Emission characteristics, source profiles and associated environmental impacts of volatile organic compounds (VOCs) from a typical oilfield centralized processing plant in Southern Xinjiang, China.

Volatile organic compounds (VOCs) emitted from oilfield processing activities have become an increasingly pressing issue for pollution mitigation in China. However, emission characteristics from oilfield processing facilities remain insufficiently understood, particularly at the process-unit level, hindering the development of precise control strategies. In this study, comprehensive field-based investigations and process-specific measurements were conducted to quantify and characterize VOCs emissions, environmental impacts and occupational carcinogenic risks in a typical oilfield centralized processing (OCP) plant in Southern Xinjiang, China. The developed emission inventory showed that storage tanks were the dominant source (79.1%), followed by component leaks (8.8%), wastewater treatment (6.4%), loading operations (5.6%), and combustion flue gas (0.1%). Localized emission factors varied among sources, with a plant-wide emission factor of 0.14 kg VOCs·t-1 produced oil processed. The overall uncertainty based on the probabilistic model was -31% to +56%. A total of 86 VOCs species were identified across three typical processes, including primary processing and gathering (PPG), produced water treatment (PWT), fracturing flowback treatment (FFT). Alkanes (66.52%-92.43%) were the dominant VOCs group, followed by aromatics (1.77%-16.51%), OVOCs (0.02%-13.46%), alkenes/alkyne (0.39%-9.26%) and haloalkanes (0.1%-2.85%), although key species varied among process units. The composite source profile weighted by VOCs emissions revealed methylcyclohexane (9.98%), n-octane (8.81%), n-heptane (7.49%) as the characteristic species of the OCP plant. Evaluations of ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAP) indicated that alkanes and aromatics were the primary contributors, respectively, with p/m-xylene, o-xylene, n-heptane, toluene and n-octane identified as shared key contributors. The PPG and PWT processes exhibited higher overall OFP and SOAP values, whereas the FFT process showed greater impact intensity per unit emission. Carcinogenic risk assessments further identified benzene, 1,2-dichloroethane, and acetaldehyde as major toxic species. The findings provide important insights for local control policies, and the process-specific framework aim to offer a methodological reference for the oilfield sector.