Volume 9, No. 4, December 2009, Pages 441-452 PDF(467 KB)
Using a Photochemical Index to Discuss the Ozone Formation and Estimate Hydroxyl Concentration at Downwind Area
Kuo-Hsin Tseng1, Jia-Lin Wang2, Pei-Hsuan Kuo1, Ben-Jei Tsuang1
1 Department of Environmental Engineering, National Chung-Hsing University, Taichung, 402, Taiwan
2 Department of Chemistry, National Central University, Taoyuan, 320, Taiwan
Ozone problem is deteriorating in the mountainous areas in central Taiwan. High level of reactive ozone precursor coming from traffic, industrial activities and vegetation upwind produces ozone episodes in the downwind area. Continuously monitoring of ozone and its precursors with hourly resolution was performed by three photochemical assessment monitoring stations (PAMS) forming a line of upwind, midway and downwind observation. A ratio (ethylbenzene/m, p-xylene) which showed high agreement with ozone concentrations were used as a sensitive photochemical index to represent the degree of photochemical reaction. It was found that both the peaks of the photochemical index and the ozone concentration around noon exhibited a consistent descending order of Jhushan (downwind) > Caotun (midway) > Chonglun (upwind). Furthermore, when coupling photochemical index of the three PAMS with kinetic equations and the trajectory model, OH concentrations were estimated. The results showed that the OH concentration reached the maximum (2.1 × 106 - 2.3 × 106 molecule/cm3) at noon to early afternoon on a daily cycle.
Volatile organic compounds; Photochemical index; Backward trajectory; OH concentration.