites; the daily normalized mean bias and standard deviation for the three sites were -27.5 % ± 6.5%, 1.8% ± 7.5%, and −6.6 % ± 17.3%, respectively. Monthly averaged data shows good correlation with Pearson correlation coefficients (R) of 0.90, 0.78 and 0.92, at three MAX-DOSA sites, respectively. The global spatial distribution of glyoxal showed large areas of high-concentration glyoxal distributed over tropical rainforests near the equator, which were attributed to biomass combustion and biogenic processes. Numerous urban hotspots were identified to be mainly concentrated in developing countries, especially those in East Asia and the Middle East. The highest glyoxal vertical column densities were observed over eastern China, and the high-glyoxal concentration areas were mainly located over urban and industrial areas, indicating a significant anthropogenic glyoxal source. Kilometer-level TROPOMI can identify factory emission sources that are undetectable by Ozone Monitoring Instrument due to the higher resolution of TROPOMI.