United States EPA-600 /R-93-177 Environmental Protection Aa<">cy September 1993 4>EFA Research and Development CONTRIBUTION TO INDOOR OZONE LEVELS OF AN OZONE GENERATOR Prepared for Office of Air and Radiation Prepared by Air and Energy Engineering Research Laboratory Research Triangle Park NC 27711 ------- EPA-600/R-93-177 September 1993 CONTRIBUTION TO INDOOR OZONE LEVELS OF AN OZONE GENERATOR Final Report by Raymond S. Steiber U.S. Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park, North Carolina 27711 Prepared for: U.S. Environmental Protection Agency Office of Research and Development Washington, D.C. 20460 ------- EPA REVIEW NOTICE This report has been reviewed by the U.S. Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policy of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. This document is available to the public through the National Technical Informa- tion Service, Springfield, Virginia 22161. ------- ABSTRACT Ozone generators are claimed to provide a way to clean indoor air. The amount of ozone generated by these devices is a major concern. A study of a commonly used commercially available unit was undertaken to determine the impact of the ozone generator on indoor ozone levels. Experiments were conducted in a typical mechanically ventilated office and in a test house. The ozone generated by the unit and the in-room ozone concentrations were measured. The results showed that, when the unit was operated at the manufacturer's recommended setting, it generated little if any ozone. The indoor concentrations in this case were not significantly above natural background. When operated at the maximum setting the generator produced large amounts of ozone. In this situation the indoor ozone concentration exceeded 100 ppb in well ventilated spaces and nearly 1 ppm in poorly ventilated spaces. When the ozone generator was turned off, ozone levels quickly returned to background. No measurements were made to determine the effect of the device on other aspects of indoor air guality, such as the elimination of volatile organic compounds. ------- CONTENTS Page Abstract ii Tables iii Metric Conversions iv Introduction 1 Test Group 1 2 Test Group 2 3 Test Group 3 4 Conclusions 5 References 6 Appendix. Quality Evaluation Report 7 TABLES 1 Test Conditions (Test Group 2) 3 2 Test Conditions (Test Group 3) 4 3 Ozone Generator: Settings vs Ozone Output 6 111 ------- METRIC CONVERSIONS Nonmetric units are used in this report for the reader's convenience. Readers more familiar with the metric system may use the following factors to convert to those units. Nonmetric Multiplied by Yields Metric ft 0.3048 m ft2 0.0929 m2 in. 2.54 cm IV ------- INTRODUCTION Ozone generators are claimed to help purify indoor air and remove odors and other pollutants. Large industrial scale ozone generators have been found useful in ameliorating unpleasant odors, particularly in fire-damaged buildings. Ozone generators are also claimed to be effective in combatting molds and bacteria. There are no published data supporting these claims. Although manufacturers of ozone generators claim that their units do not increase indoor levels of ozone, they offer no supporting data other than testimonials. This study was undertaken to determine the impact of a commercial ozone generator on indoor ozone levels under typical conditions. No measurements were made to determine the effect of the device on other aspects of indoor air quality, such as the elimination of volatile organic compounds. The unit selected for test was an ozone generator designed for use in the home or office. It has two user-adjustable controls: one that varies the speed of the circulating fan and another that controls the output of the ozone. The unit was tested under three different sets of conditions. Test Group 1 was a 24-hour test under normal operating conditions in a well-ventilated room. Test Group 2 also took place in a well- ventilated room, but this time only the higher ozone generator settings were used. Test Group 3 was conducted in a poorly ventilated room. Here the emphasis was on what happened when the ozone generator was left running overnight with no air circulation but normal leakage around the door and through the walls. In running these tests, our chief interest was in the amount of ozone being contributed to room air and not the ozone levels at the face of the instrument. However, these were also measured (see Table 3). At this point it might be well to insert a few words on how room background levels were determined. Obviously background levels could not be measured when a test was in progress, yet at the same time results could be seriously affected by this number, particularly at the lowest concentrations. In any indoor setting where there are no secondary sources of ozone, such as actually operating copiers, the chief source of ozone will be outside air brought into the building through natural leakage or mechanical ventilation. Weschler et al.1 have observed that there is roughly a 2:1 correlation between outdoor and indoor or.one levels: that is to say, if there is a 50 ppb concentration of ozone outside, indoor concentrations will measure around 25 ppb. Insofar as these tests are concerned, this is important not so much in terms of the numbers themselves as it is in the manner in which indoor air rigorously tracks outdoor air. Although the absolute 1 ------- concentrations may vary from day to day, the rise and fall of ozone levels over the course of a day, given warm, sunny weather, is absolutely predictable. In the early morning (before 8 am) ozone concentrations will hover between 0 and 2-3 ppb. As the day progresses, the levels will gradually rise, reaching their zenith sometime between noon and 1:30 pm. On cloudy days the ozone levels will remain at 0-2 ppb. Now how does this relate to determining background indoor ozone levels? If a background reading of 2 ppb is measured before a test begins, and another background reading of 20 ppb is measured after it ends, then a straight line increase from 2 to 20 ppb over the course of the test can be inferred and subtracted sequentially as background. On the other hand, if the pre-test reading in the afternoon is 40 ppb and the after-test reading several hours later is still 40 ppb, then it can be assumed that no significant excursions have occurred. Imperfect as this system of background correction may seem, it produces surprisingly consistent results, particularly when checked against a standard ozone generator, such as the TECO Model 565 ozone generator, the instrument used to calibrate EPA's air network ozone detectors. As an additional hedge against background excursions, many readings were taken during these tests, instead of only a few, so that the overall trend could be observed. TEST GROUP I Test Group 1 was run in a mechanically ventilated office with continuously operating air ducts in the ceiling. The room area was approximately 200 square feet* and there was a sealed window at one end and a hallway door at the other. The unit was placed on top of a 5-foot high filing cabinet located 3 feet from the hallway wall. It was turned at a slight angle in order to give coverage to the entire room. As in all these tests, measurements were made with a Model 560 Thermo-Environmental Ozone Analyzer. This instrument had recently been calibrated by personnel of the Research Triangle Institute, located in Research Triangle Park, North Carolina (see Appendix for details). The Model 560 was placed on top of a 3-foot high table 6 feet 10 inches from the ozone generator. Background ozone levels in the room ranged from a few parts per billion (ppb) in the early morning hours to over 40 ppb by mid-afternoon. By far the greatest contributor to these background levels was the effect of sunlight on atmospheric oxygen. When it was cloudy during any of the tests, background ozone levels fell, when it was sunny they rose, and when it was sunny with visible air pollution they rose dramatically. Test Group 1 consisted of two experiments: one that lasted 29 *Readers more comfortable with the metric system may use the factors listed on page iv to convert to those units. 2 ------- straight hours, during which the ozone generator unit ran continuously, and a second in which the ozone generator unit was shut off. For the first experiment both the fan knob and the generator knob were moved to the medium setting (12 o'clock). This is slightly above the manufacturer's recommended setting for normal use (11 o'clock). The ozone concentration 14 inches from the face of the unit is a continuous 5 ppb with the dial set at 12 o'clock. Measurements were taken every 30-40 minutes except during the nighttime hours when no one was present and the room was secured. At no time during the 29-hour test did the ozone levels contributed to room air by the ozone generator rise to the point where they could be distinguished from the background; nor did room ozone levels fall when the unit was shut off for the second test. TEST GROUP 2 This group of experiments was also conducted in a mechanically ventilated office with the same configuration and area as the office used in Test Group 1. The test conditions for this group of tests were the same as for the first except that much higher settings were used on the ozone generator. Four separate tests were run under the conditions listed in Table 1. TABLE 1. Test Conditions (Test Group 2) TEST # 1 2 3 4 TIME (hr) 2.0 22.5 24.0 43.0 FAN SETTING (o'clock) 1 3 5* Off GENERATOR SETTING (o'clock) 1 3 5* Off *Maximum setting The average concentration of ozone contributed to room air during Test 1 was 12.2 ppb and during Test 2 was 13.3 ppb. The slightness of the difference in readings between Tests 1 and 2 is probably indicative of the difficulty of taking measurements at such low concentrations vis-a-vis the background and the non- linearity of the controls on the ozone generator. During Test 3 ozone readings were much higher, averaging 100 ppb. All the above averages have been corrected for the background. Test 4 was an attempt to track room background across a number of different meteorological conditions. Concentrations during the period of its run ranged between 10 and 22 ppb. 3 ------- TEST GROUP 3 Test Group 3 was a repetition (with some modifications) of all the previous tests, only in a closed room without mechanical ventilation. This room had an area of 90 square feet and was roughly the same size as a small bedroom. It had a single door at one end and a closed window at the other. The background ozone averaged 5.6 ppb in the daytime and 1.5 ppb in the early morning. A total of six tests were run. The conditions are given in Table 2. TABLE 2. Test Conditions (Test Group 3) TEST # 1 2 3 4 5 6 TIME (hr) 1.0 0.5 1.0 1.5 22.5 1.0 FAN SETTING (o'clock) 12 5* 3 5* 5* Off GENERATOR SETTING (o ' clock) 12 12 3 3 5* Off *Maximum setting During Tests 1 and 2 no concentrations of ozone distinguishable from the background were detected in the room. During Test 3 an average of 20.1 ppb was detected. When the fan speed was increased during Test 4, ozone concentrations more than doubled for an average of 43.1 ppb. During Test 5 both fan and generator settings were at their maximum. Of all the tests that were conducted, this was the only one in which room concentrations outran the amount being produced by the ozone generator; that is, ozone was being produced at a rate higher than it could either be reacted or dispersed by passive air flow. Starting at an initial concentration of 150 ppb during the first few minutes of the test, ozone levels rose to a high of 814 ppb, then leveled off between 600 and 700 ppb. As the level of these concentrations seemed to vary according to the frequency with which the door was opened, it was decided to let the unit run overnight with the door secured. By 7 o'clock the next morning room concentrations had risen to 996.5 ppb. At those levels it was decidedly unpleasant for test personnel to enter the room, and eye, throat, and olfactory irritation reached the point where it was nearly impossible to breathe. The last test was an attempt to see how quickly high levels 4 ------- of ozone would dissipate from a closed room when their source was eliminated. At the beginning of the test the ozone concentration was 758.5 ppb. Within an hour it had dropped to 2.0 ppb with most of the decay occurring in the first 10 minutes. However, for some time afterward, a not unpleasant ozone-type odor persisted in the room. This odor is best described as similar to that of sheets and towels when they are fresh out of the drier, only much stronger. Apparently this is not the odor of the ozone itself, but of some typical reaction product. For those who might be interested, Table 3 lists the ozone output in parts per billion for six selected generator settings. To obtain these readings, the intake nozzle of the analyzer was held 14 inches from the face of the generator. The generator fan was set at medium (12 o'clock on the dial), and all readings were corrected for the background. CONCLUSIONS When operated at the recommended setting for normal use (dial set at the 11 o'clock position), the ozone generator contributes little or no ozone to the background air levels. At the highest setting, however, it can contribute as much as 100 ppb to a well- ventilated room and 10 times that much to a poorly ventilated one. Our personal experience shows that at that level the air becomes difficult to breathe and there is some irritation of the eyes and the mucous membranes, perhaps due to excessive drying. ------- TABLE 3. Ozone Generator: Settings vs Ozone Output SETTING CORRECTED READOUT (o'clock) (PPb ozone) 7 0.0 9 2.0 11* 3.0 12 5.0 1 8.0 3 69.0 5** 520.0 *Manufacturer's recommended setting **Maximum setting References; 1. Weschler, C.J., Shields, H.C., Naik, D.V. (1989), "Indoor Air Exposures", APCA Journal 39:1562 ------- APPENDIX: QUALITY EVALUATION REPORT This study was designed to assess qualitatively the amount of ozone generated by a commercially available product claimed by its manufacturer to purify indoor air and remove odors and other pollutants. Since validated test procedures and comparable data were unavailable, planning for the study was restricted to designing the test system and considering fundamental research needs, and a quality assurance plan was not prepared. In accordance with EPA's quality policy, data reported in this document cannot be defended and should be considered for qualitative purposes only. However, quality control practices, such as routine good laboratory practices, were applied. A specific example was the calibration of the Model 560 Ozone Analyzer. On April 11 and 12, 1990, the Model 560 Ozone Analyzer (Serial No. 666864) was calibrated against an ozone photometer in accordance with 40 CFR, Part 50, Appendix D. This was done by Robert Murdoch and Richard Shores at the Center for Environmental Quality Assurance (CEQA) at the Research Triangle Institute, Research Triangle Park, North Carolina, 27709-5929. The results were as follows: CEQA Calibration Concentrations in ppm 0.030 0.044 0.058 0.073 0.037 Analyzer Response in millivolts (0.1 ppm scale)* oToo 0.30 0.44 0.58 0.72 0.86 *CEQA Analyzer Response (ppm) = (Voltage) (0.100) - 0.000 The CEQA ozone photometer (Dasibi Model 1003AH, Ser. No, 2629) is periodically checked against the EPA/EMSL QAD National Institute of Standards and Technology (formerly Bureau of Standards) NIST- traceable photometer. ------- TEST GROUP 1 The room had continuously running mechanical sir ventilation. It was approximately 200 square feet in area and had a sealed window at one end and a door at the other. Test # 1 Date: April 25-26, 1990 Settings: Fan, 12 o'clock Weather: Sunny and hot with Generator, 12 o'clock visible air pollution and highs near 90 on the 25th; hazy overcast till 11 am on the 26th followed by hot and sunny. TIME UNCORRECTED READOUT CORRECTED READOUT 9:10 am 16 ppb * 10:30 am 16 ppb * 11:30 am 24 ppb * 1:00 pm 38 ppb * 2:3 0 pm 38 ppb * 4:0 0 pm 39 ppb * 8:00 am** 8 ppb * 8:30 am 5 ppb * 9:00 am 2 ppb * 9:40 am 3 ppb * 10:30 am 4 ppb * 11:10 am*** 18 ppb * 11:40 am 27 ppb * 12:35 pm 41 ppb * 1:15 pm 35 ppb * 1:55 pm 41 ppb * *Corrected readout was indistinguishable from background. **Unit was left running unattended overnight in secured room. ***At this point the sun broke through the haze, thereby revealing the true source of the ozone readings. ------- Test # 2 Date: April 26, 1990 Settings: Fan off Weather: Hot, sunny, and Generator off polluted. TIME UNCORRECTED READOUT 2:25 pro 42 ppb 2:55 pm 42 ppb 3:25 pm 44 ppb 3:45 pm 42 ppb 3:50 pro Experiment Shut Down ------- TEST GROUP 2 The room had a continuously running mechanical ventilation system and was approximately 200 square feet in area. There was a single sealed window and a single door. Test # 1 Date: May 7, 1990 Settings: Fan 1 o'clock Weather: Sunny and Generator 1 o'clock clear, high around 70 TIME UNCORRECTED READOUT CORRECTED READOUT 2:00 pm 34 ppb 11 ppb 2:35 pm 36 ppb 13 ppb 3:08 pm 34 ppb 11 ppb 3:40 pm 38 ppb 15 ppb 4:05 pm 34 ppb 11 ppb Test # 2 Date: May 7-8, 1990 Settings: Fan 3 o'clock Weather: Sunny and Generator 3 o'clock clear both days with highs in the 70s TIME UNCORRECTED READOUT CORRECTED READOUT 4:10 pm 37 ppb 14 ppb 7:25 am* 12 ppb 12 ppb 8:05 am 11 ppb 11 ppb 8:40 am 32 ppb 10 ppb 9:20 am 30 ppb 8 ppb 10:00 am 35 ppb 13 ppb 10:30 am 32 ppb 10 ppb 11:10 am 34 ppb 12 ppb 11:40 am 38 ppb 16 ppb 12:30 pm 38 ppb 16 ppb 2:3 0 pm 46 ppb 2 4 ppb *Unattended unit was allowed to run overnight in the secured room. 10 ------- Test # 3 Date: May 8-9, 1990 Weather: Sunny and clear with a high of 75 on the 8th; overcast with a high of 70 on the 9th. Settings: Fan 5 o'clock (max) Generator 5 o'clock (max) TIME 3:15 pm 4:08 pm 7:20 am* 8:10 am 8:38 am 10:20 am 12:40 pm 3:00 pm UNCORRECTED READOUT 110 ppb 140 ppb 100 ppb 100 ppb 100 ppb 98 ppb 120 ppb 120 ppb CORRECTED READOUT 88 ppb 118 ppb 100 ppb 100 ppb 100 ppb 98 ppb 98 ppb 98 ppb *Unattended unit left running overnight in the secured room. Room background varied from near zero in the forenoon to 22 ppb from 12 o'clock on. Test # 4 Date: May 9, 10, 11, 1990 Weather: Overcast and 70 on the 9th; rain and 70 on the 10th; sunny and 60 on the llth. Settings: Fan off Generator off TIME 3:04 pm 3:50 pm 8:30 am 11:20 am 8:00 am 9:10 am 10:30 am 10:35 am UNCORRECTED READOUT 90 ppb* 22 ppb 10 ppb 22 ppb 10 ppb 21 ppb 21 ppb Experiment Shut Down *The ozone generator unit had just been shut down when this reading was taken, and it is corrected for background. 11 ------- TEST GROUP 3 The room had no mechanical ventilation and was approximately 90 square feet in area. It had a closed window and a single door. Background ozone averaged 5.6 ppb during the principal hours of daylight and 1.5 ppb in the early morning. Test # 1 Date: May 21, 1990 Settings: Fan 12 o'clock Weather: Partially sunny, Generator 12 o'clock highs in the 80s TIME UNCORRECTED READOUT CORRECTED READOUT 2:10 pm 4.8 ppb * 2:2 0 pm 4.6 ppb * 2:3 0 pm 5.5 ppb * 2:4 0 pm 6.4 ppb * 2:5 0 pm 5.4 ppb * 3:0 0 pm 6.1 ppb * *Indistinguishable from background Test # 2 Date: May 21, 1990 Settings: Fan 5 o'clock Weather: As above. Generator 12 o'clock TIME UNCORRECTED READOUT CORRECTED READOUT 3:10 pm 5.5 ppb * 3:20 pm 5.5 ppb * *Indistinguishable from background 12 ------- Data/6 Test # 3 Date: May 21, 1990 Weather: Partially sunny, high in the 80s Settings: Fan 3 o'clock Generator 3 o'clock TIME 3:25 pm 3:35 pm 3:45 pro 3:55 pm 4:05 pro 4:17 pro UNCORRECTED READOUT 23 ppb 24 ppb 27 ppb 27 ppb 26 ppb 27 ppb CORRECTED READOUT 17.4 ppb 18.4 ppb 21.4 ppb 21.4 ppb 20.4 ppb 21.4 ppb Test # 4 Date: May 22, 1990 Weather: Windy, rain, high around 60 Settings: Fan 5 o'clock Generator 5 o'clock TIME 8:05 am 8:20 am 8:35 am 8:50 am 9:05 am 9:15 am 9:25 am UNCORRECTED READOUT 54 ppb 50 ppb 34 ppb 46 ppb 46 ppb 42 ppb 40 ppb CORRECTED READOUT 52 48 32 44 44 40 38 , 5 ppb 5 ppb . 5 ppb 5 ppb 5 ppb 5 ppb 5 ppb 13 ------- Test # 5 Date: May 22, 1990 Settings: Fan 5 o'clock Weather: Windy, rain, Generator 5 o'clock high around 60 TIME UNCORRECTED READOUT CORRECTED READOUT 9:30 am 160 ppb 158.5 ppb 9:40 am 260 ppb 258.5 ppb 10:25 am 270 ppb 268.5 ppb 10:45 am 360 ppb 354.4 ppb 11:15 am 340 ppb 334.4 ppb 12:10 pm 600 ppb 594.4 ppb 1:45 pm 820 ppb 814.4 ppb 2:45 pm 700 ppb 694.4 ppb 3:30 pm 680 ppb 674.4 ppb 4:15 pm* 620 ppb 614.4 ppb 7:10 am 998 ppb 996.5 ppb 7:50 am 760 ppb 758.5 ppb *At this point the room was secured and no more readings were taken until the next morning. May 23rd dawned sunny and cool with morning temperatures in the low 50s. Test # 6 (Shutdown/Decay) Date: May 23, 1990 Settings: Fan off Weather: Sunny and cool, Generator off temp, in low 50s TIME UNCORRECTED READOUT CORRECTED READOUT 7:54 am Ozone Generator Shut Off 758.5 ppb 7:55 am 540 ppb 538.5 ppb 8:02 am 70 ppb 68.5 ppb 8:10 am 4 ppb 4.0 ppb 8 : 2 0 am 2 ppb 2 . 0 ppb 8:4 5 am 2 ppb 2.0 ppb 8:50 am Experiment Shut Down 14 ------- TECHNICAL REPORT DATA (Please read Instructions on the reverse before completing' 1. REPORT NO. EPA-600/R-93-177 2. 4. TITLE AND SUBTITLE Contribution to Indoor Ozone Levels of an Ozone Generator 3. Rl 5. REi «... ~~, _ September 1993 6. PERFORMING ORGANIZATION CODE 7, AUTHOR(S) Raymond S. Steiber 8. PERFORMING ORGANIZATION REPORT NO 9. PERFORMING OROANIZAT1ON NAME AND ADDRESS 10. PROGRAM ELEMENT NO. See Block 12 11. CONTRACT/GRANT NO. NA (Inhouse) 12, SPONSORING AGENCY NAME AND ADDRESS EPA, Office of Research and Development Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 13. TYPE OF REPORT AND PERIOD COVERED Final; 4/90 - 12/92 14, SPONSORING AGENCY CODE EPA/600/13 15. SUPPLEMENTARY NOTES ^EERL project officer is Raymond S. Steiber, Mail Drop 54, 919 / 541-2288. 16. ABSTRACT repOrt gives results of a study of a commonly used commercially avail- able ozone generator, undertaken to determine its impact on indoor ozone levels. Ex- periments were conducted in a typical mechanically ventilated office and in a test house. The generated ozone and the in-room ozone concentrations were measured. The results showed that, when the unit was operated at the manufacturer's recom- mended setting, it generated little if any ozone. The indoor concentrations in this case were not significantly above natural background. When operated at the meximum setting, the generator produced large amounts of ozone: over 100 ppb in well ventila- ted spaces, and nearly 1 ppm in poorly ventilated spaces. When the ozone generator was turned off, ozone levels quickly returned to background. No measurements were made to determine the effect of the device on other aspects of indoor air quality such as the elimination of volatile organic compounds. 7. KEY WORDS AND DOCUMENT ANALYSIS DESCRIPTORS b.tDENTIFiERS/OPEN ENDED TERMS c. COSATI Field/Group Pollution Ozone Pollution Control Stationary Sources Ozone Generators Indoor Air Quality 13 B 07B 3. DISTRIBUTION STATEMENT Release to Public 19. SECURITY CLASS (This Report) Unclassified 21. NO. OF PAGES 19 20. SECURITY CLASS (This page) Unclassified 22. PRICE EPA Form 2220-i (9-73) 15 ------- U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Research and Development Center for Environmental Research Information Cincinnati. Ohio 45268 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE. S3OO AN EQUAL OPPORTUNITY EMPLOYER If your address is incorrect, please change on the above label tear off; and return to the above address. If you do not desire to continue receiving these technical reports, CHECK HERED; tear off label, and return it to the above address. Publication No. EPA-eoo /R- 93-177 ------- |