7 P h o t o c h e m i c a l S m o g and the A t m o s p h e r i c R e a c t i o n s of S o l v e n t s
Downloaded by UNIV OF AUCKLAND on December 28, 2017 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0124.ch007
J O H N L. LAITY,1 ISRAEL G. BURSTAIN, and B R U C E R. A P P E L Shell Development Co., Emeryville, Calif. 94608
This paper presents the chemical measurements observed in our
smog chambers
components.
for individual
irradiations
of solvent
To correlate chemical reactivity with struc
ture, we review many observations from other investigations of solvent reactivities, and we present generalizations the smog-forming tendencies of solvent ingredients.
about Olefins
and aromatics decompose primarily from electrophilic attack at unsaturated
sites, and chemical reactivity
therefore is
raised by electron-donating groups on the double bond or ring. Alcohols ethers, and esters react at an α-carbon atom, and reactivity is reduced if no hydrogens are present on the α-carbon.
With
ketones, chemical reactivity apparently
is
increased by the presence of alkyl or other stabilizing groups on the carbon atoms adjacent to the carbonyl.
nphe A
advent of Los Angeles County s Rule 66, as well as similar regu-
lations which attempt to limit the amounts and compositions of solvents
emitted into the atmosphere, has focused considerable attention on the smog-forming tendencies of solvents. A primary goal of smog research in several laboratories has been to develop a scale of atmospheric reactivities of solvent components. Hopefully such a scale, when coupled with an evaluation of air pollution sources, would allow at least qualitative estimation of the amount and type of material that could be released to an atmosphere without resulting in intolerable levels of photochemical smog. 1 Present address: Shell Development Co., MTM Product Research and Develop ment Laboratory, P.O. Box 262, Wood River, Ill. 62025.
95 Tess; Solvents Theory and Practice Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
96
SOLVENTS THEORY
AND PRACTICE
In areas suffering from photochemical smog, the atmospheric reactions and effects of solvents are invariably dwarfed by reactions and effects of automotive emissions.
A n actual urban atmosphere is simply
too unwieldy for controlled, scientific studies of many solvent reactions. Hence, laboratory irradiation chambers are commonly used to assess solvent reactivities under simulated conditions. Chemical reactions of photochemical smog formation are unquestionably influenced by experimental conditions and constraints of each irradiation chamber, thus greatly complicating attempts to assign absolute reactivities to solvents.
How-
ever, from studies of many solvent materials under fixed conditions Downloaded by UNIV OF AUCKLAND on December 28, 2017 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0124.ch007
(varying only the solvent component under study), it is possible to derive the relative contributions of solvent ingredients to several aspects of photochemical smog production. Although concern about automotive emissions has led to a large number of useful reports [see, for example, Glasson and Tuesday
(1)]
on the reactivities of hydrocarbons in irradiation chambers, there are few comprehensive publications devoted to the contributions that solvents can make to photochemical smog.
Los Angeles County's A i r Pollution
Control District ( L A - A P C D ) evaluated several solvents (2,3)
in a smog
chamber in the early 1960s, and Battelle Memorial Institute, in work sponsored by the National Paint, Varnish and Lacquer Association, recently investigated a variety of solvents and solvent components (4).
The
L A - A P C D study concentrated mainly on the contributions of solvents to eye irritation and ozone formation in photochemical smog, while Battelle examined eye irritation and several chemical manifestations of smog. O u r solvent studies, which began in 1967, have involved only chemical measurements which are related to the production of photochemical smog.
T h e most obvious symptoms of photochemical smog are eye
irritation, visibility reduction, and plant damage, but the connections between such physical or biological smog measurements ous (5).
symptoms
and chemical
(like the rate of nitric oxide photooxidation) are tenu-
Results presented here take on additional significance since
the observation by several groups (6, 7, 8) that carbon monoxide can be mildly reactive in smog formation. Several investigators (4, 9, 10) have used relatively high concentrations of carbon monoxide in their irradiation chambers as a measure of air replenishment. O u r chamber studies were conducted in the absence ( < 1
ppm) of carbon monoxide.
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. T o 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
Tess; Solvents Theory and Practice Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
7.
LAITY
ET AL.
97
Atmospheric Reactions of Solvents
are very complex and not completely understood, the principles presented here account for the reactivity differences solvent
components
observed among classes of
including hydrocarbons,
alcohols,
ethers,
esters,
amides, and ketones.
Downloaded by UNIV OF AUCKLAND on December 28, 2017 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0124.ch007
Experimental Irradiation Chambers. Most of the data were determined in a 397liter vessel constructed chiefly of stainless steel. This chamber is a pol ished stainless steel cylinder 4-feet long and 2-feet in diameter with blacklight fluorescent lamps inside. Temperature is controlled by circu lating liquid in coils around the chamber from a constant temperature bath. Several ports are on the chamber for removing and analyzing air samples. T h e general cleaning procedure between experiments was to evacuate the vessel to 1μ H g and heat overnight at 5 0 ° - 6 5 ° C . Values for the half-life of ozone (1 ppm) in the chamber air varied from 1.5 to 6 hours in the dark and 1.3 to 2.5 hours with the lights on. T h e rate of thermal oxidation of nitric oxide (1.5 ppm) in the chamber air is 1.7 ( ± 0 . 3 ) Χ 104 liter 2 mole' 2 sec"1. Light intensity is measured by the firstorder rate constant for photolytic decomposition of nitrogen dioxide, giv ing Kd = 0.40 min" 1 during the first 2 minutes of irradiation. T h e chamber and its characteristics were described previously ( I I ) . T w o glass irradia tion chambers (a 235-liter vessel and a 23-liter flask) used in our investiga tions are also described elsewhere (II, 12). During dosing, samples of solvent and doubly-distilled water are vaporized into the evacuated chamber through a glass vacuum manifold. Nitric oxide gas in nitrogen (Matheson) is passed in, and Ultrapure air (Air Products and Chemicals) is then used to purge the manifold and fill the chamber to atmospheric pressure. The pure air supply contains < 2 ppm methane as the only hydrocarbon, < 1 ppm carbon monoxide, and
