Ozone formation potential of organic compounds

Abstract

1 A reactivity scale for organic compounds based on ozone production is developed. It is based on the concept that ozone can be considered as the intermediate ( B ) of two consecutive reactions, A -B -C. The organic compound, A, is assumed to react only with OH radicals that are present in the atmosphere. It is also assumed that the organic compound is completely oxidized to either COz and/or formic acid. A reactivity scale based on these premises heavily weighs the number of carbon and hydrogen atoms present in the compound. The scale, developed only on theoretical grounds, predicts that all hydrocarbons lead to ozone formation and that the larger molecules lead to larger quantities of ozone. The reactivity scale predicts that high concentrations of ozone would be expected in rural downwind areas away from high emissions sources. This is in agreement with recent findings of high ozone levels in rural areas.Organic matter including hydrocarbons is essential for the formation of photochemical smog. However, not all hydrocarbons manifest themselves equally in the smog symptoms such as eye irritation, plant damage, visibility reduction, and oxidant formation. The literature suggests that several of these symptoms of reactivity must be considered when planning control strategies (1-3). However, for the present, oxidant/ozone is the only photochemical product for which there is an Air Quality Standard. Achievement of the oxidant standard is based on control of organic emissions.The role of the oxidant precursors, Le., the hydrocarbons, has been extensively studied in many laboratories over the past several years. Various parameters such as types of hydrocarbons, HC/NO, ratios, light intensity, water vapor, and temperature have all been investigated for possible effects on oxidant formation (1). From these studies, definitions of reactive organics such as those given in Rule 66 ( 4 ) have been developed by the Los Angeles County. The Rule 66 approach is to limit the emissions of hydrocarbons that are relatively high in reactivity with the expectation that this will result in a decrease in the amount of oxidant produced in the atmosphere of Los Angeles County.Appendix B in the Federal Register (August 1971) tends to overlook the relative reactivities of different hydrocarbons and puts forth the concept that all but a few hydrocarbons should be controlled. This approach severely limits emissions of all but the most unreactive hydrocarbons.More recently, a linear summation model for the control of hydrocarbons has been proposed ( 5 ) . With this model, hydrocarbons are classified according to five reactivity classes. Any combination of these five classes could be emitted into the atmosphere as long as the linear summation does not exceed the reactivity of the class of least reactive hydrocarbons.Some recent findings in the Midwest by EPA (6), as well as recent investigations ( 7 , 8 ) of high oxidant in rural areas, have led us to look into the formation of high oxidant concentrations from the so-called unreactive hydroca...

Rate coefficients for the gas-phase reaction of OH radical with α-pinene: an experimental and computational study

“…The number of O 3 molecules formed from any hydrocarbon is determined by the number of NO 2 molecules formed during its degradation process. Bufalini et al [46] developed a methodology to calculate the ozone formation potential of various organic compounds based on theoretical grounds. They also predicted that the larger molecules lead to the formation of larger quantity of ozone.…”

“…They also predicted that the larger molecules lead to the formation of larger quantity of ozone. The maximum number of ozone molecules which can be formed from one hydrocarbon molecule is based on the number of carbon atoms and number of hydrogen atoms present in that molecule [46]. In α-pinene, the maximum number of ozone molecules can be formed is 26 (nC + nH = 26).…”

Organic Compounds in Urban Atmospheres: A Review of Distribution, Collection and Analysis

“…Other ozone-forming organics have been investigated. 65 Hence, a great deal of effort has been spent classifying hydrocarbons on the basis of their reactivity with hydroxyl radicals or other photochemical intermediates. 66 - 67 However, the most direct method to classify compounds might be simply by their functional groups and degree of unsaturation, i.e., saturated hydrocarbons, aromatic and condensed aromatic hydrocarbons, etc.…”

Part I. Definition of Key Issues

“…Third, the problem, now recognized in other countries, has acquired international dimensions because of the possibility of inter-country pollution transport and because of the impact of emission control regulations upon international trade. These developments raised the question of the need to reexamine the oxidant control policies and their underlying scientific bases, and eventually instigated the International Conference on Photochemical Oxidant Pollution and Its Control, held in Raleigh, NC, Sept. [12][13][14][15][16][17][18][19][20]1976, under the auspices of EPA and the Organization for Economic Cooperation and Development (OECD). 2 Some one hundred reports on new evidence and/or viewpoints were presented at the International Conference by researchers and air pollution specialists representing the entire spectrum of the scientific community, and, as expected, brought into focus some important and controversial issues.…”

“…Answers have been calculated for an ideal atmospheric system containing no HC and NO* pollutants, except for methane (and CO) at their global background levels. 16 It is conceivable, however, that in the presence of trace-levels of HC and NO*- The question pertains to HC and NO r pollutants as a mixture, not to the individual precursors, and is concerned with the maximum distance downwind that a HC-NO* mixture can travel without excessive loss of its potential for oxidant formation, (e.g. no more loss of oxidant potential than 80%).…”