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.

Multiphase chemistry of NO3 in the remote troposphere

Abstract: The effect of NO3 uptake at night into marine aerosol and cloud droplets on (1) sulfur oxidation, (2) NO3 ambient concentrations, and (3) NO3 atmospheric lifetime is examined using a simple chemical kinetics model. It is shown that the atmospheric lifetime toward multiphase removal of NO3 is < 10 min in presence of cloud droplets. We also show that at low mixing ratios of H2O2 (<150 pmol/mol), NO3 can enhance sulfur oxidation in clouds via a catalytic cycle with a chain length of ∼8. Finally, in presence of sea-salt aerosol, the uptake of NO3 leads to low ambient concentrations of NO3, efficient S(IV) oxidation, and possibly, to release of halogens from the aerosol. The results of this study imply that the multiphase reaction of NO3 may be important in the remote marine boundary layer.

Oxidation of CS2 by reaction with OH. 1. Equilibrium constant for the reaction OH + CS2 .dblarw. CS2OH and the kinetics of the CS2OH + O2 reaction

Abstract: The reaction of OH with CS{sub 2} was studied in He (50 Torr), N{sub 2} (9-40 Torr), and SF{sub 6} (30-60 Torr) over the temperature range 249-318 K by using pulsed laser photolysis to generate OH and pulsed-laser-induced fluorescence to detect OH. The rapid approach of (OH) to equilibrium was observed at each temperature, indicating reversible formation of a CS{sub 2}OH adduct. Analysis of the (OH) temporal profiles provided the rate coefficients for the forward and reverse components of the reaction OH + CS{sub 2} + M {r reversible} CS{sub 2}OH + M and, hence, the equilibrium constant.

Measurements of UV refractive indices and densities of H2SO4/H2O and H2SO4/HNO3/H2O solutions

Abstract: Refractive indices of aqueous solutions of sulfuric acid and sulfuric acid/nitric acid were measured at 365, 313, 308, 254, and 214 nm at 298 K. The solution concentrations were H 2 SO 4 /H 2 O : 88.6, 78.7, 63.0, 52.3, 39.8 wt % SA (sulfuric acid) ; H 2 SO 4 /HNO 3 /H 2 O : 50.3 SA 2.5 NA (nitric acid), 45.4 SA 5.1 NA, 41.9 SA 7.4 NA, 37.9 SA 10.4 NA wt %. Densities of the solutions were also measured at low temperatures in order to calculate the refractive indices of these solutions at stratospheric temperatures.

Kinetics of the Reactions of the CF3O Radical with Alkanes

Abstract: Utilizing the technique of pulsed laser photolysis/pulsed laser induced fluorescence, we have investigated the atmospherically important reactions of the (trifluoromethyl)peroxy radical, CF[sub 3]O, with several alkanes. The reaction rate coefficients for CF[sub 3]O + CH[sub 4] (k[sub 3]), C[sub 2]H[sub 6] (k[sub 4]), C[sub 3]H[sub 8] (k[sub 5]), (CH[sub 3])[sub 3]CH (k[sub 6]), and CD[sub 4] (k[sub 7]) were measured, as functions of temperature, to be k[sub 3] = (1.92 [+-] 0.33) x 10[sup [minus]12] exp[[minus](1370 [+-] 85)/T] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1], k[sub 4] = (4.84 [+-] 1.11) x 10[sup [minus]12] exp[-(400 [+-] 70)/T] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1], k[sub 5] = (5.12 [+-] 1.12) x 10[sup [minus]12] exp[-(15 [+-] 30)/T] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1], k[sub 6] = (4.32 [+-] 0.42) x 10[sup [minus]12] exp[(135 [+-] 30)/T] cm[sup 3] molecule[sup 1] s[sup [minus]1], and k[sub 7] = (0.91 [+-] 0.31) x 10[sup [minus]12] exp[-(1540 [+-] 100)] cm[sup 3] molecule[sup [minus]1] s[sup [minus]1], respectively. These kinetic data are compared with results from previous studies. The atmospheric implications of these findings are discussed. 28 refs., 7 figs., 4 tabs.

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)