sored by National Air Pollution Control Association, Oxford, Ohio, October 1970. Graff, R. A., Pfeffer, R., Squires, A. M., in Proc. Clean Air Congr., pp 764-71, Academic Press, New York, N.Y., 1971. Paretsky, L.,Theodore, L.,Pfeffer, R., Squires, A. M., J. Air Pollut. Contr. Ass., 21, 204-9 (1971). Pell, M., PhD thesis, The City University of New York, 1971. Pell, M., Graff, R. A., Squires, A. M., in “Sulfur & SOz Developments,” “Chem. Eng. Progr. Tech. Manual,” pp 151-7, 1971. Robson, F. L.,Giramonti, A. J., Lewis, G. P., Gruber, G., “Technological and Economic Feasibility of Advanced Power Cycles and Methods of Producing Nonpolluting Fuels for Utility Power Stations,” report from United Aircraft Research Laboratories to National Air Pollution Control Administration, December 1970.
Squires, A. M., Aduan. Chem. Ser., 69, 205-29 (1967). Squires, A. M., in “Power Generation and Environmental Change,” D. A. Berkowitz and A. M. Squires, Eds., pp 175-227, MIT Press, Cambridge, Mass., 1971. Squires, A. M., U S . Patent 3,402,998 (September 24, 1968). Squires, A. M., Graff, R. A., Pell, M., Chem. Eng. Progr. S y m n Ser.. 67. 23-34 (1971). Squires, A. M,, Pfeffer, R., J Air Pollut. Contr. Assoc., 20, 534-8 (1970). Received for review November 12, 1971. Accepted August 14, 1972. This work was supported by Research Grant No. AP-00945 from the Ofice of Air Programs of the Enoironmental Protection Agency. Presented at the Division of Industrial and Engineering Chemistry, 161st meeting, ACS, Los Angeles, Calif:,March 1971.
Effects of Ambient Levels of Ozone on Navel Oranges C. Ray Thompson,’ Gerrit Kats, and Earl Hensel Statewide Air Pollution Research Center, University of California, Riverside, Calif. 92502
Mature navel orange trees were enclosed in plastic-covered greenhouses and exposed to ambient air, carbon-filtered air, and carbon-filtered air containing either ambient or one-half ambient air levels of ozone for eight months, from blooming to picking time, to determine how much injury this pollutant is causing to citrus trees. No visible leaf injury was observed. Leaf drop, fruit drop, and total yield were determined. Fruit drop, as measured by the percent of total fruit-set which dropped, showed an increase with the amount of ozone. One half the ambient level of ozone had no statistical effect on yield of either number or weight of mature fruit, but a significant reduction was shown by the ambient level of ozone. However, ambient air containing the totsll photochemical smog complex reduced yields considerably, further showing that the deleterious effect of peroxyacyl nitrates, oxides of nitrogen, etc., add to the injury caused by Los Angeles-type smog.
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ir pollutants in the Los Angeles Basin and in other major U.S. and foreign cities are produced by incomplete burning of fossil fuels. The principal source is usually the automobile. The pollutants consist of hydrocarbons, carbon monoxide, nitric oxide, lead derivatives, and many other minor compounds. Some of these emissions react rapidly in sunlight to form photochemical smog which contains ozone as the major component and much lower levels of peroxyacyl nitrates and nitrogen dioxide. Major losses to agricultural and forest plants are caused by this mixture of pollutants. Previous studies at this Center have shown photochemical smog to cause severe reductions in the yield of both citrus and grapes (Thompson and Taylor, 1969; Thompson and Kats, 1970).
To whom correspondence should be addressed. 1014 Environmental Science & Technology
Ambient air levels of nitrogen dioxide had little effect on yield of citrus in a subsequent study (Thompson et al., 1971). Thus, because ozone is the component of smog which occurs in the highest concentration in the atmosphere and the effects shown by fumigating greenhouse-grown vegetables with similar concentrations of this gas cause extensive injury, a study was carried out to find out how much injury ambient levels of ozone were causing to mature, producing navel orange trees in the field. Methods
Twenty-seven navel orange trees enclosed in ventilated plastic-covered greenhouses (Thompson and Taylor, 1969) located near Upland, Calif., were used for this study. The trees were 16 years old and in good condition. The area has climatic conditions and photochemical smog levels typical of the Los Angeles Basin which extends 30-40 airline miles inland from the Pacific Ocean. The trees were irrigated on a 14-day schedule, but when soil suction near the trees exceeded 50 cbars at a depth of 0.5 meter and at a point 1.5 meters from the tree trunk, supplementary water was provided. Fertilization followed commercial practice. Biological controls for pests were used where feasible and were successful in controlling aphids and scale insects. Red citrus mites required spraying with a mixture of chlorobenzilate and ovotran twice during the study. Experimental treatments were randomized to minimize effects of a previous study in which fumigations with NOz (Thompson et al., 1971; Cochran and Cox, 1957) at ambient levels had been carried out in 1968. This randomization was used to avoid the large expense involved in moving the structures and the attendant equipment to another location. The previous experiment had shown minimal effects on the trees and randomization was considered adequate to remove the influence of previous treatments. Cross contamination between greenhouses was not a problem because ozone escaping from any one house would never exceed ambient levels of ozone of the previous day and the dis-
tance between outlet from one structure and intake of another was such that a severalfold dilution would occur. Thus, the amount reaching the inlet of another ambient air house would be small. If exhaust gas from houses given ozone was picked up by blowers providing carbon-filtered air, these absorbers would remove it. The experimental design is summarized in Table I. Four replicate trees were selected as outside checks. Seven houses, each enclosing one tree, received air that was passed through activated carbon filters (CF)to remove ambient oxidants, and seven houses received unfiltered ambient air (Amb). Ozone was generated (Ozone Res. Equip. Corp.) and introduced into the carbon-filtered air entering 13 houses; six received ozone concentrations equal to the total ambient oxidant levels measured the previous day (CF Amb 0,) and seven others received half that ozone concentration (CF Amb 0,)(Thompson and Ivie, 1965; Thompson et al., 1970). Flowmeters, installed on the greenhouses which received the diluted mixture of ozone, were checked several times daily to ensure that the intended level of diluted pollutant was being delivered to the trees. A check for NO2 in the diluted ozone mixture showed no elevation over background levels in air. Ozone in this study was considered equal to total oxidant as measured by the KI-I2 coulometric analyzer (Mast Development Co., Davenport, Iowa). It was recognized that other pollutants such as SOz interfere negatively in this measurement and both peroxyacyl nitrates and nitrogen dioxide interfere positively. However, these contaminants occurred at much lower levels than ozone in the area and tended to compensate for each other in the measurement. Total oxidant in the outside air was recorded continuously. To check on the dispensing system, a second Mast ozone analyzer was used to sample the air inside the greenhouses. Illustrative, typical data showing the amount of oxidant in ambient air and the amount actually recorded in one greenhouse receiving the ambient level of ozone are shown in Table
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Ambient levels of total oxidant varied from 0 to 69 pphm. The monthly maximum hourly average concentrations, average of maximum hourly concentrations, and peak concentrations are shown in Table 111. Performance of the trees was recorded by measuring leaf drop, fruit drop, and yield. Leaf drop was determined by raking leaves around each tree monthly, air drying, and weighing. Fruit drop was measured by collecting and counting all fallen fruit 1.0 cm in diam or larger. Yield was determined by picking, counting, and weighing mature fruit. Differences due to treatments were tested using analysis of variance and the multiple range test. The study was begun May 1, 1970 and ran continuously with only minor difficulties until the fruit was picked January 27, 1971. The ozone generator supplied ample amounts of ozone and performed reliably. Recording instruments were kept in operation by daily servicing and maintenance. Ozone levels supplied to the trees in the greenhouses approximated closely the amounts of total oxidant recorded in ambient air (Table 11). The amounts of oxidant were high during the period from April through November and relatively high levels occurred occasionally during every month of the experimental period. Results and Discussion
Leaf drop data (Table IV) showed that there was no statistiAmb 0 3 cal difference in trees receiving CF air and CF air or Amb air. The total drop was 5.11, 5.13, and 5.69 kg, respec-
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Table I. Experimental Design of Field Study to Determine Effect of Ozone on Navel Orange Trees No. of
trees 7 7 7 6 4
Treatment Ambient air (Amb air) Carbon-filtered air (CFair) Carbon-filtered air ambient level of ozone (CF air Amb 0,) Carbon-filtered ambient level of ozone (CFair Amb 0,) Outside checks (checks)
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Table 11. Levels of Total Oxidant in Ambient Air and Comparable Levels Dispensed One Day Later in Greenhouses Ambient Ozone levels in greenhouse, oxidant levels, Date PPhm Date PPhm Sept. 3 37 f 1 . O Sept. 2 37 i 1 . O 5 27* 1 . 0 4 26* 0 . 7 30+ 1.2 28+ 1.1 9 8 37+ 1 . 3 41 i 1 . 3 11 10 14 14+ 0.3 13 13+ 0.2 21 22* 0 . 6 2 2 i 0.7 20 Table 111. Ambient Levels of Total Oxidant at Experimental Site, 23rd Street and Euclid Avenue, Upland, Calif.. Max. Av of hourly max. hourly Peak Month av concn concn 15 5 Feb. 1970 14 2 1 2 Mar. 1970 42 12 Apr. 1970 28 38 19 May 1970 36 60 30 56 June 1970 51 37 July 1970 49 57 36 53 Aug. 1970 69 36 Sept. 1970 67 25 46 45 Oct. 1970 28 12 Nov. 1970 25 11 6 10 Dec. 1970 22 22 8 Jan. 1971 Q
Parts per hundred million.
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tively. The trees which received CF Amb 0 , dropped more leaves than these three treatments, 7.55 kg. This was statistically valid at the 1 level. The initial fruit set per tree (Table IV) show that there is no significant difference between CF air, CF air Amb 03, and CF air Amb 0 3However, . trees which received Amb air and check trees show a decided reduction in fruit-set, significant at 1 level. Trees exposed to Amb air apparently dropped more flowers and fruits smaller than 1 cm while the check trees could also have done likewise or produced less flowers. Since the absolute fruit drop and yield data are obviously related to the total initial fruit-set, relative as well as absolute data are given. Average total numbers of fruit dropped per tree show no definite statistical trends. However, when the fruit drop relative to the total initial fruit-set in percent was calculated, an orderly increase in fruit loss related to amount of oxidant the trees received was observed. Average fruit drop Amb 0 3 was from trees which received CF air or CF air
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Table IV. Leaf and Fruit Drop of Navel Orange Trees Receiving Different Amounts of Ozone Fruit drop Av fruit Av no. Yield of fruit/tree av, drop/tree, Leaf drop, of fruit, kg/tree set/tree no./tree No. Kg Carbon-filtered air 5.11 897.3 452.3 50.84 445.0 81.1 Carbon-filtered air ' 1 2 ambient ozone 5.13 848.2 441.9 52.94 406.3 77.0 Carbon-filtered air ambient ozone 7. 55" 792.6 487.8 62.75' 304.8' 52,6' Ambient air 5.69 547. 2' 505.1 76.19' 142.1' 28.5' Outside checks 5.28 435. 7" 334.2 79.60" 101 . 5' 24.0'
z
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a
Significantly different from carbon-filtered air treatment, 1 %.
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0.1%.
* 5%.
Table V. Summary of Analysis of Variance and Multiple Range Test of Average Kg of Fruit Pickedpree Carbon Carbon filtered Carbon filtered Ambient filtered ambient Oa ambient O3 air Carbon filtered NS 1% 0.1% Carbon filtered ' 1 2 ambient O3 NS NS 0.1% Carbon filtered ambient O3 1% NS 1% Ambient air 0.1% 0.1% Outside checks 0.1% 0.1% 1% NS
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statistically the same but CF Amb O3caused an increase in the percent of fruit dropped (5% level of significance) and trees which received Amb air or check trees reported a greater drop which was significant at the 0.1 %level (Table V). The retention of fruit was shown by the yield data as the average number and weight of the fruit per tree as we!l as the percent of the total initial fruit-set. Although there was an obvious relationship between fruit drop and retention expressed as percent of the total initial fruit-set, some analysis of the data is useful. The absolute as well as the relative average yield from trees exposed to CF air and CF air Amb O3 showed that there is no statistical significant difference. The ambient levels of ozone reduced the yield in an absolute and relative sense (significant at 5 % level). The very low absolute yield data for trees receiving Amb air and check trees as compared to CF air was partly owing to the lower numbers of initial fruit-set and, therefore, can only be considered as to total sum of effects. Compared to CF air, the differences were significant at the 1 % level. Both these treatments, however, show also a remarkable reduction (5x level) of yield when expressed in percent of the total initial fruit-set. Previous work (Dugger et al., 1963) showed that ozone fumigation caused acute effects on leaves of sensitive plants, especially tissues of a particular age. The amount of light and regimen of exposure is also of vital importance in causing acute injury. This air pollutant will also reduce leaf carbohydrate (Dugger et al., 1966) and change the permeability of leaf tissue. Continuous 1-hr fumigation with 70 pphm caused leaf damage to 14-day-old pinto beans (Dugger et al., 1962) even when the stomates were closed. The action on stomates was confirmed by Hill and Littlefield (1969) who found 10 pphm would cause stomatal closure. However, no one has compared the long-term, chronic effects of ambient levels of ozone with
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Outside checks 0.1% 0.1% 1% NS
the effects of the total photochemical oxidant complex to find out whether or not most of the deleterious effects can be attributed to this single but major component. These studies showed that ambient ozone levels did indeed reduce yield significantly but that the oxidant complex in ambient air had a considerably greater effect in causing fruit drop and, consequently, reducing yield than an equivalent amount of ozone, thus proving that oxides of nitrogen, peroxyacyl nitrates, and the remainder of this complex mixture which is called photochemical smog had an additional deleterious effect over that caused solely by ozone. Literature Cited Cochran, W. G., Cox, G. M., "Experimental Designs," 2nd ed., p 447-9, Wiley, New York, N . Y . , 1957. Dugger, W. M., Jr., Koukol, J., Palmer, R. L., J. Air Pollut. Contr. Ass., 16 (9), 467-71 (1966). Dugger, W. M., Jr., Taylor, 0. C., Cardiff, E., Thompson, C. R., Plant Physiol., 37 (4), 487-91 (1962). Dugger, W. M., Jr., Taylor, 0. C., Thompson, C. R., Cardiff, E., J . Air Pollut. Contr. Ass., 13, 423-8 (1963). Hill, A. C., Littlefield, N., ENVIRON. SCI. TECHNOL., 3 (l), 52-6 (1969). Thompson, C. R., Hensel, E. G., Kats, G., Taylor, 0. C., Atmos. Environ., 4, 349-55 (1970). Thompson, C. R., Ivie, J. O., Int. J. Air Water Pollut., 9, 799805 (1965). Thompson, C. R., Kats, G., CaliJ Agr., 24, 12-3 (1970). Thompson, C. R., Kats, G., Hensel, E. G., ENVIRON. SCI. 5 (lo), 1017-19 (1971). TECHNOL., SCI. TECHNOL., 3, Thompson, C. R., Taylor, 0. C., ENVIRON. 934-40 (1969). Received for review January 7 , 1972. Accepted July 24, 1972. Supported in part by Grant AP 00270 ,from the Environmental Protection Agency and by Kaiser Steel Corp., Sunkist, Inc., San Bernardino County Air Pollution Control District, and Southern California Edison Co.
