Measurement of the background levels and study of the chemistry of trace organic carbon species in the remote marine troposphere occurred during an April-July 1987 SAGA II cruise in remote regions of the Pacific and Indian Oceans. Measured compounds included carboxylic acids, formaldehyde, light hydrocarbons (C2-C4), and ozone. The results show seasonal, diel, and spatial dependencies for the organic acids. Distinct latitudinal gradients are seen for most sampled compounds. Formic acid is well correlated with suspected precursors, formaldehyde and light hydrocarbons. Acetic acid follows a similar pattern as formic acid, although its precursors are as yet undefined. Did patterns of low amplitude for the organic acids in the remote marine troposphere suggest a natural contribution to tropospheric photochemistry, and to the global carbon cycle as well. For the northern hemisphere Pacific Ocean, the mean formic acid mixing ratio was 0.80 + 0.30 ppbv, the mean acetic acid value was 0.78 + 0.32 ppbv. For the southern hemisphere Pacific Ocean, formic acid averaged 0.22 + 0.13 ppbv, for acetic acid, the mean was 0.28 +_ 0.18 ppbv. For the northem hemisphere Indian Ocean, the mean formic acid mixing ratio was 0.75 + 0.24 ppbv, and the mean acetic acid value was 0.69 + 0.27 ppbv. For the southern hemisphere Indian Ocean, the mean formic acid value was 0.19 + 0.17 ppbv, and the mean acetic acid value was 0.29 + 0.16 ppbv. Highest levels of organic acids were encountered near known anthropogenic source regions, in air masses of continental origin, or near regions of naturally produced alkenes (C 2, C3). The ozone-alkene oxidation scheme appears to play a major role in gas phase organic acid production in the remote marine troposphere. Nighttime gas phase deposition of the organic acids onto the ocean surface appears to be a major sink. 2Now at College of Sciences, University of Maine, Orono. in the gas phase. Analogous aqueous-phase reactions leading 3Now at NOAA, GMCC Samoa Observatory, Pago Pago, American Samoa. to the production of acetic acid are recognized as being 4Now at Joint Institute for the Study of the Atmosphere and Ocean, negligibly slow [Jacob and Wofsy, 1988a] and therefore not a University of Washington, Seatfie. significant source. Such reactions are also limited by the lower solubility of acetaldehyde. Predicted gas-phase formic acid mixing ratios calculated from aqueous phase reaction Copyright 1990 by the American Geophysical Union. mechanisms are between 35 and 65 pptv [Charneides and Paper number 90JD01223. Davis, 1983]. Since it is generally agreed that aqueous-phase 0148-0227/90/90JD-01223505.00 production of organic acids alone cannot account for the 16,391 16,392 ARLANDER ET AL.: GASEOUS OXYOENATED HYDROCARBONS FTIR spectroscopic evidence for the formation of CH2(OH)OOH in D.R. Cronn, College of Sciences, University of Maine, Orono, ME the gas phase reaction of HO e with CH:O, Chem. Phys. Lett., 75, 04469. 533, 1980b. J.C. Farmer, NOAA, GMCC Samoa Observatory, Pago Pago, Norton, R. B., Measurement ...
The first known vertical distributions of ethane and acetylene which extend into the lower stratosphere are reported. The average upper tropospheric concentrations, between 20,000 ft (6 km) and 35,000 ft (11 km), near 37°N ‐ 123°W were 1.2 µg/m³ (1.0 ppb) for ethane and 0.24 µg/m³ (0.23 ppb) for acetylene while the values near 9°N ‐ 80°W were 0.95 µg/m³ (0.77 ppb) and 0.09 µg/m³ (0.09 ppb), respectively. Detectable quantities of both ethane and acetylene are present in the lower stratosphere. There is a sharp decrease in the levels of these two compounds as one crosses the tropopause and ascends into the lower stratosphere. The observed levels of ethane and acetylene may allow some impact on the background chemistry of the troposphere and stratosphere.
The distribution of gaseous atmospheric hydrocarbon compounds, halocarbons, and nitrous oxide were studied. Whole air samples were collected aboard the NCAR Electra aircraft platform during the Monsoon Experiment (MONEX) flights in Kuala Lumpur, Malaysia, and on ferry flights to and from the United States. Foliage emission rates were also measured on some tropical plants. The average free tropospheric TNMHC (total non‐methane hydrocarbon) levels from both the transit flight and mission flights were low (2.5 μg/m3). TNMHC just above the forest canopy over Borneo but within the mixing layer was higher and the concentrations over land were higher than those obtained over the ocean. The fluorocarbons showed a small latitude gradient or a difference between continental and oceanic air masses or (possibily) both. Methyl chloroform also showed a significant latitude profile. Nitrous oxide was uniformly distributed in the atmosphere. The C2 hydrocarbons, ethane and acetylene, also showed latitudinal gradients. The emission rates of foliage in the tropics were higher than those reported by other investigators for the mid‐latitudes. The species sampled indicated that most tropical vegetation emits predominantly isoprene, rather than terpenes.
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