A. R. Ravishankara

Bio: A. R. Ravishankara is an academic researcher from National Oceanic and Atmospheric Administration. The author has contributed to research in topics: Reaction rate constant & Kinetics. The author has an hindex of 41, co-authored 88 publications receiving 5129 citations. Previous affiliations of A. R. Ravishankara include Cooperative Institute for Research in Environmental Sciences & University of Colorado Boulder.

Oxidation of carbon disulfide by reaction with hydroxyl. 2. Yields of hydroperoxyl and sulfur dioxide in oxygen

Abstract: The products of the OH-initiated oxidation of CS{sub 2} have been investigated. Analysis of the OH loss and the HS production using a laser magnetic resonance (LMR) discharge-flow apparatus yielded k{sub 1} < 3 {times} 10{sup {minus}15} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} for the reaction OH + CS{sub 2} {yields} HS + OCS (1) (340 K and 5 Torr (He)). HO{sub 2} was identified by LMR detection as a major product from this chemistry.

Reactions on tropospheric condensed matter Plenary Lecture

Abstract: Reactions on/in condensed media play important roles in the chemistry of the troposphere. These reactions can be classified as heterogeneous reactions, those occurring on the surfaces of solids, and multiphase reactions, those occurring inside a liquid droplet. A few general considerations in the treatment of heterogeneous and multiphase reactions are discussed. Based on the knowledge and experience obtained from the study of stratospheric heterogeneous and multiphase reactions, possible characteristics of such processes in the troposphere are described and illustrated using a few examples. It is noted that the variety of condensed media in the troposphere makes this a rich field for investigation. The possible importance of reduction reactions in the oxidizing atmosphere is examined. The reactions on soot are highlighted and the potential importance of reactions on organic aerosol and other media is discussed. Finally, the outlook for progress in this area is very briefly discussed.

Kinetics and mechanism of the self-reaction of the bromine oxide radical

Abstract: A flash photolysis-long path absorption technique was used to measure the rate coefficients for the self-reaction of BrO at 298 and 220 K over a pressure range of 75-600 Torr of He, N 2 , and SF 6 . The rate coefficients were measured using both a conventional monochromator/photomultiplier (PMT) system and a diode array spectrometer system. The overall rate coefficient for this reaction was found to be (2.75±0,50)×10 -12 cm 3 molecule -1 s -1 , independent of pressure at 298 K but dependent on pressure at 220 K, ranging from (2.00±0.41)×10 -12 at 100 Torr to (3.10±0.30)×10 +12 cm 3 molecule -1 s -1 at 400 Torr

Atmospheric Chemistry of (Z)-CF3CH═CHCF3: OH Radical Reaction Rate Coefficient and Global Warming Potential

Abstract: Rate coefficients, k, for the gas-phase reaction of the OH radical with (Z)-CF(3)CH═CHCF(3) (cis-1,1,1,4,4,4-hexafluoro-2-butene) were measured under pseudo-first-order conditions in OH using pulsed laser photolysis (PLP) to produce OH and laser-induced fluorescence (LIF) to detect it. Rate coefficients were measured over a range of temperatures (212-374 K) and bath gas pressures (20-200 Torr; He, N(2)) and found to be independent of pressure over this range of conditions. The rate coefficient has a non-Arrhenius behavior that is well-described by the expression k(1)(T) = (5.73 ± 0.60) × 10(-19) × T(2) × exp[(678 ± 10)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K) was measured to be (4.91 ± 0.50) × 10(-13) cm(3) molecule(-1) s(-1) and the uncertainties are at the 2σ level and include estimated systematic errors. Rate coefficients for the analogous OD radical reaction were determined over a range of temperatures (262-374 K) at 100 Torr (He) to be k(2)(T) = (4.81 ± 0.20) × 10(-19) × T(2) × exp[(776 ± 15)/T], with k(2)(296 K) = (5.73 ± 0.50) × 10(-13) cm(3) molecule(-1) s(-1). OH radical rate coefficients were also measured at 296, 345, and 375 K using a relative rate technique and found to be in good agreement with the PLP-LIF results. A room-temperature rate coefficient for the O(3) + (Z)-CF(3)CH═CHCF(3) reaction was measured using an absolute method with O(3) in excess to be <6 × 10(-21) cm(3) molecule(-1) s(-1). The atmospheric lifetime of (Z)-CF(3)CH═CHCF(3) due to loss by OH reaction was estimated to be ~20 days. Infrared absorption spectra of (Z)-CF(3)CH═CHCF(3) measured in this work were used to determine a (Z)-CF(3)CH═CHCF(3) global warming potential (GWP) of ~9 for the 100 year time horizon. A comparison of the OH reactivity of (Z)-CF(3)CH═CHCF(3) with other unsaturated fluorinated compounds is presented.

Atmospheric fate of several hydrofluoroethanes and hydrochloroethanes: 2. UV absorption cross sections and atmospheric lifetimes

Abstract: The temperature dependent UV absorption cross-sections of the hydrochlorofluoroethanes CF3CHFCl, CH3CF2Cl, and CF3CHCl2 are reported. The UV absorption cross-sections were measured over the temperature range 203 to 295 K and the wavelength range 190 to 230 nm. The hydrofluorocarbons CH3CF2H and CF3CH2F were also studied at 295 K and upper limits for their UV absorption cross-sections over the wavelength range 190 to 230 nm were obtained. The atmospheric lifetimes of these species were calculated using a one-dimensional atmospheric model, using the kinetic data obtained in the previous paper (Gierczak et al. 1991) and the absorption cross-section data obtained in the present study.

The HITRAN 2008 molecular spectroscopic database

Abstract: This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Anthropogenic and Natural Radiative Forcing

Abstract: This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)