Emissions and chemistry of volatile organic compounds (VOCs) in urban air: important contributions from oxygenated compounds

Abstract

<p>Volatile organic compounds (VOCs) play central roles in formation of ozone and secondary particles. However, emissions and evolution of VOCs remain uncertain in different environments, including urban regions. A field campaign was conducted at an urban site of Guangzhou in September-November of 2018 to study ozone and particle pollution in this region. VOCs species were measured by both a gas chromatography mass spectrometer (GC-MS/FID) and a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). Another PTR-MS associated with comparative reactivity method (CRM) was used for quantifing OH reactivity in the atmosphere. In total, around 1700 ions were detected in mass spectra of PTR-TOF during this campaign, among of which 438 ions are with noticeable concentrations in the atmosphere. For all of the measured VOCs species, the total average concentrations of oxygenated VOCs was 28.2 ppb, which are significantly higher than other VOCs classes, namely alkanes (19.6 ppb), aromatics (4.4 ppb) and alkenes (2.9 ppb). These oxygenated VOCs contribute large fractions (campaign-average: 28%) of the total measured OH reactivity, which leaves only a small fraction of measured reactivity as “missing”. We will show that primary emission and secondary formation both contribute to the measured OVOCs. These results indicate important roles of OVOCs in emissions and evolution budget of VOCs in the atmosphere.</p>