Levels and pattern of alkyl nitrates, multifunctional alkyl nitrates, and halocarbons in the air over the Atlantic Ocean

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The Albatross Campaign was a research cruise of the German research vessel RV Polarstern (cruise ANT XFV/1) in October and November 1996 across the Atlantic Ocean. The cruise started in Bremerhaven, Germany, reached the polar region at 67°N, followed the 30°W meridian longitude, crossed the equatorial region, and ended at 50°S at Punta Quilla, Argentina. A second cruise leg closer to the African continent started from Capetown, South Africa, passed the Canary Island, and ended through the English Channel at Bremerhaven, Germany, in May/June 1998. Measurements of atmospheric levels of C1–C13 alkyl mononitrates, 24 alkyl dinitrates (C3–C6), 19 hydroxy alkyl nitrates (C2–C6), and benzyl nitrate, as well as the halocarbons tetrachloroethene, hexachloroethane, and bromoform are presented in this work. The halocarbons are used to assess the origin of the air parcels analyzed. Levels and patterns of multifunctional alkyl nitrates in the marine air are described here for the first time. The air masses include polluted air from the northern Europe, as well as highly degraded air masses of the South Atlantic trade wind region that represent global baseline levels. Two independent analytical methods were used in combination to cover the whole range of organic nitrates. First, the low‐volume adsorptive enrichment of organic traces on Tenax, followed by thermodesorption cold trap HRGC‐ECD and thermodesorption cold trap HRGC‐(EI)MSD was used. Second, high‐volume adsorptive enrichment of organic traces on silica gel was applied followed by solvent desorption, NP‐HPLC group separation, and HRGC‐(EI)‐MSD. Short‐chain alkyl nitrates (C4–C6) showed mixing ratios in the range of 0.2–2.5 parts per trillion by volume (pptv), with a local minimum for the tropical regions and significantly lower ratios for the Southern Hemisphere. The mixing ratio of the sum of 36 long‐chain alkyl mononitrates (C7–C13) ranged from 0.02–0.43 pptv, the mixing ratio of the sum of 23 alkyl dinitrates (C3–C6) ranged from 0.005–1.08 pptv, and the mixing ratio of the sum of 7 hydroxy alkyl nitrates (C2–C4) ranged from 0.005–1.07 pptv, respectively. The average alkyl nitrate concentration in ambient air of central Europe (Ulm, Germany) turned out to be a factor of 10–100 higher than in the marine samples. The low concentrations in marine air reflect chemical and physical loss processes during long‐range transport of the air starting from the continents. Our results are compared with earlier field studies to complete the data set of global occurrence of alkyl nitrates in the troposphere.