Severe photochemical pollution was found in large petrochemical complexes: A typical case study in North China

Large petrochemical complex (PC) widely exists in both developing and developed countries, and is expected to have a special photochemical pollution in local scale due to huge VOCs emissions. Here, a typical large-scale PC in North China was selected as the study case, to explore the character, formation and influence of local photochemical pollution regarding PCs based on an improved 0-D chemical model. In the study PC, VOCs-rich character was apparent with THCs level of 90.8 ± 28.0 ppb and THCs/NOx ratio of ∼26.2 mol/mol. Severe O₃ pollution was found in warm months with monthly mean MDA1O3 of 67.3-96.0 ppb. Model simulations showed the heavy O₃ pollution in this PC was attributed to high precursors rather than to unfavorable meteorology, and was more sensitive to NOx (with response of 1.42 g/g) than to THCs (with response of 0.12 g/g). The photochemical pollution formation potential of the emission plumes of this PC was very enormous, with production rate of 19.6 ppb h^-1 for O₃, 2.9 ppb h^-1 for HCHO and 1.1 ppb h^-1 for CH₃CHO on daytime average, 1-5 greater than in normal urban areas. The higher production rates happened in morning hours, which explained the earlier peak time of observed O₃ in PCs. And about 70% of photochemical pollution (represented by O₃) would be transported to surroundings, leading to the significant photochemical-pollution hazard to the vicinity of PCs.