Between September and October, 1991, scientists from the US, Japan, Taiwan, Korea China and Hong Kong participated in the intensive observation of the PEM-west program. Intensive airborne measurements of forty different kinds of chemical species were made by scientists aboard the NASA DC-8 aircraft. On October 4, 1991, the DC-8 made a special effort to fly around Taiwan. The synoptic condition was Taiwan on the edge of the cold continental High and subtropic High. The prevailing wind was northeasterly over western Taiwan and easterly over eastern Taiwan. The DC-8 flew from Hong Kong toward the northeastern corner of Taiwan, and then along the eastern coast, before heading back to Hong Kong from the southern tip of Taiwan. The data collected show that a locally emitted plume was detected over northern Taipei aat an altitude of 3 km, and was characterized by high levels of chemical species, such as [O₃] 60 ppbv, [NO_y] 4500 pptv, [CO] 275 ppbv, etc. Over eastern Taiwan, most of the chemical species had a vertical profile of increasing concentration with respect to altitude. Below 4 km, the low level of chemical species was typically associated with a clean maritime airmass. The level of ozone was about 20 ppbv, with [NO] below 20 pptv, [NO_y] around 300 pptv, [CO]below 80 pptv, etc. The mean vertical profile of each species is listed in this paper, and it can be used as the initial state for model simulation. The data discussed in this paper provide important information to local scientists.