Spectroscopic Analysis of Industrial Emissions for Nitric Oxide, Nitrogen Dioxide, and Sulfur Dioxide A. J. Haagen-Smit California Institute of Technology, Pasadena, Calif. Vincent D. T a y l o r Massachusetts Institute of T e c h nology, Cambridge, Mass. M a r g a r e t F. Brunelle
Los Angeles C o u n t y Air Pollution Control District, Los Angeles, Calif.
T H E emission of oxides of nitrogen is recognized as a factor in the formation of Los Angeles-type smog. Reduction of these emissions by chemical means and by modification of combustion conditions has been studied. I n this work the need for continuous monitoring of nitric oxide (NO) became imperative. Continuous recording of the concentrations of nitric oxide and sulfur dioxide in flue gases has been made possible by modifications in the sampling system preceding two Beckman Model LB 21 infrared analyzers. Because the major absorption bands for sulfur dioxide and nitric oxide occur at different wave lengths, a separate detector cell was used for each constituent. The presence of dust and water vapor containing sulfuric acid was a major deterrent in the application of the infrared spectrometer to the analysis of a direct stream of stack effluent, and it was decided to minimize both these constituents in the sample stream, by passing the gas through a condenser at approximately 0' C. to remove the major part of the water vapor, and then through an electrostatic precipitator to remove the dust. The gas was next allowed to flow through the spectrometers. Preliminary tests had shown that the nitrogen oxides were present in the flue gas as nitric oxide, rather than nitrogen dioxide. The voltage on the precipitator was kept relatively low, and it was shown that no significant amount of nitrogen dioxide was formed during the passage of the gas through the precipitator. The equipment has been in successful operation for more than one year. The infrared values for nitric oxide agree satisfactorily with values simultaneously measured by modified Griess and phenoldisulfonic acid methods., The infrared provides a continuous record, and its response is practically instantaneous, whereas a minimum of several hours is usually required before results can be
772
obtained on the grab samples normally used for chemical analysis. In the laboratory, the infrared spectrometer has performed most efficiently as an analytical tool. Both the number of experiments performed and their accuracy were increased far above what could be expected in the same period of time using standard methods of analysis. Because the nitric oxide formation reflects temperature conditions in the furnace, the use of the infrared spectrometer as an aid to operational control is suggested. The incorporation of standard recorders for carbon monoxide, carbon dioxide, and oxygen in the sampling line with the infrared recorders provides a complete picture of the major gaseous constituents of the flue gases, which should be of great assistance in obtaining maximum efficiency from the fuel combustion. RECEIVED for review September 18, 1958 ACCEPTEDFebruary 9, 1959
Bacteriological Test for Air-Borne Irritants Alexander Goetz California Institute of Technology, Pasadena, Calif. Noel Tsuneishi
AG Chemical Co., Pasadena, Calif.
F O R specific systems such as atmospheric oxidants, a microbiological test was desired for measuring physiological irritation caused by air pollutants. Despite their evolutionary distance from mammals, microorganisms such as bacteria and yeasts are promising, particularly for measuring the synergistic effects between atmospheric gaseous and particulate matter. For such tests, bacteria have certain advantages over mammals-they are easily available at negligible cost, and because of their large numbers, statistical fluctuations are absent. Their sensitivity can be conditioned by factors such as temperature or nutrient composition over much wider ranges, to respond to specific irritants. Use of membrane culture technique allows exposure of a single cell layer without the chemical protection by its nutrient environment to the irritant.
Experimental
The bacterial cell deposit was prepared by passing a highly diluted 24hour broth culture of E. coli through a 2 X 8 cm. strip (I-strip) of a membrane filter in a concentrometer (2). The latter
INDUSTRIAL AND ENGINEERING CHEMISTRY
produces automatically the logarithmic variation of the cell density, n, in the deposit along one direction, x , of the Istrip according to : [log n
=
A
+ x/k]
where A and k are instrument constants. An impactor, designed for this specific application, consists of a slowly rotating cylindrical drum, D,as carrier of the Istrip. The cells borne thereon are impacted by the air flow through the inlet tube, C1, leading to a narrow slit (0.03 X 0.63 cm.). The slit length, being half of the width of the I-strip, leaves a major part of the cells unexposed for control purposes. The impactor is activated by a vacuum pump connected with N , the exposure occurs during one turn of the drum while being driven with a clock motor of 12 (or 4) r.p.h. For these angular velocities the total impacted air volume is 40 (120) liters [1.4 (4.2) cu. feet], evenly distributed over a membrane area of 5.2 sq. cm., resulting in a maximal concentration factor of 7.7 (23) liters per sq. cm. [1.7 (5.2) cu. feet per sq. inch]. The flow rate used in most tests was 6 to 7 liters per minute [0.2 to 0.25 cu. feet per minute] amounting to an impaction velocity of about 20 meters per second (150 feet per second). After exposure, the I-strip is removed from the drum, and a suitable nutrient is applied from below, and incubated ( 5 ) . The degree of growth inhibition is then indicated by the length of the impacted track where colonies are absent. The relative irritant intensity of analogous samples can be determined by the slide rule principle due to the log-distribution of n along x (4).
Discussion After a standardized procedure was developed, several specific applications referring to air pollution were explored. A series of tests on irradiated automobile exhaust ( 3 ) demonstrated that removal of the particulate components by centrifugal action (aerosol spectrometer) substantially decreased the eye irritation. Two similar tests were conducted at the identical installation with a 30 to 40% olefin-containing-i.e. aerosol-forming-fuel of high irritant capacity. The irradiated exhaust was fed to the impactor directly and subsequent to passage through either a membrane filter or the aerosol spectrometer. Figure 1 presents the resulting Istrips with clearly defined tracks of growth inhibition (Ia,IIa). The association of the inhibitory agent with the particulate matter is indicated by the fact that passage of the aerosol through a membrane filter ( I a , us. b ) substantially decreased, and passage through the aerosol spectrometer eliminated the growth inhibition (Ia, IIa us. IC, Zlc), by removing all particles of a Stokes'
A I R POLLUTION
4 Figure 1. I-strips with stained E. coli cultures show path of impaction by highly diluted autombile exhaust la, Ila. Direct impaction lib. After passage through membrane filter After passage through aerasol spectrometer
IC, Ilc.
b Figure 2. Two series of I-strips were exposed to synthetic aerosols
B 4 Figure 3.
The aero-
sol is brought in contact with the bacteria in a rotary impactor Arrows Indicate air path before and after impacI
I
K’
diameter (d > 0.2 micron) with a centrifugal field of approximately 20,000 g (gravity). To explore the possibility of reproducing the synergistic irritation recorded with animals by LaBelle, Long, and Christofano (6) and recently by Amdur (I), synthetic aerosols containing formaldehyde (HCHO) as gaseous irritant, and potassium chloride or a monodisperse polystyrene latex (d = 0.26 micron) as particulate components, were generated by nebulizing their aqueous solutions (suspension) under well controlled conditions into a channel so that an “age” of 45 to 60 seconds a t relative humidity of 50 to 6070 resulted prior to impaction. Both irritant and aerosol concentrations were of the order of magnitude employed in the animal experimentsnamely, H C H O : 12 p.p.m. for the 12minute and 32 p.p.m. for the 4-minute exposure of the I-strip; KCl: 12 and
tion on drum D
I
1
28 mg. per cubic meter and latex: 1.7 and 3.3 mg. per cubic meter, or 1.8 and 3.5 X 106 particles per cc. No. 1 2 3 4
Schematic Test Pattern HCHO KC1 Latex X X
5 6
X
-
X
X
-
-
-
X
X
The potentially synergistic combinations (Nos. 5 and 6) were tested also by passing them through the aerosol spectrometer, prior to entry into the impactor. Figure 2 represents photographic reproductions of two series of I-strips, exposed to such synthetic aerosols and selected to illustrate the following:
Nos. 1, 2. The plain control ( A , u ) proved that exposure of the I-strip to impaction by clean air or the presence
Agent Quantities Impacted on Strip Area (59 Cm.)
Formaldehyde, MI./Sq. Cm.
Strip in Figure 2 A t=
a
. ..
KC1, Gram/Sq. Cm.
... ...
(Control)
e
1 . 9 x 10-1 1.9 x 10-1 4 x 10-4 1 . 9 X 10-1 (centrifuged) 4 X 10-4 1 . 9 X 10-1 4 x 10-4
B
a
6.7
t =
b
12 min.
b C
d
4 min.
C
C
a
t=
b
4 min.
C
d
x 10-3 1.7 X 10-1 1.7 X 10-1 6.7 x 10-3 1.7 X 10-1 1.7 X 10-1 1.7 X 10 -1 (centrifuged)
1 . 4 x 10-4
7 1.4
x x
10-6 10-4
... ... ... ...
Latex, No. of Complete Layers
... ... ... 1.3
... ... ...
1.3 0.65 1.3 1.3
ff
d
c
l
o
d
c
d
C
of KC1 aerosols had no effect on the growth. No. 3. Heavy latex deposits on the I-strip proved partially inhibitory; light deposits showed, if at all, a negligible effect. No. 4. Formaldehyde alone (A, b ) produced a diffuse partial growth inhibition rather than a discrete path of impaction, obviously due to rapid diffusion of the free gas molecules in the impacting gas flow. No. 5. Coexistence of formaldehyde with KCl produced a clearly defined path of inhibition ( A , c; B, b, c), strongly indicative of a synergism. Comparison of ( A , c with A, 6) shows better growth development in the not impacted area, and lesser for the path of impaction. This can be interpreted as due to an association of the irritant gas with the particles, causing a topical intensification when impacting, also a depletion of the gaseous component available for difhsion. No. 6. Coexistence of H C H O with latex resulted in a pattern similar to No. 5 but much more distinct (A, c us.
A , 8). Passage through the aerosol spectrometer-i.e., eliminating all particles of (a’ 2 0.2 micron) and the majority of still smaller sizes-resulted in a significant reduction of inhibition by the potassium chloride-formaldehyde aerosol ( A , c us. A, d), and in its complete elimination for the latex-formaldehyde Combination (C, a, 6 , c us. C, d). Exploratory studies of the variation of the effect with the concentration ratio (gas-aerosol) indicate the following: For the potassium chloride aerosol which consists for the relative humidity conditions of the test as supersaturated submicron droplets ( d < 0.3 micron) (7) the effect decreases markedly, when the gas concentration is largely reduced (B, a Us. B, c). The same irritant level shows a noticeable intensification for a twofold increased potassium chloride concentration ( B , b us. B , c ) . The dependence of the effect of the latex concentration is more distinct VOL. 51, NO. 6
JUNE 1959
773
