I CIRCULAR 76 5, U. S. DEPARTMENT OF AGRICULTURE 



its harmless decomposition product, oxygen. It is widely used as a 

 deodorizing agent because of its ability to oxidize many objectionable 

 odors and gases into nonobjectionable products. Air containing 0.01 

 to 0.04 p. p. in. ( parts per million) of ozone has a pleasant odor: that 

 containing 2 to 3 p. p. m. is not unpleasant, but it may be irritating 

 to the throat and may cause headache and nausea if exposure to it is 

 prolonged. High concentrations have a strong, unpleasant odor and 

 may cause headache and nausea when the exposure is short. There- 

 fore, if concentrations of ozone as high as 2 to 3 p. p. m. are main- 

 tained, the generators are operated only when there are no workmen 

 continuously in the room. The gas is unstable and decomposes rap- 

 idly : its disappearance under storage conditions results from a mono- 

 molecular decomposition by oxidation as demonstrated by Ewell (J). 2 

 who used the following monomolecular equations : 



Velocity of decomposition =u=k (c — x) 



t e c — X 



Ewell (-5) found that the value for k in the equation was 0.0205 in 

 an empty chamber in which he later placed apples. In the empty 

 chamber the concentration of ozone was reduced from 1 to 0.54 p. p. m. 

 after one-half hour. In the presence of apples the value for h was 

 0.051 and the ozone concentration was reduced from 1 to 0.21 p. p. m. 

 after one-half hour, showing that the apples would absorb 0.33 p. p. m. 

 in one-half hour and 0.66 p. p. m. in 1 hour. This finding indicates 

 that the material of the exposed apple surfaces is readily oxidizable. 

 The rate of ozone decomposition diminishes with the time of exposure, 

 but removal of the apples to fresh air restores the higher absorption 

 power. 



A number of investigators (6. 10. 19. 21. 22. 23. &£) have recom- 

 mended the use of ozone to reduce fruit decay and extend the storage 

 period. Others (1. 20) . however, have reported that it has little or no 

 effect on fruit decay or that more decay appeared in apples in ozonized 

 than in normal atmospheres. Because of these divergent findings the 

 United States Department of Agriculture is frequently asked about 

 the advisability of using ozone. The studies reported in this circular 

 were therefore undertaken to determine the effects of measured con- 

 centrations of ozone on the keeping qualities and appearance of apples 

 and on certain apple pathogens. 



During the first storage season ( 1941—42 ) of the experiment the 

 ozone generator was operated 1 to 2 hours daily for 5 months, and 

 the concentration of ozone in the storage atmosphere at the time 

 of maximum ozone content averaged 1.95 p. p. m. by volume. Xo 

 reduction of fruit decay occurred at this concentration. Because of 

 the failure of ozone to reduce decay the concentration was increased 

 during the 1942— L3 storage season and averaged 3.25 p. p. m. during the 

 hours of ozone production for 7 months of storage. During this 

 season the ozonizer was opemted about 8 hours per day. As during the 

 previous season, there was little or no reduction of decay. 



Although decay of the fruit was not checked during either storage 

 season, air-borne fungus spores were killed by continuous exposure to 



2 Italic numbers in parentheses refer to Literature Cited, p. 23. 



