Integrated ozone depletion as a metric for ozone recovery

The Montreal Protocol is successfully protecting the ozone layer. The main halogen gases responsible for stratospheric ozone depletion have been regulated under the Protocol, their combined atmospheric abundances are declining and ozone is increasing in some parts of the atmosphere¹. Ozone depletion potentials^2-4, relative measures of compounds' abilities to deplete stratospheric ozone, have been a key regulatory component of the Protocol in successfully guiding the phasing out in the manufacture of the most highly depleting substances. However, this latest, recovery phase in monitoring the success of the Protocol calls for further metrics. The 'delay in ozone return' has been widely used to indicate the effect of different emissions or phase-down strategies, but we argue here that it can sometimes be ambiguous or even of no use. Instead, we propose the use of an integrated ozone depletion (IOD) metric to indicate the impact of any new emission. The IOD measures the time-integrated column ozone depletion and depends only on the emission strength and the whole atmosphere and stratospheric lifetimes of the species considered. It provides a useful complementary metric of the impact of specific emissions of an ozone depleting substance for both the scientific and policy communities.

Spatio-Temporal Variability of Aerosol Optical Depth, Total Ozone and NO2 Over East Asia: Strategy for the Validation to the GEMS Scientific Products

In this study, the spatio-temporal variability of aerosol optical depth (AOD), total column ozone (TCO), and total column NO2 (TCN) was identified over East Asia using long-term datasets from ground-based and satellite observations. Based on the statistical results, optimized spatio-temporal ranges for the validation study were determined with respect to the target materials. To determine both spatial and temporal ranges for the validation study, we confirmed that the observed datasets can be statistically considered as the same quantity within the ranges. Based on the thresholds of R2>0.95 (temporal) and R>0.95 (spatial), the basic ranges for spatial and temporal scales for AOD validation was within 30 km and 30 min, respectively. Furthermore, the spatial scales for AOD validation showed seasonal variation, which expanded the range to 40 km in summer and autumn. Because of the seasonal change of latitudinal gradient of the TCO, the seasonal variation of the north-south range is a considerable point. For the TCO validation, the north-south range is varied from 0.87° in spring to 1.05° in summer. The spatio-temporal range for TCN validation was 20 min (temporal) and 20–50 km (spatial). However, the nearest value of satellite data was used in the validation because the spatio-temporal variation of TCN is large in summer and autumn. Estimation of the spatio-temporal variability for respective pollutants may contribute to improving the validation of satellite products.

Fossil pollen and spores as a tool for reconstructing ancient solar-ultraviolet irradiance received by plants: an assessment of prospects and challenges using proxy-system modelling

Ultraviolet-B radiation (UV-B, 280-315 nm) constitutes less than 1% of the total solar radiation that reaches the Earth's surface but has a disproportional impact on biological and ecological processes from the individual to the ecosystem level. Absorption of UV-B by ozone is also one of the primary heat sources to the stratosphere, so variations in UV-B have important relationships to the Earth's radiation budget. Yet despite its importance for understanding atmospheric and ecological processes, there is limited understanding about the changes in UV-B radiation in the geological past. This is because systematic measurements of total ozone and surface UV-B only exist since the 1970s, so biological or geochemical proxies from sediment archives are needed to reconstruct UV-B irradiance received at the Earth surface beyond the experimental record. Recent developments have shown that the quantification of UV-B-absorbing compounds in pollen and spores have the potential to provide a continuous record of the solar-ultraviolet radiation received by plants. There is increasing interest in developing this proxy in palaeoclimatic and palaeoecological research. However, differences in interpretation exist between palaeoecologists, who are beginning to apply the proxy under various geological settings, and UV-B ecologists, who question whether a causal dose-response relationship of pollen and spore chemistry to UV-B irradiance has really been established. Here, we use a proxy-system modelling approach to systematically assess components of the pollen- and spore-based UV-B-irradiance proxy to ask how these differences can be resolved. We identify key unknowns and uncertainties in making inferences about past UV-B irradiance, from the pollen sensor, the sedimentary archive, and through the laboratory and experimental procedures in order to target priority areas of future work. We argue that an interdisciplinary approach, modifying methods used by plant ecologists studying contemporary responses to solar-UV-B radiation specifically to suit the needs of palaeoecological analyses, provides a way forward in developing the most reliable reconstructions for the UV-B irradiance received by plants across a range of timescales.

Stratospheric ozone depletion due to nitrous oxide: influences of other gases

The effects of anthropogenic emissions of nitrous oxide (N(2)O), carbon dioxide (CO(2)), methane (CH(4)) and the halocarbons on stratospheric ozone (O(3)) over the twentieth and twenty-first centuries are isolated using a chemical model of the stratosphere. The future evolution of ozone will depend on each of these gases, with N(2)O and CO(2) probably playing the dominant roles as halocarbons return towards pre-industrial levels. There are nonlinear interactions between these gases that preclude unambiguously separating their effect on ozone. For example, the CH(4) increase during the twentieth century reduced the ozone losses owing to halocarbon increases, and the N(2)O chemical destruction of O(3) is buffered by CO(2) thermal effects in the middle stratosphere (by approx. 20% for the IPCC A1B/WMO A1 scenario over the time period 1900-2100). Nonetheless, N(2)O is expected to continue to be the largest anthropogenic emission of an O(3)-destroying compound in the foreseeable future. Reductions in anthropogenic N(2)O emissions provide a larger opportunity for reduction in future O(3) depletion than any of the remaining uncontrolled halocarbon emissions. It is also shown that 1980 levels of O(3) were affected by halocarbons, N(2)O, CO(2) and CH(4), and thus may not be a good choice of a benchmark of O(3) recovery.

Does cosmic-ray-induced heterogeneous chemistry influence stratospheric polar ozone loss?

Cosmic-ray (CR) -induced heterogeneous reactions of halogenated species have been suggested to play the dominant role in causing the Antarctic ozone hole. However, measurements of total ozone in Antarctica do not show a compact and significant correlation with CR activity. Further, a substantial CR-induced heterogeneous loss of chlorofluorocarbons is incompatible with multiyear satellite observations of N2O and CFC-12. Thus, CR-induced heterogeneous reactions cannot be considered as an alternative mechanism causing the Antarctic ozone hole.

Testing the applicability of artificial intelligence techniques to the subject of erythemal ultraviolet solar radiation. Part two: an intelligent system based on multi-classifier technique

The problem we address here describes the on-going research effort that takes place to shed light on the applicability of using artificial intelligence techniques to predict the local noon erythemal UV irradiance in the plain areas of Egypt. In light of this fact, we use the bootstrap aggregating (bagging) algorithm to improve the prediction accuracy reported by a multi-layer perceptron (MLP) network. The results showed that, the overall prediction accuracy for the MLP network was only 80.9%. When bagging algorithm is used, the accuracy reached 94.8%; an improvement of about 13.9% was achieved. These improvements demonstrate the efficiency of the bagging procedure, and may be used as a promising tool at least for the plain areas of Egypt.

Temperature Dependence of the HO2 + ClO Reaction. 2. Reaction Kinetics Using the Discharge-Flow Resonance-Fluorescence Technique

The total rate coefficient, k3, for the reaction HO2 + ClO --> products has been determined over the temperature range of 220-336 K at a total pressure of approximately 1.5 Torr of helium using the discharge-flow resonance-fluorescence technique. Pseudo-first-order conditions were used with both ClO and HO2 as excess reagents using four different combinations of precursor molecules. HO2 molecules were formed by using either the termolecular association of H atoms in an excess of O2 or via the reaction of F atoms with an excess of H(2)O(2). ClO molecules were formed by using the reaction of Cl atoms with an excess of O3 or via the reaction of Cl atoms with Cl(2)O. Neither HO2 nor ClO were directly observed during the course of the experiments, but these species were converted to OH or Cl radicals, respectively, via reaction with NO prior to their observation. OH fluorescence was observed at 308 nm, whereas Cl fluorescence was observed at approximately 138 nm. Numerical simulations show that under the experimental conditions used secondary reactions did not interfere with the measurements; however, some HO2 was lost on conversion to OH for experiments in excess HO2. These results were corrected to compensate for the simulated loss. At 296 K, the rate coefficient was determined to be (6.4 +/- 1.6) x 10(-12) cm3 molecule(-1) s(-1). The temperature dependence expressed in Arrhenius form is (1.75 +/- 0.52) x 10-12 exp[(368 +/- 78)/T] cm3 molecule(-1) s(-1). The Arrhenius expression is derived from a fit weighted by the reciprocal of the measurement errors of the individual data points. The uncertainties are cited at the level of two standard deviations and contain contributions from statistical errors from the data analysis in addition to estimates of the systematic experimental errors and possible errors from the applied model correction.

Ozone and UV Radiation over Southern South America: Climatology and Anomalies

Ozone and UV radiation were analyzed at eight stations from tropical to sub-Antarctic regions in South America. Ground UV irradiances were measured by multichannel radiometers as part of the Inter American Institute for Global Change Radiation network. The irradiance channels used for this study were centered at 305 nm (for UV-B measurements) and 340 nm (for UV-A measurements). Results were presented as daily maximum irradiances, as monthly averaged, daily integrated irradiances and as the ratio of 305 nm to 340 nm. These findings are the first to be based on a long time series of semispectral data from the southern region of South America. As expected, the UV-B channel and total column ozone varied with latitude. The pattern of the UV-A channel was more complex because of local atmospheric conditions. Total column ozone levels of < 220 Dobson Units were observed at all sites. Analysis of autocorrelations showed a larger persistence of total column ozone level than irradiance. A decreasing cross-correlation coefficient between 305 and 340 nm and an increasing cross-correlation coefficient between 305 nm and ozone were observed at higher latitudes, indicating that factors such as cloud cover tend to dominate at northern sites and that ozone levels tend to dominate at southern sites. These results highlight the value of long-term monitoring of radiation with multichannel radiometers to determine climatological data and evaluate the combination of factors affecting ground UV radiation.