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Extensive undersaturations of carbon tetrachloride (CCl4) in Pacific, Atlantic, and Southern Ocean surface waters indicate that atmospheric CCl4 is consumed in large amounts by the ocean. Observations made on 16 research cruises between 1987 and 2010, ranging in latitude from 60° N to 77° S, show that negative saturations extend over most of the surface ocean. Corrected for physical effects associated with radiative heat flux, mixing, and air injection, these anomalies were commonly on the order of −5 to −10 %, with no clear relationship to temperature, productivity, or other gross surface water characteristics other than being more negative in association with upwelling. The atmospheric flux required to sustain these undersaturations is 12.4 (9.4–15.4) Gg yr−1, a loss rate implying a partial atmospheric lifetime with respect to the oceanic loss of 183 (147–241) yr and that ∼ 18 (14–22) % of atmospheric CCl4 is lost to the ocean. Although CCl4 hydrolyzes in seawater, published hydrolysis rates for this gas are too slow to support such large undersaturations, given our current understanding of air–sea gas exchange rates. The even larger undersaturations in intermediate depth waters associated with reduced oxygen levels, observed in this study and by other investigators, strongly suggest that CCl4 is ubiquitously consumed at mid-depth, presumably by microbiota. Although this subsurface sink creates a gradient that drives a downward flux of CCl4, the gradient alone is not sufficient to explain the observed surface undersaturations. Since known chemical losses are likewise insufficient to sustain the observed undersaturations, this suggests a possible biological sink for CCl4 in surface or near-surface waters of the ocean. The total atmospheric lifetime for CCl4, based on these results and the most recent studies of soil uptake and loss in the stratosphere is now 32 (26–43) yr.

Airborne molecular contamination (AMC) is a significant contributor to the loss of yield in semiconductor processes [1–4]. Impact of weak acids has only been considered for process technologies of 22 nm and below [5–8]. One such weak acid is nitrous acid (HNO 2 or HONO), which has no demonstrated direct impact on processes or equipment, but has nevertheless been a target for removal by AMC filtration. HNO 2 is commonly formed on all surfaces in all environments from NO 2 gas, one of the main oxides of nitrogen formed from combustion processes and ambient air photochemistry. This study investigated the behavior of the NO X /HNOx system around typical AMC filter adsorbents. We find that NO gas passes through AMC filters unchanged, whereas NO 2 is converted mostly to NO, but also to HNO 2 at the low ppb level, increasing AMC load downstream of filters. Various adsorbents can capture HNO 2 , but filter lifetimes are short due to the release of the volatile compound over time. The recommendation is to critically evaluate the impact of HNO 2 on processes and equipment and adjust AMC filtration needs accordingly.

[1] We present results that improve the estimates of the global net sea-to-air flux, global oceanic emission, global oceanic uptake, and partial atmospheric lifetime of methyl chloride (CH3Cl) with respect to oceanic loss. This study includes improved parameterizations for solubility and saturation anomaly-sea surface temperature relationships for CH3Cl, along with the use of an updated gas transfer velocity from a recent study. By measuring solubilities of CH3Cl in pure water and seawater over a temperature range from 0°C to 40°C, we obtained a new solubility function with both temperature and salinity dependencies. We also developed a new parameterization of seasonal CH3Cl saturation anomaly (∆%) as a function of both sea surface temperature and wind speed using data from 10 different cruises with an extensive coverage in the global surface ocean. Using the new solubility function and the new seasonal ∆%-(SST, wind speed) relationships, we estimated the global net sea-to-air flux of CH3Cl at 335 (210 to 480) Gg yr−1. For the first time, the global flux of CH3Cl was broken into a unidirectional gross emission and a unidirectional gross uptake, which were estimated at 700 (510 to 910) Gg yr−1 and −370 (−430 to −300) Gg yr−1. The partial atmospheric lifetime of CH3Cl with respect to the oceanic uptake was revised to 12 (10–15) years, resulting in a revision on the atmospheric lifetime of CH3Cl from the previous estimate of 1.0 year to 1.2 years.

Monitoring airborne molecular contamination (AMC) at the parts per trillion (ppt) level in cleanroom environments, scanner applications and compressed gas lines is essential for processes, equipment and yield-control. For the operation of EUV tools, in particular, volatile organic contamination is known to have as much impact as condensable organic compounds, which requires a suitable sampling and measurement methodology. Some of the current industry standards use sample traps comprised of porous 2,6-diphenylene-oxide polymer resin, such as Tenax®, for measuring volatile organic ( 6 C atoms, about toluene and higher) AMC. Inherent problems associated with these traps are a number of artifacts and chemical reactions that reduce accuracy of reported organic AMC concentrations. The break-down of the polymeric material forms false positive artifacts when used in the presence of reactive gases, such as nitrous acid and ozone, which attack and degrade the polymer to form detectable AMC. Most importantly, these traps have poor capture efficiency for volatile organic compounds (VOC). To address the disadvantages of polymer-based sample traps, we developed a method based on carbonaceous, multi-layered adsorbent traps to replace the 2,6-diphenylene-oxide polymer resin sample trap type. Along with the new trap’s ability to retain volatile organics, the trap was found to provide artifact-free results. With industry trends towards detecting more contaminants while continuously reducing required reporting limits for those compounds, artifact-free and accurate detection of AMC is needed at the parts per quadrillion (ppq) level. The proposed, multi-layered trap substantially increases laboratory productivity and reduces cost by eliminating the need to analyze condensable and volatile organic compounds in two separate methods. In our studies, even some organic compounds with six C-atoms, that are part of exposure tool OEM requirements, were not effectively retained by polymeric traps, but were fully retained on the multi-layered adsorbent trap. This demonstrates that the standard trap used in the industry will result in significantly underreporting actual AMC concentrations for volatile organic compounds, including some siloxanes (TMS, HMDSO, D3). Performance of the proposed trap was excellent at both zero and 50% relative humidity, an important metric, as the trap is used for AMC detection in dry supply gases and humidified environments. Retention of all organic compounds was quantitative for more than 30 liters of air, sufficient for ppq-level detection limits. Desorption efficiency was 94% for C26 compounds. Pressure drop through the new trap was comparable to that of polymer-based traps and much lower than other, commercially available carbonaceous traps. Precision of repeated analyses was 5%, a very good result. Resolution of IPA and acetone was complete and that of a mix of halogenated refrigerants was much improved over existing methods. We propose to adopt this methodology as a new industry standard to overcome widespread inaccuracy in the reporting of volatile organic AMC and false positive condensable AMC.

The measurement of parts-per-trillion (ppt) level acidic and basic airborne molecular contamination (AMC) is essential for process protection and yield control in semiconductor photo-lithography and adjacent applications. Real-time monitoring solutions are highly desired, as they provide instantaneous and continuous measurement. However, even the most advanced monitors cannot achieve detection limits in the low parts-per-trillion (ppt) range and many restrictions apply for the detection of acidic AMC. High cost of ownership is another disadvantage. Discontinuous sampling with sample traps is capable of achieving ppt-level measurement, but the currently accepted methods use sample traps filled with de-ionized water (impingers) to capture soluble acidic and basic AMC. Several inherent disadvantages of these methods result in inconsistent data and increased detection limits. Some proprietary solid state solutions have been reported, but involve complex preparation, have high background signals and require 24-72 hour sample duration, or they are protected trade secrets that are not available as an industry standard. To eliminate these disadvantages, we developed a liquid-free sample trap that allows parts-per-quadrillion level (ppq) measurement of acidic and basic AMC within one work shift, typically a 4-6 hour sample period. The traps can easily be manufactured and prepared in small lab operations, are sealed and protected from the outside and operator handling in the field, have months of shelf life and show high capture efficiencies while minimizing reactions and artifacts. Capacity results for the liquid-free base trap using ammonia (NH 3 ) as a test gas yielded more than 200 ppb-h at 100% capture efficiency without any moisture (simulating sampling of CDA or N 2 ) and 350 ppb-h at 40% RH. The capacity results for sulfur dioxide (SO 2 ) were highly dependent on moisture content of the sample gas and yielded 5 ppb-h at 90% capture efficiency and 0% RH, but increased exponentially to more than 1200 ppb-h at 40% RH. Performance testing indicates that the liquid-free trap provides both more precise and more accurate results for NH 3 , SO 2 and HF in comparison to standard impinger in lab testing, with a relative standard deviation not exceeding 8% and capture efficiency greater than 95% for all three compounds. Acetic acid was the only compound that shows slightly decreased performance but still maintained a precision and accuracy comparable to the other compounds tested. In-field validation deployment to external and internal customers in parallel with standard wet impingers resulted in less than 10% difference between the traps, providing the necessary evidence that liquid-free traps are suitable for replacement of and better than wet impingers.

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.

Measurements made during the Indian Ocean Experiment (INDOEX) have shown the presence of large aerosol loadings over the region of the northern Indian Ocean and Arabian Sea. In recent years there has been significant interannual variability in the magnitude of this aerosol loading during the NE monsoon months of January-April. Monitoring of the integrated atmospheric column effective aerosol optical properties was initiated in early 1998 and continued in 2000 on the island of Kaashidhoo in the Republic of Maldives. An Aerosol Robotic Network Sun-sky radiometer at the Kaashidhoo Climate Observatory made spectral measurements of the direct Sun and directional sky radiances which were utilized to infer spectral aerosol optical depths τa, single scattering albedos, asymmetry factors, and aerosol size distributions. Monthly average aerosol optical depths at 500 nm varied by more than a factor of 2 during January through April for the 3 years that were investigated, 1998–2000. Interannual variations in the monthly mean Angstrom wavelength exponent were also observed, resulting from differences in the bimodal aerosol size distributions. Spectral variations in the Angstrom wavelength exponent were observed, especially at high aerosol optical depths when fine mode aerosols dominated over the optical influence of coarse-mode aerosols. Some differences in spectral single scattering albedo and asymmetry factor were observed for 1999 versus 2000 in the infrared wavelengths, but with relatively little change in the visible wavelengths. The spectral variation in the retrieved single scattering albedo was large, with approximately linear wavelength dependence averaging from 0.91 at 440 nm to 0.83 at 1020 nm for January–March 1999 for observations where τa at 440 nm >0.4.

The physical, chemical and radiative properties of aerosols are investigated over the tropical Indian Ocean during the first field phase (FFP) of the international Indian Ocean Experiment. The FFP was conducted during February 20 to March 31, 1998. The results shown here are from the Kaashidhoo Climate Observatory (KCO), a new surface observatory established on the tiny island of Kaashidhoo (4.965°N, 73.466°E) in the Republic of Maldives. From simultaneous measurements of aerosol physical, chemical, and radiative properties and the vertical structure from lidar, we have developed an aerosol model which, in conjunction with a Monte Carlo radiative transfer model, successfully explains (within a few percent) the observed solar radiative fluxes at the surface and at the top of the atmosphere. This agreement demonstrates the fundamental importance of measuring aerosol physical and chemical properties for modeling radiative fluxes. KCO, during the northeast monsoon period considered here, is downwind of the Indian subcontinent and undergoes variations in the aerosol visible optical depth τν from ∼0.1 to 0.4, with a monthly mean of ∼0.2. Lidar data suggest that the aerosol is confined largely to the first 3 kms. Sulfate and ammonium contribute ∼29% to τν; sea-salt and nitrate contributes ∼17%; mineral dust contributes ∼15%; and the inferred soot, organics, and fly ash contribute 11%, 20%, and 8% respectively. We estimate that anthropogenic sources may contribute as much as 65% to the observed τν. We consider both an externally and an internally mixed aerosol model with very little difference between the two in the computed radiative forcing. The observed scattering coefficients are in the upper range of those reported for other oceanic regions, the single-scattering albedos are as low as 0.9, and the Angstrom wavelength exponents of ∼1.2 indicate the abundance of submicron aerosols. In summary, the data and the model confirm the large impact of anthropogenic sources. The surface global fluxes (for overhead Sun) decrease by as much as 50 to 80 W m−2 owing to the presence of the aerosols, and the top of the atmosphere fluxes increase by as much as 15 W m−2, thus indicating that anthropogenic aerosols are having a large impact on the tropical Indian Ocean.

Emissions of reactive chlorine-containing compounds from nine discrete classes of biomass burning were estimated on a 1° latitude by 1° longitude grid based on a biomass burning inventory for carbon emissions. Variations on approaches incorporating both emission ratios relative to CO and CO2 and the chlorine content of biomass burning fuels were used to estimate fluxes and associated uncertainties. Estimated, global emissions are 640 Gg Cl yr -1 for CH3Cl; 49 Gg Cl yr -1 for CH2Cl2; 1.8 Gg Cl yr -1 for CHCl3; 13 Gg Cl yr -1 for CH3CCl3; and 6350 Gg Cl yr -1 for the sum of volatile- inorganic and particulate chlorine. Biomass burning appears to be the single largest source of atmospheric CH3Cl and a significant source of CH2Cl2; contributions of CHCl3 and CH3CCl3 are less than 2% of known sources.

Emission inventories for major reactive tropospheric CI species (particulate CI, HC1, C1NO2, CH3CI, CHCI3, CH3CCI3, C2C14, C2HC13, CH2C12, and CHCIF2) were integrated across source types (terrestrial biogenic and oceanic emissions, sea-salt production and dechlorination, biomass burning, industrial emissions, fossil-fuel combustion, and incinera- tion). Composite emissions were compared with known sinks to assess budget closure; relative contributions of natural and anthropogenic sources were differentiated. Model cal- culations suggest that conventional acid-displacement reactions involving Sov)+O3, S(Iv)+ H202, and H2SO4 and HNO3 scavenging account for minor fractions of sea-salt dechlorina- tion globally. Other important chemical pathways involving sea-salt aerosol apparently pro- duce most volatile chlorine in the troposphere. The combined emissions of CH3CI from known sources account for about half of the modeled sink, suggesting fluxes from known sources were unde:estimated, the OH sink was overestimated, or significant unidentified sources exist. Anthropogenic activities (primarily biomass burning) contribute about half the net CH3CI emitted from known sources. Anthropogenic emissions account for only about 10% of the modeled CHCl3 sink. Although poorly constrained, significant fractions of tropo- spheric CH2C12 (25%), C2HC13 (10%), and C2C14 (5%) are emitted from the surface ocean; the combined contributions of C2C14 and C2HC13 from all natural sources may be substan- tially higher than the estimated oceanic flux.

Although there are many chlorine-containing trace gases in the atmosphere, only those with atmospheric lifetimes of 2 years or fewer appear to have significant natural sources. The most abundant of these gases are methyl chloride, chloroform, dichloromethane, perchloroethylene, and trichloroethylene. Methyl chloride represents about 540 parts per trillion by volume (pptv) Cl, while the others together amount to about 120 pptv Cl. For methyl chloride and chloroform, both oceanic and land-based natural emissions have been identified. For the other gases, there is evidence of oceanic emissions, but the roles of the soils and land are not known and have not been studied. The global annual emission rates from the oceans are estimated to be 460 Gg Cl/yr for CH3Cl, 320 Gg Cl/yr for CHCl3, 160 Gg Cl/yr for CH2Cl2, and about 20 Gg Cl/yr for each of C2HCl3, and C2Cl4. Land-based emissions are estimated to be 100 Gg Cl/yr for CH3Cl and 200 Gg Cl/yr for CHCl3. These results suggest that the oceans account for about 12% of the global annual emissions of methyl chloride, although until now oceans were thought to be the major source. For chloroform, natural emissions from the oceans and lands appear to be the major sources. For further research, the complete database compiled for this work is available from the archive, which includes a monthly emissions inventory on a 1° × 1° latitude-longitude grid for oceanic emissions of methyl chloride.

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.

Sulfur hexafluoride (SF6), an anthropogentically produced compound that is a potent greenhouse gas, has been measured in a number of NOAA GMDL air sampling programs. These include high resolution latitudinal profiles over the Atlantic and Pacific oceans, weekly flask samples from seven remote, globally distributed sites, hourly in situ measurements in rural North Carolina, and a series of archived air samples from Niwot Ridge, Colorado. The observed increase in atmospheric mixing ratio is consistent with an overall quadratic growth rate, at 6.9±0.2% yr−1 (0.24±0.01 ppt yr−1) for early 1996. From these data we derive an early 1996 emission rate of 5.9±0.2 Gg SF6 yr−1 and an interhemispheric exchange time of 1.3±0.1 years.

A new instrument, the Airborne Chromatograph for Atmospheric Trace Species IV (ACATS-IV), for measuring long-lived species in the upper troposphere and lower stratosphere is described. Using an advanced approach to gas chromatography and electron capture detection, the instrument can detect low levels of CFC-11 (CCl 3 F), CFC-12 (CCl 2 F 2 ), CFC-113 (CCl 2 F-CClF 2 ), methyl chloroform (CH 3 CCl 3 ), carbon tetrachloride (CCl 4 ), nitrous oxide N 2 O), sulfur hexafluoride (SF 6 ), Halon-1211 (CBrClF 2 ), hydrogen (H 2 ), and methane (CH 4 ) acquired in ambient samples every 180 or 360 s. The instrument operates fully-automated onboard the NASA ER-2 high-altitude aircraft on flights lasting up to 8 hours or more in duration. Recent measurements include 24 successful flights covering a broad latitude range (70°S-61°N) during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/ MAESA) campaign in 1994.

Ozone has been observed in elevated concentrations by satellites over areas previously believed to be ‘background’. There is meteorological evidence, that these ozone ‘plumes’ found over the Atlantic Ocean originate from vegetation fires on the African continent.

Gaseous nitrogen compounds (NO x , NO y , NH3, N2O) were measured at ground level in smoke plumes of prescribed savanna fires in Lamto, in the southern Ivory Coast, during the FOS/DECAFE experiment in January 1991. During the flaming phase, the linear regression between δ[NO x ] and δ[CO2] (differences in concentration between smoke plumes and atmosheric background) results volumic emission ratio δ[NO x ]/δ[CO2]=1.37×10−3 with only slight differences between heading and backing fires. Nearly 90% of the nitrogen oxides are emitted as NO. Average emission ratios of other compounds are: 1.91, 0.047, and 0.145×10−3 for NO y , NH3 and N2O, respectively. The emission ratios obtained during this field experiment are compred with corresponding values measured during former experiments with the same plant species in combustion chambers. An accurate determination of both the biomass actually burned and of the plant nitrogen content, allows an assessment of emission fluxes of N-compounds from Guinean savanna burns. Preliminary results dealing with the influence of fire on biogenic emissions from soils are also reported.

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 . DOI: 10.1034/j.1600-0889.1998.00004.x

1. ABSTRACT Trimethylsilanol (TMS) is a low molecular weight / low boilin g point silicon-containing, airborne contaminant that has received increased interest over the past few years as an important cause for contamination of optical surfaces in lithography equipment. TMS is not captured well by carbon-based filters, and hexame thyldisiloxane (HMDSO), even though captured well, can be converted to TMS when using acidic filter media comm only used for ammonia remova l. TMS and HMDSO co-exist in a chemical equilibrium, which is affected by the acidity and moisture of their environment. This publication shows that HMDSO is converted to TMS by acidic media at concentrations typically found in cleanroom environments. This is contrary to published results that show a re-combination of TMS to HMDSO on acid media. We also demonstrate that, based on its conversion to TMS, HMDSO is not a suitable test compound for hybrid chemical filter performance, as the apparent lifetime/capacity of the filter can be substantially skewed towards larger numbers when conversion to TMS is involved. We show lifetime test results with toluene and HMDSO on acidic and non-acidic filter media. Appropriately designed, asymmetric hybrid chemical filters significantly minimize or eliminate the conversion of HMDSO to TMS, thereby reducing the risk to scanner optical el ements. Similarly, such filters can also prevent or reduce acid-sensitive reactions of other AMC wh en passing through filter systems. Keywords: TMS, HMDSO, AMC, chemical filter, filter performance, silicon, silo xanes, photolithography, optics hazing. 2. INTRODUCTION Silicon containing hydrocarbons are a clas s of airborne molecular contamination (AMC) causing persistent degradation of UV exposure tool optical surfaces

A new analytical method for semiconductor-specific applications is presented for the accurate measurement of low molecular weight, silicon-containing, organic compounds TMS, HMDSO and D3. Low molecular weight / low boiling point silicon-containing compounds are not captured for extended periods of time by traditional chemical filters but have the same potential to degrade exposure tool optical surfaces as their high molecular weight counterparts. Likewise, we show that capturing these compounds on sample traps that are commonly used for organic AMC analysis does not work for various reasons. Using the analytical method described here, TMS, HMDSO and D3 can be measured artifact-free, with at least a 50:1 peak-to-noise ratio at the method detection limit, determined through the Hubaux-Vos method and satisfying a conservative 99% statistical confidence. Method detection limits for the compounds are 1-6 ppt in air. We present calibration curve, capacity, capture efficiency, break-through and repeatability data to demonstrate robustness of method. Seventy-one real-world samples from 26 projects taken in several fab environments show that TMS is found in concentrations 100 times higher than those of HMDSO and D3. All compounds are found in all environments in concentrations ranging from zero to 12 ppm, but most concentrations were below 50 ppb. All compounds are noticeably higher in litho-bays than in sub-fabs and we found all three compounds inside of two exposure tools, suggesting cleanroom and/or tool-internal contamination sources.

Fifteen experiments were conducted in an open burning system to determine the amounts of N{sub 2}O produced from burning savanna grass (Venezuelan Trachypogon, Australian Sorghum intrans), straw, hay, oak, pine needles and litter of pine forest. Samples in stainless steel canisters were analyzed within one day after sampling in order to avoid artifact N{sub 2}O formation during storage. Emissions of N{sub 2}O were observed to be nearly coincident with the emissions of CO{sub 2} during the burning period for all the experiments. The amount of N{sub 2}O produced was dependent on the nitrogen content of the biomass. About 0.7% of the fuel nitrogen was oxidized to N{sub 2}O and most of the N{sub 2}O was formed during the flaming stage. Using the experimental data and the amounts of different types of vegetation burned globally per year, the authors estimate that about 2.7 {times} 10{sup 11} g of N{sub 2}O-N are produced per year from burning biomass, contributing only 2% to the global source of N{sub 2}O.

[1] 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 ,C H2Br2, 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.

Received 2 June 2005; revised 31 October 2005; accepted 23 November 2005; published 22 February 2006. [1] 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 ,N H3, 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 ,N H3, 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 SO4� 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.

During the Mediterranean Intensive Oxidant Study MINOS in August 2001, 87 air samples were collected at the ground-based station Finokalia (35°19'N, 25°40'E) on the north coast of Crete and subsequently analysed by GC-MS. The analysis includes various hydrocarbons, organo-halogens, HCFCs and CFCs. These compounds have a wide variety of sources and sinks and a large range of atmospheric lifetimes. We evaluated the characteristics of the sampling site in terms of proximity to individual sources by plotting the measured variability of these species against lifetime. The resulting linear relationship suggests that the sampling site is representative of intermediate conditions between a remote site and one that is in the vicinity of a wide variety of sources. Our analysis of air mass origin and chemical ratios also shows that several distinct anthropogenic sources influenced the atmospheric composition over Crete. Propane observations are compared to a global model to assess the fossil fuel related emission inventory. Although the model reproduces the general pattern of the propane variations, the model mixing ratios are systematically too low by a factor of 1.5 to 3, probably due to an underestimation of the propane emissions from east European countries in the underlying global database EDGAR. Another important finding was that methyl chloroform, a compound banned under the Montreal protocol, showed significant enhancements from background, which were well correlated with CFC-113. This suggests continued use and emission of methyl chloroform by one or more European countries. We also discuss the observed variations of methyl bromide and suggest that the significant peak observed on 12 August 2001 reflects heavy agricultural use as a soil fumigant in Italy.

[1] 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.

THE burning of biomass (forest vegetation, savannah grass, firewood and agricultural wastes) due to human activities in the tropics is an important source of nitrogen compounds in the atmosphere1–4. A recent experimental study5 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 ∼10–50 Tg N yr−1 or 5–50% of global nitrogen fixation, may be particularly important for tropical ecosystems.

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 NOX, 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 1012g of biomass nitrogen ('pyrodenitrification'), equal to ∼9–20% of the estimated global rate of terrestrial nitrogen fixation.

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.

Dry mole fractions of methyl bromide (CH3Br) in marine boundary layer air and in air equilibrated with surface water were measured in the Southern Ocean. Saturation anomalies were consistently negative at −36±7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH3Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at −21 (−11 to −32) Gg y−1.

biomass burning are also included in the model. The model captures 40% of the variance in the observed seawater CH3I(aq) concentrations. Simulated concentrations at midlatitudes in summer are too high, perhaps because of a missing biological sink of CH3I(aq). We define a marine convection index (MCI) as the ratio of upper tropospheric (8–12 km) to lower tropospheric (0–2.5 km) CH3I concentrations averaged over coherent oceanic regions. The MCI in the observations ranges from 0.11 over strongly subsiding regions (southeastern subtropical Pacific) to 0.40 over strongly upwelling regions (western equatorial Pacific). The model reproduces the observed MCI with no significant global bias (offset of only +11%) but accounts for only 15% of its spatial and seasonal variance. The MCI can be used to test marine convection in global models, complementing the use of radon-222 as a test of continental convection. INDEX TERMS: 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: methyl iodide, marine convection, atmospheric tracer, global budget of methyl iodide

Fluxes of CO 2 , CH 4 , and N 2 O from forest soils were measured with an enclosed chamber technique between October 1990 and December 1991 in a deciduous forest near Darmstadt, Germany. Flux measurements were made before and after the removal of leaves and humus layer from the forest floor, and gas fluxes from the leaves and humus alone were also measured as well as depth profiles of CH 4 , N 2 O, and soil moisture. Except for N 2 O, large seasonal variations were observed with generally higher gas fluxes during the summer. CO 2 and CH 4 fluxes were significantly dependent on changes in ambient temperature, whereas N 2 O fluxes were more affected by soil moisture. A good correlation between CO 2 production and CH 4 uptake was observed, but no relationship was found between N 2 O emissions and either CO 2 or CH 4 fluxes. Depth profiles of the CH 4 mixing ratio in soil air consistently showed an exponential decrease with depth, whereas N 2 O profiles were highly variable and appeared to be related to changes in soil moisture. The manipulated soil experiments indicate that the leaves and the humus layers contribute significantly to the soil-atmosphere exchange of trace gases. DOI: 10.1034/j.1600-0889.1998.t01-2-00003.x