Problems with and Improvement of HCHO/NO2 for Diagnosing Ozone Sensitivity—A Case in Beijing

Rfn (formaldehyde/nitrogen dioxide) is a common indicator based on satellite observations used to classify ozone formation sensitivity. However, it may underestimate anthropogenic volatile organic compounds (VOCs) in heavily polluted cities when only formaldehyde (HCHO) measure VOCs, since mainly derived from natural sources worldwide. In this study, we multiaxis differential optical absorption spectroscopy acquire tropospheric of nitrogen dioxide (NO2), HCHO and glyoxal (CHOCHO) Beijing 1 April 2019 31 March 2020. Combined with VOCs detected simultaneously by gas chromatography—mass spectrometry proton transfer reaction–time-of-flight/mass near the ground, evaluated representativeness column densities total (TVOC) equivalent propylene concentrations, which called reactivity. The results showed that there were significant seasonal differences response TVOC reactivity, fitting slopes 2.3 (spring), 2.6 (summer), 2.9 (autumn) 1.0 (winter) four seasons, respectively. Since CHOCHO can be partly characterize contribution VOC emissions demonstrated better reactivity winter, 0.2 0.5 respectively, introduced construct new (HCHO + 6 × CHOCHO). seasons more similar, being 3.2 3.6 4.0 (winter). ratio NO2, Rmn ((HCHO CHOCHO)/NO2), was reclassify sensitivity urban areas North China, revealing transition regime before 1300 LST (LST = UST 8) an NOx-limited afterwards. improved VOC-limited regime, enhancing NOx providing robust support for pollution prevention control.