摘要:

We use a simple box model to evaluate the impact of temporal changes of the atmosphere's14C/C on ventilation fluxes for the deep Atlantic calculated from radiocarbon measurements. The conclusion is that despite the fact that over the 300 year period from 1650 to 1950 the atmosphere's radiocarbon content declined at the same rate as radiocarbon decays, this temporal change has a relatively small impact (10–15%) on radiocarbon‐based estimates of the ventilation rate of the deep Atlantic. The reason is that the radiocarbon content of the source waters for deep Atlantic are reasonably well buffered against changes in atmospheric14

ISSN:0094-8276    

DOI:10.1029/90GL02707

年代:1991

数据来源: WILEY

摘要:

Rate constants have been measured for the gas phase reactions of the hydroxyl radical (OH) with the hydrochlorofluorocarbons CF3CF2CHCl2(HCFC‐225ca) over the temperature range 270 to 400 K and CF2ClCF2CHClF (HCFC‐225cb) over the temperature range 298 to 400 K. The Arrhenius expressions k(225ca) = (1.92 ± 0.52) × 10−12exp(−1290 ± 90/T) cm3molecule−1s−1and k(225cb) = (6.75 ± 3.70) × 10−13exp(−1300 ± 180/T) cm3molecule−1s−1were deri

ISSN:0094-8276    

DOI:10.1029/90GL02647

年代:1991

数据来源: WILEY

摘要:

The formation of H2O2and organic peroxides in the reaction of O3with trans‐2‐butene and naturally occurring alkenes has been studied using a 31 m3reaction chamber. H2O2and organic peroxides were found to be products of the O3reaction with trans‐2‐butene, isoprene, α and ß‐pinene, and limonene. Water is necessary for the formation of H2O2and most of the H2O2is formed via a route that does not involve HO2radicals. Our results indicate that the reaction of O3with natural alkenes may be a significant source of atmospheric H2O2, particularly in forest and

ISSN:0094-8276    

DOI:10.1029/90GL02602

年代:1991

数据来源: WILEY

摘要:

We propose a novel mechanism for isotopic exchange between CO2and O3via O(1D) + CO2→ CO3*followed by CO3*→ CO2+ O(3P). A one‐dimensional model calculation shows that this mechanism can account for the enrichment in18O in the stratospheric CO2observed by Gamoet al.[1989], using the heavy O3profile observed by Mauersberger [1981]. The implications of this mechanism for other stratospheric species and as a source of isotopically heavy CO2in the troposphere are briefly disc

ISSN:0094-8276    

DOI:10.1029/90GL02478

年代:1991

数据来源: WILEY

摘要:

Gaseous N2O5/air mixtures were flowed over solid NaCl at 298 K and the gaseous product ClNO2measured using FTIR. With excess NaCl, one ClNO2was produced per N2O5in the initial mixture, and from the contact time between N2O5and the salt, a lower limit to the fraction of collisions leading to reaction was estimated to be 2.5 × 10−3. This reaction is sufficiently rapid that it may lead to the formation of ppb levels of ClNO2overnight in polluted marine urban areas. The ClNO2will photolyze at dawn to give chlorine atoms which initiate the photooxidation of organics in a manner analogous to OH. This reaction may also play a role in remote Arctic chemistry if the reaction is significantly faster than our lower limit. This supports the hypothesis of Michelangeli et al. (1990) that the N2O5(g)+ NaCl(s)reaction may contribute significantly to stratospheric chemistry after the eruption of alkalic volcanoes such as El Chich

ISSN:0094-8276    

DOI:10.1029/90GL02595

年代:1991

数据来源: WILEY

摘要:

In situ measurements of ClO in the winter lower stratosphere are presented for six flights of the NASA ER‐2 aircraft from 38°N to 61°N. Enhanced abundances, increasing in severity with date, were observed below 20 km, where HCl and ClONO2dominate the inorganic chlorine budget. The greatest mixing ratios, over 150 pptv, were encountered on February 20 and 21, 1989, as the vortex experienced a major warming. Although the timing of these ClO enhancements and the evidence that vortex air can reach midlatitudes suggest that heterogeneous conversion of chlorine compounds within the vortex influences chemistry at midlatitudes, the enhancements observed early in the winter could have been caused by unknown chemistry occurring outside the vortex. In either case, photochemical loss of ozone due to catalytic reactions involving ClO at these mixing ratios may be responsible in part for the ozone decreases observed at high latitudes in the northern hemisph

ISSN:0094-8276    

DOI:10.1029/90GL02673

年代:1991

数据来源: WILEY

摘要:

Three dimensional model calculations with the NASA/GSFC chemistry and transport model have been designed to consider the impact of heterogeneous processes occurring on polar stratospheric clouds (PSC's) in the Arctic vortex on the HCl distribution. By examining the HCl concentration for a calculation with PSC's relative to a calculation with gas phase chemistry only, we infer the impact of polar processing on reactive chlorine species at middle latitudes. Results from the chemistry and transport model reproduce basic features of the ClO measurements [Toohey et al., 1991], which were made on the ferry flights of the ER‐2 from Stavanger, Norway to Moffett Field, California via Wallops Island, Virginia on February 20 and 21, 1989. The model indicates that perturbed air which is contained within the polar vortex during winter is not homogeneously mixed, and that the ferry flights were made through air with the largest conversion of HCl to reactive chlorine that is seen at middle latitude

ISSN:0094-8276    

DOI:10.1029/90GL02601

年代:1991

数据来源: WILEY

摘要:

Simulations of the spatial and temporal variability of the extent of chemically processed air in the Arctic stratosphere have been carried out using a three‐dimensional chemistry‐transport model for the winters of 1979 and 1989, Chemically processed air is identified in the model as that in which the amounts of hydrogen chloride (HCl) calculated with parameterized loss for conditions appropriate to polar stratospheric cloud (PSC) formation are substantially smaller than those calculated in a model with gas phase chemistry only. It is seen that chemically processed air may be identified over much of the Arctic lower stratosphere from early January to late February, with HCl depletions being larger in 1989 than in 1979. Near the latitude of the Arctic circle, there is important spatial and temporal variability in the extent of chemically processed air. There is some evidence for transport to mid‐latitudes of processed air during these winters, but the HCl reductions are much smaller and more sporadic than those near the pole. At 62 and 42N, processed air is calculated to occur preferentially over the longitude regions from 60‐120E and 2

ISSN:0094-8276    

DOI:10.1029/90GL02597

年代:1991

数据来源: WILEY

摘要:

Total ozone fields over Northern Europe and Arctic regions were calculated during the winter 1989 using the TOVS/HIRS2 infra‐red radiances. During that same period ground‐based and airborne ozone and PSCs measurements were performed as part of the AASE and TECHNOPS campaigns. Comparisons have also been made with the TOMS ozone data. They show a generally good agreement, except above northernmost regions where TOMS observations seem affected by the high solar zenith angles encountered near the polar night region. This result is confirmed by the ozone measurements made from Kiruna on the 23 and 30 of January. A major type II PSC event is clearly identified in the TOVS ozone field on January 31. The cloud location is consistent with airborne lidar soundings made on the same day from DC‐8 aircraft, which measured scattering and depolarization ratios characteristic of high concentration of large ice crystals. TOVS observations show that type II PSCs covering large areas may form above the Arctic regions. However, only two major water‐ice PSCs events have been identified from January 3 to February 10. These events may not be frequent enough for the polar air to reach a completely processed state, with high ClO amounts and significant denitrification as it is observed in the Antarctic early

ISSN:0094-8276    

DOI:10.1029/90GL02600

年代:1991

数据来源: WILEY

摘要:

We calculate the rate of heating that occurs in the middle atmosphere (50 – 105 km) due to four exothermic reactions involving members of the odd‐hydrogen family. These reactions are O + OH → O2+ H, H + O2+ M → HO2+ M, H + O3→ OH + O2, and O + HO2→ OH + O2. The energy lost from vibrationally excited OH (produced in the third reaction) by spontaneous emission is explicitly accounted for by using detailed kinetic models, so that only a portion of the exothermicity of this reaction is converted into heat. The heating rates due to these four reactions are found to rival the oxygen‐related heating rates conventionally considered in models of the middle atmosphere, e.g., those due to O + O + M → O2+ M, O + O2+ M → O3+ M, O2+ hv → O + O, and O3+ hv → O + O2The conversion of chemical potential energy into molecular translational energy (heat) by these odd‐hydrogen reactions is a significant source of energy in the middle atmosphere which has not bee

ISSN:0094-8276    

DOI:10.1029/90GL02672

年代:1991

数据来源: WILEY