Characteristics and formation mechanisms of atmospheric carbonyls in an oilfield region of northern China

Abstract

Oil and natural gas (O&NG) associated oxygenated volatile organic compounds (OVOCs) have been reported to play a significant role in ozone formation. However, little is known about the characteristics of O&NG-related OVOCs and their environmental impacts in China. In this work, C1–C8 carbonyls, an important member of the OVOCs family, were measured at a rural site and an oilfield in the Yellow River Delta region (YelRD) in winter and summer 2017. The well-defined seasonal (higher in summer) and diurnal variation (peak in the afternoon) patterns of carbonyls indicated a significant influence of secondary formation. Spatially, the measured carbonyls showed higher concentrations in the oilfield than in the rural air due to the strong oilfield emissions of hydrocarbon precursors. The chemical budget and formation mechanisms of formaldehyde and acetaldehyde were explored with the application of an observation-based model coupled with Master Chemical Mechanism. Alkenes (including both anthropogenic and biogenic species) played dominant roles in the secondary formation of formaldehyde both in the oilfield and in the rural area. Seasonally, anthropogenic alkenes showed the highest positive relative incremental reactivity (RIR) for formaldehyde within most winter-cases, while biogenic alkenes showed the highest positive RIR in summer. Spatially, anthropogenic hydrocarbon precursors showed larger RIR values in the oilfield than in the rural area. This study presents for the first-time detailed characteristics of carbonyls in a typical oilfield region of China and quantitatively reveals the impacts of oilfield emissions on the photochemical formation of major carbonyl compounds.