Ozone forming potential

Hayman GD, RG Derwent (1997) Atmospheric chemical reactivity and ozone-forming potentials of potential CFG replacements. Environ Sci Technol 31 317-336. 

Japar SM, TJ Wallington, SJ Rudy, TY Chang (1991) Ozone-forming potential of a series of oxygenated organic compounds. Environ Sci Technol 25 415-420. 

Research Priorities for Airborne Particulate Matter (3 reports, 1998-2001) Ozone-Forming Potential of Reformulated Gasoline (1999)... 

P-series also has many environmental benefits. Emissions from the production and use of P-series are substantially better than those from gasoline. Each unit of P-series fuel emits approx 50% less carbon dioxide, 35% less hydrocarbons, 15% less carbon monoxide than gasohne. It also has 40% less ozone-forming potential. 

The reason that the ODPs of these CFC replacements are much smaller than those of the original CFCs is the presence of an abstractable hydrogen with which OH can react. However, this also means that they can also contribute to ozone formation in the troposphere. Hayman and Derwent (1997) have used their photochemical trajectory model to calculate tropospheric ozone-forming potentials of some of these CFC replacements. Table 13.10 summarizes these relative ozone-forming potentials, expressed taking that for ethene as 100. Clearly, although they react in the troposphere, their contribution to tropospheric ozone formation is expected to be very small. 

Hayman, G. D., and R. G. Derwent, Atmospheric Chemical Reactivity and Ozone-Forming Potentials of Potential CFC Replacements, Enriron. Sci. Techno/., 31, 327-336 (1997). 

The TLEV, LEV, and ULEV standards incorporate the concept of reactivity-weighted mass emissions of VOC, concurrent with increasingly strict NOx control. The intent is to regulate based on equal ozone-forming potentials of the VOC emissions rather than simply on their total mass. That is, the emission standards for organics are set in terms of the amount of ozone formed in the atmosphere per mile traveled by a given vehicle/fuel combination rather than in terms of the simple total mass of VOC emitted per mile. 

Determination of the specific reactivity of the exhaust emissions requires accurate knowledge of both the types and amounts of compounds emitted as well as how each contributes to 03 formation. The latter factor, the ozone-forming potential, is treated in terms of its incremental reactivity (IR), which is defined as the number of molecules of ozone formed per VOC carbon atom added to an initial surrogate atmospheric reaction mixture of VOC and NOx ... 

Bufalini, J. J., and M. C. Dodge, Ozone-Forming Potential of Light Saturated Hydrocarbons, Enciron. Sci. Technoi., 17, 308-311 (1983). 

Chang, T. Y., and S. J. Rudy, Ozone-Forming Potential of Organic Emissions from Alternative-Fueled Vehicles, Atmos. Environ., 24A, 2421-2430 (1990a). 

Japar, S. M T. J. Wallington, S. J. Rudy, and T. Y. Chang, Ozone-Forming Potential of a Series of Oxygenated Organic Compounds, Environ. Sci. Technol., 25, 415-420(1991). 

Through the last sequence H02 is reformed to react with NO. The main point here is that nitrogen oxides are cycled through reactions R1 - R2, and therefore, this cycle will not limit the ozone forming potential. However, the formation of the other compound involved in the initial step in the ozone formation, H02, requires that CO be oxidised. The number of ozone molecules formed is therefore determined by the amount of CO present. H02 molecules can in a similar way be formed through the oxidation of CH4 and other hydrocarbons. The initial methane oxidation mainly through the reaction with OH ... 

Thus, decomposition of PAN in the presence of NO can lead to the formation of OH radicals and conversion of NO to NOj merely from thermal reactions. This could be very important because PAN can be an indicator of the urban ozone-forming potential (see Section 8.4.1) and of the organic-oxidizing capacity of the urban air mass. The thermal decomposition of PAN also leads to the formation of NOj radicals. 

Alkoxy radicals have several potential reaction channels which compete under atmospheric conditions. The study of these reactions is difficult due to their complexity and the absence of suitable techniques for direct monitoring of the kinetics. The relative importance of these channels has been established accurately for several individual RO radicals and also for groups of RO radicals of similar structural type in the LACTOZ project. This aids the definition of the ozone forming potential for alkanes. A particularly important achievement is the characterisation of the isomerisation reactions of larger alkoxy radicals, which has been a significant uncertainty in modelling photochemical ozone formation in the polluted boundary layer. 

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