A. R. Ravishankara

Bio: A. R. Ravishankara is an academic researcher from Cooperative Institute for Research in Environmental Sciences. The author has contributed to research in topics: Absorption spectroscopy & Laser-induced fluorescence. The author has an hindex of 10, co-authored 13 publications receiving 6699 citations. Previous affiliations of A. R. Ravishankara include National Oceanic and Atmospheric Administration & University of Colorado Boulder.

Chemical kinetics and photochemical data for use in stratospheric modeling

Abstract: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available from the Jet Propulsion Laboratory.

Chemical kinetics and photochemical data for use in stratospheric modeling

Abstract: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available from the Jet Propulsion Laboratory.

Ozone depletion and global warming potentials of CF3I

Abstract: Laboratory measurements of the infrared and near-ultraviolet absorption characteristics of CF{sub 3}I (a potentially useful substitute for halons) are presented. Using these data together with a detailed photochemical model, it is shown that the lifetime of this gas in the sunlit atmosphere is less than a day. The chemistry of iodine in the stratosphere is evaluated, and it is shown that any iodine that reaches the stratosphere will be very effective for ozone destruction here. However, the extremely short lifetime of CF{sub 3}I greatly limits its transport to the stratosphere when released at the surface, especially at midlatitudes, and the total anthropogenic surface release of CF{sub 3}I is likely to be far less than that of natural iodocarbons such as CH{sub 3}I on a global basis. It is highly probable that the steady-state ozone depletion potential (ODP) of CF{sub 3}I for surface releases is less than 0.008 and more likely baelow 0.0001. Measured infrared absorption data are also combined with the lifetime to show that the 20-year global warming potential (GWP) of this gas is likely to be very small, less than 5. Therefore this study suggests that neither the ODP nor the GWP of this gas represent significant obstaclesmore » to its use as a replacement for halons. 34 refs., 3 figs., 2 tabs.« less

Absorption cross sections for OClO as a function of temperature in the wavelength range 240-480 nm

Abstract: The absorption spectrum of OClO has been measured by using a diode array spectrometer with a resolution of 0.25 nm at 204, 296, and 378 K in the wavelength range of 240-480 nm. Absolute absorption cross sections were determined by measuring OClO concentration using two independent methods. The general features of the spectrum at 396 K agree with previous observations. The individual bands of OClO get sharper and the peak cross sections increase as the temperature is lowered from 378 to 204 K.

Reactions of O(3P) with alkyl iodides: Rate coefficients and reaction products

Abstract: The rate coefficients for the reactions of O(3P) with CF3I (1) and CH3I (2) were measured between 213 and 364 K to be: k1(T) = (7.9 ± 0.8) x 10-12 exp[−(175 ± 40)/T] and k2(T) = (1.0 ± 0.2) x 10-11 exp[(160 ± 50)/T] cm3 molecule-1 s-1. The rate coefficients for the reaction of O(3P) with CD3I, (CH3)2CHCH2I, (CH3)2CHI, CF3CH2I, CF3CHFI, and CF3CF2I at 298 K were also measured. The yields of the IO and CF3O products in reaction 1 at 298 K were found to be 0.83 ± 0.09 and <0.01, respectively. Product yields of reaction 2 at 298 K were measured to be IO (0.44 ± 0.04), OH (0.16 ± 0.05), H (0.07 ± 0.02), CH3O (<0.03), and HI (<0.05). IO, OH, and CH3O were detected via laser-induced fluorescence, O and H atoms via resonance fluorescence, and IO, CF3O, and HI by chemical ionization mass spectrometry. The IO yield from reactions 1 and 2 showed a slight positive temperature dependence. Within our experimental error the OH yield from reaction 2 was temperature independent. An upper limit for the enthalpy of formati...

Chemical kinetics and photochemical data for use in stratospheric modeling

Abstract: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available from the Jet Propulsion Laboratory.

Perfluoroalkyl and polyfluoroalkyl substances in the environment: Terminology, classification, and origins

Abstract: The primary aim of this article is to provide an overview of perfluoroalkyl and polyfluoroalkyl substances (PFASs) detected in the environment, wildlife, and humans, and recommend clear, specific, and descriptive terminology, names, and acronyms for PFASs. The overarching objective is to unify and harmonize communication on PFASs by offering terminology for use by the global scientific, regulatory, and industrial communities. A particular emphasis is placed on long-chain perfluoroalkyl acids, substances related to the long-chain perfluoroalkyl acids, and substances intended as alternatives to the use of the long-chain perfluoroalkyl acids or their precursors. First, we define PFASs, classify them into various families, and recommend a pragmatic set of common names and acronyms for both the families and their individual members. Terminology related to fluorinated polymers is an important aspect of our classification. Second, we provide a brief description of the 2 main production processes, electrochemical fluorination and telomerization, used for introducing perfluoroalkyl moieties into organic compounds, and we specify the types of byproducts (isomers and homologues) likely to arise in these processes. Third, we show how the principal families of PFASs are interrelated as industrial, environmental, or metabolic precursors or transformation products of one another. We pay particular attention to those PFASs that have the potential to be converted, by abiotic or biotic environmental processes or by human metabolism, into long-chain perfluoroalkyl carboxylic or sulfonic acids, which are currently the focus of regulatory action. The Supplemental Data lists 42 families and subfamilies of PFASs and 268 selected individual compounds, providing recommended names and acronyms, and structural formulas, as well as Chemical Abstracts Service registry numbers. Integr Environ Assess Manag 2011;7:513–541. © 2011 SETAC

The reaction of no with superoxide

Abstract: The rate constant for the reaction of NO with ·O2− was determined to be (6.7 ± 0.9) × 109 1 mol−1 s−1, considerably higher than previously reported. Rate measurements were made from pH 5.6 to 12.5 ...