Surface waters along a cruise track in the East Pacific Ocean were undersaturated in methyl bromide (CH(3)Br) in most areas except for coastal and upwelling regions, with saturation anomalies ranging ...from + 100 percent in coastal waters to -50 percent in open ocean areas, representing a regionally weighted mean of -16 (-13 to -20) percent. The partial lifetime of atmospheric CH(3)Br with respect to calculated oceanic degradation along this cruise track is 3.0 (2.9 to 3.6) years. The global, mean dry mole fraction of CH3Br in the atmosphere was 9.8 +/- 0.6 parts per trillion, with an interhemispheric ratio of 1.31 +/- 0.08. These data indicate that approximately 8 percent (0.2 parts per trillion) of the observed interhemispheric difference in atmospheric CH3Br could be attributed to an uneven global distribution of oceanic sources and sinks.
Biomass burning is a primary source of many trace substances that are important in atmospheric chemistry1-6. More than 80% of the world's biomass burning takes place in the tropics3 as a result of ...savanna fires, forest-clearing activity, and the burning of agricultural waste and wood. Here we report results from laboratory studies on the emission of nitrogen-containing compounds from the burning of dry vegetation. We find that the emission rates of NO,, HCN and CH3CN are sufficient to contribute significantly to the global atmospheric budget of the compounds. Furthermore, possibly up to half of the biomass nitrogen can be converted to molecular nitrogen, N2, leading to an estimated annual loss of 12-28 x 1012 g of biomass nitrogen ('pyrodenitrification'), equal to -9-20% of the estimated global rate of terrestrial nitrogen fixation.
Using data from seven cruises over a 10‐year span, we report marine boundary layer mixing ratios (i.e., dry mole fractions as pmol mol−1 or ppt), degrees of surface seawater saturation, and air‐sea ...fluxes of three short‐lived halocarbons that are significant in tropospheric and potentially stratospheric chemistry. CHBr3, CH2Br2, and CH3I were all highly supersaturated almost everywhere, all the time. Highest saturations of the two polybrominated gases were observed in coastal waters and areas of upwelling, such as those near the equator and along ocean fronts. CH3I distributions reflected the different chemistry and cycling of this gas in both the water and the atmosphere. Seasonal variations in fluxes were apparent where cruises overlapped and were consistent among oceans. Undersaturations of these gases were noted at some locations in the Southern Ocean, owing to mixing of surface and subsurface waters, not necessarily biological or chemical sinks. The Pacific Ocean appears to be a much stronger source of CHBr3 to the marine boundary layer than the Atlantic. The high supersaturations, fluxes, and marine boundary layer mixing ratios in the tropics are consistent with the suggestion that tropical convection could deliver some portion of these gases and their breakdown products to the upper troposphere and lower stratosphere.
We give an overview of the regional meteorological situation during the Indian Ocean Experiment INDOEX intensive field phase (IFP) in February and March 1999. The INDOEX domain, reaching from 30°N to ...30°S and from 50°E to 100°E, was chosen because the low‐level outflow of pollution from India is carried by the northeasterly trades into the tropical convergence zone, where cloud processing modifies the properties of the aerosols. In contrast, there is also an inflow of pristine southern hemispheric air by the southeasterly trades into the convergence zone. However, during the 1999 IFP some deviations from the climatological mean were observed. In 1999 the Intertropical Convergence Zone (ITCZ) was broken into a northern convergence zone and a southern convergence zone. During February the northern zone was more active and the cross‐equatorial flow (N‐→S) was weak, both suggesting that less pollution was transported to the southern hemisphere. In February it was occasionally possible to sample a southern hemispheric air mass on the southern side of the INDOEX domain. During March 1999 the southern convergence zone became dominant and moved to a more southern position (near 5°–10°S).
It is shown that four channels carry pollution into the INDOEX domain: (1) NE trades over the western Arabian Sea, (2) NW‐NE flow along the west coast of India, (3) NE trades over the west Bay of Bengal, and (4) NE flow from SE Asia. The strength of each channel is modulated by transients moving across Pakistan and northern India (western disturbances). The heating of the Indian subcontinent in March resulted in a eastern shift of the subtropical high from central India to the Bay of Bengal, which also affected channels 2, 3, and 4. Episodes of high and low carbon monoxide concentrations as measured in Kaashidhoo (Maldives) during the 1999 IFP can qualitatively be explained by the operationality of the flow channels, determined through trajectory analyses, in combination with the intensity of the northern convergence zone.
Carbon monoxide (CO) was measured at the Kaashidhoo Climate Observatory (KCO, Republic of Maldives) between February 1998 and March 2000 to assess the regional pollution of the remote atmosphere in ...the northern Indian Ocean. CO showed a distinct annual cycle with maximum daily mixing ratios of around 240 parts per billion (ppb), a seasonal difference of about 200 ppb, and high variability during the dry seasons. Detailed air mass trajectory analysis for 1998, 1999, and 2000 was used to identify source regions and to associate them with various levels of pollution encountered at KCO. We conclude that most significant changes in local pollution throughout the year are caused by changes in air masses. Air at KCO generally originated from three main regions with decreasing pollution: India and southeast Asia, the Arabian Sea, and the Southern Hemisphere. We show that isentropic air mass trajectories can be used to predict CO pollution levels at KCO to a certain extent and vice versa. Nitrous oxide, CFC‐11, CFC‐12, CCI4, and SF6 were measured during the Indian Ocean Experiment (February to March 1999) to support pollution analysis and to confirm that India is the main source for heavy pollution measured at KCO. Correlations between CO and other gases and aerosol properties measured at the surface illustrate that CO may also be used as a proxy for aerosol loading and general pollution at the surface.
A source analysis of carbon monoxide (CO) over the Indian Ocean is presented using marked tracers in a chemistry general circulation model. The model includes a nonmethane hydrocarbon chemistry ...scheme and has been used at two different resolutions (3.75° × 3.75° and 1.9° × 1.9°). European Centre for Medium‐Range Weather Forecasts meteorological analyses have been assimilated into the model to represent actual meteorology during February and March of 1999. A comparison with measurements indicates that the model simulates realistic CO distributions. In general, the model performance is more realistic at higher resolution. Discrepancies exist close to the Indian coasts, possibly related to a sea breeze circulation at the Indian west coast, not resolved by the model. Discrepancies are also found in the vicinity of convection at the Intertropical Convergence Zone (ITCZ). The marked tracer study suggests that biofuel use and agricultural waste burning in India are major CO sources for the Indian Ocean north of the ITCZ, with minor contributions from Middle East, China, and Southeast Asia. In the much cleaner boundary layer over the southern Indian Ocean, CO from hydrocarbon oxidation is a dominant source. There are no other regions around the globe where biofuel use and biomass burning contribute so much to the CO mixing ratios. In general, most of the Asian CO over the Indian Ocean remains north of the ITCZ, although some of the CO is transported to the southern hemisphere in the free troposphere near the African east coast.
Growth and distribution of halons in the atmosphere Butler, James H.; Montzka, Stephen A.; Clarke, Andrew D. ...
Journal of Geophysical Research,
20 January 1998, Letnik:
103, Številka:
D1
Journal Article
Recenzirano
The atmospheric burden of halons has continued to increase in recent years, despite an international ban on their production and sales in developed nations as of January 1, 1994. Halon emissions ...persist because of a lack of suitable substitutes for critical uses as fire extinguishants. As of January 1, 1997, halons H‐1301 (CBrF3), H‐1211 (CBrClF2), and H‐2402 (CBr2F4) were present in the troposphere at 2.3±0.1, 3.5±0.1, and 0.45±0.03 pmol mol−1. During 1995–1996 the tropospheric mole fraction of H‐1301 increased at 0.044±0.011 pmol mol−1 yr−1, while that for H‐1211 grew at 0.16±0.016 pmol mol−1 yr−1. These increases are significant and of concern because of the efficiency of bromine in depleting stratospheric ozone and because of the long atmospheric lifetimes of these gases. Given the current atmospheric record and the reported amount of halon produced before the ban on production, emission of H‐1301 at the 1995–1996 rate could continue for another 40 years, but H‐1211 would be depleted in 8–12 years. Exemptions to the ban on production may extend these periods. Tropospheric H‐2402 is increasing at 9±1 fmol mol−1 yr−1, but historical data on its production and use are lacking.
The burning of biomass (forest vegetation, savannah grass, firewood and agricultural wastes) due to humanactivities in the tropics is an important source of nitrogen compounds in the atmosphere. A ...recent experimental study identified a gap of 35-60% in the nitrogen balance between its content in the fuel and that recovered in the ash and in gaseous emissions of NOx, NH3, HCN, CH3CN and other nitriles, N2O, higher-molecular-weight organic compounds and in the smoke. It was suggested that the missing compound had to be molecular nitrogen. We have now carried out appropriate experiments and find that molecular nitrogen is indeed the most important nitrogen species emitted from biomass burning, with the largest contribution coming from flaming combustion. The loss of nutrient nitrogen by biomass burning, which is approximately 10-50 Tg N yr-1 or 5-50% ofglobal nitrogen fixation, may be particularly important for tropical ecosystems.
Characteristic vegetation and biofuels in major ecosystems of southern Africa were sampled during summer and autumn 2000 and burned under semicontrolled conditions. Elemental compositions of fuels ...and ash and emissions of CO2, CO, CH3COOH, HCOOH, NOX, NH3, HONO, HNO3, HCl, total volatile inorganic Cl and Br, SO2 and particulate C, N, and major ions were measured. Modified combustion efficiencies (MCEs, median = 0.94) were similar to those of ambient fires. Elemental emissions factors (EFel) for CH3COOH were inversely correlated with MCEs; EFels for heading and mixed grass fires were higher than those for backing fires of comparable MCEs. NOX, NH3, HONO, and particulate N accounted for a median of 22% of emitted N; HNO3 emissions were insignificant. Grass fires with the highest EFels for NH3 corresponded to MCEs in the range of 0.93; grass fires with higher and low MCEs exhibited lower EFels. NH3 emissions for most fuels were poorly correlated with fuel N. Most Cl and Br in fuel was emitted during combustion (median for each = 73%). Inorganic gases and particulate ions accounted for medians of 53% and 30% of emitted Cl and Br, respectively. About half of volatile inorganic Cl was HCl indicating significant emissions of other gaseous inorganic Cl species. Most fuel S (median = 76%) was emitted during combustion; SO2 and particulate SO42− accounted for about half the flux. Mobilization of P by fire (median emission = 82%) implies large nutrient losses from burned regions and potentially important exogenous sources of fertilization for downwind ecosystems.
ABSTRACT
Carbon monoxide (CO) fluxes between soil and atmosphere were measured between October 1990 and December 1991 in a temperate, deciduous forest near Darmstadt, Germany. Flux measurements were ...made with an enclosed chamber technique before and after the removal of leaves and humus from the forest floor as well as from leaves and humus alone. CO depth profiles were obtained during the period July to December, 1991. A net uptake of CO was observed under all conditions with an average of − 47.3 ± 24.0 ng CO m−2 s−1 for undisturbed forest soils, which increased significantly when the leaves or both leaves and humus were removed from the forest floor. The mean deposition velocity in undisturbed conditions was 0.027 ± 0.008 cm s −1. Our results indicate that CO has a short lifetime within the soil and that the consumption of atmospheric CO occurs mainly in the top few centimeters of the humus layer (O horizon). We conclude that temperate forests are a significant net sink for atmospheric CO and that leaves and humus significantly affect CO fluxes. The global soil sink for atmospheric CO was estimated to be 115–230 Tg CO yr−1.
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