Figure 9. Same as Fig. 8 except that horizontal coordinates are changed to photochemically consumed precursors of ozone.

regime. In order to find the regime of NOK sensitivity, one may need to be at least 200 km away from Guangzhou, i.e. the PRD megacity plume which is in the NMHCs-sensitive regime may be as large as 400 x 400 km2. In this context, given the widespread emissions of ozone precursors in the vast plain in northern China, it may be difficult to find any rural area in northern China where the ozone formation is limited by NOK. This has a profound implication for the ozone control strategy for China in general and for the 2008 Beijing Olympics in particular.

Large amounts of ozone and ozone precursors are transported from megacities to rural and background atmospheres where the ozone production is known to be limited by NOK. Therefore, reduction of NOK emissions must be considered with regard to the synoptic-to-global-scale ozone problem.

3. Ozone Trends

3.1. Ozone trends in Taiwan

Taiwan is located in the southern part of East Asia, where the background ozone is influenced by long range transport of air pollutants from the Asian continent, which has undergone rapid economic development since the 1970s. Taiwan itself has experienced extraordinarily rapid economic development in the last few decades. The local photochemical production due to large emissions of ozone precursors plays a controlling role in the ozone distribution. In recent years the high levels of surface ozone have increasingly become a major air pollution problem. Since 2001, ozone has replaced particulate matter (PM10) as the major air pollutant responsible for most violations of the ambient air quality standards. In fact, efforts to control air pollutant emissions have significantly lowered the ambient

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