Acknowledgment
Literature Cited American Public Health Association, “Standard Methods for the Examination of Water and Wastewater,” 12th ed., New York, 1965, pp 66 and 67. Anderson, T., Madsen, H. E. L., Anal. Chem. 37, 49 (1965). Galal-Gorchev, H., Morris, J. C., Division of Water and Waste Chemistry, 142nd Meeting, ACS, Atlantic City, N.J., September 1962. Hashmi, M. H., Ayaz, A. A., Anal. Chem. 35,908 (1963). Johannesson, J. K., Analyst 83,155 (1958). Palin, A. T., Water Sew. Works 108,461 (1961). Stenger, V. A,, Kolthoff, I. M., J. Amer. Chem. Soc. 57, 831 (1935).
This research was sponsored by the U.S. Army Medical Research and Development Command, under contract no. DA-49-193-MD-2909.
Received for review October 13, 1969. Accepted December 4 , 1970. Presented at the Division of Water, Air, and Waste Chemistry, 157th Meeting, ACS, Minneapolis, Minn., April 1969.
is added to the sample. The MO test is also suitable for the determination of total halogen, in the presence of bromide ion, It can be concluded also, from studies of the reaction of chlorine with solutions containing bromide ion and ammonia that, to form bromamines in a water supply by addition of chlorine and bromide ion, these would have to be added to a small volume of the water at low p H to form free bromine, and subsequently this solution would have to be mixed with the remainder of the water to be treated.
Natural Synthesis of Ozone in the Troposphere Lyman A. Ripperton, Harvey Jeffries, and James J. B. Worth’ Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, N.C. 27514
I Observational
and experimental data suggest or demonstrate that some of the nonurban, tropospheric ozone is synthesized in situ rather than being transported from the stratosphere. Experiments showed that ozone can be synthesized from naturally occurring precursors at concentrations comparable to those found in nature. Two precursor systems which produced ozone were NO2 a-pinene hv + and CH20 a-pinene hv e.This work provides chemical evidence for the theory proposed by Frenkiel and Paetzold, on the basis of diffusion theory, that there is a “tropospheric source” of ozone.
+
+
+
+
I
t is well known that ozone (03)is synthesized in the polluted air of cities (Leighton, 1961; Wayne, 1962) and in the stratosphere (Junge, 1963). It has not been established that O3 is synthesized in the natural troposphere. There are, however, scattered references to this possibility. In 1941, Regener (Junge, 1963) proposed the theory that O3observed in the troposphere originated in the stratosphere. On the basis of diffusion theory, however, Frenkiel(l960) and Paetzold (19til), concluded that not all tropospheric O3has a stratospheric origin. McKee (1961) measured O3in Greenland and concluded that some of it was probably of local photochemical origin. Although the available evidence suggests that most tropospheric O3 (outside the polluted areas) originates in the stratosphere, there is evidence of tropospheric synthesis. In seven cases of 250 (Hering and Borden, 1967), 0 3 concentrations were greater at or below 2.5 km than at the tropopause. In 44 of 251 cases, the O3 concentration at altitudes below 5 km was greater than at 5 km. Layers of relatively high tropospheric O3concentration near the tropopause can be caused by
Research Triangle Institute, Research Triangle Park, N.C. 27705. 246 Environmental Science & Technology
stratospheric intrusion as suggested by Kroening and Nye (1962). High values near the ground, however, are more easily explained by in situ synthesis than by subsidence, through half the troposphere, of a layer of high 0 3 content. Went (1960) suggested a mechanism for tropospheric synthesis similar to that by which 0 3 is thought to be formed in polluted air, NOz olefin hv +, with “terpenoid” compounds replacing the simpler olefins of polluted air. Stephens (1962) experimented with the system NO2 apinene hv +, and observed the formation of PAN (which would register as O 3 on a KI method of analysis), but he did not determine O 3itself. Rasmussen and Went (1965) found an average of 1.0 pphm (maximum 5.0 pphm) of atmospheric terpenoid compounds in the Appalachians and the Ozarks. Lodge and Pate (1963) found an average of 0.09 pphm (maximum 0.50) of atmospheric NO2 in Panama, and Worth et a/. (1967) measured an average of 0.40 pphm (maximum 2.6 pphm) in the southern Appalachians. The experiments discussed below were part of a long-term study of the behavior of O 3 in the lower troposphere. Field data were examined for evidence of natural tropospheric synthesis of 03,and experiments were designed specifically to examine the possibility of natural tropospheric O3 synthesis. Other experiments were designed to explore mechanisms by which natural O3synthesis occurs in the troposphere.
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+
Procedure Synthesis in Untreated Natural Air, In the late summer of 1964 and 1965, continuous oxidant readings were made simultaneously with Mast Ozone Meters on Green Knob, N.C., and in Little Lost Cove, an adjacent valley. At a site in rural piedmont North Carolina, 0 3 has been measured with Mast Meters at 1.2, 9.2, 18.2, and 36.6 m on a tower on the campus of the Research Triangle Institute. Some data at 9.2 and 36.6 m have been obtained with Regener chemiluminescent ozone meters. At the piedmont tower site, air was blown, untreated, into a large Mylar bag with a Gelman “hurricane blower” and
irradiated with either sunlight or artificial light. A number of similar experiments were carried out utilizing a 29-m3 Mylar balloon and sunlight. Ozone concentration was followed in both sets of experiments with both Mast and Regener instruments. Synthesis in Manganese Dioxide-Treated Natural Air. Air was drawn through a trap containing manganese dioxide (Mn02), beyond which point O3 was measured with a Mast meter. The air then entered a 72-liter borosilicate-glass flask, which was exposed to sunlight. Oawas measured in air leaving the flask. (MnO? destroys O,],presumably without affecting other gases.) Synthesis in Synthetic Blends. Various synthetic blends were made up in both “zero” air (Matheson) and in air cleaned by being passed through silica gel, Ascarite, and activated carbon. The first system tested was NO2 a-pinene Irv -+. In a second bag into which NO2 had never been introduced, the system C H 2 0 $- terpentine vapors h v was studied, and a third bag was utilized for CH?O a-pinene / I V -+. Both Mast and oxyluminescent instruments were utilized to measure O3 changes. The blends in the Mylar or Teflon bags were irradiated with artificial light froni mercury vapor (EH) and “daylight” flourescent lamps. Concentrations of reactants are presented in Table I.
+ + +
+
-+
+
Results and Discussion
Field data from 1964 and 1965 show the oxidant level in valley higher than the simultaneous reading on the adjacent mountain top during times of good mixing (Figure 1). Barring unusual circumstances of circulation, one would expect to find higher concentrations of O3 at higher levels if subsidence accounted for the presence of all ground-level 0 3 . The differentials between the lower and the higher elevations were generally small when the higher oxidant concentration occurred in the valley. The calibration and control maintained on the instruments, the fact that different Mast instruments were utilized at dif’ferent times, and the number of cases observed indicate that this phenomenon was not an “instrument artifact.” I n the 1966 data from the piedmont tower, 140 cases occurred in which an inversion condition of 0.56OC or greater occurred between the 1.2 and 36.6-m levels at sunup. In
MIDNIGHT GREEN KNOB OZONE LITTLE LOST COVE OZONE
Table I. Ozone Production in Synthetic Blends Max. photochemical 0 3 , _ _PPhm _ _ ~ Bag Mast Regener Reactants and concn, pphm material Mylar 1.1 1.3 NO, (1) a-pinene ( 5 ) 8 ... Teflon NO, (10) a-pinene (50) 8 ... Teflon NOs (10) a-pinene (50) ... Teflon 8 NOr (10) a-pinene (50) 8 ... Teflon NOn (10) a-pinene (50) ... Teflon 8 NOs (10) a-pinene (50) ... Teflon 10 NO, (10) a-pinene (50) ... Teflon 10 NOs (10) a-pinene (50) 4.8 Mylar 6.7 NOr (12) a-pinene (10) 6.6 Mylar 10.6 NOa (12) a-pinene (10) 1 1 Mylar CHZO (-10) 2 1 Mylar CHZO (-20) 2 2 Mylar CHaO (-20) CH,O (-10) terpentine Mylar 5 5 vapors (unknown) 1 4 Mylar CH,O (-20) a-pinene (10) 2 Mylar 5 C H 2 0 (-20) a-pinene (50) 0 Mylar 0 Clear air (gas-cleaning train) “Zero air” (gas chromatic, 0 Mylar 0 Matheson)
+ + + + + + + + + +
+ + +
Table 11. Ozone Synthesis in Rural Air in Mylar Bags Reading before irradiation, pphm Reading after irradiation Mast Regener Mast RegenerType light In 600-liter Mylar bag 0.0 1.4 0.0 1.1 ...
0.8
0.0 0.0 0.0 0.4 0.0 0.0
0.2 1.9 0.5 1.3 ... decreased
0.5 0.3 0.5 0.8 0.3 0.0
artificial sunlight sunlight artificial sunlight sunlight
0.3
sunlight sunlight sunlight sunlight sunlight sunlight
In 29-cm3 Mylar balloon
0.6 1.5 1. 3 2.5 1.8 1.9
0 1 ...
0.4 1. O 0.6 0.7
0.9 1.7 decreased decreased 2.0 2.5
. . .
decreased 1.2 1.2 1. o
NIGHTTIME
41 of the 140 cases, the O3values at 1.2 m, as measured on the Mast meter, began to increase after sunup, but before the base of the inversion lifted above the tower. The same pattern has been observed with the Regener chemiluminescent O3 meter, although fewer data points were obtained. The nocturnal inversion extended t o a height above the tower and the vertical flux of gases was strongly inhibited. An increase in oxidant and O3would have to be caused by in situ synthesis of 0 3 in natural air near the ground, not to vertical transport of O3downward. Table I1 presents data from captive atmosphere experiments. The required manipulation of the air in setting up the experiment was usually accompanied by a decrease in the O3 concentration from the ambient value. I n most of the cases observed, both the Mast and the Regener O3 meters registered increases in O 3 concentration upon irradiation. Supporting chemical data relating to possible O3 precursors were not Volume 5, Number 3, March 1971 247
A
AMBIENT 0, 0, EXHAUST
0 FLASK
FLASK SOLAR
0, INITIALLY
RADIATION
Flow = 2.14 I/min. Residence = 33.5 min.
06 07
08 09
IO
I1 12 13 14 I5 16 TIME INTERVAL (hrs.)
17
18
19
20
Figure 2. Ozone potential of ambient atmosphere
With the observational and experimental evidence accumulated by ourselves and others, we concluded that O 3 synthesis does occur in the troposphere. The paths by which O3 is synthesized in photochemical primary and secondary reactions in polluted air have been discussed (Altshuller et al., 1967; Leighton, 1961 ; Wayne, 1962). The processes in unpolluted air are probably similar, and O3has been produced in this laboratory by the irradiation of the synthetic blends listed in Table I. Ozone is considered by some atmospheric scientists to be a “conservative” constituent in the troposphere, being destroyed almost exclusively by contact with the earth’s surface. However, ozone is destroyed by reaction with many other trace gases and its “conservative” appearance may be partially maintained by tropospheric synthesis, which decreases the net rate of destruction. Acknowledgment
obtained or are not presented here. The purpose of these experiments was to establish the fact of tropospheric O 3 synthesis. The O3 potential of the ambient atmosphere is represented by the Mast meter recorder chart shown in Figure 2. Ozone in the air entering the flask was destroyed by M n 0 2 . Irradiation with sunlight then produced O3 from photochemical precursors in each of 10 runs. Average residence time in the flask was about 30 min. Ozone concentration in the ambient air and in the precursor flask began to increase after sunrise. The ambient value continued t o rise until midafternoon, but O 3values produced from the precursors peaked at about 10 :00 a.m. and then began to decrease, in spite of the fact that sunlight intensity continued to increase for about 2 hr. This would indicate that other factors were having an effect opposite to that of the increasing light flux. N o temperature profile is available for the time of this run, but probably the inversion lifted between 8:30 and 9:30 a.m. and the ozone precursors (presumed to have ground-based sources) were diluted with precursor-depleted, 03-rich air from aloft. Ozone precursors would also be depleted by being utilized in the photochemical production of O 3as the day progressed. As the data in Table I indicate, O3was synthesized in all the synthetic atmospheres irradiated except the “blanks.” Nitrogen dioxide is considered the most important photoacceptor in the chemical reactions of polluted air, and, as these experiments demonstrate, can be important in natural air. Oxygenated compounds such as the aldehydes may also be active in the synthesis of O3 in the natural atmosphere. (In twelve 2-hr samples we found a range of 0.7 to 1.3 pphm of formaldehyde at our tower site.) Our data demonstrate that O3 can be synthesized from compounds known t o exist in or to be emitted into the atmosphere.
248 Environmental Science & Technology
The authors thank the Atmospheric Science Section, National Science Foundation (NSF Grant ~ ~ - 1 0 2 2 )for , financial support which made this work possible. Thanks are also due to the University of North Carolina Research Council for funds [344-FAC-1 (518)] which permitted us to purchase the 1026-m3Mylar balloon. Literature Cited Altshuller, A. P., Kopczynski, S. L., Lonneman, W. A., 1, 899 Becker, T. L., Slater, R., ENVIRON.SCI. TECHNOL. (1967). Frenkiel, F. N., International Union of Geodesy and Geophysics, Monographs 1-7, Monograph 3,1960, p 35. Hering, W. S., Borden, I. R., Jr., “Ozonesonde Observations over North America,” Volume 4, Clearinghouse, Department of Commerce, Washington, D.C., 1967. Junge, C. E., “Air Chemistry and Radioactivity,” Academic Press, New York, 1963, p 49. Kroening, J. L., Nye, E. P.,J. Geoph.ys. Res. 67,1881 (1962). Leighton, P. A., “Photochemistry of Air Pollution,” Academic Press, New York, 1961, p 254. Lodge, J. P., Jr., Pate, J. B., Science 153,408 (1963). McKee, H. C.,J. Air Pollut. Contr. Ass. 11,562 (1961). Paetzold, H . K., in “Chemical Reactions in the Lower and Upper Atmosphere,” Interscience, New York, 1961, p 181. Rasmussen, R . A., Went, F. W., Proc. Nut. Acud. Sci. 53, 215 (1965). Stephens, E. R., Proc. A . P. 1. Sect. 3, Vol42, p 665 (1962). Wayne, L. G., “The Chemistry of Urban Atmosphere,” L. A. County Air Pollution Control District, 1962, p 180. Went, F. W., Proc. Nat. Acad. Sci. 46,212 (1960). Worth, J. J. B., Ripperton, L. A,, and Berry, C. R., J . Geophys. Res. 72,2063 (1967). Receiced Jor reciew February 11, 1969. Accepted October 13, 1970. Presented at the Dicision of Water, Air and Waste Chemistry, 152nd Meeting, ACS, New York, N . Y., September 1966.
