Ozone Loss Rates Research Articles

Arctic ozone loss in threshold conditions: Match observations in 1997/1998 and 1998/1999

Chemical ozone loss rates inside the Arctic polar vortex were determined in early 1998 and early 1999 by using the Match technique based on coordinated ozonesonde measurements. These two winters provide the only opportunities in recent years to investigate chemical ozone loss in a warm Arctic vortex under threshold conditions, i.e., where the preconditions for chlorine activation, and hence ozone destruction, only occurred occasionally. In 1998, results were obtained in January and February between 410 and 520 K. The overall ozone loss was observed to be largely insignificant, with the exception of late February, when those air parcels exposed to temperatures below 195 K were affected by chemical ozone loss. In 1999, results are confined to the 475 K isentropic level, where no significant ozone loss was observed. Average temperatures were some 8°–10° higher than those in 1995, 1996, and 1997, when substantial chemical ozone loss occurred. The results underline the strong dependence of the chemical ozone loss on the stratospheric temperatures. This study shows that enhanced chlorine alone does not provide a sufficient condition for ozone loss. The evolution of stratospheric temperatures over the next decade will be the determining factor for the amount of wintertime chemical ozone loss in the Arctic stratosphere.

A Comparison of Match Ozonesonde-Derived and 3D Model Ozone Loss Rates in the Arctic Polar Vortex during the Winters of 1994/95 and 1995/96

Ozone loss rates from ozonesonde data reported in the Match experiments of winters 1994/95 and 1995/96 inside the Arctic polar vortex are compared with simulations of the same winters performed using the SLIMCAT 3D chemistry and transport model. For 1994/95 SLIMCAT reproduces the location and timing of the diagnosed ozone destruction, reaching 10 ppbv/sunlit hour in late January as observed. SLIMCAT underestimates the loss rates observed in February and March by 1–3 ppbv/sunlit hour. By the end of March, SLIMCAT ozone exceeds the observations by 25–35%. In January 1995 the ozonesonde-derived loss rates at levels above 525 K are not chemical in origin but due to poor conservation of air parcels. Correcting temperature biases in the model forcing data significantly improved the agreement between the model and observed ozone at the end of winter 1994/95, increasing ozone destruction in SLIMCAT in February and March. The SLIMCAT simulation of winter 1995/96 does not reproduce the maximum ozone loss rates diagnosed by Match of 13 ppbv/sunlit hour. Comparing the data for the two winters reveals that the SLIMCAT photochemistry is least able to reproduce observed losses at low temperatures or when low temperatures coincide with high solar zenith angles (SZA). When cold (T = 192 K), high SZA (≥90°)matches are excluded from the 1995/96 analysis, agreement between the diagnoses and SLIMCAT is better with ozone loss rates of up to 6 ppbv/sunlit hour. For the rest of the winter SLIMCAT consistently underestimates the Match rates of ozone loss by 1–3 ppbv/sunlit hour. In March 1996 the monthly mean SLIMCAT ozone is 50% greater than observations at 430–540 K. In both winters, ozone destruction rates peaked more rapidly and declined more slowly in the Match observations than in the SLIMCAT simulations. The differences between the observed and modelled cumulative ozone losses demonstrate that the total ozone destruction by the end of the winter is sensitive to errors in the instantaneous ozone loss rates of 1–3 ppbv/sunlit hour.

The Effects of Ozonated Irrigation Water on Soil Physical and Chemical Properties

There are reports that ozone in irrigation water can improve crop vigor, reduce insect and disease, enhance water penetration, and reduce fertilizer needs. It has been noted that ozone treated field soils seem spongier and have less standing water. Here we report on a laboratory column study on the effects of ozonated irrigation water on hydraulic conductivity, soil hardness (aggregate strength), clay dispersion, soil swelling, and changes to the chemical composition of the leachate water. Additional batch studies were conducted to characterize the factors affecting the rate of ozone loss in soil/water suspensions and the results used in a mathematical model to predict ozone movement into a soil. We found that ozone increased the saturated hydraulic conductivity and decreased clay dispersion in a loamy soil, but not if the soil had an exchangeable sodium percentage >15%. In two other soils tested, the ozone effects were mixed or insignificant. In every soil tested, the drainage water from the ozone-treated columns had lower pH's and higher electrolyte concentrations. This is attributed to organic matter oxidation and the weak acid properties of ozone. The rate of ozone degradation in soil water could be modeled using the total organic carbon content of the soil, the pH, and the soil/water ratio. Based on the rate of ozone loss in soil/water suspensions, the calculated depth of ozone penetration during the initial wetting of the soil was <2 mm, indicating that the reaction may be limited to the surface.

Mid‐latitude marine boundary‐layer ozone destruction at visible sunrise observed at Cape Grim, Tasmania, 41°S

An analysis is made of 13 years of observations of ozone concentrations in the remote marine boundary layer at Cape Grim, Tasmania 41°S. These data reveal a decrease in ozone concentration in the first few hours following sunrise at a rate of around 0.1 ppb h−1 in mid‐summer and in mid‐winter. This ozone destruction phenomenon causes an asymmetry in the daily ozone loss rate with enhanced destruction following sunrise, is statistically distinguishable from the O3‐HOx destruction cycle that peaks at mid‐day, and occurs at similar rates in mid‐summer and in mid‐winter. The cause of this sunrise ozone decrease is examined using the conservation equation for ozone. We speculate that ozone destruction at sunrise arises due to halogen chemistry. The absence of sunrise ozone decrease in models of marine boundary‐layer photochemistry means that the ozone destruction rate in the remote marine boundary layer is underestimated by perhaps a factor of two.

Model study of stratospheric chlorine activation and ozone loss during the 1996/1997 winter

Chlorine activation and ozone depletion in the Arctic winter stratosphere of 1996–1997 have been studied with a newly developed stratospheric chemistry‐transport model (CTM). The chemistry scheme, using a Euler Backward Iterative approximation method, includes a comprehensive set of reactions on ternary aerosol and ice particles, which has been tested against a numerically exact solver. Tracer transports in the CTM are calculated from European Centre for Medium‐Range Weather Forecasts (ECMWF) meteorological analyses. Comparisons have been made with O3 and ClO measurements, and with ozone loss rates derived from observations during February and March 1997. ClO production and ozone depletion are somewhat underestimated by the model. Furthermore, uncertainties regarding the aerosol phase are tested. Assuming nitric acid trihydrate (NAT) particles to form at their melting point, while liquid aerosol is present simultaneously in the model, gives rise to the largest ClO production and the strongest ozone depletion. By correcting for an ECMWF temperature warm bias we obtain a similar large effect on calculated ClO production and ozone depletion for the 1996/1997 Arctic winter, whereas uncertainties in the chlorine abundance seem less important. An average warm bias of 1.3 K at polar stratospheric cloud temperatures on the 50 hPa model level reduces the calculated ozone depletion rates over February and March by 35%. Observations of ClO are reproduced when lower temperatures and maximum Cly abundance are assumed, but ozone depletion is slightly overestimated in that case.

Arctic and Antarctic ozone layer observations: chemical and dynamical aspects of variability and long-term changes in the polar stratosphere

The altitude dependent variability of ozone in the polar stratosphere is regularly observed by balloon-borne ozonesonde observations at Neumayer Station (70°S) in the Antarctic and at Koldewey Station (79°N)in the Arctic. The reasons for observed seasonal and interannual variability and long-term changes are discussed. Differences between the hemispheres are identified and discussed in light of differing dynamical and chemical conditions. Since the mid- 1980s, rapid chemical ozone loss has been recorded in the lower Antarctic stratosphere during the spring season. Using coordinated ozone soundings in some Arctic winters, similar chemical ozone loss rates have been detected related to periods of low temperatures. The currently observed cooling trend of the stratosphere, potentially caused by the increase of anthropogenic greenhouse gases, may further strengthen chemical ozone removal in the Arctic. However, the role of internal climate oscillations in observed temperature trends is still uncertain. First results of a 10000 year integration of a low order climate model indicate significant internal climate variability. on decadal time scales, that may alter the effect of increasing levels of greenhouse gases in the polar stratosphere.

The Rate of Ozone Uptake on Carpets: Experimental Studies

Ozone can react with surfaces, reducing indoor concentrations. Carpets may be important ozone sinks because of their high surface area. We conducted laboratory experiments to measure ozone uptake on four samples of whole carpet and on the corresponding carpet fibers and carpet backing. Results were parametrized in terms of reaction probability, defined as the rate of ozone loss on a surface normalized by the rate of ozone-surface collisions. For whole carpet and carpet-backing samples, we found the apparent reaction probability to be of magnitude 10-5 to 10-4. These results are referenced to the floor area that would be covered by the carpet, rather than to the total surface area of the carpet and its fibers. Reaction probabilities of the order of 10-7 to 10-6 were measured on carpet fibers, referenced to total estimated fiber area. The results indicate that carpet is of comparable significance to painted walls in scavenging ozone from indoor air. All samples tested exhibited aging, such that the rate of ozone uptake diminished with increasing cumulative exposure. Although reactions on carpeting can reduce human exposure to ozone, we caution that the reaction products may include volatile carbonyls that have low odor or irritation thresholds.

Ozone loss rates in the Arctic stratosphere in the winter 1994/1995: Model simulations underestimate results of the Match analysis

We present box model simulations of ozone loss rates in the Arctic lower stratosphere for the winter 1994/1995. The ozone loss was simulated along each of the trajectories of the Match data set for 1994/1995 to conduct a quantitative comparison with the Match results. The simulated ozone loss rates reach their maximum value of ≈ 4 ppb per sunlit hour at the end of January. For this period and for potential temperatures below 475 K the model results are in good agreement with the Match results, but for potential temperatures above 475 K the model underestimates the ozone loss rate by up to a factor of 2. This difference cannot be explained by known uncertainties of the model. Enhanced ozone loss has also been observed in March 1995 for potential temperatures below 475 K. These loss rates are also substantially underestimated by the model, but are within the range of the model uncertainties. In particular, the ozone loss rates simulated for March 1995 strongly depend on the extent of denitrification.

Match observations in the Arctic winter 1996/97: High stratospheric ozone loss rates correlate with low temperatures deep inside the polar vortex

With the Match technique, which is based on the coordinated release of ozonesondes, chemical ozone loss rates in the Arctic stratospheric vortex in early 1997 have been quantified in a vertical region between 400 K and 550 K. Ozone destruction was observed from mid February to mid March in most of these levels, with maximum loss rates between 25 and 45ppbv/day. The vortex averaged loss rates and the accumulated vertically integrated ozone loss have been smaller than in the previous two winters, indicating that the record low ozone columns observed in spring 1997 were partly caused by dynamical effects. The observed ozone loss is inhomogeneous through the vortex with the highest loss rates located in the vortex centre, coinciding with the lowest temperatures. Here the loss rates per sunlit hour reached 6 ppbv/h, while the corresponding vortex averaged rates did not exceed 3.9 ppbv/h.

ILAS observations of chemical ozone loss in the Arctic vortex during early spring 1997

Chemical ozone loss rates were estimated for the Arctic stratospheric vortex by using ozone profile data (Version 3.10) obtained with the Improved Limb Atmospheric Spectrometer (ILAS) for the spring of 1997. The analysis method is similar to the Match technique, in which an air parcel that the ILAS sounded twice at different locations and at different times was searched from the ILAS data set, and an ozone change rate was calculated from the two profiles. A statistical analysis indicates that the maximum ozone loss rate was found on the 450 K potential temperature surface in February, amounting to 84 ppbv/day. The integrated ozone loss for two months from February to March 1997 showed its maximum of 1.5±0.1 ppmv at the surface that followed the diabatic descent of the air parcels and reached the 425 K level on March 31. This is about 50% of the initial (February 1) ozone concentration. The present study demonstrated that data from a solar occultation sensor with a moderate altitude resolution can be used for the Match analysis.

Arctic and Antarctic ozone layer observations: chemical and dynamical aspects of variability and long-term changes in the polar stratosphere

The altitude dependent variability of ozone in the polar stratosphere is regularly observed by balloon-borne ozonesonde observations at Neumayer Station (70&deg;S) in the Antarctic and at Koldewey Station (79&deg;N)in the Arctic. The reasons for observed seasonal and interannual variability and long-term changes are discussed. Differences between the hemispheres are identified and discussed in light of differing dynamical and chemical conditions. Since the mid- 1980s, rapid chemical ozone loss has been recorded in the lower Antarctic stratosphere during the spring season. Using coordinated ozone soundings in some Arctic winters, similar chemical ozone loss rates have been detected related to periods of low temperatures. The currently observed cooling trend of the stratosphere, potentially caused by the increase of anthropogenic greenhouse gases, may further strengthen chemical ozone removal in the Arctic. However, the role of internal climate oscillations in observed temperature trends is still uncertain. First results of a 10000 year integration of a low order climate model indicate significant internal climate variability. on decadal time scales, that may alter the effect of increasing levels of greenhouse gases in the polar stratosphere.

The GEOS ozone data assimilation system

A data assimilation system for ozone observations has been developed at NASA's Goddard Space Flight Center. The initial objective is to provide total ozone and ozone profiles in near-real time for satellite remote sensing applications. In addition, historical ozone observations will be assimilated for climate and chemistry studies. The forecast model is a chemistry and transport model with prescribed, zonally symmetric ozone production and loss rates. The analysis equation is solved after each model time step, using observations obtained within a time window with a length of one time step. In this article, the overall design of the system is described, and examples from the validation of the initial configuration assimilating TOMS total ozone and SBUV/2 ozone profile measurements are presented. The assimilation produces realistic total ozone fields and lower stratospheric ozone profiles. A substantial bias with respect to observed profiles remains in the upper stratosphere.

The heterogeneous reaction of ozone with soot aerosol

The loss of ozone on carbon soot aerosol was investigated in the temperature range 238–330 K for reaction times up to 72 h: 200 μg m −3 ozone in dry synthetic air is depleted with an initial reaction probability γ=1.2×10 −6 at 296 K. The reaction probability decreases with a characteristic time τ of about 12 h (1/ τ= k 3=(2.3±0.6)×10 −5 s −1) due to surface passivation. The reaction rate has a positive temperature dependence, and a complex negative dependence on the ozone concentration. A minimum set of four quasi-elementary reactions is required to model the observed concentration and time dependencies of the ozone loss rate: rapid destruction of one monolayer equivalent of ozone on pristine surface sites (SS): SS+O 3→SSO+O 2 (I), ozone-induced recovery of reactive sites: SSO+O 3→SS+2O 2 (or SS'+O 2+CO 2) (IIa,b), spontaneous recovery of reactive sites: SSO→SS'+CO, and spontaneous site passivation: SSO→SS p (III). The kinetic parameters γ 2ab, k 2c , and k 3, which were determined in 11 independent experiments, lead to the following analytical expression for the effective reaction probability γ eff which applies when the fast initial surface oxidation has reached a steady state: γ eff =[2γ 2ab+2.6×10 15k 2c/([ O 3]〈c〉)] exp (−k 3t). This equation is valid over a wide range of atmospheric conditions. It implies that ozone depletion on dry soot aerosol is negligible both in the troposphere and lower stratosphere.

Radiative forcing due to stratospheric ozone changes 1979–1997, using updated trend estimates

Recent estimates of stratospheric ozone changes since 1979, both from satellites and ground‐based instruments, show a smaller rate of ozone loss than previous measurements indicated. This paper calculates the radiative forcing resulting from these ozone changes. The trends are derived from a combination of Stratospheric Aerosol and Gas Experiment (SAGE), Total Ozone Mapping Spectrometer (TOMS), and ground‐based data. By combining these data in a variety of ways, several problems of determining an accurate forcing from available data are highlighted. Using only statistically significant changes, a “best guess” radiative forcing of −0.10±0.02 W m−2 is estimated for the 1979–1997 period which is about 50% less negative than previous estimates of this forcing, but provides an offset of about 10% to the well‐mixed greenhouse gas forcing over the same period.

A test of our understanding of the ozone chemistry in the Arctic polar vortex based on in situ measurements of ClO, BrO, and O3 in the 1994/1995 winter

We present an analysis of in situ measurements of ClO, BrO, O3, and long‐lived tracers obtained on a balloon flight in the Arctic polar vortex launched from Kiruna, Sweden, 68°N, on February 3, 1995. Using the method of tracer correlations, we deduce that the air masses sampled at an altitude of 21 km (480 K potential temperature), where a layer of enhanced ClO mixing ratios of up to 1150 parts per trillion by volume was observed, experienced a cumulative chemical ozone loss of 1.0±0.3 ppmv between late November 1994 and early February 1995. This estimate of chemical ozone loss can be confirmed using independent data sets and independent methods. Calculations using a trajectory box model show that the simulations underestimate the cumulative ozone loss by approximately a factor of 2, although observed ClO and BrO mixing ratios are well reproduced by the model. Employing additional simulations of ozone loss rates for idealized conditions, we conclude that the known chlorine and bromine catalytic cycles destroying odd oxygen with the known rate constants and absorption cross sections do not quantitatively account for the early winter ozone losses infered for air masses observed at 21 km.

Ozone and temperature profiles measured above Kiruna inside, at the edge of, and outside the Arctic Polar Vortex in February and March 1997

Ozone depletion above Kiruna (67.9°N, 21.1°E), Sweden, was investigated using daily ozone and temperature measurements by ozonesondes between 1 February and 25 March 1997. Using UKMO Ertel's potential vorticity (EPV) and wind fields, three dynamically distinct regions were defined on a grid of isentropic surfaces viz.: the polar vortex boundary region characterized by steep EPV gradients, the area poleward of the boundary region (inside the polar vortex), and the area equatorward of the boundary region (outside the polar vortex). Due to dynamically induced displacements of the vortex, measurements were made in all three regions. By calculating the isentropic EPV at each measurement point and comparing it with the values defining the equatorward and poleward edges of the vortex boundary region, all ozone and temperature measurements could be binned according to their position relative to the vortex edge. Since the data outside the polar vortex were highly variable, mean ozone profiles and their standard deviations were calculated and compared only for the two other regions. To investigate whether differences between these mean profiles were indicative of ozone loss, the temporal evolution of ozone mixing ratios measured along several isentropic surfaces was examined, taking into account the diabatic descent of airmasses. Finally, ozone loss rates were calculated for six potential temperature surfaces and loss rates of up to 0.63ppm/month were found inside the Arctic vortex at surfaces descending from approximately 475 K (1 February) to 460 K (25 March).

Correction to “Ozone loss rates in the Arctic stratosphere in the winter 1991/92: Model calculations compared with match results”

Correction to “Ozone loss rates in the Arctic stratosphere in the winter 1991/92: Model calculations compared with match results”

Chemical Ozone Loss in the Arctic Winter 1994/95 as Determined by the Match Technique

The chemically induced ozone loss inside the Arctic vortex during the winter 1994/95 has been quantified by coordinated launches of over 1000 ozonesondes from 35 stations within the Match 94/95 campaign. Trajectory calculations, which allow diabatic heating or cooling, were used to trigger the balloon launches so that the ozone concentrations in a large number of air parcels are each measured twice a few days apart. The difference in ozone concentration is calculated for each pair and is interpreted as a change caused by chemistry. The data analysis has been carried out for January to March between 370 K and 600 K potential temperature. Ozone loss along these trajectories occurred exclusively during sunlit periods, and the periods of ozone loss coincided with, but slightly lagged, periods where stratospheric temperatures were low enough for polar stratospheric clouds to exist. Two clearly separated periods of ozone loss show up. Ozone loss rates first peaked in late January with a maximum value of 53 ppbv per day (1.6 % per day) at 475 K and faster losses higher up. Then, in mid-March ozone loss rates at 475 K reached 34 ppbv per day (1.3 % per day), faster losses were observed lower down and no ozone loss was found above 480 K during that period. The ozone loss in hypothetical air parcels with average diabetic descent rates has been integrated to give an accumulated loss through the winter. The most severe depletion of 2.0 ppmv (60 %) took place in air that was at 515 K on 1 January and at 450 K on 20 March. Vertical integration over the levels from 370 K to 600 K gives a column loss rate, which reached a maximum value of 2.7 Dobson Units per day in mid-March. The accumulated column loss between 1 January and 31 March was found to be 127 DU (∼36 %).

Ozone loss rates in the Arctic stratosphere in the winter 1991/92: Model calculations compared with match results

We present box model calculations of ozone loss rates corresponding to the results of the Match experiment 1991/92. The Match technique infers chemical ozone depletion from an analysis of pairs of balloon soundings that measure ozone in the same airparcel at different points of a calculated trajectory. It allows a quantitative comparison with model results because the exposure of the observed air‐masses to sunlight is well known. The model significantly underestimates the loss rates inferred for January to mid‐February. Extensive sensitivity studies show that the discrepancy between model and Match results cannot be explained by the known uncertainties in the model parameters.

Ground based millimeter‐wave observations of Arctic Ozone depletion during winter and spring of 1996/97

Ground based millimeter‐wave measurements of Arctic stratospheric ozone in the winter 1996/97 are presented. The measurements have been performed at one of the primary Arctic stations of the Network for the Detection of Stratospheric Change (NDSC) in Ny‐Ålesund, Spitsbergen (78.9°N, 11.9°E). Over the period 11 February to 26 April the measurements show an ozone mixing ratio decrease of 1.3 ppm in the lower stratosphere. Correspondingly, stratospheric ozone column densities decreased by more than 50 DU. Taking into account the transport of ozone due to diabatic decent, we estimated chemical ozone loss rates of 22 ppb/day in February decreasing to 15 ppb/day in late April 1997.