Assessment of traffic contribution to hydrocarbons using 2,2-dimethylbutane as a vehicular indicator

This study investigated the feasibility of using 2,2-dimethylbutane (22DMC4) as an unambiguous indicator for traffic emissions, and applied it to assess traffic contribution to individual hydrocarbons in an atmospheric environment. The concept involves using concentration ratios of individual non-methane hydrocarbons (NMHCs) to 22DMC4, which are characteristic of traffic emissions to reveal excess concentration contributed by non-traffic sources. Air samples from three collections were analyzed for 22DMC4 and other NMHCs simultaneously to examine ratios of NMHCs/22DMC4. Two sample collections were made at different traffic transportation links in Kaohsiung City, and high concentration correlation was observed between 22DMC4 and most NMHCs for samples collected during heavy traffic hours. The third collection was made in the great Kaohsiung metropolitan area for comparison of NMHCs/22DMC4 ratios in different environments. Ratios of toluene/22DMC4 and ethene/22DMC4 obtained from the third collection were significantly greater than those from the two roadside collections in Kaohsiung City, suggesting other sources existed in addition to traffic. Comparing the NMHCs/22DMC4 ratios observed in a given area with the values obtained from pure traffic emissions as a reference can provide a quick diagnosis for non-traffic contributions. Another merit of using NMHCs/22DMC4 ratios of atmospheric components is to provide a basis of normalization, so that direct comparison of emission profiles collected in different times and places is possible.