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Journal ArticleDOI

Nitrate-induced photooxidation of trace organic chemicals in water.

01 May 1987-Environmental Science & Technology (American Chemical Society)-Vol. 21, Iss: 5, pp 443-450
TL;DR: The oxidation kinetics of butyl chloride, nitrobenzene, anisole, and methylmercury in the presence of hydroxyl radical (OH) scavengers were used to determine the rate and quantum efficiency for production of OH from irradiated nitrate ions in water.
Abstract: The oxidation kinetics of butyl chloride, nitrobenzene, anisole, and methylmercury in the presence of hydroxyl radical (OH) scavengers were used to determine the rate and quantum efficiency for production of OH from irradiated nitrate ions in water. The experiments were conducted under steady-state irradiations with monochromatic radiation (313 nm) and with sunlight. The mean quantum efficiency for OH production at 313 nm rises from 0.013 +/- 0.002 at 20 /sup 0/C to 0.017 +/- 0.003 at 30 /sup 0/C in the pH range 6.2-8.2. Results of this study are used to estimate nitrate-induced photooxidation rates of trace organic chemicals under a variety of environmental conditions. 27 references, 6 figures, 2 tables.
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TL;DR: For six selected pharmaceuticals present in the STP effluents, the persistence towards abiotic photodegradation was evaluated submitting them to solar experiments at 40 degrees N latitude during spring and summer, based on experimentally measured quantum yields for the direct photolysis in bi-distilled water, half-life times at varying seasons and latitude were predicted for each substance.

1,239 citations

Journal ArticleDOI
TL;DR: It will be several years before the beginning of an ozone recovery can be unambiguously identified at individual locations, and future changes in greenhouse gases will affect the future evolution of ozone through chemical, radiative, and dynamic processes.
Abstract: Stratospheric ozone levels are near their lowest point since measurements began, so current ultraviolet-B (UV-B) radiation levels are thought to be close to their maximum. Total stratospheric content of ozone-depleting substances is expected to reach a maximum before the year 2000. All other things being equal, the current ozone losses and related UV-B increases should be close to their maximum. Increases in surface erythemal (sunburning) UV radiation relative to the values in the 1970s are estimated to be: about 7% at Northern Hemisphere mid-latitudes in winter/spring; about 4% at Northern Hemisphere mid-latitudes in summer/fall; about 6% at Southern Hemisphere mid-latitudes on a year-round basis; about 130% in the Antarctic in spring; and about 22% in the Arctic in spring. Reductions in atmospheric ozone are expected to result in higher amounts of UV-B radiation reaching the Earth's surface. The expected correlation between increases in surface UV-B radiation and decreases in overhead ozone has been further demonstrated and quantified by ground-based instruments under a wide range of conditions. Improved measurements of UV-B radiation are now providing better geographical and temporal coverage. Surface UV-B radiation levels are highly variable because of cloud cover, and also because of local effects including pollutants and surface reflections. These factors usually decrease atmospheric transmission and therefore the surface irradiances at UV-B as well as other wavelengths. Occasional cloud-induced increases have also been reported. With a few exceptions, the direct detection of UV-B trends at low- and mid-latitudes remains problematic due to this high natural variability, the relatively small ozone changes, and the practical difficulties of maintaining long-term stability in networks of UV-measuring instruments. Few reliable UV-B radiation measurements are available from pre-ozone-depletion days. Satellite-based observations of atmospheric ozone and clouds are being used, together with models of atmospheric transmission, to provide global coverage and long-term estimates of surface UV-B radiation. Estimates of long-term (1979-1992) trends in zonally averaged UV irradiances that include cloud effects are nearly identical to those for clear-sky estimates, providing evidence that clouds have not influenced the UV-B trends. However, the limitations of satellite-derived UV estimates should be recognized. To assess uncertainties inherent in this approach, additional validations involving comparisons with ground-based observations are required. Direct comparisons of ground-based UV-B radiation measurements between a few mid-latitude sites in the Northern and Southern Hemispheres have shown larger differences than those estimated using satellite data. Ground-based measurements show that summertime erythemal UV irradiances in the Southern Hemisphere exceed those at comparable latitudes of the Northern Hemisphere by up to 40%, whereas corresponding satellite-based estimates yield only 10-15% differences. Atmospheric pollution may be a factor in this discrepancy between ground-based measurements and satellite-derived estimates. UV-B measurements at more sites are required to determine whether the larger observed differences are globally representative. High levels of UV-B radiation continue to be observed in Antarctica during the recurrent spring-time ozone hole. For example, during ozone-hole episodes, measured biologically damaging radiation at Palmer Station, Antarctica (64 degrees S) has been found to approach and occasionally even exceed maximum summer values at San Diego, CA, USA (32 degrees N). Long-term predictions of future UV-B levels are difficult and uncertain. Nevertheless, current best estimates suggest that a slow recovery to pre-ozone depletion levels may be expected during the next half-century. (ABSTRACT TRUNCATED)

1,152 citations

Journal ArticleDOI
TL;DR: In this article, a chemical probe method was developed to identify the active radical species, and differences between the reactivity of the probe compounds and the potential radical species were observed, and the usage of various probes, including tert-butyl alcohol, phenol, and nitrobenzene, for simultaneously identifying SO4−•/HO• was investigated.
Abstract: Thermal activation can induce persulfate (S2O82−) degradation to form sulfate radicals (SO4−•) that can undergo radical interconversion to form hydroxyl radicals (HO•) under alkaline conditions. The radicals SO4−•/HO• can be present either individually or simultaneously in the persulfate oxidation system. To identify the active radical species, a chemical probe method was developed. An excess of probe compounds was added to the system, and differences between the reactivity of the probes and the potential radical species were observed. The usage of various probes, including tert-butyl alcohol, phenol, and nitrobenzene (NB), for simultaneously identifying SO4−•/HO• was investigated. NB can only react with radicals: it cannot react with persulfate. The reaction rate of NB with HO• is 3000−3900 times greater than that of NB with SO4−•, which is a good candidate for use as a probe for differentiating between SO4−•/HO• reactivity. Furthermore, the effects of pH on the formation of SO4−•/HO• were demonstrated b...

1,018 citations

Journal ArticleDOI
TL;DR: A review of the experimental work on NO2− and NO3− photolysis in the context of recent advances in the understanding of the chemistry of the peroxynitrite anion (ONOO−) in biological experiments is presented in this article.
Abstract: It has long been known that the photolysis of nitrite and nitrate solutions results in the formation of OH radicals. The mechanism of NO3− photolysis has been the subject of considerable controversy in the literature, however. This review summarizes the experimental work on NO2− and NO3− photolysis in the context of recent advances in the understanding of the chemistry of the peroxynitrite anion (ONOO−) in biological experiments. ONOO− has been found to play a far more significant role in the overall reaction mechanism of NO3− photolysis than had previously been suspected. Research on NO2− and NO3− photolysis, as a pathway to the destruction of organic contaminants in natural waters, is summarized. The possible impact of NO2− and NO3− on Advanced Oxidation Technologies (AOTs), in which OH radicals are used to initiate the destruction of hazardous organic pollutants in drinking water and industrial waste streams, is explored.

918 citations

Journal ArticleDOI
TL;DR: For a given oxidant dose, the selective oxidants were more efficient than hydroxyl radicals for transforming ERMs-containing micropollutants, while hydroxy radicals are capable of transforming micropolutants even without ERMs.

656 citations