R C E I - Publications and Data

Abstract: 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 tri-chloro-ethy-lene. 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° x 1° latitude-longitude grid for oceanic emissions of methyl chloride.

Associated data file (oceanic data only) CH3Cl.90.yr.1.1a.oceanic.htm (736 kb)

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Abstract: As part of the Global Emission Inventory Assessment Reactive Chlorine Emissions Inventory, a global model of chemical processes in the marine boundary layer, (MBL), Marine Aerosol and Gas Phase Interactions (MAGPI), was developed to calculate direct monthly production of HCl and ClNO₂ from sea salt dechlorination on a 2.8° 2.8° latitude-longitude grid. Sea salt mass and size distributions and associated surface exchange fluxes were calculated using the Canadian General Circulation Model; integrated annual production of sea salt Cl^- was 1785 Tg Cl yr^-1. Corresponding distributions of gas-phase HNO₃, SO₂, N₂O₅, H₂O₂, O₃, H₂SO₄ and NH₃ were calculated using different global chemical transport models in which sea salt reactions were not considered. A chemical scheme was developed to estimate the monthly mean steady-state phase partitioning of product and reactant species at each grid point. Average annual gridded fluxes of HCl and ClNO₂ varied spatially from 1 to 300 mg Cl m^-2 yr^-1 and from 1 to 8 mg Cl m^-2 yr^-1, respectively. Maxima occurred in polluted coastal regions of the North Atlantic, the western North Pacific and the Mediterranean where up to 20% of the total Cl and 80% of the sub-micron Cl volatilized. In remote oceanic regions, available acidity was insufficient to titrate all sea salt alkalinity, thus, significant HCl was not produced via acid displacement. However, in these regions virtually all HNO₃ was scavenged by sea salt. The integrated annual global fluxes for HCl and ClNO₂ were 7.6 Tg Cl yr^-1 and 0.06 Tg Cl yr^-1, respectively; virtually all in the Northern Hemisphere. Largest HCl and ClNO₂ fluxes occur in northern hemisphere winter due to high sea salt loading and elevated HNO₃, SO₂ and N₂O₅ concentrations. 70% of the HCl dechlorination occurs on particles between 0.75 µm and 4 µm radius; ClNO₂ volatilized from slightly larger particles. The aerosol pH of each particle size bin equilibrates towards the same value once the alkalinity has been titrated.

Associated data file ClNO2.90.yr.1.1a.seasalt.htm (642 kb)
Associated data file HCl.90.yr.1.1a.seasalt.htm (635 kb)

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Abstract: 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.

Associated data file CH3Cl.90.yr.1.1a.bioburn.htm (236 kb)
Associated data file Cl.90.yr.1.1a.bioburn.htm (236 kb)
Associated data file CHCl3.90.yr.1.1b.bioburn.htm (236 kb)
Associated data file CH2Cl2.90.yr.1.1a.bioburn.htm (236 kb)
Associated data file CH3CCl3.90.yr.1.1b.bioburn.htm (236 kb)

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Abstract: Much if not all of the chlorine present in fossil fuels is released into the atmosphere as hydrogen chloride (HCl) and chloromethane (CH₃Cl, methyl chloride). The chlorine content of oil-based fuels is so low that these sources can be neglected, but coal combustion provides significant releases. On the basis of national statistics for the quantity and quality of coal burned during 1990 in power and heat generation, industrial conversion and residential and commercial heating, coupled with information on the chlorine contents of coals, a global inventory of national HCl emissions from this source has been constructed. This was combined with an estimate of the national emissions of HCl from waste combustion (both large-scale incineration and trash burning) which was based on an estimate of the global quantity released from this source expressed per head of population. Account was taken of reduced emissions where flue gases were processed, for example to remove sulphur dioxide. The HCl emitted in 1990, comprising 4.6 ± 4.3 Tg Cl from fossil fuel and 2.0 ± 1.9 Tg Cl from waste burning, was spatially distributed using available information on point sources such as power generation utilities and population density by default. Also associated with these combustion sources are chloromethane emissions, calculated to be 0.075 ± 0.07 Tg as Cl (equivalent) from fossil fuels and 0.032 ± 0.023 Tg Cl (equivalent) from waste combustion. These were distributed spatially exactly as the HCl emissions, and a further 0.007 Tg Cl in chloromethane from industrial process activity was distributed by point sources.

Associated data file HCl.90.yr.1.1a.anthro.htm (190 kb)
Associated data file CH3Cl.90.yr.1.1a.anthro.htm (190 kb)

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Abstract: The identified emissions of the title compounds come predominantly from their use in industrial and commercial processes. Trichloroethene and tetrachloroethene have also been found as byproducts of gasoline and coal combustion; these sources were also considered but shown to be insignificant compared with industrial releases. Global emissions during 1990, amounting to 0.241±0.013 Tg of trichloroethene, 0.366±0.020 Tg of tetrachloroethene, and 0.583±0.032 Tg of dichloromethane (0.195±0.010, 0.313±0.017, and 0.487±0.027 Tg as chlorine, respectively) have been assigned to individual countries and thence to a 1° latitude x 1° longitude grid based on a combination of three data sets: regional sales data that were available on a continental scale; economic activity in the form of national Gross Domestic Products; and the population distribution within each country. For those countries where they were available, data for the quantities and locations of reported emissions were also incorporated. Uncertainty in the distributed emissions is ±4% relative to countries with the largest emissions. The results, which are complementary to the marine fluxes and releases from biomass burning reported by Khalil et al. [1999] and Lobert et al. [1999], respectively, are recorded here as maps and are also available from the Global Emissions Inventory Activity web site at http://www.geiacenter.org/rcei . While the industrial regions of North America, Europe, and Japan are the largest sites of anthropogenic emissions, there are also significant sources in the developing nations of Asia; in contrast, anthropogenic emissions within the southern hemisphere are much smaller and more widely dispersed. The total emissions of dichloromethane appear to match the observed atmospheric concentrations, but about 25% of the flux of tetrachloroethene calculated from observations remains unaccounted, and significant extra emissions of trichloroethene are necessary to effect a balance. The known sources have been examined thoroughly in this work, and so it is reasonably certain that the additional emissions are not a deliberate result of human activity; however, there is no means of discriminating their origin unequivocally, and the missing quantities may be inadvertent byproducts of anthropogenic activities.

Associated data file Trik.90.yr.1.1a.anthro.htm (201 kb)
Associated data file Perc.90.yr.1.1a.anthro.htm (201 kb)
Associated data file CH2Cl2.90.yr.1.1a.anthro.htm (201 kb)

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Abstract: Emission inventories for major reactive tropospheric Cl species (particulate Cl, HCl, ClNO₂, CH₃Cl, CHCl₃, CH₃CCl₃, C₂Cl₄, C₂HCl₃, CH₂Cl₂, and CHClF₂) were integrated across source types (terrestrial biogenic and oceanic emissions, sea-salt production and dechlorination, biomass burning, industrial emissions, fossilfuel combustion, and incineration). Composite emissions were compared with known sinks to assess budget closure; relative contributions of natural and anthropogenic sources were differentiated. Model calculations suggest that conventional acid displacement reactions involving S_(IV)+O₃, S_(IV)+ H₂O₂, and H₂SO₄ and HNO₃ scavenging account for minor fractions of seasalt dechlorination globally. Other important chemical pathways involving sea-salt aerosol apparently produce most volatile chlorine in the troposphere. The combined emissions of CH₃Cl from known sources account for about half of the modeled sink, suggesting fluxes from known sources were underestimated, the OH sink was overestimated, or significant unidentified sources exist. Anthropogenic activities (primarily biomass burning) contribute about half the net CH₃Cl emitted from known sources. Anthropogenic emissions account for only about 10% of the modeled CHCl₃ sink. Although poorly constrained, significant fractions of tropospheric CH₂Cl₂ (25%), C₂HCl₃ (10%), and C₂Cl₄ (5%) are emitted from the sur-face ocean; the combined contributions of C₂Cl₄ and C₂HCl₃ from all natural sources may be substan-tially higher than the estimated oceanic flux.

Associated data file CH3Cl.90.yr.1.1a.composite.htm (975 kb)
Associated data file Cl.90.yr.1.1a.composite.htm (887 kb)
Associated data file CH3CCl3.90.yr.1.1a.composite.htm (383 kb)

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