Measurements Of ClO Research Articles

Synthesis and Characterization of a Novel Concentration-Independent Fluorescent Chloride Indicator, ABP-Dextran, Optimized for Extracellular Chloride Measurement.

GABA, the primary inhibitory neurotransmitter, stimulates GABAA receptors (GABAARs) to increase the chloride conductance of the cytosolic membrane. The driving forces for membrane chloride currents are determined by the local differences between intracellular and extracellular chloride concentrations (Cli and Clo, respectively). While several strategies exist for the measurement of Cli, the field lacks tools for non-invasive measurement of Clo. We present the design and development of a fluorescent lifetime imaging (FLIM)-compatible small molecule, N(4-aminobutyl)phenanthridiunium (ABP) with the brightness, spectral features, sensitivity to chloride, and selectivity versus other anions to serve as a useful probe of Clo. ABP can be conjugated to dextran to ensure extracellular compartmentalization, and a second chloride-insensitive counter-label can be added for ratiometric imaging. We validate the utility of this novel sensor series in two sensor concentration-independent modes: FLIM or ratiometric intensity-based imaging.

A novel tethered phenothiazine-coumarin fluorescence probe for rapid detection of hypochlorite ion and its applications

A novel tethered phenothiazine-coumarin fluorescent probe C-Ptz was synthesized for the detection of ClO− ion. Upon the reaction of C-Ptz with ClO− ions, a fluorescence enhancement (∼42 folds) was observed by blocking PET quenching pathway. The probe C-Ptz showed highly selectivity and fast “turn-on” response (within 3 s) towards ClO− with detection limit down to 12.6 nM. Furthermore, the fluorescent probe C-Ptz was utilized to the fluorescence imaging of ClO− in living cells. In addition, its measurement of ClO− was also performed in real-life water samples.

The Relationship between CRP Levels and Gastritis in Children with or without Helicobacter pylori Infection

Background: Helicobacter pylori infection is the cause of most gastritis in the world population. In establish and determining the severity of gastiritis, a combination of clinical symptoms, physical examination, and support laboratories is needed. Gastritis is a chronic inflammation which can increase inflammatory markers, including CRP. Investigation such as CRP, can measure the level of inflammation objectively, and can help to evaluate clinical patient. Previous studies have shown that H.pylori infection causes increased CRP concentrations. Methods: This study is a cross sectional of data on children who are treated in the Gastrohepatology division aged 2-18 years old, that have been diagnosed with gastritis through endoscopic examination with CLO measurements, and have CRP level, according to inclusion and exclusion criteria. The data with gastritis were further divided into positive H.pylori and negative H.pylori. The caracteristics of children and parents were recorded. Result: This study involved 62 data children who met the inclusion and exclusion criteria. From the CLO examination, there were 30 children with positive H.pylori and 32 children with negative H.pylori. the dominant clinical symptom in both groups was recurrent abdominal pain, but there was no significant difference between them. The mean CRP value obtained in the positive H.pylori group was 36,78, while in the negative H.pylori group it was 11,73. There were significant differences in CRP valus between them (p<0,001). Conclusion: There was an association between CRP level in pediatric gastritis with H.pylori infection compared to without H.pylori infection. Keyword: CRP, Helicobacter pylori, Gastritis in children

Novel Platinum(II) Complex-based Luminescent Probe for Detection of Hypochlorite in Cancer Cells.

Hypochlorite (ClO⁻) is of great importance either for the metabolism of living organisms or as disinfectant in daily life. However, improper concentration levels of ClO⁻ lead to serious health problems including erythrocyte damage, cardiovascular problems, neuron degeneration, lung/kidney injury and cancer. Therefore, a sensitive and selective detection method is required for the visualization and measurement of ClO⁻. In this work, a novel platinum(II) complex-based luminescent probe Pt-CHO was synthesized and utilized to detect ClO⁻. This "turn-off" probe exhibits high sensitivity, excellent selectivity, good pH stability, low limit of detection and instantaneous response ability. Moreover, the luminescent response is caused by the oxidation of aldehyde into carboxyl groups combined with the coordination of hydroxyl groups at the Pt center, which is rarely reported. The cell imaging of HeLa cells proved the considerable potential of the probe for ClO⁻ imaging in living cells.

Initial Results and Diurnal Variations Measured by a New Microwave Stratospheric ClO Instrument at Mauna Kea

AbstractWe present the first year of ClO and O3 measurements from a new 278 GHz Chlorine monOxide Experiment (ChlOE) microwave instrument on Mauna Kea. We make use of comparisons with the Aura Microwave Limb Sounder (MLS) O3 measurements to recalibrate the ground‐based instrument and find that the recalibrated ground‐based O3 retrievals remain stable relative to MLS throughout the year. The MLS measurements provide daily daytime (~1330 local solar time) and nighttime (~0200 local solar time) ClO retrievals, and we find that the monthly ChlOE ClO retrievals show mixing ratios slightly smaller than those from MLS in the vicinity of Mauna Kea, with daytime values near the peak ~6–8% lower at 30–45 km for the average of the 12 months in this study. The nighttime monthly ClO values are almost all within ±0.03 ppbv over most of this altitude range, with very little overall bias. We have also made detailed hourly diurnal O3 comparisons with a multiyear analysis of previous retrievals from the much stronger 110 GHz O3 emission line being measured by our instrument at Mauna Loa and find that the hour‐to‐hour differences are within ±2% at 40 km, which indicates that the overall calibration of the ChlOE instrument is stable relative to time of day. We show hourly diurnal variations of ClO and compare these to 2010 measurements from the Submillimeter‐Wave Limb‐Emission Sounder and to a model.

Modeling the Sources and Chemistry of Polar Tropospheric Halogens (Cl, Br, and I) Using the CAM‐Chem Global Chemistry‐Climate Model

AbstractCurrent chemistry climate models do not include polar emissions and chemistry of halogens. This work presents the first implementation of an interactive polar module into the very short‐lived (VSL) halogen version of the Community Atmosphere Model with Chemistry (CAM‐Chem) model. The polar module includes photochemical release of molecular bromine, chlorine, and interhalogens from the sea‐ice surface, and brine diffusion of iodine biologically produced underneath and within porous sea‐ice. It also includes heterogeneous recycling of inorganic halogen reservoirs deposited over fresh sea‐ice surfaces and snow‐covered regions. The polar emission of chlorine, bromine, and iodine reach approximately 32, 250, and 39 Gg/year for Antarctica and 33, 271, and 4 Gg/year for the Arctic, respectively, with a marked seasonal cycle mainly driven by sunlight and sea‐ice coverage. Model results are validated against polar boundary layer measurements of ClO, BrO, and IO, and satellite BrO and IO columns. This validation includes satellite observations of IO over inner Antarctica for which an iodine “leapfrog” mechanism is proposed to transport active iodine from coastal source regions to the interior of the continent. The modeled chlorine and bromine polar sources represent up to 45% and 80% of the global biogenic VSLCl and VSLBr emissions, respectively, while the Antarctic sea‐ice iodine flux is ~10 times larger than that from the Southern Ocean. We present the first estimate of the contribution of polar halogen emissions to the global tropospheric halogen budget. CAM‐Chem includes now a complete representation of halogen sources and chemistry from pole‐to‐pole and from the Earth's surface up to the stratopause.

First measurements of ClO in the Venus atmosphere – Altitude dependence and temporal variation

The 352.88 GHz submm absorption spectrum of 35ClO in the Venus atmosphere was observed on Oct 23 and Nov 11, 2010, using the James Clerk Maxwell Telescope (JCMT) on Mauna Kea, HI. This is the first detection of Venus ClO, which is found to exhibit much larger abundances in the upper (85–100 km) versus lower (70–85 km) mesosphere, based upon retrieval of the altitude distribution from the shape of the pressure broadened absorption. The 2-day average of all collected data indicates 2.6 ±0.5 ppb above 85 ±2 km, and undetectable below. Temporal variation is evident between the Oct 23 and Nov 11 observations, which indicate upper mesospheric mixing ratios of 3.7 ±0.9 and 1.5 ±0.5 ppb, respectively. At these abundances catalytic destruction of ozone by highly reactive chlorine compounds (ClOx) must occur, reinforcing the (Montmessin et al., 2011) conclusion that their measured ozone profiles were consistent with chlorine-catalyzed ozone destruction above 90 km. Detection of ClO in the nightside atmosphere reveals that ClOx abundances exceed those of highly reactive nitrogen (NOx). Recent observations of HCl in both the night- and day-side atmosphere (Sandor and Clancy, 2012; 2017) demonstrate that upper mesospheric HCl represents less than half the total chlorine budget. This required a non-HCl reservoir consisting of highly reactive gas-phase chlorine compounds (ClOx), HCl aerosol particles, or both. The measured 1.5–3.7 ppb ClO directly indicates hundreds of ppb of Cl, demonstrating that ClOx (rather than aerosol) is a primary upper mesospheric chlorine reservoir. Finally, this first detection of ClO constitutes the first empirical corroboration that the (Yung and DeMore, 1982) chlorine-catalysis mechanism is responsible for stabilizing the Venus atmosphere as 97% CO2, 3% N2 (rather than comparable (within a factor of 2) CO, O2 and CO2 abundances).

Constraints on Arctic Atmospheric Chlorine Production through Measurements and Simulations of Cl2 and ClO

During springtime, unique halogen chemistry involving chlorine and bromine atoms controls the prevalence of volatile organic compounds, ozone, and mercury in the Arctic lower troposphere. In situ measurements of the chlorine monoxide radical, ClO, and its precursor, Cl2, along with BrO and Br2, were conducted using chemical ionization mass spectrometry (CIMS) during the Bromine, Ozone, and Mercury Experiment (BROMEX) near Barrow, Alaska, in March 2012. To our knowledge, these data represent the first ClO measurements made using CIMS. A maximum daytime ClO concentration of 28 ppt was observed following an early morning peak of 75 ppt of Cl2. A zero-dimensional photochemistry model was constrained to Cl2 observations and used to simulate ClO during a 7-day period of the field campaign. The model simulates ClO within the measurement uncertainty, and the model results highlight the importance of chlorine chemistry participation in bromine radical cycling, as well as the dependence of halogen chemistry on NOx levels. The ClO measurements and simulations are consistent with Cl2 being the dominant Cl atom source in the Arctic boundary layer. Simulated Cl atom concentrations, up to ∼1 × 106 molecules cm-3, highlight the importance of chlorine chemistry in the degradation of volatile organic compounds, including the greenhouse gas methane.

Constraints for the photolysis rate and the equilibrium constant of ClO‐dimer from airborne and balloon‐borne measurements of chlorine compounds

AbstractWe analyze measurements of ClO across the terminator taken by the Airborne Submillimeter Radiometer (ASUR) in the activated vortices of the Arctic winters of 1995/1996, 1996/1997, and 1999/2000 to evaluate the plausibility of various determinations of the ClO‐dimer photolysis cross section and the rate constant controlling the thermal equilibrium between ClO‐dimer and ClO. We use measured ClO during sunlit conditions to estimate total active chlorine (ClOx). As the measurements suggest nearly full chlorine activation in winter 1999/2000, we compare ClOx estimates based on various photolysis frequencies of ClO‐dimer with total available inorganic chlorine (Cly), estimated from an N2O‐Cly correlation established by a balloon‐borne MkIV interferometer measurement. Only ClO‐dimer cross sections leading to the fastest photolysis frequencies in the literature (including the latest evaluation by the Jet Propulsion Laboratory) give ClOx mixing ratios that overlap with the estimated range of available Cly. Slower photolysis rates lead to ClOx values that are higher than available Cly. We use the ClOx calculated from sunlit ClO measurements to estimate ClO in darkness based on different equilibrium constants, and compare it with ASUR ClO measurements before sunrise at high solar zenith angles. Calculations with equilibrium constants published in recent evaluations of the Jet Propulsion Laboratory give good agreement with observed ClO mixing ratios. Equilibrium constants leading to a higher ClO/ClOx ratio in darkness yield ClO values that tend to exceed observed abundances. Perturbing the rates for the ClO + BrO reaction in a manner that increases OClO formation and decreases BrCl formation leads to lower ClO values calculated for twilight conditions after sunset, resulting in better agreement with ASUR measurements.

Re-analysis of ground-based microwave ClO measurements from Mauna Kea, 1992 to early 2012

Abstract. We present a re-analysis of upper stratospheric ClO measurements from the ground-based millimeter-wave instrument from January 1992 to February 2012. These measurements are made as part of the Network for the Detection of Atmospheric Composition Change (NDACC) from Mauna Kea, Hawaii, (19.8° N, 204.5° E). Here, we use daytime and nighttime measurements together to form a day–night spectrum, from which the difference in the day and night profiles is retrieved. These results are then compared to the day–night difference profiles from the Upper Atmosphere Research Satellite (UARS) and Aura Microwave Limb Sounder (MLS) instruments. We also compare them to our previous analyses of the same data, in which we retrieved the daytime ClO profile. The major focus will be on comparing the year-to-year and long-term changes in ClO derived by the two analysis methods, and comparing these results to the long-term changes reported by others. We conclude that the re-analyzed data set has less short-term variability and exhibits a more constant long-term trend that is more consistent with other observations. Data from 1995 to 2012 indicate a linear decline of mid-stratospheric ClO of 0.64 ± 0.15% yr−1 (2σ).

Trace gas evolution in the lowermost stratosphere from Aura Microwave Limb Sounder measurements

[1] Daily global measurements from NASA's Aura Microwave Limb Sounder (MLS) allow comprehensive investigation of interhemispheric and interannual variations in chemical and transport processes throughout the lowermost stratosphere (LMS). We analyze nearly seven years of MLS O3, HNO3, HCl and ClO measurements along with meteorological analyses to place chemical processing in and dispersal of processed air from the winter polar lowermost vortex and subvortex in a global context. The MLS data, the first simultaneous observations of HCl and ClO covering much of the LMS, reveal that chlorine activation is widespread in the Antarctic subvortex and can occur to a significant degree in the Arctic subvortex. Unusually low temperatures and strong, prolonged chlorine activation in the lowermost vortex and subvortex promoted large ozone losses there in the 2006 (and 2008) Antarctic and 2004/2005 Arctic winters, consistent with reported record low column ozone. Processed air dispersing from the decaying vortex in spring induces rapid changes in extravortex trace gas abundances. After vortex breakdown, the subtropical jet/tropopause becomes the major transport barrier in the LMS. Quasi-isentropic transport of tropical tropospheric air into the LMS, associated with the summer monsoon circulations, leads to decreases in extratropical O3, HNO3, and HCl in both hemispheres. Strong mixing in the summertime LMS homogenizes extratropical trace gas fields. MLS measurements in the tropics show signatures of monsoon-related cross-equatorial stratosphere-to-troposphere transport. Observed seasonal and interannual variations in trace gas abundances in the LMS are consistent with variations in the strength of transport barriers diagnosed from meteorological analyses.

Ground-based measurements of ClO from Mauna Kea and intercomparisons with Aura and UARS MLS

[1] The ground-based measurements of upper stratospheric ClO, made with a ground-based millimeter wave instrument at Mauna Kea, Hawaii (19.8°N, 204.5°E) starting in 1992, are compared with UARS (Upper Atmosphere Research Satellite) MLS ClO measurements (1991–1998) and the Aura MLS ClO measurements (2004–2009). The ground-based measurements are made as part of the Network for the Detection of Atmospheric Composition Change (NDACC). Intercomparisons between the ground-based measurements and the Aura MLS measurements show that both instruments retrieve similar seasonal variations over Mauna Kea. The seasonal variation in ClO is also compared with measurements of variations in stratospheric CH4, which affects the partitioning of total inorganic chlorine. Using the ground-based instruments as a transfer standard, we find that the agreement between UARS and Aura MLS ClO measurements near the peak of the mixing ratio profile is within ∼1%. Combining the uncertainties in the biases calculated from the coincident ground-based and satellite measurements, we find that using the ground-based data as a transfer standard allows us to provide a 2σ limit to the bias between the UARS and Aura measurements of 3%–4% near the peak of the ClO profile. Given agreement between UARS and Aura MLS of ∼1% ± 4%, there is no reason to apply any bias correction in order to use the UARS and Aura MLS ClO measurements as a single data set.

Development and field testing of a mobile chlorine dioxide generation system for the decontamination of buildings contaminated with Bacillus anthracis

The numerous buildings that became contaminated with Bacillus anthracis (the bacterium causing the disease anthrax) in 2001, and more recent B. anthracis – related events, point to the need to have effective decontamination technologies for buildings contaminated with biological threat agents. The U.S. Government developed a portable chlorine dioxide (ClO 2) generation system to decontaminate buildings contaminated with B. anthracis spores, and this so-called mobile decontamination trailer (MDT) prototype was tested through a series of three field trials. The first test of the MDT was conducted at Fort McClellan in Anniston, AL. during October 2004. Four test attempts occurred over two weekends; however, a number of system problems resulted in termination of the activity prior to any ClO 2 introduction into the test building. After making several design enhancements and equipment changes, the MDT was subjected to a second test. During this test, extensive leak checks were made using argon and nitrogen in lieu of chlorine gas; each subsystem was checked for functionality, and the MDT was operated for 24 h. This second test demonstrated the MDT flow and control systems functioned satisfactorily, and thus it was decided to proceed to a third, more challenging field trial. In the last field test, ClO 2 was generated and routed directly to the scrubber in a 12-h continuous run. Measurement of ClO 2 levels at the generator outlet showed that the desired production rate was not achieved. Additionally, only one of the two scrubbers performed adequately with regard to maintaining ClO 2 emissions below the limit. Numerous lessons were learned in the field trials of this ClO 2 decontamination technology.

A study of stratospheric chlorine partitioning based on new satellite measurements and modeling

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, ClONO2, 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 ClONO2, 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 ClONO2, then both reservoirs are produced concurrently but ClONO2 continues to significantly exceed HCl, and finally slow repartitioning between ClONO2 and HCl occurs; in 2005/2006, HCl and ClONO2 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.

Validation of the Aura Microwave Limb Sounder ClO measurements

We assess the quality of the version 2.2 (v2.2) ClO measurements from the Microwave Limb Sounder (MLS) on the Earth Observing System Aura satellite. The MLS v2.2 ClO data are scientifically useful over the range 100 to 1 hPa, with a single‐profile precision of ∼0.1 ppbv throughout most of the vertical domain. Vertical resolution is ∼3–4 km. Comparisons with climatology and correlative measurements from a variety of different platforms indicate that both the amplitude and the altitude of the peak in the ClO profile in the upper stratosphere are well determined by MLS. The latitudinal and seasonal variations in the ClO distribution in the lower stratosphere are also well determined, but a substantial negative bias is present in both daytime and nighttime mixing ratios at retrieval levels below (i.e., pressures larger than) 22 hPa. Outside of the winter polar vortices, this negative bias can be eliminated by subtracting gridded or zonal mean nighttime values from the individual daytime measurements. In studies for which knowledge of lower stratospheric ClO mixing ratios inside the winter polar vortices to better than a few tenths of a ppbv is needed, however, day − night differences are not recommended and the negative bias must be corrected for by subtracting the estimated value of the bias from the individual measurements at each affected retrieval level.

Polar stratospheric chlorine kinetics from a self‐match flight during SOLVE‐II/EUPLEX

In‐situ measurements of ClO made onboard the Geophysica aircraft on 30 January 2003 in the Arctic afford a novel approach to constrain the kinetic parameters governing polar stratospheric chlorine chemistry using atmospheric observations. The self‐match flight pattern, i.e. sampling individual air masses twice at different zenith angles, was utilized by simulating the evolution of ClO mixing ratios between two ‘matching’ points using a photochemical model and optimizing the model parameters to fit the observations within a retrieval framework. Our results suggest a ClO/ClOOCl thermal equilibrium constant Keq a factor of 5 smaller and a ratio J/kf a factor of 2 larger than the values based on the JPL recommendations. This concurs with other studies based on observed ClOx partitioning and corroborates that our understanding of stratospheric chlorine chemistry is incomplete, particularly in the light of the most recent laboratory experiments pointing to a J/kf ratio almost an order of magnitude below the JPL recommendation.

Comparison of ClO measurements from the Aura Microwave Limb Sounder to ground‐based microwave measurements at Scott Base, Antarctica, in spring 2005

We have examined measurements of chlorine monoxide, ClO, in the lower stratosphere by the Microwave Limb Sounder (MLS) on the Aura satellite in the austral spring of 2005. These measurements have been compared to those of a ground‐based spectrometer at Scott Base, Antarctica. The data analysis is performed in both cases by subtracting nighttime measurements from daytime ones. The transition from full darkness to full daylight at the high latitude of Scott Base limits the time during which both day and night measurements are made. After further selection for good observing conditions and the position of the polar vortex, 16 valid profile comparisons are made. The day‐to‐day variability of ClO is observed to be large, ∼30% of its peak value. The daily column densities of the two instruments are correlated with a significance of 3σ with most of the mean difference arising from 2 days. The statistical agreement between MLS and the Scott Base instrument is good. Scott Base values are on average marginally but not significantly larger, by 0.10 ± 0.07 ppb, or 11 ± 8% (1σ), in peak mixing ratio, than the MLS values.

Chlorine activation near the midlatitude tropopause

We report on substantial chlorine activation near the midlatitude tropopause over the central United States (39–42°N 102–105°W) during the WB‐57F Aerosol Mission (WAM) in April 1998. The extent of activation was determined by simultaneous in situ measurements of ClO and ozone and calculations of total inorganic chlorine (Cly) based on recently reported relationships between HCl, ozone, and halocarbons for similar latitudes. Levels of [ClO]/[Cly] approaching 50% occurred in a region of strong gravity wave activity, high particulate surface areas (5–20 μm2 cm−3), low ozone, and relatively high humidities (20–25 ppm of H2O, yet undersaturated with respect to ice), consistent with a heterogeneous mechanism on particles formed in recently lofted tropospheric air as it mixed into the lowermost stratosphere. These observations are similar to a previous one of chlorine activation on volcanic aerosol, suggesting a common heterogeneous chemical mechanism involving HCl, ClNO3, and HOCl that even in volcanically quiescent years can impact ozone photochemistry in regions of the lowermost stratosphere influenced by mixing from the tropopause region. Models not incorporating this chlorine activation process may be underestimating the impact on ozone in the midlatitude lowermost stratosphere by decomposition of very short lived halocarbon compounds, including substitutes for ozone‐depleting compounds.

Understanding the kinetics of the ClO dimer cycle

Abstract. Among the major factors controlling ozone loss in the polar vortices in winter/spring is the kinetics of the ClO dimer catalytic cycle. Here, we propose a strategy to test and improve our understanding of these kinetics by comparing and combining information on the thermal equilibrium between ClO and Cl2O2, the rate of Cl2O2 formation, and the Cl2O2 photolysis rate from laboratory experiments, theoretical studies and field observations. Concordant with a number of earlier studies, we find considerable inconsistencies of some recent laboratory results with rate theory calculations and stratospheric observations of ClO and Cl2O2. The set of parameters for which we find the best overall consistency – namely the ClO/Cl2O2 equilibrium constant suggested by Plenge et al. (2005), the Cl2O2 recombination rate constant reported by Nickolaisen et al. (1994) and Cl2O2 photolysis rates based on absorption cross sections in the range between the JPL 2006 assessment and the laboratory study by Burkholder et al. (1990) – is not congruent with the latest recommendations given by the JPL and IUPAC panels and does not represent the laboratory studies currently regarded as the most reliable experimental values. We show that the incorporation of new Pope et al. (2007) Cl2O2 absorption cross sections into several models, combined with best estimates for other key parameters (based on either JPL and IUPAC evaluations or on our study), results in severe model underestimates of observed ClO and observed ozone loss rates. This finding suggests either the existence of an unknown process that drives the partitioning of ClO and Cl2O2, or else some unidentified problem with either the laboratory study or numerous measurements of atmospheric ClO. Our mechanistic understanding of the ClO/Cl2O2 system is grossly lacking, with severe implications for our ability to simulate both present and future polar ozone depletion.

A global inventory of stratospheric chlorine in 2004

Total chlorine (ClTOT) in the stratosphere has been determined using the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) measurements of HCl, ClONO2, CH3Cl, CCl4, CCl3F (CFC‐11), CCl2F2 (CFC‐12), CHClF2 (HCFC‐22), CCl2FCClF2 (CFC‐113), CH3CClF2 (HCFC‐142b), COClF, and ClO supplemented by data from several other sources, including both measurements and models. Separate chlorine inventories were carried out in five latitude zones (60°–82°N, 30°–60°N, 30°S–30°N, 30°–60°S, and 60°–82°S), averaging the period of February 2004 to January 2005 inclusive, when possible, to deal with seasonal variations. The effect of diurnal variation was avoided by only using measurements taken at local sunset. Mean stratospheric ClTOT values of 3.65 ppbv were determined for both the northern and southern midlatitudes (with an estimated 1σ accuracy of ±0.13 ppbv and a precision of ±0.09 ppbv), accompanied by a slightly lower value in the tropics and slightly higher values at high latitudes. Stratospheric ClTOT profiles in all five latitude zones are nearly linear with a slight positive slope in ppbv/km. Both the observed slopes and pattern of latitudinal variation can be interpreted as evidence of the beginning of a decline in global stratospheric chlorine, which is qualitatively consistent with the mean stratospheric circulation pattern and time lag necessary for transport.