Solvents photochemical smog reactivity

Levy A. 1973. The photochemical smog reactivity of organic solvents. Solvent theory and practices. American Chemical Society, Washington, DC Adv Chem Ser 124 70-94. 

The solvent should not contain substances that contribute significantly to the production of photochemical smog and troposphere ozone. The volatile organic content of the product, as used, should not exceed 50 g/L. None of the components of the product will have a maximum incremental reactivity (MIR) exceeding 1.9 g Ofg of compound (the MIR for toluene). MIR values can be obtained from the maximum incremental reactivity list found in Appendix VII of the California Air Resources Board s California Exhaust Emission Standards and Test Procedures for 1988 and Subsequent Model Passenger Cars, Light-Duty Trucks and Medium-Duty Vehicles as amended on September 22, 1993. 

This paper presents some of the chemical measurements observed in our chambers in 200 experiments involving approximately 50 individual compounds, most of which are commercial solvent components. To correlate chemical reactivity with structure, we also review many of the observations and conclusions of other investigations into solvent reactivities. Although the chemical reactions leading to photochemical smog... 

Rule 66 was adopted in 1966 and became effective according to a designated schedule. The rule was based on the premise that the extent of smog produced depended upon the chemical structure of the solvents. Deemed to be conducive to smog production were aromatic hydrocarbons except benzene, branched chain ketones, and especially unsaturated compounds. The regulation specified that solvent blends were considered to be photochemical ly reactive or unreactive on the basis of their composition as defined in the box on page 687. 

As introduced in 17.1.2.3, solvents may be photodegraded in both water and air. Atmospheric chemical reactions have been studied in detail, particularly in the context of smog formation, ozone depletion, and acid rain. The absorption of light by chemical species generates free radicals which are atoms, or groups of atoms that have unpaired electrons. These free radicals are very reactive, and can degrade atmospheric solvents. Atmospheric ozone, which occurs in trace amounts in both the troposphere (sea level to about 11 km) and in the stratosphere (11 km to 50 km elevation), can degrade solvents. Ozone is produced by the photochemical reaction ... 

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