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.

Observation of methylthiyl radical addition to oxygen in the gas phase

Abstract: This report observes for the first time the reversible addition of: CH{sub 3}S + O{sub 2} {r_equilibrium} CH{sub 3}SOO, in the gas phase (T = 216-258 K) by detecting CH{sub 3}S radicals. Also briefly described is the thermochemical and kinetic information of this system and its importance to the atmospheric oxidation of reduced sulfur compounds.

Photodissociation of HNO3 at 193, 222, and 248 nm: Products and quantum yields

Abstract: The quantum yields for OH, O(3P), O(1D), and H(2S) from the photolysis of HNO3 have been determined at 248, 222, and 193 nm at 298 K. The quantum yield for OH was observed to be near unity at 248 [Φ(OH)=0.95±0.09] and 222 nm [Φ(OH)=0.90±0.11]. However, at 193 nm the quantum yield for OH was found to be 0.33±0.06. The quantum yield for O atoms [O(3P)+O(1D)], Φ(O), was observed to be 0.031±0.010, 0.20±0.03, 0.81±0.13, at 248, 222, and 193 nm, respectively. Both O(3P) and O(1D) were observed at 222 and 193 nm, but only O(3P) was detected at 248 nm. It was observed that 40% of the O atoms formed at both 193 and 222 nm were O(1D) atoms. The upper limits for H(2S) quantum yields: Φ(H)≤0.002 at 248 nm, ≤0.01 at 222 nm, and ≤0.012 at 193 nm were also determined. This present work quantifies the photolysis channel producing HONO+O and show that it accounts for a large fraction at HNO3 photolysis at 193 nm.

Atmospheric fate of several alkyl nitrates Part 1Rate coefficients of the reactions of alkyl nitrates with isotopically labelled hydroxyl radicals

Abstract: The rate coefficients for the reaction of OH radical with CH 3 ONO 2 (k 1 ), CD 3 ONO 2 (k 6 ), C 2 H 5 ONO 2 (k 2 ) and 2-C 3 H 7 ONO 2 (k 3 ) between 220 and 410 K were measured to be: k 1 =(8.2±1.6)×10 -13 exp{-(1020±60)/T}, k 6 =(1.6±0.2)×10 -12 exp{-(1730±40)/T}, k 2 =3.68×10 -12 exp(-1077/T)+5.32×10 -14 exp(126/T) and k 3 =4.3×10 -12 exp(-1250/T)+2.5×10 -13 exp(-32/T) cm 3 molecule -1 s -1 . The quoted errors in the Arrhenius expressions are at the 95% confidence limit and include estimated systematic errors. The measured rate coefficients for the reactions of 18 OH were roughly the same as those for 16 OH reactions while the rate constants for OD reactions were slightly (ca. 10–15%) higher than those for OH reactions. The hydroxyl radicals were generated by pulsed laser photolysis and detected by pulsed laser induced fluorescence. The observed large primary kinetic isotope effect (k 1 /k 6 =4.5 at 298 K), the independence of the measured rate coefficients on the gas composition, and the trend in the reactivity with the alkyl group suggests that the above reactions proceed via abstraction of an H atom from the alkyl group. Our results are compared with those from previous studies.

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)