Modeling approach for emission reduction of O 3 precursors in Southern Taiwan

Abstract

Although the upgraded criteria air quality standards (O 3, SO x , NO x and PM 10) and more stringent stack emission standards have significantly improved the overall air quality in Taiwan, the southern region of Taiwan frequently exhibits undesirable PSI (pollutant standard index), due to intensive industrial outputs and heavy traffic volume. For example, the percent of the time with PSI >100 in Taiwan has been reduced from 7% in 1994 to 4.3% in 2005, but there is still about 6.5% of the time with PSI > 100 in the southern region in 2005, of which 77% is due to O 3 contribution. The main goal of the present study is to develop a control strategy for reduction of NO x and NMHCs for reducing O 3 levels. The maximum 1-h O 3 isopleth profiles for southern Taiwan were first established based on 40 cases of different emission quantities of NO x and NMHCs using Taiwan Air Quality Model (TAQM) with four-level nested domains. The emission rates of O 3 precursors from other regions are assumed to be constant and exert the same effect on the air quality under different weather conditions in southern Taiwan. To meet the air quality goals, the allowable capacity for NO x and NMHCs in this region was determined by the following two methods: (a) linear and (b) cumulated frequency. The allowable capacity of NO x and NMHC to meet a certain goal can be easily demonstrated by plotting arbitrary reduction lines in the O 3 isopleth profiles. To meet the goal in the year 2011 (or O 3 151 ppb from the cumulated frequency method), for example, the emission reduction NO x /NMHC for 1:4 case amounts to 75 and 300 ton d −1, respectively, for NO x and NMHC; the corresponding emission rates are 290 and 430 ton d −1 (or 21 and 41% reduction, respectively). Clearly, there are many possibilities for achieving the desirable goal by manipulating reduction quantities in both NO x and NMHC.