speed, while a manifold vacuum gage helps detect erratic motor operation. Recently, a Clayton chassis dynamometer was installed to study exhaust produced under road operating conditions. By using an auxiliary fuel system, various types of fuel may be studied also. A number of methods for measuring oxidant have been developed, but their chief disadvantage is lack of specificity. All common methods are used in this work to determine if any gives good correlation with eye irritation. In Los Angeles smogs, such a correlation, although not high, exists. Two Goodrich ozonometers keep a continuous record of rubber-cracking properties of the smog produced. These are simple modifications of HaagenSmit’s rubber-cracking technique, but they measure continuously. Colorimetric oxidant is measured by scrubbing air samples in midget impingers using as reagents, potassium iodide, phenolphthalein, and also ferrous thiocyanate which has been reported to respond almost quantitatively to peroxides but only slightly to ozone. The others are commonly used in Los Angeles studies. A continuous oxidant recorder originally designed by Littman and Benolie1 is also used with buffered potassium iodide reagent. This records released iodine and represents a complex composite of oxidizing and reducing agents which, in the absence of sulfur dioxide, is believed to represent largely ozone. Nitrogen dioxide and organic peroxides also produce some iodine but only 10 to 20% of these are recorded. This instrument samples the reaction chambers alternately a t 6-minute intervals. The response time is about 3 minutes; hence, each period of analysis gives both level of oxidant and rate of change. When not in use otherwise, the instrument monitors outside air. An instrument supplied by the Air
Smog Experiments in large Chambers Equipment and Procedure
F O R OVER 5 years many laboratories have worked on air pollution problems in the Los Angeles atmosphere. Causes are better understood, but severity and frequency of smog attacks grow annually. Haagen-Smit, by irradiating mixtures of hydrocarbons and nitrogen oxides, first produced typical Los Angeles smog symptoms and other workers have confirmed his results. If nitrogen oxide content is high enough, irradiated automobile exhaust produces these symptoms. A general equation for this reaction is light Hydrocarbons air NO,oxidation products and smog symptoms Determining the amount of smog produced generally involves measuring symptoms-eye irritation, oxidant, plant damage, or reduced visibility-which d o not always occur simultaneously. Aerometric survey data gathered by the Air Pollution Foundation showed poor correlation between eye irritation and plant damage. The relationships between oxidant measurements and concentrations of various chemicals in polluted air are not clearly understood. In this work, smog formation is studied in a pair of large glass reaction chambers built from a small greenhouse. Automobile exhaust or known chemical mixtures are introduced into the chambers in the presence of sunlight. As reactions proceed, smog intensity is measured chemically and by eye irritation
+
tests, for which a panel of 20 students enter the chambers. Analyses are made a t regular intervals for hydrocarbons, carbon monoxide, aldehydes, nitric oxide, nitrogen dioxide, and-by four different methods-oxidant. Temperature, relative humidity, and light levels are recorded continuously. The greenhouse was divided with a glass partition. A glass floor was installed and glass panels were set u p to cover the metal heating coils and foundation wall. The chambers have a volume of 2200 cubic feet and a volume-surface ratio of 2 to 1. The surfaces are 80% glass and 20y0 white alkyd resin paint. By carefully caulking and weatherstripping all openings, the chambers are fairly gas tight. Nitric oxide, nitrogen dioxide, and hydrocarbons have an approximate half life of 11/2 hours in the absence of sunlight. This loss may be partially caused by surface adsorption. A roof sprinkling system helps control temperature inside the chambers. Splitting the greenhouse into two nearly identical reactors serves a double purpose-cost is nearly halved because twice as many experiments can be run in a given time, and two different treatments a t the same light exposure can be studied. This is desirable because amount of light is important. The automobile supplying exhaust gas is maintained in top operating condition. A tachometer measures motor
+
Run Numbers and Design of the Experiment NO Level NO2 Level %00%idle
85’%idle, 15% 2-hexene
1 1MS
3
2
... ... ... ... 8AS .17MN ... ... ... ... ... 14AN ... ... ... ... ...
4 3 2 1 4 3 25MN 2 1 4 3 2 12AN
.
I
.
4
... ... ... 16AN ... ...
20AS
... 4AS ... ... ... ... ... 17MS ... .... ... ... ISMN ... . . L
85%idle, 15% 3-methylpentane € 70% idle, 15% 4 2-hexene, 3 15% 2 3-methyl1 18AS pentane N = north chamber.
...
... ... ...
2iMs
I
..%
...
27MS
...
3
2
1
.
.
7MN 26AN
... ...
... ... ...
S = south chamber.
1
2
3 3MN
4
...... ... . . . . . . . . . 4AN 5MS .......... ... 12AS . . . . . . . . . . . . . . . 6AS . . . . . . 19MS ... ... 20AN . . . . . . 23MN ......... 24AN . ........ ... 31MN . . . . . . . . . . . . 28AS ... . . . . . . . . . 25MS ... 15MS ....... 14AS ......... . . . . . . . . . 1MN . . . . . . 6AN ...
1
2
4
3
.
4
.. .. .. .. .... .l3MN . . l8AN ... 26AS ...... iiMs . . . . . . . . . .. .. .. .. ... . .3MS ... . . IOAS IlMN . . . . . . . . . ... IOAM . . . . . . ... 9MN ...... 32AN ...... . . 2 9... MS .. .. .. ..... . .24AS 22AS . . . . ..... .. .. .. ... 23MS . . . . . . 30AN ... . . . . . . . . . 19MN
1
2 16AS
3
4
... ... 13MS ...... ... . . . . . . 2iAN ... ... 27MN ... 21MN . . . . . . ... 2AN ... ... ... ... PMS ... ... . . . . . . 30AS ... . . . . . . 31MS ... ... 2AS ... ... 29MN ... ... 8AN ...... ... ... 22AN ... ... . . . . . . 5MN 32AS . . . . . . ... ... ... ... 7MS
...
. . I
. . I
M = morning. A = afternoon.
VOL. 49, NO. 8
0
AUGUST 1957
1249
Pollution Foundation, using color formation by nitrogen dioxide in Saltzman’s reagent, continuously records nitrogen dioxide and nitric oxide. This instrument samples the smog chambers alternately at 9-minute intervals and when not otherwise in use, it monitors outside air. Total oxides of nitrogen in the automobile exhaust are determined by the phenoldisulfonic acid method. Low moleffilar weight aldehydes are collected in sodium bisulfite and determined by iodometry. With increasing molecular weight, however, efficiency of this method drops off rapidly. Hydrocarbon samples in the reaction chambers are collected by passing air over Dehydrite, through traps immersed in liquid nitrogen, and then transferred to an evacuated 1-meter gas cell built into a Beckman IR-2 spectrophotometer. By a method essentially that of Mader and others, absorption at 3.45 microns is compared with a standard curve prepared from hexane, and hydrocarbons are calculated as hexane. Samples taken directly from the car’s exhaust are collected as grab samples. Light intensity is continuously recorded on a Leeds & Northrup electronic recorder. The impulse is obtained from a 10-junction Epply pyrheliometer. A 10-junction thermopile measures difference in temperature between two concentric metallic rings-one black and the other white. The apparatus is calibrated in fundamental units of gram calories per square centimeter and accepts radiation of all wave lengths. Because many samples are needed, collection methods were simplified. Standardized all-glass midget impingers collect samples and a large manifold was constructed with a number of outlets, each controlled by a manual valve. A vacuum pump and a controlled bleed-in valve control the vacuum which is measured with a mercury manometer. Glass sampling lines, each with four outlets, carry air to the sampling point where four sets of impingers may simultaneously take samples from each chamber. Two impingers in series measure collection efficiency. Thus, only the time required for collection and known flow rate are needed to calculate sample volume. At regular intervals, the students who measure eye irritation remain in each chamber for 2 minutes and then complete a questionnaire. Through these studies, it is believed fuel types and engine operating conditions can be evaluated in smog production and effectiveness of automotive control devices can be determined. Nitrogen Oxide Influence Nitrogen oxides and hydrocarbons, contributing to smog formation, come to a large extent from automobile exhaust, and catalytic mufflers, afterburner de-
1250
signs, and carburetor cutoffs are being developed for their removal. This work, based on the assumption that this smog is formed by photochemical reactions between these contaminants, and sponsored by the ,4ir Pollution Foundation, was undertaken to determine if reducing these contaminants would decrease frequency and severity of smogs, and to define final tests for control devices. Using the converted greenhouse. an experiment of 64 runs was madea quarter replicate of a 2243 factorial experiment for studying effects on oxidant production and eye irritation of hydrocarbon source and level (1 to 6 p.p.m.) of nitric oxide and nitrogen dioxide, both 0.1 to 0.5 p.p.m. These factors, which seemed the most important which control devices might alter, were studied at four levels each and appeared four times with each level of other variables. Thus, interactions between any two variables could be studied. The hydrocarbons were idle exhaust from a 1952 Ford Ranch IVagon, 3methylpentane, and 1-hexene. Nitric oxide and nitrogen dioxide were drawn from cylinders into glass syringes and injected into the chambers. Only the most important effects are discussed here-those a t the 95% and, in most cases, confidence levels. Data statistically analyzed with covariance correction for light substantiated those of other workers; each of the four factors studies influenced oxidant formation and also interacted. Increasing nitrogen oxides, either nitric oxide or nitrogen dioxide, generally increased oxidant-producing potential. Initial rate of production, however, was depressed when nitric oxide was increased, and accelerated when nitrogen dioxide was increased. This coincides with the theory that the initiating photochemical reaction is dissociation of nitrogen dioxide into oxygen atoms and into nitric oxide. The latter readily combines with ozone. Raising hydrocarbon levels increased both eye irritation and the peak oxidant value, which also occurred sooner. This agrees with the theory mentioned ; formation of more nitrogen dioxide from accelerated oxidation of nitric oxide and higher hydrocarbon concentration will increase the initiating rate of free radical chains. Substituting 3-methylpentane for part of the automobile exhaust increased the time needed to reach the peak oxidant value. The peak was lower, but rate of oxidant decline was less. This indicates that 3-methylpentane was less reactive than hydrocarbons it replaced. In large experimental designs such as this. not only the main effects of each variable can be studied, but also effects of interactions. For example, an interaction occurred between nitric oxide
INDUSTRIAL AND ENGINEERING CHEMISTRY
level and hydrocarbon source-at low nitric oxide levels, oxidant production was higher with 3-methylpentane than without. As the initial nitric oxide level was increased this trend reversed, and substituting 3-methylpentane decreased oxidant production. Interaction of 3-meth.ylpentane with hydrocarbon levels affected curves for nitrogen oxide concentration. Runs containing this pentane gave, on the average. more recordable nitrogen oxide totals than those without. Also, rate of decline for these oxides depended on hydrocarbon level and source. At low hydrocarbon levels, runs with the pentane declined faster, but as the hydrocarbon level was increased, this trend reversed and a t high levels the opposite was true. Curves for recorded nitrogen dioxide were similarly affected. Source of hydrocarbons and their interactions could be important in studying effects of reducing hydrocarbon concentrations by removing a particular hydrocarbon type. The most startling results were effects of nitrogen oxides on analytical hydrocarbon valves-both low nitric oxide levels and high nitrogen dioxide levels produced hydrocarbon analyses lower than expected and both were favorable to fast oxidant production. Thus, reactions were fast and most of the hydrocarbons had been converted to products removed by the Dehydrite drying column during the 45-minute sampling. Because analytical hydrocarbon depends on oxides of nitrogen charge, it is impossible to determine total reactive organic matter by the conventional freeze-out procedure. With high oxidant present, these values will be lower than the amount of hydrocarbon charged and represent only residual, relatively unreactive hydrocarbons. Over-all half life of total nitrogen oxides was approximately 55 minutes. but the chamber leakage value, determined in night experiments, was 90 minutes. Thus, nitrogen oxides formed compounds which were measured either incompletely or not at all by the nitric oxide-nitrogen dioxide recorder. Interactions among variables are important. Future research for Los Angeles atmospheres must cover a wide range of experimental concentrations. Otherwise, conclusions may be correct only for a limited set of conditions.
FRANCIS V. MORRISS CALVIN BOLZE JOHN T. GOODWIN, Jr. and FRANK KING Midwest Research Institute Kansas City, Mo. The complete manuscript may be obtained from Francis V. Morrisa at the above address. Division of Analytical Chemistry, 130th Meeting, ACS, Atlantic City, N. J., September 1956.
