employing 3,4-xylenol rather than 2,4-xylenol. While concentrations of interferents were not given, a 34% negative interference was found with a Cl-/NO; ratio of 5:l w/w. This increased to 40% a t the ratio 1 O : l w/w. Hydrogen peroxide yielded a 55% negative error at an HzOZ/NO; ratio of 1O:l w/w. Lead ion (from PbS04) showed no measurable effect a t a Pb/NO, ratio of about 1OO:l w/w. Presumably, similar results should be observed with 2,4-xylenol as well. To determine the cause of the negative interference, the total halide ion concentration was determined by the silver nitrate turbidimetric procedure (4).For the 22 extracts analyzed by the two nitrate methods, the range in total halogen (chloride plus bromide) concentration was from 0.3 to 1.1 pg/ml or about two orders of magnitude below the level reported for threshold interference effects by chloride ion (i.e., 100 pg/ml). Since analysis of nitrate was done on extracts obtained with boiling water, extraction of significant amounts of lead was not expected. Nevertheless, the 22 extracts were analyzed for lead by atomic absorption. Of the 22 samples, only one exceeded the limit of detection, 0.5 pg/ml. The exception had a value of 0.8 pg/ml. Thus, if lead is the interfering species in nitrate determination by the 2,4-xylenolmethod, it is effective at quite low levels in contrast to the findings of Holler and Huch ( 3 ) .Finally, a test for peroxides with a 10%potassium iodide solution proved negative with a representative set of the samples.
Conclusions Regardless of the origin of interference, we can conclude the following: At atmospheric lead levels below ca. 2 ~ g / mthe ~ , ratio of Technicon nitrate to 2,4-xylenol nitrate was about 0.8. A t lead levels above about 2 pg/m3, the ratio increased sharply with increasing lead concentrations due to negative
interference by a traffic-related aerosol constituent. This constituent appears to be something other than halide, lead, or peroxide. Because of the observed substantial interference in the 2,4-xylenol method, its use should be restricted to samples collected away from high-density vehicular traffic. [A recent comparison (5) of the xylenol and automated nitrate made by the Southern California Air Pollution Control District (Los Angeles) Zone with 24-h high-volume samples collected at the District’s monitoring sites did not reveal significant differences between the two methods.] Further work is needed to elucidate the cause of the interference.
Acknowledgment The particulate lead values quoted were obtained by R. D. Giauque, B. Garrett, and L. Goda, University of California Lawrence Berkeley Laboratory, by use of x-ray fluorescence analysis. Literature Cited (1) Intersociety Committee Tentative Method 12306-01-70T, in
“Methods of Air SamDline and Analvsis”. American Public Health Assoc., Washington, D.C, 1972. ( 2 ) Technicon Industrial Svstems, Method 100-7OW, Tarrvtown, N.Y., 1973. (3) Holler, A. C., Huch, R. V., Anal. Chem., 21,1385 (1949). (4) Luce. E. N.. Denice. E. C.. Akerlund.. F. E.,. Ind, Enp. Chem.. Anal. Ed., 15,365 (1943). ’ (5) Wadley, M. W., private communication, 1975. I
I
Received for review May 17, 1976. Accepted August 30,1976. Work supported in part by the California Air Resources Board, Research Section. The statements and conclusions in this note are those of the authors and not necessarily those of the California Air Resources Board. The mention of commercial products, their sources, or use in connection with material reported herein is not to be construed as either an actual or implied endorsement of such product.
Removal of Nitrogen Oxides with Aqueous Solutions of Inorganic and Organic Reagents Haruo Kobayashi’, Nobutsune Takezawa, and Toshinori Niki Department of Chemical Process Engineering, Hokkaido University, Sapporo, Japan
The removal of nitrogen oxides with various inorganic and organic reagents is studied. The efficiency of the removal is best described as a function of the standard redox potentials of half reactions in which the reagents take part. H
Great efforts have been made to find a system appropriate for the removal of nitrogen oxides with aqueous solutions of inorganic reagents in connection with air pollution control (1-7). Although a number of systems capable of removing nitrogen oxides are briefly reported in the “Official Patent Gazettes”, little research related to the removal has been systematically carried out. We have studied the removal of nitrogen oxides of low concentration with aqueous solutions of inorganic and organic reagents and found that the removal efficiency is closely related to the oxidizing and reducing properties of the reagents.
Experimental Method. The experiments were carried out in a flow system at room temperature. Nitric oxide or nitrogen dioxide (diluted 190
Environmental Science & Technology
with a nitrogen stream to 250 ppm) was bubbled through a Munenke scrubbing bottle in which 100 ml of aqueous solution of the inorganic or organic reagent was contained. The total flow was always kept a t 820 ml/min, and the concentrations of nitrogen oxides at the inlet and the outlet of the scrubbing bottle were determined by a chemiluminescence-type NO, analyzer (Yanagimoto Co. Ltd.). Materials. The inorganic reagents used are listed in Tables I and 11. The organic reagents used are also listed in Table V. They are all of extra pure grade and were used by dissolving in distilled water. Runs were carried out with aqueous solutions containing 0.4 and 0.1 mol/l. of inorganic and organic reagents, respectively, unless otherwise noted.
Results and Discussion Removal of NO and NOz. Inorganic Reagents. When NO or NO2 containing gas is bubbled through the aqueous solution of the inorganic reagent, the nitrogen oxide reacts with the reagent and is removed. Tables I and I1 show the results obtained for various inorganic reagents. The efficiency E f ( N 0 ) or Ef(N02)of NO or NO2 removal in the second columns of the tables is defined as E f ( N O )= 1 - ( C N O ( ~ ) / C N Oand (~))
Table 1. NO Removal with Aqueous Solutions of Inorganic Reagents
-
€t(NO)
Reagents
(1)
FeS04
(2) (3)
H A
0.19 0.13 0.8 0.06 0.06 0.075 0.03 1.o 0.05 0.07 0.14 0
KMn04
(4)
Na2Cr207
(5) NaClO (6) (9) (10) (1 1) (12) (13) (14)
Na~S03 Na~S203 NaC102 SnC12 FeS04(NH4)2S04 FeC12
,.. NO2 was evolved
(5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19)
1.0
F
*
\@'
'
-1
Table 111. Standard Redox Potentials ( 70) Used in Figure 1
Et(N02)
Remarks
NO was evolved
'
Reagents
Half reaction
FeS04, FeCI2, FeS04(NH4)2- Fe = Fez+
so4 NO was evolved NO was evolved NO was evolved NO was evolved NO was evolved
-+
'
+ 2e+
+
+ + + +
NaClO Na2S03 Na2S203 NaC102 SnCI2 CuCl
+ + +
+ + + + + + + +
+
Standard redox ,potential, V
0.44
40H- = H202 2eMn02 2H20 = MnO; 4H+ 3e2Cr3+ f 7H20 = Cr& 14H+ 46 eGI20H- = CIOH20 2eS23H20 = SO:6H+ 2e3H20 = S20,'6H+ 8e2s'GI40H- = ClO; 2H20 4eSn = Sn2+ 2ecu = Cu+ e-
H A KMn04 Na2Cr2O7
+
-0.88
- 1.70 - 1.33 -0.89 0.231 0.006 - 1.55 0.136 -0.184
Table IV. Standard Redox Potentials ( 70) Used in Figure 2
'
'
'
'
'
-I
Reagents
Half reaction
FeS04, FeCI,, FeS04(NH4)2- Fe2+ = Fe3+
so4
CIOSO,'HSO;
Na 2S203 NaC102 SnC12 CuCl NiS04
S t a n d a r d Redox P o t e n t i a l
~20:-
Na~S204
0
(volt)
Figure 1. Standard redox potentials of inorganic reagents vs. efficiencies of NO removal Numbers in figure: see Table I
Ef(N02) = 1- ( C N O ~ ( ~ ) / C N O where ~ ( ~ )the ) , subscripts (i) and ( 0 ) represent the inlet and the outlet conditions, respectively. The arrows in the second columns indicate that the efficiency changes: with time. From Table I, the strong oxidizing agents such as KMn04 and NaC102 remove NO efficiently, although NO is partly converted into NO2.
+ e-
+ 20H- = C102 + H20 + 2e+ 20H- = SO:- + H20 + 2e+ 30H- = 2H20 + SO:- + 2es2- = S + 2e= ('/2)~4~i+ eClO; + 20H- = C102 + eSn2+ = Sn4+ + 2ecu+ = cu2+ + eNi" + 2H20 = Ni02 + 4H+ + 2eS20:- -I-40H- = 2SOE- + 2H20 -I2 el- = (Y2)l2 + eMn2+ = Mn3+ + e-
NaClO Na2S03 NaHS03 Na2S
-1
(volt)
Figure 2. Standard redox potentials of inorganic reagents vs. efficiencies of NO2 removal Numbers in figure: see Table II. Concentrationof reagent: 0 . 4 mol/l.
0.715 0.66 0.14 1.o 0.99 1.o 0.67 0.60 0.46 1.o 0.58 0.52 0.755 0.79 -,0.32 0.19 0.96 0.83 0.255 0.290
'
1
3
S t a n d a r d Redox P o t e n t i a l
0
-
'
0
NO2 was evolved
-
Reagents
FeS04 NaClO Na~S03 NaHS03 Na2S Na~S203 NaC102 SnC12 FeS04(NH4)2S04 FeCI2 CuCl NiS04 Na2S204 KI MnCI2 COS04
0
w
Table II. NO2 Removal with Aqueous Solutions of Inorganic Reagents (1)
N
-
w
-
CuCl
Remarks
0
KI MnC12
co2+ = co3+
COS04
-
+ e-
Standard redox potential, V
-0.77 -1.82 0.93 0.575 0.506 -0.04 -1.16 -0.147 -0.152 - 1.68 1.12 -0.267 -1.51 - 1.82
On the other hand, Table I1 shows that NO2 reacts readily with the strong reducing agents such as Na2S03, NaHS03, NazS, Na2S204,and SnC12. It was therefore suggested that the oxidation-reduction reaction is involved in the NO, removal. The rate of the reaction is closely related to the thermodynamic quantity of the reaction such as the standard free enVolume 11, Number 2, February 1977
191
1.0
I
~
”
“
’
”
0
Table V. Removal of NOP with Aqueous Solutions of Organic Reagents Reagent
€1 ( NOz)
Remarks
pAminophenol Neutral red Xanthine Hydroquinone Pyrogallol (6) Methyl red (7) Crystal violet (8) Methyl orange (9) Pyoctanin blue (10) Phenolphthalein
0.91 0.98 0.87 0.57 0.61 0.57 0.81 0.94 0.73 0.87
0.03 molll. 0.1 mol/l., NO was evolved 0.05 mol/l. NaOH (0.05 mol/l.) 0.1 mol/l. 0.1 mol/l. 0.1 mol/l. 0.01 mol/l., NO was evolved 0.025 mol/l. Saturated in water 0.01 mol/l. NaOH (0.06 mol/l.)
(1) (2) (3) (4) (5)
’
+
I
I
4
+
-1
ergy of the reaction (8, 9). The efficiencies obtained a t the initial period of the removal are plotted in Figures 1 and 2 against the standard redox potentials of possible half reactions in which the reagents take part. The redox potentials (10)used in Figures 1and 2 are listed together with their half reactions in Tables I11 and IV, respectively. The reagents which have lower standard redox potentials than -1.4 V are effective for NO removal, whereas the efficiency of the NO1 removal is increased as the redox potential of the reagent is increased. Organic Reagents. Table V shows the results of NO2 removal with aqueous solutions of various organic reagents. The organic reagents are also favorable for NO2 removal. As Figure 3 shows, the relation similar to the plots in Figure 2 holds also for the organic redox system. The standard redox potential of the reagents is therefore an important parameter for the prediction of the efficiency of NO, removal when either an organic or inorganic reagent is employed. The oxidation-reduction reaction (the electron transfer from or to nitrogen oxides) should then be involved in the removal as one of the rate-determining steps.
Literature Cited (1) Ganz, S. N., Lokshin, M. A,, Priklad. Khim., 30,1525 (1957). (2) Ganz, S. N . , J . Appl. Chem. USSR, 29,1107 (1956).
1
0
S t a n d a r d Redox P o t e n t i a l
(volt)
Figure 3. Standard redox potentials of organic reagents vs. efficiencies of NO2 removal Numbers in figure: see Table V. Standard redox potentials: Clark ( 7 7). Those for methyl red, crystal violet, methyl orange. pyoctaninblue, and phenolphthalein not available. Concentrationof reagent: 2, 4, 5, 0.1 mol/l.; 1, 0.03mol/l.; 3, 0.05 mol/l.
(3) Ganz, S.N., Mamon, L. I., ibid., 30,391 (1957). (4) Wendel, M., Pigford, R. L., AIChE J., 4,249 (1958). ( 5 ) Ganz, S. N . , J . ADDLChern. USSR. 26.927 (1953). (6) Kato, S., Chem. &g., Jpn., 1086 (1973).
( 7 ) Lowell, P. S., Parsons, T. B., “A Theoretical Study of NO, AbsorDtion Usine Aaueous Alkaline and Drv Solvents”. Technical Report, OAP eont‘ract No. EHSD 71-5, 1i71. (8) Wells, P. R., Chem. Reo., 39, 171 (1962). (9) Leffler, J. E., Grunwald, E., “Rates and Equilibria of Organic Reactions”, Wiley, New York, N.Y., 1963. (10) Latimer, W. M., “The Oxidation States of the Elements and Their Potentials in Aqueous Solutions”, Prentice-Hall, New York, N.Y., 1952. (11) Clark, W. M., “Oxidation Reduction Potentials of Organic Systems”, Williams & Wilkins, Baltimore, Md., 1960. Received for review November 21,1975. Accepted August 31, 1976. Work supported in part by a grant from the National Research Znstitute for Pollution and Resources.
Stain Method for Measurement of Drop Size Lung Cheng Pittsburgh Mining and Safety Research Center, Bureau of Mines, 4800 Forbes Avenue, Pittsburgh, Pa. 15213
w A theoretical relation between water drop and stain diameters, D and S, presented elsewhere is in agreement with the empirical expression of D = a s b ,where a and b are constants. The present theoretical value of a depends upon impact velocity and the natures of the liquid and target surface, and the value of b equals jiS. For large drops moving with terminal velocities, the value of a becomes insensitive to impact velocity, and the value of b becomes 2/3. Values of D are predicted to within f 1 6 % for a wide range of drop sizes and velocities and to within f 2 % for large drops moving a t their terminal velocities.
A popular method for measuring the size of liquid drops is the stain technique wherein the drop is allowed to impact onto a target surface and leave a permanent impression or stain. 192
Environmental Science & Technology
Stains have been produced, for example, on solid surfaces coated with a layer of lampblack (1,2),magnesium oxide ( 3 ) , or liquid-sensitive films ( 4 , 5 ) , on Ozalid paper ( 6 ) ,and on filter papers (7-11). The drop and stain diameters, D and S, are reportedly related by the expression
D = asb
(1)
where a and b are empirical constants. Numerical values of a and b appear to depend upon the specific experimental conditions (namely, the impact velocity of the drop and the nature of the target surface), Le., a ranges from 0.33 to 0.47 (6-8, IO),while b ranges from 0.67 to 0.93 (6-10). While b = 0.67 according to “simple” geometry (presumably, the simple geometry assumes the volume of the impacted drop is proportional to the square of the stain diameter) (7,8,10) and b = 1.0 for the impacting drop taking a form of a spherical cap (12,13),and a is predicted by the spherical model in terms of
