A Study of Stratospheric Chlorine Partitioning in the Winter Polar Vortices Based on New Satellite Measurements and Modeling (original) (raw)
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A study of stratospheric chlorine partitioning based on new satellite measurements and modeling
Journal of Geophysical Research, 2008
1] Two recent satellite instruments, the Microwave Limb Sounder (MLS) on Aura and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on SCISAT-1, provide an unparalleled opportunity to investigate stratospheric chlorine partitioning. We use measurements of ClO, HCl, ClONO 2 , and other species from MLS and ACE-FTS to study the evolution of reactive and reservoir chlorine throughout the lower stratosphere during two Arctic and two Antarctic winters characterizing both relatively cold and relatively warm and disturbed conditions in each hemisphere. At middle latitudes, and at high latitudes at the beginning of winter, HCl greatly exceeds ClONO 2 , representing $0.7-0.8 of estimated total inorganic chlorine. Nearly complete chlorine activation is seen inside the winter polar vortices. In the Arctic, chlorine recovery follows different paths in the two winters: In 2004/2005, deactivation initially takes place through reformation of ClONO 2 , then both reservoirs are produced concurrently but ClONO 2 continues to significantly exceed HCl, and finally slow repartitioning between ClONO 2 and HCl occurs; in 2005/2006, HCl and ClONO 2 rise at comparable rates in some regions. In the Antarctic, chlorine deactivation proceeds in a similar manner in both winters, with a rapid rise in HCl accompanying the decrease in ClO. The measurements are compared to customized runs of the SLIMCAT three-dimensional chemical transport model. Measured and modeled values typically agree well outside the winter polar regions. In contrast, partly because of the equilibrium scheme used to parameterize polar stratospheric clouds, the model overestimates the magnitude, spatial extent, and duration of chlorine activation inside the polar vortices. Citation: Santee, M. L., I. (2008), A study of stratospheric chlorine partitioning based on new satellite measurements and modeling,
Journal of Geophysical Research, 2001
We examine inorganic chlorine (Cly) partitioning in the summer lower strait)sphere using in situ ER-2 aircraft observations made during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) campaign. New steady state and numerical models estimate [C1ONO2]/[HC1] using currently accepted photochemistry. These models are tightly constrained by observations with OH (parameterized as a function of solar zenith angle) substituting for modeled HO2 chemistry. We find that inorganic chlorine photochemistry alone overestimates observed [C1ONO2]/[HC1] by approximately 55-60% at mid and high latitudes. On the basis of POLARIS studies of the inorganic chlorine budget, [C10]/[C1ONO2], and an intercomparison with balloon observations, the most direct explanation for the model-measurement discrepancy in Cly partitioning is an error in the reactions, rate constants, and measured species concentrations linking HC1 and C10 (simulated [C10]/[HC1] too high) in combination with a possible systematic error in the ER-2 C1ONO2 measurement (too low). The high precision of our simulation (+15% 1(5 for [C1ONO2]/[HC1], which is compared with observations) increases confidence in the observations, photolysis calculations, and laboratory rate constants. These results, along with other findings, should lead to improvements in both the accuracy and precision of stratospheric photochemical'models.
Atmospheric Chemistry and Physics, 2006
From January to March 2005, the Atmospheric Chemistry Experiment high resolution Fourier transform spectrometer (ACE-FTS) on SCISAT-1 measured many of the changes occurring in the Arctic (50-80 • N) lower stratosphere under very cold winter conditions. Here we focus on the partitioning between the inorganic chlorine reservoirs HCl and ClONO 2 and their activation into ClO. The simultaneous measurement of these species by the ACE-FTS provides the data needed to follow chlorine activation during the Arctic winter and the recovery of the Cl-reservoir species ClONO 2 and HCl. The time evolution of HCl, ClONO 2 and ClO as well as the partitioning between the two reservoir molecules agrees well with previous observations and with our current understanding of chlorine activation during Arctic winter. The results of a chemical box model are also compared with the ACE-FTS measurements and are generally consistent with the measurements.
The budget and partitioning of stratospheric chlorine during the 1997 Arctic summer
Journal of Geophysical Research, 1999
Volume mixing ratio profiles of HCl, HOC1, ClN03, CH3C1, CFC-12, CFC-11, CC14, HCFC-22, and CFC-113 were measured simultaneously from 9 to 38 km by the Jet Propulsion Laboratory MkIV Fourier Transform Infrared solar absorption spectrometer during two balloon flights from Fairbanks, Alaska (64.8"N) on 8 May and 8 July 1997, The altitude variation of total organic chlorine (CCl,), total inorganic chlorine (Cl,), and the nearly constant value (3.7h0.2 ppbv) of their sum (ClTOT) demonstrates that the stratospheric chlorine species available to react with O3 are supplied by the decomposition of organic chlorinated compounds whose abundances are well quantified. Measured profiles of HC1 and ClN03 agree well with photochemical model values (differences < 10% for altitudes below 34 km), particularly when production of HC1 by ClO+OH is included in the model. Our results demonstrate that the production of HC1 by C10 + OH plays a small role (< 5%) in the partitioning of HC1 and ClN03 for the sampled air masses for altitudes below-28 km because the concentration of C10 is suppressed during summer at high latitudes. Both the measured and calculated [ClN03]/[HCl] ratios exhibit the expected near linear variation with [03I2/[CH4] over a broad range of altitudes. MkIV measurements of HC1, ClN03, and CC1, agree well with ER-2 in situ observations of these quantities for directly comparable air masses. These results demonstrate good understanding of the budget of stratospheric chlorine and that the partitioning of inorganic chlorine is accurately described (differences < 10%) by photochemical models that employ JPL97 reaction rates for the environmental conditions encountered: relatively warm temperatures, long periods of solar illumination, and relatively low aerosol surface areas.
Variability of active chlorine in the lowermost Arctic stratosphere
J. Geophys. …, 2005
We examine the variability of ClO in the Arctic upper troposphere and lowermost stratosphere (UTLS) during the winter of 1999–2000. Data are binned relative to NO y , a species that is a proxy for photochemical age and a photochemical source of NO x . Enhancements in the [ClO]/[Cl y ] ratio relative to values expected from gas-phase chemistry alone were observed throughout the region and were largest in the coldest sampled regions, where T < 208 K. At low NO y values, where particles containing NO y and water were often detected, twilight ClO abundances in the afternoon were nearly a factor of 3 larger than those in the morning. At higher NO y values, where much lower particle surface areas were measured, ClO abundances in morning twilight were somewhat larger than those in the afternoon. These observations are consistent with a daytime mechanism of rapid heterogeneous activation of inorganic chlorine in particle-rich, low-NO y regions, with slower deactivation in relatively particle-poor, higher-NO y regions of the lowermost stratosphere. While the data clearly show widespread chlorine activation, knowledge of the precise value of the [ClO]/[Cl y ] ratio is limited because of the lack of available data on inorganic chlorine species, notably HCl, believed to be the dominant reservoir of inorganic chlorine at these altitudes.
Geophysical Research Letters, 1996
Measured mixing ratios of HC1, CINOS, and CIO from ATMOS and MAS are poorly rcproduccc] by models using recommended kinetic parameters. This discrepancy is not resolved by new rate constants for the reactions CI+C}14 and OH-tlIC.l derived from weighted fits to laboratory measurements. The deficit in modeled [1 ICI] and corresponding ova-prediction of [CINO~] and [C1O], which increases with altitude, suggests the existence of a mechanism responsible for enhanced photochcmical production of HC1 in the stratosphere bctwccn 20 and 50 km. lnfroclucfion identifying and determining the rates of reactions involved in partitioning inorganic chlorine is critical to understanding the processes that regulate stratospheric ozone. Collections of recommended rates published by NASA [Dd140re et al., 1994] and NIST [A fkinsm ct al., 1992] have been invaluable for consolidation and review of the vast amount of kinetic information for hundreds of reactions.
In situ observations of ClO near the winter polar tropopause
Journal of Geophysical Research, 2003
1] Significant abundances of chlorine oxide (ClO) were observed throughout the lowermost stratosphere at high latitudes during winter from the NASA DC-8 aircraft during the SAGE III-Ozone Loss and Validation Experiment and Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO 2000) campaign. Mixing ratios of ClO averaging 15-20 parts per trillion by volume (pptv) were observed near the tropopause, a region where ClO abundances are usually only a pptv or less at lower latitudes. The ratio of ClO to inferred inorganic chlorine ([ClO]/[Cl y ]) was found to be largest ($7%) in air characterized by low abundances of ozone ($100-250 parts per billion by volume (ppbv)). This was the region where cirrus clouds were also observed occasionally during the measurement period, although abundances of ClO directly within cirrus clouds were not significantly different than background abundances. Nonzero instrument signals during darkness are attributed to detection of $5-15 pptv of OClO. BrO mixing ratios between 2 and 4 pptv are sufficient to produce these amounts of OClO, assuming daytime mixing ratios of ClO between 15 and 20 pptv. At these levels of ClO and BrO, approximately 10% of the ozone at these altitudes is chemically destroyed per month in springtime by reactions of ClO and BrO, representing an effective loss process for ozone near the high-latitude tropopause.
Journal of Geophysical Research, 1995
Aircraft sampling has provided extensive in situ and flask measurements of organic chlorine species in the lower stratosphere. The recent Airborne Arctic Stratospheric Expedition II (AASE II) included two independent measurements of organic chlorine species using whole air sample and real-time techniques. From the whole air sample measurements we derive directly the burden of total organic chlorine (CCly) in the lower stratosphere. From the more limited real-time measurements we estimate the CCly burden using mixing ratios and growth rates of the principal CCly species in the troposphere in conjunction with results from a two-dimensional photochemical model. Since stratospheric chlorine is tropospheric in origin and tropospheric mixing ratios are increasing, it is necessary to establish the average age of a stratospheric air parcel to assess its total chlorine (C1Total) abundance. Total inorganic chlorine (Cly) in the parcel is then estimated by the simple difference, Cly-C1Tota 1-CCly. The consistency of the results from these two quite different techniques suggests that we can determine the CCly and Cly in the lower stratosphere with confidence. Such estimates of organic and inorganic chlorine are crucial in evaluating the photochemistry controlling chlorine partitioning and hence ozone loss processes in the lower stratosphere.
Journal of Geophysical Research, 1996
Chlorine-catalyzed ozone destruction is clearly observed during austral spring in the Antarctic lower stratosphere. While high concentrations of ozone-destroying C10 radicals have likewise been measured during winter in the Arctic stratosphere, the chemical ozone depletion there is more difficult to quantify. Here we present observations of the Halogen Occultation Experiment on the Upper Atmosphere Research Satellite in the vortex region of the Arctic lower stratosphere during the winter and spring months of measurements indicate an almost complete conversion of the otherwise main chlorine reservoir species HC1 to chemically more reactive forms. Using CH4 as a chemically conserved tracer, we show that significant chemical ozone loss occurred in the Arctic vortex region during all four winters. The deficit in column ozone was about 60 and 50 Dobson units (DU) in the winters 1991/1992 and 1993/1994, respectively. During the two winters of 1992/1993 and 1994/1995 a severe chemical loss in lower-stratospheric ozone took place, with local reductions of the mixing ratios by over 50% and a loss in the column ozone of the order of 100 DU. al., 1990, 1993] albeit to a much smaller extent than over Antarctica. Recent observations [Larsen et al., 1994; Manney et al., 1994a] indicate a particularly strong ozone loss in the Arctic vortex for early 1993. 1Now at In the Arctic, dynamical processes cause considerable ozone variations, making chemical ozone depletion more difficult to quantify than for the Antarctic. A high-pressure system in the troposphere causes a high tropopause, cold temperatures, and a low total ozone column in the lower stratosphere [Dobson et al., 1929; McKenna et al., 1989; Poole et al., 1990; Petzoldt et al., 1994]. On the other hand, 12,531
Geophysical Research Letters, 1996
Volume mixing ratio (VMR) profiles of the chlorine-bearing gases HC1, C1ONO2, CC13F, CC12F•, CHC1F2, CC14, and CH3C1 have been measured between 3 and 49 ø northern-and 65 to 72 ø southern latitudes with the Atmospheric Trace MOlecule Spectroscopy (ATMOS) instrument during the ATmospheric Laboratory for Applications and Science (ATLAS)-3 shuttle mission of 3 to 12 November 1994. A subset of these profiles obtained between 20 and 49øN at sunset, combined with C10 profiles measured by the Millimeter-wave Atmospheric Sounder (MAS) also from aboard ATLAS-3, measurements by balloon for HOCI, CH3CCI3 and C2C13F3, and model calculations for COC1F indicates that the mean burden of chlorine, Cl,o,, was equal to (3.53 4-0.10) ppbv (parts per billion by volume), 1sigma, throughout the stratosphere at the time of the ATLAS 3 mission. This is some 37% larger than the mean 2.58 ppbv value measured by ATMOS within the same latitude zone during the Spacelab 3 flight of 29 April to 6 May 1985, consitent with an exponential growth rate of the chlorine loading in the stratosphere equal to 3.3%/yr or a linear increase of 0.10 ppbv/yr over the Spring-1985 to Fa11-1994 time period. These findings are in agreement with both the burden and increase of the main anthropogenic Cl-bearing source gases at the surface during the 1980s, confirming that the stratospheric chlorine loading is primarily of anthropogenic origin. Earth's middle atmosphere [Farmer, 1987; Gunson et al., 1996].