Atmospheric residence time of CH3Br estimated from the junge spatial variability relation

The atmospheric residence time for methyl bromide (CH3Br) has been estimated as 0.8 +/- 0.1 years from its empirical spatial variability relative to C2H6, C2Cl4, CHCl3, and CH3Cl. This evaluation of the atmospheric residence time, based on Junge's 1963 general proposal, provides an estimate for CH3Br that is independent of source and sink estimates. Methyl bromide from combined natural and anthropogenic sources furnishes about half of the bromine that enters the stratosphere, where it plays an important role in ozone destruction. This residence time is consistent with the 0.7-year value recently calculated for CH3Br from the combined strength estimates for its known significant sinks

Effect of soil applied zinc sulphate on wheat (Triticum aestivum L.) grown on a calcareous soil in Pakistan

A field experiment was conducted to investigate the effect of soil application of zinc fertilizer on yield and yield components of wheat (Triticum aestivum L. cv. Inqlab 91) grown on calcareous soil in Pakistan. The levels of zinc sulphate were 0 (control), 5, 10, 15, 20, 25 and 30 kg ha-2 and the zinc sulphate was combine-drilled at the time of sowing. Zinc sulphate increased the Leaf Area Index, the total number of fertile tillers m -2, number of spikelets spike-2, spike length, grain spike-2, thousand grain weight, grain yield, straw yield and biological yield and decreased harvest index. Most of the response trends were curvilinear although the decrease in harvest index was linear. All applications of zinc sulphate gave economic increases in margins over costs but the application of 5 kg ha-2 gave the highest marginal rate of return. It is recommended that under such calcareous soil conditions growers can expect good returns from the application of 5 kg zinc sulphate ha-2 at the time of sowing but if the grain price were to increase or the price of zinc sulphate were reduced economic responses could be expected from higher levels of zinc sulphate. © 2008 Akadémiai Kiadó

methane concentrations and source strengths in urban locations

Higher atmospheric concentrations of methane are found in air samples from urban locations than in contemporary samples at the same latitude in remote locations. Higher concentrations of several trace chlorocarbon gases are also found in the same urban samples than in the corresponding remote samples. The “urban excess”, i.e. urban concentration minus remote concentration, is generally 1000 to 2000 times larger on a molar basis for CH4 than for CCl3F. Because almost all CCl3F is emitted in urban environments, the urban release of CH4 is estimated from the observed molar ratios to be 30 to 60 megatons per year world‐wide. The fraction of world‐wide methane release occurring in the urban environment can be estimated from the concentration ratios, urban to remote, for CH4 vs. CCl3F. About 8% to 15% of the atmospheric methane release is observed to occur in urban locations. Copyright 1984 by the American Geophysical Union

Estimation of global vehicular methyl bromide emissions: Extrapolation from a case study in Santiago, Chile

Between June 1 and June 8, 1996, 144 whole air samples were collected in Santiago, Chile. The temporal and geographical enhancement of CH3Br correlated with incomplete combustion tracers emitted from vehicles during the morning commute. From these, a city-wide CH3Br/CO volume emission ratio of 2.2 × 10-6 was measured in ambient air. Without using the CO measurements, we estimate an annual release of 8.9 tons of CH3Br in Santiago based solely upon enhanced concentrations observed throughout the study area during the morning traffic period. This enhancement corresponds to 8.0 × 10-6 kg CH3Br emitted for each liter of gasoline used (leaded and unleaded). By scaling the annual gasoline usage in Santiago to countries still using leaded gasoline, and assuming the above 8.0 × 10-6 kg/L value holds true, a global vehicular CH3Br emission of 4 ± 3 Gg/year is calculated. This small vehicular CH3Br emission source strength will not improve the current CH3Br budget imbalance

Nonmethane hydrocarbon and halocarbon distributions during Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange, June 1992

Aircraft measurements of selected nonmethane hydrocarbon and halocarbon species were made in the lower troposphere of the NE Atlantic near the Azores, Portugal, during June 1992 as part of the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange. In this paper, the impact of continental outflow from both Europe and North America on the study region were assessed. Four main air mass types were characterized from trajectories and trace gas concentrations: clean marine from the Atlantic, and continental air from the Iberian Peninsula, the British Isles and Northern Europe, and North America. Each classification exhibited trace gas concentrations that had been modified en route by photochemical processes and mixing. Comparison with the clean marine boundary layer (MBL) shows that the boundary layer of the predominantly continental air masses were enhanced in hydrocarbons and halocarbons by factors of approximately 2 for ethane, 5 for propane, 2-6 for ethyne and benzene, and 2-3 for C2Cl4. The same air masses also exhibited large ozone enhancements, with 2 to 3 times higher mixing ratios in the continental boundary layer air compared to the clean MBL. This indicates a primarily anthropogenic photochemical source for a significant fraction of the lower tropospheric ozone in this region. Methyl bromide exhibited on average 10-20% higher concentrations in the boundary layer affected by continental outflow than in the clean MBL, and was seen to be enhanced in individual plumes of air of continental origin. This is consistent with significant anthropogenic sources for methyl bromide. In addition, median MBL concentrations of ethene and methyl iodide showed enhancements of approximately a factor of 2 above free tropospheric values, suggesting primarily coastal/oceanic sources for these species. Copyright 1996 by the American Geophysical Union

Dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) emissions from biomass burning in Australia

We identify dimethyl disulfide (DMDS) as the major reduced sulfur-containing gas emitted from bushfires in Australia's Northern Territory. Like dimethyl sulfide (DMS), DMDS is oxidized in the atmosphere to sulfur dioxide (SO2) and methane sulfonic acid (MSA), which are intermediates in the formation of sulfuric acid (H2SO4). The mixing ratios of DMDS and DMS were the highest we have ever detected, with maximum values of 113 and 35 ppbv, respectively, whereas background values were below the detection limit (10 pptv). Molar emission ratios relative to carbon monoxide (CO) were [1.6 ± 0.1] × 10-5 and [6.2 ± 0.3] × 10-6, for DMDS and DMS respectively, while molar emission ratios relative to carbon dioxide (CO2) were [4.7 ± 0.4] × 10 6 and [1.4 ± 0.4] × 10 7, respectively. Assuming these observations are representative of biomass burning, we estimate that biomass burning could yield up to 175 Gg/yr of DMDS (119 Gg S/yr) and 13 Gg/yr of DMS

Unexplained enhancements of CH3Br in the Arctic and sub-Arctic lower troposphere during TOPSE spring 2000

Elevated concentrations of methyl bromide (CH3Br) were observed in the Arctic atmospheric boundary layer (BL) during periods of widespread BL ozone (O3) depletion episodes (ODEs: O3 mixing ratios < 20 × 10-9 or parts per billion by volume, ppbv) particularly during major ODEs (MODES: O3 < 4 ppbv). No other organic gases measured during TOPSE (Tropospheric Ozone Production about the Spring Equinox) exhibited anti-correlations with O3 during these ODEs. Methyl bromide has both natural and anthropogenic sources and contributes ∼ half of the bromine (Br) to the stratosphere, where it can catalytically destroy O3. Several known CH3Br sources are evaluated, but the current knowledge cannot explain the observed enhancements. If the mechanism is direct gasphase photochemical production, a significant portion of the unknown CH3Br source may be found