J. G. Anderson

Free Radicals Within the Antarctic Vortex: The Role of CFCs in Antarctic Ozone Loss

How strong is the case linking global release of chlorofluorocarbons to episodic disappearance of ozone from the Antarctic stratosphere each austral spring? Three lines of evidence defining a link are (i) observed containment in the vortex of ClO concentrations two orders of magnitude greater than normal levels; (ii) in situ observations obtained during ten high-altitude aircraft flights into the vortex as the ozone hole was forming that show a decrease in ozone concentrations as ClO concentrations increased; and (iii) a comparison between observed ozone loss rates and those predicted with the use of absolute concentrations of ClO and BrO, the rate-limiting radicals in an array of proposed catalytic cycles. Recent advances in our understanding of the kinetics, photochemistry, and structural details of key intermediates in these catalytic cycles as well as an improved absolute calibration for ClO and BrO concentrations at the temperatures and pressures encountered in the lower antarctic stratosphere have been essential for defining the link.

RANDOMISED CONTROLLED TRIAL OF RECOMBINANT TISSUE PLASMINOGEN ACTIVATOR VERSUS UROKINASE IN THE TREATMENT OF ACUTE PULMONARY EMBOLISM

The effect of intravenous recombinant human tissue-type plasminogen activator (rt-PA) was compared with that of urokinase in 45 patients with angiographically documented pulmonary embolism (PE) in a randomised controlled trial. The two principal end-points were clot lysis at 2 h, as assessed by angiography, and pulmonary reperfusion at 24 h, as assessed by perfusion lung scanning. All patients received the full dose of rt-PA but urokinase infusions were terminated prematurely (on average after 18 h) in 9 patients because of allergy in 1 and uncontrollable bleeding in 8. By 2 h, 82% of rt-PA-treated patients showed clot lysis, compared with 48% of urokinase-treated patients (p = 0.008; 95% CI for the difference = 10-58%). Improvement in lung scan reperfusion at 24 h was identical in the two treatment groups. The reduction in fibrinogen did not differ significantly between the rt-PA and urokinase groups (45% vs 39% at 2 h and 34% vs 40% at 24 h). The results indicate that in the dose regimens employed, rt-PA acts more rapidly and is safer than urokinase in the treatment of acute PE.

Prognostic Factors in Neuroblastoma

Known prognostic factors in neuroblastoma were analyzed in 124 children to determine which were independent and which were most useful in predicting outcome. The following factors were analyzed: age, sex, stage of disease, serum neuron‐specific enolase (NSE), serum ferritin, E‐rosette inhibition, urinary catecholamines, and histologic type according to the criteria of Shimada. Estimates of survival were calculated using the method of Kaplan and Meier. The overall survival for 124 patients was 60% at 2 years. There were significant differences in survival by pathology, age, NSE, ferritin, vanilmandelic acid (VMA): homovanillic acid (HVA) ratio, and stage. There was a strong association among NSE, age, stage, and ferritin. Using the recursive partitioning approach, it was possible to subdivide patients into three groups (based on diagnostic values of ferritin, age, and stage) with a good, intermediate, and poor prognosis and estimated 2‐year survival of 100%, 62%, and 19%, respectively. Further analysis could not be done because of small numbers in the subgroups, but the results suggest that combinations of age, stage, serum ferritin, and histologic type may be able to define two populations: favorable with 80% + 2‐year survival and unfavorable with less than 20%.

Removal of Stratospheric O3 by Radicals: In Situ Measurements of OH, HO2, NO, NO2, ClO, and BrO

Simultaneous in situ measurements of the concentrations of OH, HO2, ClO, BrO, NO, and NO2 demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO2 with ozone, accounted for nearly one-half of the total O3 removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O3; reactions involving BrO account for one-half of this loss. Catalytic destruction by NO2, which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O3 removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO2 and ClO are inversely correlated with those of NO and NO2. The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O3 removal was inversely correlated with total NOx, loading.

Ultrasensitive absorption spectroscopy with a high-finesse optical cavity and off-axis alignment

A simple and easy to use method that allows high-finesse optical cavities to be used as absorption cells for spectroscopic purposes is presented. This method introduces a single-mode continuous-wave laser into the cavity by use of an off-axis cavity alignment geometry to eliminate systematically the resonances commonly associated with optical cavities, while preserving the absorption signal amplifying properties of such cavities. This considerably reduces the complexity of the apparatus compared with other high-resolution cavity-based absorption methods. Application of this technique in conjunction with either cavity ringdown spectroscopy or integrated cavity output spectroscopy produced absorption sensitivities of 1.5 x 10(-9) cm(-1) Hz(-1/2) and 1.8 x 10(-10) cm(-1) Hz(-1/2), respectively.

The effect of climate change on ozone depletion through changes in stratospheric water vapour

Several studies have predicted substantial increases in Arctic ozone depletion due to the stratospheric cooling induced by increasing atmospheric CO2 concentrations. But climate change may additionally influence Arctic ozone depletion through changes in the water vapour cycle. Here we investigate this possibility by combining predictions of tropical tropopause temperatures from a general circulation model with results from a one-dimensional radiative convective model, recent progress in understanding the stratospheric water vapour budget, modelling of heterogeneous reaction rates and the results of a general circulation model on the radiative effect of increased water vapour. Whereas most of the stratosphere will cool as greenhouse-gas concentrations increase, the tropical tropopause may become warmer, resulting in an increase of the mean saturation mixing ratio of water vapour and hence an increased transport of water vapour from the troposphere to the stratosphere. Stratospheric water vapour concentration in the polar regions determines both the critical temperature below which heterogeneous reactions on cold aerosols become important (the mechanism driving enhanced ozone depletion) and the temperature of the Arctic vortex itself. Our results indicate that ozone loss in the later winter and spring Arctic vortex depends critically on water vapour variations which are forced by sea surface temperature changes in the tropics. This potentially important effect has not been taken into account in previous scenarios of Arctic ozone loss under climate change conditions.

Late complications of therapy in 213 children with localized, nonorbital soft-tissue sarcoma of the head and neck : A descriptive report from the intergroup rhabdomyosarcoma studies (IRS)-II and - III

Background. This review of children and adolescents with nonorbital soft-tissue sarcoma of the head and neck was undertaken to describe late sequelae of treatment, as manifested primarily by problems with statural growth, facial and nuchal symmetry, dentition, vision and hearing, and school performance, Procedure. Four hundred sixty-nine patients entered the IRS-II and -III protocols with localized, nonorbital soft-tissue sarcomas of the head and neck from 1978 through 1987, Their overall survival rate was 53% (250/469) at 5 years. Two hundred thirteen patients were surviving relapse free 5 or more years after diagnosis, for whom there were serial height measurements at 2 or more years after initiation of therapy. Their me dian age at diagnosis was 5 years; the median length of follow-up was 7 years. All received multiple-agent chemotherapy, and all but 3 received irradiation to the primary tumor volume Sixty-eight percent of the tumors arose in cranial parameningeal sites, 22% in nonparameningeal sites, and 10% in the neck. We reviewed flow sheets submitted to the IRS Group Statisti cal Office to ascertain which late sequelae were recorded. Results. One hundred sixty-four patients (77%) had one or more problems recorded. One hundred ninety of the two hundred thirteen patients (89%) were under 15 years of age at study entry, and at follow-up 92 (48%) had failed to maintain their initial height velocity, which had decreased by more than 25 percentile points from the original value. Thirty-six of the one hundred ninety patients (19%) were receiving growth hormone injections.

Achieving Climate Change Absolute Accuracy in Orbit

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREOs inherently high absolute accuracy will be verified and traceable on orbit to Systeme Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earths thermal infrared spectrum (5–50 μm), the spectrum of solar radiation reflected by the Earth and its atmosphere (320–2300 nm), and radio occultation refractivity from which...

Chlorine chemistry on polar stratospheric cloud particles in the Arctic winter

Simultaneous in situ measurements of hydrochloric acid (HCl) and chlorine monoxide (ClO) in the Arctic winter vortex showed large HCl losses, of up to 1 part per billion by volume (ppbv), which were correlated with high ClO levels of up to 1.4 ppbv. Air parcel trajectory analysis identified that this conversion of inorganic chlorine occurred at air temperatures of less than 196 � 4 kelvin. High ClO was always accompanied by loss of HCI mixing ratios equal to �(ClO + 2Cl2O2). These data indicate that the heterogeneous reaction HCl + ClONO2 → Cl2 + HNO3 on particles of polar stratospheric clouds establishes the chlorine partitioning, which, contrary to earlier notions, begins with an excess of ClONO2, not HCl.

New fast response photofragment fluorescence hygrometer for use on the NASA ER‐2 and the Perseus remotely piloted aircraft

We have developed an in situ instrument to measure water vapor on the NASA ER‐2 as a prototype for use on the Perseus remotely piloted aircraft. It utilizes photofragment fluorescence throughout the stratosphere and the upper to middle troposphere (mixing ratios from 2 to 300 ppmv) with simultaneous absorption measurements in the middle troposphere (water vapor concentrations ≳5×1014 mol/cc). The instrument flew successfully on the NASA ER‐2 aircraft during the 1993 CEPEX and SPADE campaigns. The 2σ measurement precision for a 10 s integration time, limited by variation in the background from scattered solar radiation, is ±6% and the data were tightly correlated with other long‐lived stratospheric tracers throughout the SPADE mission. Its accuracy is estimated to be ±10%, based on laboratory calibrations using a range of water vapor concentrations independently determined by both standard gas addition techniques and by absorption. This accuracy is confirmed by in‐flight absorption measurements in the trop...