Chemical aspects of the photooxidation of the propylene-nitrogen oxide system

Abstract

The photooxidation of part-per-million concentrations of propylene in the presence of similar concentrations of nitric oxide has been investigated. The product yields were measured over a wide range of reactant concentrations and reactant ratios. Series of experiments were carried out with varying light intensities, with both static and dynamic flow conditions. The products measured by colorimetric, gas chromatographic, and various monitoring instruments included nitrogen dioxide, oxidant (ozone and other oxidizing agents), formaldehyde, acetaldehyde, carbon monoxide, peroxyacetyl nitrate, and methyl nitrate. The mechanism of the reactions involved is considered, including stoichiometry and the role of free radical intermediates. Carbon and nitrogen balances are computed, and difficulties in obtaining balances are considered.he photooxidation of various olefin-nitrogen oxide T systems has been studied (Altshuller and Bufalini, 1965;Leighton, 1961 ;Wayne, 1962). Much of this previous work is limited, however, by use of reactant concentrations well above atmospheric levels and by measurements of only a limited number of products over a narrow range of reactant cancentrations. Furthermore, measurements of eye irritation and plant damage often have not been obtained along with the chemical or physical results.Although it is not possible to represent fully all of the diverse effects associated with photochemical air pollution by studies of a single hydrocarbon, propylene was chosen as a representative reactive hydrocarbon. The propylene-nitrogen oxide system when irradiated reacts readily t o produce oxidant, formaldehyde, acetsldehyde, carbon monoxide, peroxyacetyl nitrate (PAN), and methyl nitrate and causes 070ne and PAN-type plant damage and eye irritation. Thus, major "smog" manifestations can be reproduced, although not necessarily at the intensities experienced in the ambient atmosphere.This paper reports the chemical and physical measurements of the photooxidation of propylene-nitrogen oxide over a range of reactant concentrations, a t several light intensity evels, and under static or dynamic flow conditions. Biological indicator measurements will be reported in another paper. ExperimentalThe propylene concentrations used included 0.25, 0.5, 1, 2, and 3 p.p.m. by volume, while the nitric oxide concentrations included0.125,0.20,0.25,0.50,0.6,0.7,0.75,1.0, 1.25, 1.50,2, 3, and 4 p.p.m. by volume. Irradiations also were conducted with 1, 2, or 3 p.p.m. of propylene in the chamber. but with only the background nitric oxide concentrations of 0.02 to 0.04 p.p.m normally present in the dilution air. The molar ratio3 of propylene to nitric oxide were varied from about 100 to 1 to 8.

Nitrogen Balance in Smog Chamber Studies

“…In the photooxidation of the propylene-nitrogen oxide system, Altshuller et a/. 5 reported good nitrogen balances up to the time when NO2 reached a maximum. After that time, the nitrogen balance depended on the initial NO* concentration.…”

Computer modeling of photochemical ozone formation: a simplified approach

“…The first manifestation of the problem occurred the Los Angeles area and included accelerated deterioration of rubber products, damage to vegetation, and eye irritation (6)(7)(8). While the problem is severest in the southwest part of the U.S, high levels of oxidants are known to occur in every major urban center in this country and, through short and long range transport, oxidant spreads to non-urban areas and even to other countries (9).…”

“…Extensive research has uneqivocally identified several components of photochemical oxidant mixtures (7,(10)(11). Thus, photochemical oxidants are known to consist mainly of ozone (03) radicals.…”

“…For a detailed discussion of this photo-induced equilibrium see Leighton (1) He + OX -----> R02 (6) R02+ NO -----> N02 (7) Hydrocarbon degradation by oxidizing agents (OX), e.g. OH and 03, results in the formation of intermediates (R02) which are capable of converting NO --> N02.…”

Assessment of the Contribution of Chemical Species to The Eye Irritation Potential of Photochemical Smog

“…Peroxyacetyl nitrate yields increase curvilinearly with irradiation of increasing concentrations of olefins or aldehydes 6 -8 but show more complex behavior with maximum yield similar but not identical to that of ozone as nitrogen oxides concentrations vary in irradiated olefin-nitrogen oxide 6 and alkylbenzene-nitrogen oxide mixtures. 8 The concentration and distribution of products causing eye irritation formed from the photochemical reactions of various classes of hydrocarbons with nitrogen oxide are such that the eye irritation potentials are in the order: alkylbenzenes > olefins > paraffins > acetylene.…”