Measurement and analysis of C2-C10 hydrocarbons at Whiteface Mountain, New York

Canister-based sampling and gas chromatography-flame ionization detection analytical techniques were developed and employed in the held measurement of hydrocarbons conducted from June 1994 through December 1995 at the summit (1400 m) and lodge (600 m) of Whiteface Mountain (WFM). More than 50 ambient hydrocarbon species, including C-2-C-10 alkanes, C-2-C-6 alkenes, benzene and a select group of alkylated aromatics, and isoprene were analyzed using these techniques with an estimated accuracy of +/-20%. The instrumental limit of detection was similar to 20 parts per trillion carbon (pptC). Quality assurance of the analysis was performed, in part, via participation in the Nonmethane Hydrocarbon Intercomparison Experiment (NOMHICE). The NOMHECE results showed that for the majority of the target hydrocarbon species the percent differences between our analyses and those of the referee group were <10% for the standard mixtures and <20% for the whole air sample. Analyses of the hydrocarbon data indicate that WFM is routinely in the path of aged photochemical regional air masses which have been influenced by urban emission upwind of the site. The distribution of hydrocarbon species observed at WFM matches that of mobile sources. The seasonal variation of anthropogenic hydrocarbons at WFM is consistent with the expected seasonal variation in OH. The observed changes in the ratios of toluene/benzene from the summers of 1994-1995 are indicative of a greater reduction in the benzene emissions relative to toluene emissions over this period. One possible explanation for this change is the introduction of reformulated gasoline in many areas in the region starting in 1995. The concentrations of naturally emitted isoprene show a strong seasonal variation and temperature dependence.