Source Discrimination of Short-Term Hydrocarbon Samples Measured Aloft

Weighted least-squares fitting of 17 hydrocarbons was used to estimate ambient contributions from four source categories. The data set consisted of 192 samples collected from 300 to 1500m over Tokyo, July 16-17, 1981. Six runs (flights), 1-1.5 h long, spaced throughout each day, constituted chemical “snapshots” of the urban air. Vehicles contributed 7.0%, gasoline vapor 10.5%, petroleum refinery 26.0%, paint solvents 27.2%, and unexplained sources 29.3% of the total hydrocarbon concentration (based on the 17 components measured and all samples). These coefficients are only representative of the days and conditions sampled and should not be interpreted as annual emission fractions. On a run-averaged basis the correlation between refinery emissions per hour, adjusted for dispersion, and ambient concentrations of total hydrocarbon attributable to petroleum refineries was r² = 0.899, indicating that the refinery profile was sufficiently unique to be sensed up to 70 km. The fractions for paint solvents, gasoline vapor, and unidentified sources were also consistent with wind trajectory observations.