Short-Lived Trace Gases in the Surface Ocean and the Atmosphere

The two-way exchange of trace gases between the ocean and the atmosphere is important for both the chemistry and physics of the atmosphere and the biogeochemistry of the oceans, including the global cycling of elements. Here we review these exchanges and their importance for a range of gases whose lifetimes are generally short compared to the main greenhouse gases and which are, in most cases, more reactive than them. Gases considered include sulphur and related compounds, organohalogens, non-methane hydrocarbons, ozone, ammonia and related compounds, hydrogen and carbon monoxide. Finally, we stress the interactivity of the system, the importance of process understanding for modeling, the need for more extensive field measurements and their better seasonal coverage, the importance of inter-calibration exercises and finally the need to show the importance of air-sea exchanges for global cycling and how the field fits into the broader context of Earth System Science

Tunable diode laser measurements of formaldehyde during the TOPSE 2000 study: Distributions, trends, and model comparisons

[1] Airborne measurements of formaldehyde (CH2O) were acquired employing tunable diode laser absorption spectroscopy (TDLAS) during the 2000 Tropospheric Ozone Production About the Spring Equinox (TOPSE) study. This study consisted of seven deployments spanning the time period from 4 February to 23 May 2000 and covered a wide latitudinal band from 40degreesN to 85degreesN. The median measured CH2O concentrations, with a few exceptions, did not show any clear temporal trends from February to May in each of five altitude and three latitude bins examined. Detailed measurement-model comparisons were carried out using a variety of approaches employing two different steady state models. Because recent emissions of CH2O and/or its precursors often result in model underpredictions, background conditions were identified using a number of chemical tracers. For background conditions at temperatures warmer than -45degreesC, the measurement-model agreement on average ranged between -13% and +5% (measurement-model/measurement), which corresponded to mean and median (measurement-model) differences of 3 +/- 69 and -6 parts per trillion by volume (pptv), respectively. At very low temperatures starting at around -45degreesC, significant and persistent (measurement-model) differences were observed from February to early April from southern Canada to the Arctic Ocean in the 6-8 km altitude range. In such cases, measured CH2O was as much as 392 pptv higher than modeled, and the median difference was 132 pptv (83%). Low light conditions as well as cold temperatures may be important in this effect. A number of possible mechanisms involving the reaction of CH3O2 with HO2 to produce CH2O directly were investigated, but in each case the discrepancy was only minimally reduced. Other possibilities were also considered but in each case there was no compelling evidence to support any of the hypotheses. Whatever the cause, the elevated CH2O concentrations significantly impact upper tropospheric HOx levels at high latitudes (>57degreesN) in the February-April time frame

Methyl bromide, other brominated methanes, and methyl iodide in polar firn air

We report measurements of brominated, bromochlorinated, and iodinated methanes in air extracted from deep firn at three polar locations (two Antarctic and one Arctic). Using a firn diffusion model, we are able to reconstruct a consistent temporal trend for methyl bromide from the two Antarctic sites. This indicates a steady increase by about 2 ppt from the midtwentieth century to 8 ppt today. The Arctic firn, however, contained extremely high levels of methyl bromide as well as numerous other organic gases, which are evidently produced in situ. The other brominated species (dibromomethane, bromochloromethane, bromodichloromethane, dibromochloromethane, and bromoform) showed little or no long-term trend in Antarctic firn and therefore are evidently of entirely natural origin in the Southern Hemisphere. A clear seasonal trend was observed in the upper firn for the shortest-lived halocarbons (notably bromoform and methyl iodide). The same species were present at lower abundance at the higher altitude and more inland Antarctic site, possibly due to their origin from more distant oceanic sources