COMMUNICATION
Ammonia in Auto Exhaust John H. Harkins' and Stephen W. Nicksic* Chevron Research Co., Richmond, Calif.
94802
Ammonia in the exhaust from a laboratory V-8 engine was measured to see if the amount was sufficient to account for ambient levels. Exhaust samples were cold-trapped from an engine operated a t both steady-state conditions and over the California State Motor Vehicle Pollution Control Board traffic cycle. The concentration in the condensate ranged from 1 p.p.m. at idle to 6 p.p.m. a t 50 m.p.h. road load and averaged 2.2 p.p.m. over the entire traffic cycle. The presence of nitrogen-containing detergent additives or lead antiknock compound in the fuel did not affect the amount of exhaust ammonia. On the basis of the data, up to 10% of ammonia in the atmosphere can be accounted for by ammonia discharged from motor vehicles.
7-
A
mmonia is found in the atmosphere of urban communities in concentrations up to 0.2 p.p.m., with average concentrations of 0.02 p.p.m. (Jacobs, 1960). Ammonia results from the combustion of fuels as well as other reactions and natural sources. Although ammonium salts were suspected of causing some of the respiratory irritation in the Donora, Pa., episode in 1950 (Faith, 1959), ammonia is considered of limited importance as an atmospheric contaminant. It is reasonable to expect ammonia to neutralize, partially at least, acidic airborne constituents such as SO, and SOa, and their hydrated forms, with consequent reduction in the irritant qualities of each. This neutralizing function of NH3 in atmospheric chemistry was of interest to the authors in their studies on the role of SO, in atmospheric visibility reduction (Harkins and Nicksic, 1964, 1965). Because of the paucity of data on the concentration of ammonia in auto exhaust, a program was run to measure exhaust ammonia emitted from a laboratory engine.
Engine Conditions
Figure 1. Ammonia in automobile exhaust gas
Experimental Equipment and Procedure. The tests were run on a laboratory 1956 Oldsmobile V-8 engine a t both steady state conditions and over the California Motor Vehicle Pollution Control Board q c l e (217 West First Street, Los Angeles, Calif. 90012). ~~~~~
Present address, Scott Research Laboratories, Inc., Perkasie, Pa. 18944 Present address, Chevron Research Co., La Habra, Calif. 90633
Volume 1, Number 9, September 1967 751
Figure 2. Effect of fuel composition on ammonia concentration in exhaust gas+engine conditions : 50 m.p.h. at road load
0
1
2
3 4 Lead Concentration, mllgallon
5
,
6
Figure 3. Effect of Pb concentration on ammonia in exhaust-engine conditions: 50 m.p.h. at road load
The samples for ammonia determination were collected at the outlet of the exhaust manifold by cold trapping a typical exhaust sample. The trap temperature was -5” C., and very little ammonia was found in a second trap in series when one was used. Ammonia was determined by a n evolution-titration procedure, as in the familiar Kjeldahl method. Over-all reproducibility was within f15 % of the averages reported in Figure 1. Results. Figure 1 is a bar graph showing the ammonia concentration in auto exhaust a t three steady state conditions and over the California cycle. This figure shows that the ammonia concentration ranges from about 1 p.p.m. at idle (600 r.p.m.) to 6 p.p.m. at 50 m.p.h. (1800 r.p.m.) road load. The average concentration on the state cycle was 2.2 p.p.m. The procedure employed to measure ammonia will include volatile amines or the ammonia resulting from the combustion of nitrogen-containing additives. Although it seemed unlikely that organic nitrogen compounds would contribute t o exhaust ammonia, the possibility was investigated because the test fuel contained a nitrogen-containing additive. Figure 2 is a bar graph showing the effect of fuel composition on ammonia concentration in exhaust gas. This figure shows that within experimental error there is no difference in exhaust ammonia between commercial gasoline, iso-octane (no nitrogen compounds in the fuel), and commercial gasoline plus 30 p.p.m. of a carburetor detergent action (DA) additive (N-aminoalkyl acid amide, 7.6 N). This suggests that the ammonia is formed during the combustion process, probably by direct reaction of hydrogen and nitrogen atoms. If this is the case, lead concentration of the gasoline might possibly have a catalytic effect on the formation of ammonia. Figure 3 is a plot of the concentration of ammonia in exhaust as a function of the lead concentration. This figure shows that at concentrations up to 5 ml. per gallon, lead has no effect (within experimental error) on the ammonia content of the exhaust.
that the ammonia is formed during the combustion process. If we assume that exhaust ammonia is dispersed in the atmosphere in the same way as carbon monoxide, use a 1000 t o 1 exhaust dilution typical of dense city traffic conditions (Begeman, 1962), and use the average value of 2.2 p.p.m. ammonia in exhaust over the California cycle, we can account for 10% of the ammonia in the atmospheres of urban communities such as Los Angeles. (In less populated areas, exhaust dilutions would be greater than 1000 to 1, but sampling of atmospheric concentrations of contaminants such as ammonia is usually carried out in urban areas.) Therefore, apparently auto exhaust is not a major source of atmospheric ammonia. Ethylene dibromide and ethylene dichloride used as lead scavengers burn to yield HBr and HCl which could neutralize (and probably do) some of the ammonia, as evidenced by the findings of Hirschler et al. (1957) showing mixed PbC12NH,C1 crystalline deposits in the exhaust train. The present data do not indicate whether exhaust ammonia is free or combined ammonia and, hence, d o not necessarily reflect the ammonia available to neutralize acidic atmospheric gases. However, some atmospheric ammonia can be accounted for by the ammonia in auto exhaust. These tests were run on a n engine without an exhaust emission control system. Before any firm conclusions can be drawn, more data are needed on both the effect of emission control devices on ammonia production and on current atmospheric ammonia levels. Literature Cited
Begeman, C. R., “Carcinogenic Aromatic Hydrocarbons in Automobile Effluents,” S.A.E. Automotive Engineering Congress, January 1962. Faith, W. L., “Air Pollution Control,” p. 174, Wiley, New York, 1959. Jacobs, M. B., “The Chemical Analysis of Air Pollutants,” pp. 413-15, Interscience, New York, 1960. Harkins, J. H., Nicksic, S. W., Abstracts, p. 16Y, 148th Meeting, ACS, Chicago, Ill., Aug.-Sept. 1964. Harkins. J. H.. Nicksic. S. W.. J . Air Pollution Control Assoc. is, ~ b 5,. iis (19652. Hirschler, D. A., Gilbert, L. F., Lamb, F. W., Niebylski, L. M., Znd. Eng. Chem. 49, No. 7, 1131 (1957). ~~
Discussion
The tests showed that ammonia is present in gasoline engine exhaust in concentrations up to 6 p.p.m. and suggests 752 Environmental Science and Technology
Receiwd for recieiv April 28, 1967. Accepted August 28,1967.
