Tsai Dai-Hua, Wang Jia-Lin, Wang Chieh-Heng, Chan Chang-Chuan
Institute of Occupational Medicine and Industrial Hygiene, College of Public Health, National Taiwan University, No. 17, Xu-Zhou Rd., Taipei 100, Taiwan.
J Environ Monit. 2008 Jan;10(1):109-18. doi: 10.1039/b714479b. Epub 2007 Nov 23.
Hourly concentrations of ozone (O(3)), 55 volatile organic compounds (VOCs, ozone precursors) and nitrogen oxides (NOx) were measured at an upwind urban site, a downwind suburban site, and a rural site in central Taiwan, from January 2003 to December 2006. VOC and NOx mean concentrations showed a gradient from high to low across the urban (56 ppb and 34 ppb), suburban (38 ppb and 27 ppb) and rural sites (25 ppb and 21 ppb) but a reverse gradient in ozone across these sites (24, 27, and 29 ppb, respectively). Although there was about twice the difference in VOC concentrations between the urban and rural sites, nearly 65% ozone formation potential was contributed to by the same 9 VOCs. Seasonal patterns showed peak ozone levels in autumn and minima in summer at the urban site, but minima in winter at the downwind suburban and rural sites. Ozone precursor levels, on the other hand, were lowest in summer and highest in winter. The diurnal pattern showed that ozone levels peaked one hour later at the rural site than at the urban site. The ethylbenzene to m,p-xylene ratio, an indicator of the age of the air mass, increased from 0.4 at the urban site to 0.6 at the suburban site and 0.8 at the rural site during daily peak ozone times. This finding suggests the transport of ozone and precursors from upwind to downwind producing elevated ozone levels in the suburban and rural areas. Ozone episodes occurred mostly in days with a mean midday UV index of 6.5 (1 UV index=100 J m(-2)) and wind speed at 1.3 m s(-1) at all three sites.
2003年1月至2006年12月期间，在台湾中部的一个城市上风处站点、一个郊区下风处站点和一个农村站点，对臭氧（O₃）、55种挥发性有机化合物（VOCs，臭氧前体物）和氮氧化物（NOx）的每小时浓度进行了测量。VOC和NOx的平均浓度在城市（56 ppb和34 ppb）、郊区（38 ppb和27 ppb）和农村站点（25 ppb和21 ppb）呈现出从高到低的梯度，但臭氧浓度在这些站点呈现出相反的梯度（分别为24、27和29 ppb）。尽管城市和农村站点的VOC浓度差异约为两倍，但相同的9种VOC贡献了近65%的臭氧生成潜力。季节模式显示，城市站点秋季臭氧水平最高，夏季最低，但下风处郊区和农村站点冬季臭氧水平最低。另一方面，臭氧前体物水平夏季最低，冬季最高。日变化模式表明，农村站点的臭氧水平峰值比城市站点晚一小时出现。在每日臭氧峰值时段，作为气团年龄指标的乙苯与间、对二甲苯的比率从城市站点的0.4增加到郊区站点的0.6，再到农村站点的0.8。这一发现表明，臭氧及其前体物从上风处传输到下风处，导致郊区和农村地区臭氧水平升高。在所有三个站点，臭氧事件大多发生在中午平均紫外线指数为6.5（1个紫外线指数 = 100 J m⁻²）且风速为1.3 m s⁻¹的日子。
