(59) Barrie, L. A., Ph.D. Thesis, University of F r a n k f d M a i n , West Germany, 1975. (60) E.g., Smith, F. B., Hunt, R. D., Atmos. Enuiron., 12, 461 (1978). (61) Graedel, T . E., J . Ceophys. Res., 82,5917 (1977). NOTE ADDED IN PROOF.Very recent results now indicate that NH3 cannot be a source of NO, via this mechanism: Kurasawa, H., Lesclaux, R., paper P4 presented at the 14th Informal Conference on Photo-
chemistry, Newport Beach, Calif., March 1980. (62) During a recent (early January) field study in Northeastern Alberta, ozone levels of 20 ppb were consistently observed. Bottenheim, J. W., to be published.
Received for reuiew J u n e 26, 1978. Resubmitted July 25, 1979. Accepted March 4,1980. This work was supported by a grant from the Research Secretariat, Alberta Environment.
Low Molecular Weight Aliphatic Amines in Exhaust from Catalyst-Equipped Cars Steven H. Cadle" and Patricia A. Mulawa Environmental Science Department, General Motors Research Laboratories, Warren, Mich. 48090
A spectrophotometric method for total aliphatic amines and a gas chromatographic method for low molecular weight aliphatic amines were used to measure amine emissions in the exhaust of 17 cars which were driven on a chassis dynamometer using the 1975 FTP test. Because the extremely low concentration of amines resulted in problems with analytical sensitivity, only upper limits can be reported. It is concluded that total aliphatic amine emissions are less than 2.2 mg/mile and that the average emission rates of monomethylamine and dimethylamine are no more than 0.3 and 0.1 mg/mile, respectively. It has been suggested that automotive-derived amines react in the air with nitrogen oxides to form nitrosamines, which are suspected carcinogens. However, as shown in this study, automotive amine emissions are not high enough to account for the concentrations of nitrosamines which have been reported at roadway sites. Nitrosamines are compounds which have been shown to be carcinogenic in a wide variety of laboratory animals and, thus, are suspected human carcinogens. In recent years, it has been discovered that human exposure can come through use of water, soil, air, nitrite-preserved foods, alcohol, tobacco, tobacco smoke, cosmetics, pesticides, and other products. The discovery of dimethylnitrosamine (DMNA) in a few ambient air samples has led to a search for the sources of this compound. Industrial sources ( 1 ) of the DMNA have been identified in some cases. However, no source has been located for DMNA found near highways in New York and New Jersey or for the DMNA and diethylnitrosamine (DENA) (2) found in the Eisenhower Tunnel in Colorado. These measurements are puzzling since several studies have failed to positively identify DMNA in auto exhaust ( 3 , 4 ) . A possible source has been identified in a recent study which concluded that DMNA may exist in blowby gases from heavy-duty diesels ( 5 ) .However, more work is needed before these findings can be confirmed. Another possible DMNA source is the atmospheric reaction of dimethylamine (DMA) and nitrous acid. This reaction has been investigated by Hanst et al. (6) and Glasson (7) in the dark in long-path infrared cells. Hanst et al. calculated that dimethylamine introduced into moderately polluted urban air in the dark would react at a rate of 2% per hour. Since the DMNA yield of the reaction was not determined, this provided an upper limit to DMNA formation. It was also concluded that the reaction would not occur in daylight and that half the DMNA is destroyed in 0.5 h a t full sunlight. Glasson determined the DMNA yield from the amine reaction to be 6%. Although these studies were complicated by severe wall losses of the DMA, it was concluded that homogeneous DMNA formation in the atmosphere is insignificant, especially since the very small quantity of DMNA formed in the dark was 718
Environmental Science & Technology
destroyed by light. Recently, Grosjean et al. (8)have studied the reaction of dimethylamine, diethylamine (DEA), and triethylamine (TEA) with NO, in an 80-m3 Teflon outdoor smog chamber. DMA and DEA yielded small quantities of their respective nitrosamines (about 1%)when reactions were performed in the dark; however, these nitrosamines decomposed in the light. In contrast, nitrosamine yieids from TEA were greater in the light than in the dark. In addition, DEA and TEA yielded 11and 5%, respectively, of diethylnitramine when irradiated in sunlight. It is suspected that diethylnitramine is carcinogenic, since dimethylnitramine is a known animal carcinogen. Since it has been suggested that amines are involved in the atmospheric production of trace quantities of suspected carcinogens, it is important to identify amine sources. Auto exhaust emissions would be of particular interest since NO, emissions occur simultaneously. Hurn et ai. (9,IO)have used a gas chromatographic method to determine individual aliphatic and aromatic amines in the diluted exhaust of precatalyst cars run on several driving schedules. Fuels with various nitrogen-containing additives were used. The amine concentrations were below the 0.04-ppm limit of detection in all tests. Zweidinger et al. ( 1 1 ) used ion chromatography to measure the amine emissions from two 1977 Californiastandard Volvo automobiles which were equipped with three-way catalysts. It was concluded that the concentration of alkylamines must be several orders of magnitude less than ammonia emissions from these cars. In this report, we describe a colorimetric method and a more sensitive gas chromatographic method for determining low molecular weight aliphatic amines. Amine emission results from several cars are also presented.
Experimental The 17 cars used in this study are listed in Table I. Cars B and P were forced to run rich in some tests by restricting the air intake, Car D was tested with both the original carburetor, which had a part throttle air-fuel ratio of 14.2, and a replacement carburetor with a 13.5 part throttle air-fuel ratio. Car F was modified to run rich by adjusting the idle screw. Car G was an experimental three-way catalyst car chosen because the air-to-fuel ratio could be easily varied by adjusting the fuel injector controls. Car M was equipped with a 1978production three-way catalyst. The remaining 11 cars were randomly selected and were not modified for testing. All cars were run on the same commercial unleaded gasoline. Exhaust samples were collected during 1975 FTPs conducted on a Clayton water-brake chassis dynamometer. One continuous sample was collected through the entire 23-cycle test procedure, Initially, both amines and ammonia were sampled from a constant-volume sampler (CVS). Later, the sampling trains diagrammed in Figure 1were used. In sample
0013-936X/80/0914-0718$01.00/0
@ 1980 American Chemical Society
1 1
Table 1. Cars Tested
Propottionat Sampler
car
catalyst
A Ba
ox.
C Db
E FC
Gd H I
ox. ox. ox ox. ox.
Calil. emissions equipment
car
catalyst
yes Yes
J K
ox. ox.
no
Yes yes Yes
L M N 0
ox.
yes Yes yes
yes
3-way
ox. ox.
no
3-way
Pa
ox ox. ox.
Q
none
Calif. emissions equipment
no
Yes yes
no
Yes
a Air-to-fuel ratio decreased in some tests by restricting the air inlet. Tested with two carburetors and with the air pump connected and disconnected. Modified to run rich by adjusting the idle screw. Experimental car with fuel injection.
lmpingers
Sample t r a i n A ~
Figure 1. Sampling trains for amines and ammonia
train A, raw exhaust was drawn through a heated Teflon sample line (60 "C)a t 1.5 L/min into two midget impingers connected in series. The impingers, which contained 10 mL of 0.01 N HCl, were housed in an oven kept a t 60 "C. These samples were analyzed for both amines and ammonia. Same-day analye,is was performed on all amine samples. Sample train B had the same solutions and flow rates as A and was run simultaneouslv with it in some exDeriments. These impingers were analyzed for ammonia as well as for amines. The amine collection efficiency of the midget impingers was investigated by scrubbing both the contents of prepared bag standards and tho diluted permeand of high-rate permeation tubes. The amine concentrations ranged from 0.5 to 3.0 ppm. The permeation tubes, which were calibrated on a Cahn-1000 electrobalance before use, were kept in a Kin-Tek Model 670 permeation tube system a t 30 "C. The possibility of collecting amines on oxalic acid impregnated glass fiber filters was investigated as an alternative to the impinger scrubbing of the exhaust. Impregnated filters were prepared as described by Richards (12). After sampling, the filters were extracted ultrasonically in 10 mL of deionized water for 10 min. The extracts were made alkaline with 10 N KOH immediately before gas chromatographic analysis. The spectrophotometric method of amine analysis described by Dahlgiren (13)was used on some samples. In this method, the amine solution is buffered a t pH 8.1 and reacted with hypochlorite. After the excess hypochlorite is destroyed with nitrite, a starch-iodide solution is added. Absorbance was measured in a 1-cin cell a t 540 nm. The method was calibrated using 0-1.1 pg/mL of diethylamine. This calibration gave a straight line corresponding to a molar absorptivity of 18 700, 16% lower than the reported literature value (13).The response to several aliphatic amines was measured and is given in Table 11. Aliqu'ots of the exhaust samples were spiked with diethylamine to a1 concentration of 0.25 pg/mL. The average recovery on these seven samples was 91%, with a range from 76 to 112%. The analysis of amine samples was performed on a Perkin-Elmer Model 3920B gas chromatograph, equipped with a Perkin-Elmer thermionic N-P detector operated in the N-selective mode. The glass 1.83 m X 2.36 mm column was washed using the procedure described by Dunn (14) before being packed with GP 4% Carbowax 20M 0.8% KOH on Carbopack B. A glass-lined injector treated with 1.0 N KOH was operated a t 250 "C. The interface was likewise glass-lined and operated a t 125 "C. Chromatograms were run isothermally a t 70 "C. The column and detector flow rates were: He (carrier),48 mL/min; Hz, 3.75 mL/min; air, 100 mL/min. The
+
Table II. Relative Molar Spectrophotometric Response of Various Compounds in Dahlgren's ( 73) Amine Analysis rei sensitivity
compd
dimeth\lamine ethylamine diethylamine
comod
0.83 1.19 1.oo
dipropylamine dibutylamine ammonia
triethylamine
0.63
rei sensitivity
0.87 0.88
0.00
gas chromatograph was calibrated with acidic (0.01 N HC1) aqueous solutions of Eastman reagent grade hydrochloride salts of monomethylamine (MMA),dimethylamine (DMA), trimethylamine (TMA), and diethylamine (DEA). Prior to injection, the solutions were made alkaline with 10 N KOH. In addition to the amine measurements on samples collected from undiluted exhaust, ammonia analyses were performed on both diluted and undiluted exhaust samples by the absorptiometric indophenol blue technique described by Tetlow and Wilson (15).After the samples were collected, they were stored in a refrigerator for periods ranging from 1 to 22 days (average of 11 days) before the analyses were performed. Identification of peaks was based solely on retention time on one column. Therefore, the possibility of positive interferences cannot be dismissed. Results
Analysis. GC System Stability. Chromatography of amines is notorious for adsorption losses and the related peak tailing of these strong bases (16).The column for our analyses exhibited these same problems. Additionally, the system showed memory responses for successive injections and peak ghosting. Several attempts a t conditioning the column with large amounts of HzO (at least 300 pL) ( 17 )were moderately successful in reducing the tailing. However, the problems were not solved until an on-line conditioner filled with concentrated NH40H (36-37%) was installed in the carrier line (17) between the flow controller and column. This conditioner released ammonia which continuously conditioned the column, resulting in a dramatically improved separation of the low molecular weight amines as well as decreased tailing and improved sensitivity. However, the drop in the NH40H level in the conditioner during the day was accompanied by a decrease in sensitivity and increased tailing. The constant degradation in the response required frequent recalibration of the system, which was accomplished by bracketing every six injections with injections of standard solutions. Another source of instability in the system was the detector itself. The rubidium-bead ion source for the detector degraded and changed its characteristics continuously and unpredictably. The Volume 14, Number 6, June 1980
719
-
Table 111. Amine Collection Efficiencies
2.3 2.3 2.3 1.49 1.49 1.49 1.49 1.49 1.25 1.25 1.15
0.90 0.90 0.90 0.60 0.60 0.60 0.60 0.60 0
0 0
MMA
DMA
P
83.2 74.5 78.1 27.7
75.9 61.8 67.3 35.4 33.9 53.5 27.7 34.7
0 7.29 4.83
23.6 32.0 26.7 30.0 100 91.9 81.6
combination of NHs depletion and bead deterioration resulted in significant changes in the sensitivity. For this reason, we do not recommend this method for routine analysis. GC Sensitiuity. Under optimum conditions, solution concentrations of 0.01 ppm of MMA and DMA could easily be analyzed with a 5-pL injection. In addition, the response to low molecular weight aliphatic amines was found to be linear from 0.01 to 3.0 ppm. Although both water and the acidscrubbing solutions were found to have significantly less than 0.01 ppm of the individual amines, all samples of air scrubbed from the CVS, the laboratory, and the laboratory's compressed air supply had small chromatographic peaks corresponding to approximately 0.01 pprn of MMA and DMA. When samples were collected with impingers in series, the peaks were present and of equal size in both impingers, thus showing they were not collected amines. Although the source of these peaks was not positively identified, it is believed that they are caused by release of trace amounts of amines from the injection port and column when the samples were injected. The limit of detection of the method for MMA and DMA was set by this background concentration a t approximately 0.01 ppm in solution. Sampling. The investigation of impinger collection efficiency was complicated by adsorptive losses of the &minesto the walls of transfer tubes and containers. In the parts per million concentration range, the apparent collection efficiency of the front impinger in a double-impinger setup varied from approximately 20 to loo%, depending on the condition of the sample container and sample lines (see Table 111).Yet, the backup impinger showed negligible amine levels in all cases. It is clear from this evidence that the first impinger was removing all the amine which reached it, and that the apparent low collection efficiency can be attributed to loss of samples before the impinger. With this in mind, we considered the possible adsorption losses likely to be encountered while sampling dilute exhaust from the CVS. The large surface area of the CVS heat exchanger, the mixer, and the area of the 5 m X 10 cm stainless steel exhaust lines are potential areas for adsorptive losses. In addition, prior emission tests could have left sulfuric acid deposited on the surfaces, creating a good amine denuder. T o determine the survival rate of amines through the CVS, we conducted an experiment during which MMA was bled into the CVS before the mixer. Sampling runs were conducted with MMA concentrations in the dilution air of 0.1 and 1.0 ppm. Double-impinger samples of the spiked diluted air were collected from sample train B, shown in Figure 1.At 0.1 ppm, the recovery was a mere 10%. However, a t 1.0 ppm the recovery improved to 74%. In actual exhaust sampling, ammonia emissions may help to condition the CVS and thus decrease adsorptive losses. In the experiments discussed below (Tables IV and V), runs 1 through 15 were 720
Environmental Science & Technology
sampling method 1st 2nd collector collector
% recovered by 2nd collector
% recovered by 1st collector
concn, ppm
impinger filter filter impinger impinger impinger filter filter impinger impinger impinger
0 6.83 5.02 0 0 0 9.26 3.89
0 0 0 5.99 3.79 0 0 0
impinger impinger impinger impinger impinger impinger impinger impinger impinger impinger impinger
Table IV. Total Amines and Regulated Emissions; Measurements in Diluted Exhaust run
car
1 2 3 4
0 N P Pa
5
0
6 7 8
B Ba Q
a
regulated emissions, g/mlle HC co NOx
0.97
18.3
1.35
1.08 1.14 0.52 4.17 1.88
25.2 13.0 4.7 60.7 16.7
1.84 1.47 1.61 0.84 2.17
total amlnes, mglmile
