Direct observations indicate photodegradable oxygenated volatile organic compounds (OVOCs) as larger contributors to radicals and ozone production in the atmosphere

Abstract

Volatile organic compounds (VOCs) regulate atmospheric oxidation capacity, and the reactions of VOCs are key in understanding ozone formation and its mitigation strategies. When evaluating their impact, most previous studies did not fully consider the role of oxygenated VOCs due to limitations of measurement technology. By using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) combined with a gas chromatograph–mass spectrometer (GC–MS), a large number of oxygenated VOCs (OVOCs) have been quantified in Guangzhou city, China. Based on the new dataset, we demonstrate that constraints using OVOC observations are essential in modeling radical and ozone production, as modeled OVOCs can be substantially lower than measurements, potentially due to primary emissions and/or missing secondary sources. Non-formaldehyde (HCHO) OVOCs can contribute large fractions (22 %–44 %) of total ROx radical production, which are comparable to or larger than the contributions from nitrous acid and formaldehyde. Our results show that models without OVOC constraints using ambient measurements will underestimate the production rates of ROx and ozone, and they may also affect the determination of sensitivity regime in ozone formation. Therefore, a thorough quantification of photodegradable OVOC species is in urgent need to understand accurately the ozone chemistry and to develop effective control strategies.