ALKYL NITRATES, NONMETHANE HYDROCARBONS, AND HALOCARBON GASES OVER THE EQUATORIAL PACIFIC-OCEAN DURING SAGA-3

The third joint Soviet-American Gases and Aerosols (SAGA 3) experiment was a research cruise conducted aboard the Akademik Korolev in Februa ry and March 1990. The cruise covered a region of the equatorial Pacif ic Ocean from 15-degrees-N to 10-degrees-S latitude and 144-degrees to 165-degrees 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 rat ios of the trace gases we measured are within the range of prior measu rements in the remote atmosphere. Latitudinal gradients were found for trace gases with predominantly anthropogenic sources, e.g., methylene chloride, tetrachloroethylene, and acetylene; higher concentrations i n 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 so urce of two organobromine compounds, bromoform and dibromochloromethan e, was indicated by maximum mixing ratios of these species over the eq uator where indicators of biological productivity (e.g., chlorophyll) in the surface ocean water also maximized. Alkyl nitrates were found a t 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 e levated concentrations of alkyl nitrates in the remote troposphere. Ho wever, 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.