No abstract

Measurements of C1−C15 alkyl nitrates, perchloroethylene, and bromoform at two different sampling sites near Santa Cruz, CA, were conducted in 1995. The halocarbons were used as marker molecules to differentiate the air parcels collected into marine and continental groups. The average concentration of ∑n/i-C3−C12 alkyl nitrates at the California Coast (19.3 pptv) was lower than the levels obtained in the coastal mountains (53.9 pptv). This difference was shown to be most significant for the long chain n/i-C6−C12 alkyl nitrates. It is concluded that the ≥C6 alkyl nitrates in continental air can contribute 1−2% to the total NO y . The results are summarized together with earlier data sets to give a picture of contemporary levels and of the global occurrence of C3−C12 alkyl nitrates. In comparison with South Atlantic air (3.5 pptv), pattern analysis of n-alkyl nitrates suggests a marine source of primary n-alkyl nitrates. It is also shown that liquid chromatographic preseparation of the air sample extracts leads to a fraction that contains more polar organic nitrates. Several alkyl dinitrates and benzyl nitrate are detected in air samples from California, the South Atlantic region, and Europe. The vicinal alkyl dinitrates show increased abundance in a nighttime sample. The relative abundance of benzyl nitrate compared to alkyl (mono) nitrates is used as a tool for global air mass characterization.

SummaryHalogenated methoxybenzenes (halogenated anisoles) and hexachlorobenzene (HCB) have been analyzed in marine air samples from the lower troposphere of the East Atlantic Ocean, taken on the German research vessel "Polarstern' during two cruises in 1993 and 1994, and in air samples from the North Pacific Ocean (1995). The high-volume sampling method, sample preparation and analysis by HRGC-ECD and HRGC-MSD-SIM are described. The effectiveness of a new graphitized-carboncovered silica sorbent (ANGI-Sorb B) for the sampling of semi-volatiles is demonstrated. Eight congeners of the halogenated anisoles and HCB were detected in almost all marine air samples. The concentrations of the chloroanisoles, which show a distinct north-south interhemispherical gradient, were between 0.2 and 145 pg m-3; for the bromoanisoles concentrations were between 0.2 and 42 pg m -3. Only a weak inter-hemispheric gradient was observed for HCB at levels of 10--40 pg m -3. Levels of HCB were approximately 100 pg m -3 in continentally influenced air. Biogenic and indirect anthropogenic sources of the halogenated anisoles are discussed.

Halogenated anisoles (methyl-phenyl ethers) appear to be ubiquitous organic trace compounds in the environment. An analytical method is presented for analyzing the altogether 134 congeners of chloro-, bromo- and mixed bromochloro-anisoles on an isomer-specific basis in air. High volume sampling (20 m(3) per hour) is carried out by adsorption, using a mixture of silica gel 60 and ENVI-Carb. The preseparation of the anisoles is achieved by NP-LC on Florisil (a magnesium silicate). The interference by volatile n-alkyl nitrates in the electron-capture detection can be avoided by a LC-preseparation on a carboneous phase. The isomer-specific separation and detection is performed by HRGC-ECD and HRGC-MS-SIM. A structure-specific systematic numbering of the 134 congeners of the chloro-, bromo- and bromochloro-anisoles is suggested. The retention data are given of 16 chloroanisoles, 10 bromoanisoles and 27 bromo-chloroanisoles on three stationary phases with different polarity.