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[1] The Taiwan air quality model incorporating a dust module was applied to calculate masses of supermicron (diameter greater than 1 mm) and submicron particles (diameter less than 1 mm) and their dust fractions during the ACE-Asia airborne experiments over the northwestern Pacific. The results showed that the calculated vertical profiles of supermicron particle concentrations matched reasonably well with the observations obtained from 19 research aircraft missions. During dust storm events and at dust concentrated altitudes, the calculated dust fractions in the supermicron particles were usually greater than 90%, and the dust was concentrated in the lower troposphere mainly below 6 km. Without dust storm, dust was still the major component of the supermicron particles above boundary layer. In contrast to supermicron particles, the model results showed that the major component of the submicron particles observed during aircraft experiments was mostly from pollution. The calculated vertical profiles of submicron particle concentrations were sensitive to the emission inventory of air pollutants over east Asia. The correlation between observed anthropogenic volatile organic compound and submicron particles were used to identify the pollution fraction in the submicron particles, and the results were consistent with the model calculations of dust fraction. The model results showed that the dust fractions in the submicron particles were usually less than 28% in the boundary layer. During dust storm events the dust fractions were usually greater than 40% but can be as low as 24% when significant amount of pollutants were present.

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 nontraffic 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.