Quantification of the impact of the offshore petrochemical industrial park on ambient ozone using photochemical grid modeling and assessment monitoring

This study integrated the results of photochemical grid modeling and assessment monitoring to quantify the impact of the offshore petrochemical industrial park (OPIP), with area of 26.03 km2, on ambient ozone in a coastal region of Taiwan. A highly repetitive ozone-spreading phenomenon in the adjacent OPIP area was observed, which shows that ozone spreading follows a clear cycle between offshore and inland areas during the prevailing periods of ozone events (≥ 120 ppb). The incremental ratio of ambient ozone for the OPIP on ozone event days during the southwest and northeast monsoons in 2011–2016 ranged from 1.05 to 1.25 (average = 1.15) and 1.04–1.27 (average = 1.17), respectively. Data from ten photochemical assessment monitoring stations surrounding the OPIP in 2016 showed that the ratio of monthly average concentrations of volatile organic compounds (VOCs) during the northeast monsoon to the southwest monsoon was approximately 1.5. The ratio of the monthly latent incremental amount of ozone to the total volatile organic amount in the same month during the northeast and southwest monsoons was in the ranges of approximately 0.84–0.97 and 1.01–1.12, respectively. Moreover, the latent incremental amount of ozone during the daytime was greater than that at night. The results indicate that the observed ozone concentration increases as the latent incremental amount of ozone or ambient VOCs decreases.