| dc.description.abstract | Surface ozone has become a series pollution problem in Taiwan as well as in other major developing urban environments. While the average concentration of particular matter showed a decreasing trend, ozone on the other hand, showed an increasing trend over the past decade. To elucidate ozone formation mechanism in certain ozone plagued areas of Taiwan, in-situ VOC monitoring station network, equivalent to the US PAMS (photochemical assessment monitoring stations) program, was adopted with the first 3 station network established in central Taiwan in both urban and rural areas. Monitoring data of 2003 and 2004 was examined for their diurnal and monthly variation and three types of VOCs with different origins, namely LPG leakage, vehicular exhaust, and biogenic emissions, are discussed. While all of the VOCs have similar diurnal profile with maximum appeared in the morning and evening due largely to emissions, the change of mixing height, and photochemistry, isoprene however showed similar profile with tailpipe type of species in winter but gradually shifted its peak emission towards noon as the time progressed into later spring (May).
Our investigation has led to the development of 2 VOC indicators of air masses’ age due to photochemistry with drastic difference in indication sensitivity. Excellent agreement between ozone concentrations and ratios of ethylbenzene/xylene and pentane/t-2-pentene suggests ozone is the photochemical product of VOCs and that the car exhaust compounds control the downwind ozone peak values. Difference in the age of air parcels received at the 3 stations was also clearly revealed, based on which the Chushan (竹山) station in general received more aged air masses than the other two upwind Chunlun (崇倫) and Choaton (草屯) stations. The similarity between Choaton and Chushan proves that Chushan station can be a suitable site for representing most area of Nantou county for studying ozone formation in downwind environment.
Although biogenic emissions with isoprene being the dominant species did not appear to control the downwind ozone peak values, at least not to the same degree as the car exhaust compounds, it is shown to exert more reactivity towards ozone formation potential than other types of precursors. Production of isoprene at noon in the warm seasons synchronizes in time with the ozone peak further creates a greater possibility for ozone to exceed dangerous levels should car exhaust VOCs also been brought down to the site of observation. | en_US |