The third joint Soviet‐American Gases and Aerosols (SAGA 3) experiment was a research cruise conducted aboard the Akademik Korolev in February and March 1990. The cruise covered a region of the equatorial Pacific Ocean from 15°N to 10°S latitude and 144° to 165°W longitude. On this cruise we collected samples for the measurement of alkyl nitrates (RONO2), nonmethane hydrocarbons (NMHC) and several halocarbon gases. Though there are few data available for comparison in this region of the marine boundary layer, the mixing ratios of the trace gases we measured are within the range of prior measurements in the remote atmosphere. Latitudinal gradients were found for trace gases with predominantly anthropogenic sources, e.g., methylene chloride, tetrachloroethylene, and acetylene; higher concentrations in the North Pacific atmosphere decreased slowly across the Equator to the South Pacific. More stable gases, e.g. methyl chloride and methyl bromide, had no pronounced variation across the equator. A biogenic source of two organobromine compounds, bromoform and dibromochloromethane, was indicated by maximum mixing ratios of these species over the equator where indicators of biological productivity (e.g., chlorophyll) in the surface ocean water also maximized. Alkyl nitrates were found at levels higher than predicted from steady state calculations based on measured mixing ratios of hydrocarbons and NO. The measured levels of RONO2 suggest long‐range transport as one mechanism contributing to elevated concentrations of alkyl nitrates in the remote troposphere. However, the distributions of C2 and C3 alkyl nitrates over the equator were similar to the organobromine gases. This distribution suggests a possible oceanic source for alkyl nitrates to the atmosphere.

Atmospheric methane, nonmethane hydrocarbons, and carbon monoxide were measured at the Mauna Loa Observatory on the island of Hawaii in May and June 1988. The daily island upslope/downslope circulation resulted in a variable mixture of boundary layer and free tropospheric air at the observatory. Mixing ratios of these gases were higher during upslope flow than during downslope flow. Mixing ratios characteristic of the free troposphere at this altitude were most often measured during nighttime, downslope flow. Local marine emissions of ethylene and propylene and emissions of isoprene from island vegetation were detected during upslope circulation, but ethylene and propylene were also often detected at night during downslope circulation, indicating that air sampled during nighttime downslope flow may have included some air recently transported from the marine boundary layer. Comparison of data for methane, carbon monoxide, ethane, and propane from in situ measurements with measurements made from canister samples collected during the experiment showed very good agreement. Fluxes of isoprene from selected dominant island flora were also measured.

Volatile organic trace gases in the remote troposphere at the Mauna Loa Observatory were identified in July and August 1992 during the Mauna Loa Observatory Photochemical Experiment (MLOPEX 2) using an in situ fully automated gas chromatography mass spectrometry (GCMS) instrument. Identification was obtained for 65 organic compounds, 7 additional compounds were identified tentatively. Four target parts per trillion (ppt)-level species were detected in the selected ion monitoring mode (SIM). The experimental data show typical background air characteristics; for example, abundance of long-lived compounds such as halogenated hydrocarbons during all measurement periods. Volatile organic compounds (VOCs) from local sources from the island were also seen during daytime upslope flow conditions. These included short-lived biogenic hydrocarbons such as isoprene and monoterpenes and typical emissions from combustion processes such as alkylated aromatics.During the fourth field campaign of MLOPEX 2 in July and August 1992, gas chromatography mass spectrometry (GCMS) measurements of volatile organic trace gases were made at the site. The purpose of the GCMS experiment was to (1) support the GCFID measurements and confirm peak assignments of quantified species, (2)identify possible interferences from coeluting compounds in the GCFID measurements, (3) identify unknown compounds observed in the FID chromatograms, (4) provide reliable identification of a series of compounds tentatively identified as n-aldehydes and observed in the GCFID chromatograms in the previous field measurements (both in MLOPEX 1 and in the first three campaigns of MLOPEX 2), and (5) to allow detection of additional organic compounds that were undetected on the GCFID system. The measurements were also meant to contribute to the identification of long-lived organic trace gases at MLO and to provide additional information on the distribution of volatile organic trace gases among different chemical compound classes. ExperimentalThe GCMS experiment solely allowed qualitative measurements for compound identification, because with the changing sensitivity of the MS among different compounds, quantitative measurements would require calibration standards for each individual compound in the concentration range of the samples. The GCMS analytical system employed. has been described in detail recently [Hehnig and Greenberg, 1994] and only a brief summary of the basic principles will be given here. The inlet port was located on top of a measurement tower at about 9 m above ground. In order to accomplish compound identification on the mass spectrometer in the full scan mode, substantially larger sample volumes than the 2 1 14,697