Measurement Report: important contributions of oxygenated compounds to emissions and chemistry of VOCs in urban air

Abstract. Volatile organic compounds (VOCs) play important roles in the tropospheric atmosphere. In this study, VOCs were measured at an urban site in Guangzhou, one of the mega-cities in Pearl River Delta (PRD) using a gas chromatograph mass spectrometer/flame ionization detection (GC-MS/FID) and a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS). Diurnal profile analyses show that stronger chemical removal by OH radicals for more reactive hydrocarbons during the daytime. Diurnal profiles of OVOCs indicate evidence of contributions from secondary formation. Detailed source analyses of OVOCs using a photochemical age-based parameterization method suggest important contributions from both primary emissions and secondary formation for measured OVOCs. During the campaign, around 1700 ions were detected in PTR-ToF-MS mass spectra, among of which 462 ions with noticeable concentrations. VOCs signals from these ions without calibration in PTR-TOF-MS are quantified based on sensitivities of available VOCs species. OVOC-related ions dominated PTR-ToF-MS mass spectra with an average contribution of 77.2 %. Combining measurements from PTR-ToF-MS and GC-MS/FID, OVOCs contribute 57.4 % to the total concentration of VOCs. Using concurrent measurement of OH reactivity, OVOCs measured by PTR-ToF-MS contribute greatly to the OH reactivity (19.3 %). In comparison, hydrocarbons account for 20.0 % of OH reactivity. Adding up the contributions from inorganic gases (47.9 %), ∼ 12 % of the OH reactivity remains as missing. Our results demonstrate the important roles of OVOCs in the emission and evolution budget of VOCs in urban atmosphere.