Characteristics of C2–C15 hydrocarbons in the air of urban Kaohsiung, Taiwan

The concentrations of 71 hydrocarbons (HC) from C2 to C15 were measured simultaneously at two sites in Kaohsiung city in the morning (07–10), the afternoon (13–16), and the evening (18–21) on 14 days in spring 2003. A total of 84 3-h integrated air samples were collected using multibed stainless-steel thermal adsorption tubes and then analyzed using a GC/FID or a GC/ECD. The most abundant species of Kaohsiung's air is toluene (43.36–54.49 μg m−3), followed by i-pentane, 1,2,4-trimethylbenzene, benzene, n-butane, propane and acetylene, in the range 10.36–17.11 μg m−3. The concentrations of 14 halocarbons are in the range 0.25–4.57 μg m−3. Alkanes (around 44.8%) represent the largest proportion of the total HC, followed by aromatics (35.1%), alkenes (15.5%) and halocarbons (5.4%). The afternoon HC concentrations are much lower than those in the morning and at night, due to relatively intense photochemical reaction and favorable dispersion conditions from noon to afternoon. Notable increases in daily HC concentrations are consistent with high temperature, and low HC concentrations on Sunday coincide with low traffic volume. Photochemical activity is investigated, and HC concentrations are found to decline as the NO2/NOx ratio increases. Correlation analyses imply that vehicle exhaust is the dominant source of atmospheric hydrocarbons in Kaohsiung.