Characteristics of volatile organic compounds under different operating conditions in a petrochemical industrial zone and their effects on ozone formation

The petrochemical industry is one of the major sources of volatile organic compounds (VOCs) emissions. Current research on VOC pollution characteristics in petrochemical industrial areas predominantly focuses on normal operating conditions, overlooking VOC pollution during overhaul. This study comparatively analyzes the pollution characteristics of VOCs, the potential sensitivity of O₃ formation, and the pollution sources during normal production (PI), partial instrument overhaul (PII), and large-scale instrument overhaul (PIII) at a typical petrochemical industrial enterprise A (PEA) in Northwest China. The results revealed that with the overhaul of the petrochemical industrial enterprise, the average concentration of VOCs decreased from 70.43 ppbv during the PI period to 27.94 ppbv during the PIII period, in which the concentration of alkanes decreased by 67.99% but the concentration of aromatic hydrocarbons increased by 7.0%. The ozone formation potentials (OFPs) of the three periods were 249.28, 212.57 and 114.23 ppbv, respectively. During PI, alkanes contributed the largest share (44.23%) to the OFP, and the OFP of OVOCs was the largest during PII and PIII, with shares of 34.77% and 42.07%, respectively. During PI, O₃ formation was limited by anthropogenic volatile organic compounds (AVOCs). During PIII, O₃ formation tended to be synergistically limited by VOCs and NO_x. In PI, fuel evaporation (29.34%) and combustion sources (26.94%) made substantial contributions to VOC concentrations. However, owing to overhaul, the contribution from combustion sources decreased from 26.94% in PI to 8.54% in PII, whereas the contribution from solvent usage increased from 6.66% in PI to 11.86% in PII. In PIII, fuel evaporation (24.18%) and solvent usage sources (24.25%) significantly influenced VOC concentrations. This study can provide a reference for the control of VOCs pollution in the petrochemical industry during different production periods and is crucial for O₃ control strategy development.