Ozone in Passenger Cabins: 

Concentrations and Chemistry

William W Nazaroff

Department of Civil and Environmental Engineering

University of California, Berkeley, CA 94720-1710

Charles J. Weschler

Department of Environmental and Occupational Medicine

University of Medicine and Dentistry of New Jersey

Piscataway, NJ 08854

August 2010

Final Report

Report No. RITE-ACER-CoE-2010-2
NOTICE

___________

This document is disseminated under the sponsorship

of the U.S. Department of Transportation in the interest

of information exchange. The United States Government

assumes no liability for the contents thereof.

___________

This work was funded by the U.S Federal Aviation Administration 

Office of Aerospace Medicine under 

Cooperative Agreements 04-C-ACE and 07-C-RITE.

___________

This publication is available in full-text from 

the publications Web site of the 

National Air Transportation Center of Excellence for

Research in the Intermodal Transport Environment (RITE) at:

www.acer-coe.org
i

1. Report No. 2. Government Accession No. 3. Recipients Catalog No.

4. Title and Subtitle

Ozone in Passenger Cabins: 

Concentrations and Chemistry

5. Report Date

August 2010 

6. Performing Organization Code

7. Authors 

William W Nazaroff and Charles J. Weschler

8. Performing Organization Report No.

9. Performing Organization Name and Address

Department of Civil and Environmental Engineering

University of California, Berkeley, CA 94720-1710; 

Dept. Environmental and Occupational Medicine

University of Medicine and Dentistry of New Jersey

Piscataway, NJ 08854

10. Work Unit No.

11. Contract or Grant No.

04-C-ACE-UCB, 07-C-RITE-UCB, 

04-C-ACE-UMDNJ, 07-C-RITEUMDNJ

12. Sponsoring Agency Name and Address

Office of Aerospace Medicine

Federal Aviation Administration

800 Independence Ave., S.W.

Washington, DC 20591

13. Type of Report and Period Covered

Final Report (Aug. 2004-Aug. 2010)

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

Congressional Mandate 

Monitor ozone in the cabin on a representative number of flights and aircraft and determine 

compliance with existing Federal Aviation Regulations; carry out the studies and analysis 

called for in the NRC report.

NRC report

Recommendation 1: Calls for the FAA to demonstrate the adequacy of FARs for cabin air 

quality; Recommendation 9: Calls for investigations of how ozone concentration in the cabin is 

affected by various factors (e.g., ambient concentrations, reactions with surfaces, the presence 

and effectiveness of catalytic converters), and the relationship between ozone levels and health 

effects.

Findings

1. Measurements in passenger cabins revealed that ozone levels can be moderate to high on 

domestic flights without ozone converters. On 8 of 46 domestic flights without converters, 

ozone levels exceeded at some during the flight the ―0.1 parts per million by volume‖ (100 

ppb) level specified in the FARs. On one flight ozone levels exceeded the ―0.25 parts per 

million by volume‖ (250 ppb), a level not to be exceeded ―at any time‖. However, in the 

relevant FAR (Section 121.578), the 100 ppb level applies as a time-weighted average only 

for flight segments exceeding four hours. The highest time-weighted average over the full 

flight for the 46 domestic flights without converters was within ten percent of the 100 ppb 

limit. This was the only flight for which the time-weighted average exceeded 90 ppb. 

Furthermore, the flight planning approach specified by the FAR only requires a statistical 
ii

confidence of 84% that the limits on ozone levels will not be exceeded. Ozone converters 

reduce ozone levels substantially. Nonetheless, elevated ozone levels (up to about 60 ppb 

for the peak hourly average) were measured on transoceanic flights equipped with 

converters. There were no instances where the flight-average limit of 100 ppb was exceeded 

on aircraft with ozone converters. Within the constraints of the limitations on the number of 

flights that could be monitored, ozone levels in aircraft cabins were consistent with the 

requirements of the FARs.

2. Experiments conducted in a reconstructed section of a B-767 aircraft cabin indicated that 

more than half of the net ozone removal within the cabin was attributable to its reactions 

with passengers and crew. Ozone removal is dominated by reactions on surfaces; gas-phase 

reactions contribute little to the overall removal of ozone from cabin air.

3. Ozone reacts rapidly with skin lipids present on the exposed skin, hair and clothing of the 

cabin occupants. Ozone-initiated chemistry produces a series of carbonyls, dicarbonyls and 

hydroxycarbonyls. Inhalation of certain ozone-derived products may be meaningful for the 

health of passengers and crewmembers, especially on aircraft with elevated ozone levels.

4. Occupants judged the air quality worse and reported various symptoms in response to 

exposure to ozone and its oxidation products in cabin simulations. Self-assessed symptoms 

included complaints commonly reported by the flying public (e.g., irritated eyes and throat). 

In addition, ozone and certain byproducts of ozone-initiated chemistry are known to 

adversely affect human health at elevated levels.

5. The current FARs may not adequately protect the health of passengers and crew. This 

finding reflects the fact that the FARs were established about three decades ago, prior to i) 

the recognition that cabin occupants are exposed to products of ozone-initiated chemistry in 

addition to ozone itself; ii) the accrual of a large body of evidence regarding irritation, 

morbidity and mortality resulting from ozone exposures in polluted urban environments; and 

iii) a flying population that includes a larger number of vulnerable and sensitive individuals.

Recommendations

1. The FARs related to ozone in the cabin environment should be reevaluated since they do not 

appear to adequately protect the health of passengers and crew. Consideration should be 

given to the fact that the current national ambient air quality standard is 75 ppb measured 

over 8 hrs and a lower standard (down to 60 ppb as the peak hourly average) has been 

recommended (Federal Register, Vol. 75, No. 11, 2938, 19 Jan 2010). 

2. The benefit-cost ratio of requiring ozone converters on all commercial flights should be 

evaluated with a view toward establishing a broader requirement for passenger aircraft be 

equipped with effective ozone converters. As an alternative, the FAA should consider 

establishing a requirement that airlines report for each flight, as a passenger books a ticket, 

whether or not the scheduled plane is equipped with an ozone converter.

3. A performance specification should be assessed as an alternative to an hours-of-service 

specification to ensure effective performance of ozone converters throughout a plane’s 

service life. An FAA-mandated industry-conducted program of random, periodic testing of 

in-service ozone converter performance should be evaluated; such a program could reduce 

exposures that result from degraded or poisoned catalysts.
iii

17. Key Words

Ozone, reaction byproducts, 

oxidation, skin oils, squalene, 

permethrin, passengers, flight 

attendants, health symptoms, 

exposure

18. Distribution Statement

No restrictions. 

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (this page)

Unclassified

21. No. of Pages

18

22. Price

Form DOT F 1700.7 (8-72)
iv

ABBREVIATIONS

As used in this report, the following abbreviations/acronyms

have the meanings indicated

ABBREVIATION MEANING

ACER ------------------ Airliner Cabin Environmental Research

B-767-------------------Boeing model 767 

DTU --------------------Technical University of Denmark

EB ----------------------Eastbound (transoceanic flight)

FAA -------------------- Federal Aviation Administration

FAR -------------------- Federal Aviation Regulation

h------------------------- hour

HEPA ------------------ high efficiency particle in air

L/s ----------------------liters per second

N ------------------------ Number of flights monitored

NIOSH ----------------- National Institute of Occupational Safety and Health

NRC -------------------- National Research Council

O3 ----------------------- ozone

ppb---------------------- parts per billion (by volume)

ppbv -------------------- parts per billion by volume

P-value ----------------- probability value

RITE--------------------Research in the Intermodal Transport Environment

US ---------------------- United States

VOC-------------------- volatile organic compound

WB ---------------------Westbound (transoceanic flight)

4-OPA------------------ 4-oxopentanal

6-MHO----------------- 6-methyl-5-hepten-2-one
v

Contents

SUMMARY...............................................................................................................................1

INTRODUCTION .....................................................................................................................2

RESULTS AND DISCUSSION ...............................................................................................4

Ozone levels in passenger cabins ..................................................................................4

Ozone reactions with cabin materials ...........................................................................7

Ozone reaction with permethrin.....................................................................................7

Ozone removal in a simulated aircraft cabin .................................................................8

Ozone reaction with cabin materials and occupants in a simulated aircraft cabin ......10

Impact of ozone and ozone oxidation products on occupants’ 

self-reported symptoms................................................................................................11

CONCLUSIONS......................................................................................................................14

IMPLICATIONS .....................................................................................................................15

PUBLICATIONS DERIVED FROM THIS PROJECT..........................................................15

REFERENCES ........................................................................................................................16
1

OZONE IN PASSENGER CABINS: CONCENTRATIONS AND CHEMISTRY

"When we try to pick out anything by itself, 

we find it hitched to everything else in the universe."

—John Muir, 1911

SUMMARY

Congressional Mandate 

Monitor ozone in the cabin on a representative number of flights and aircraft and determine 

compliance with existing Federal Aviation Regulations; carry out the studies and analysis called 

for in the NRC report.

NRC report

Recommendation 1: Calls for the FAA to demonstrate the adequacy of FARs for cabin air 

quality; Recommendation 9: Calls for investigations of how ozone concentration in the cabin is 

affected by various factors (e.g., ambient concentrations, reactions with surfaces, the presence 

and effectiveness of catalytic converters), and the relationship between ozone levels and health 

effects.

Findings

1. Measurements in passenger cabins revealed that ozone levels can be moderate to high on 

domestic flights without ozone converters. On 8 of 46 domestic flights without converters, 

ozone levels exceeded at some during the flight the ―0.1 parts per million by volume‖ (100 

ppb) level specified in the FARs. On one flight ozone levels exceeded the ―0.25 parts per 

million by volume‖ (250 ppb), a level not to be exceeded ―at any time‖. However, in the 

relevant FAR (Section 121.578), the 100 ppb level applies as a time-weighted average only 

for flight segments exceeding four hours. The highest time-weighted average over the full 

flight for the 46 domestic flights without converters was within ten percent of the 100 ppb 

limit. This was the only flight for which the time-weighted average exceeded 90 ppb. 

Furthermore, the flight planning approach specified by the FAR only requires a statistical 

confidence of 84% that the limits on ozone levels will not be exceeded. Ozone converters 

reduce ozone levels substantially. Nonetheless, elevated ozone levels (up to about 60 ppb for 

the peak hourly average) were measured on transoceanic flights equipped with converters. 

There were no instances where the flight-average limit of 100 ppb was exceeded on aircraft 

with ozone converters. Within the constraints of the limitations on the number of flights that 

could be monitored, ozone levels in aircraft cabins were consistent with the requirements of 

the FARs.

2. Experiments conducted in a reconstructed section of a B-767 aircraft cabin indicated that 

more than half of the net ozone removal within the cabin was attributable to its reactions with 

passengers and crew. Ozone removal is dominated by reactions on surfaces; gas-phase 

reactions contribute little to the overall removal of ozone from cabin air.

3. Ozone reacts rapidly with skin lipids present on the exposed skin, hair and clothing of the 

cabin occupants. Ozone-initiated chemistry produces a series of carbonyls, dicarbonyls and 
2

hydroxycarbonyls. Inhalation of certain ozone-derived products may be meaningful for the 

health of passengers and crewmembers, especially on aircraft with elevated ozone levels.

4. Occupants judged the air quality worse and reported various symptoms in response to 

exposure to ozone and its oxidation products in cabin simulations. Self-assessed symptoms 

included complaints commonly reported by the flying public (e.g., irritated eyes and throat). 

In addition, ozone and certain byproducts of ozone-initiated chemistry are known to adversely 

affect human health at elevated levels.

5. The current FARs may not adequately protect the health of passengers and crew. This finding 

reflects the fact that the FARs were established about three decades ago, prior to i) the 

recognition that cabin occupants are exposed to products of ozone-initiated chemistry in 

addition to ozone itself; ii) the accrual of a large body of evidence regarding irritation, 

morbidity and mortality resulting from ozone exposures in polluted urban environments; and 

iii) a flying population that includes a larger number of vulnerable and sensitive individuals.

Recommendations

1. The FARs related to ozone in the cabin environment should be reevaluated since they do not 

appear to adequately protect the health of passengers and crew. Consideration should be given 

to the fact that the current national ambient air quality standard is 75 ppb measured over 8 hrs 

and a lower standard (down to 60 ppb as the peak hourly average) has been recommended 

(Federal Register, Vol. 75, No. 11, 2938, 19 Jan 2010). 

2. The benefit-cost ratio of requiring ozone converters on all commercial flights should be 

evaluated with a view toward establishing a broader requirement for passenger aircraft be 

equipped with effective ozone converters. As an alternative, the FAA should consider 

establishing a requirement that airlines report for each flight, as a passenger books a ticket, 

whether or not the scheduled plane is equipped with an ozone converter.

3. A performance specification should be assessed as an alternative to an hours-of-service 

specification to ensure effective performance of ozone converters throughout a plane’s service 

life. An FAA-mandated industry-conducted program of random, periodic testing of in-service 

ozone converter performance should be evaluated; such a program could reduce exposures 

that result from degraded or poisoned catalysts

INTRODUCTION

Passengers and crew in aircraft cabins may be exposed to elevated ozone that originates naturally 

in the stratosphere. The level of ozone in aircraft cabins depends on ambient concentrations, the 

presence (or absence) of control devices and their effectiveness, the rate of outdoor air supply, 

and the rate of ozone loss through within-cabin transformation processes, such as reactions with 

interior surfaces, including those associated with occupants. Ozone levels outside the aircraft 

vary with season and depend on flight altitude, tropopause height, and on meteorological 

processes that affect vertical mixing between the lower stratosphere and the upper troposphere. 

Exposure to ozone in cabin air has potential health significance for the flight crew and for the

general flying population, which includes individuals who may be particularly sensitive to 

respiratory health effects, such as asthmatics, infants, and adults with cardiopulmonary 

conditions. Exposure to ground-level ozone and its reaction byproducts are strongly associated 

with adverse respiratory and cardiovascular effects (Levy et al., 2001; Bell et al., 2006; 

Weschler, 2006; Jerrett et al., 2009). Acute effects from short-term exposure range from 
3

breathing discomfort, respiratory irritation, and headache for healthy adults (Strøm-Tejsen et al., 

2008) to asthma exacerbation and premature mortality for vulnerable populations (Gent et al., 

2003; Bell et al., 2004). Chronic exposure effects may include enhanced oxidative stress (Chen 

et al., 2007), reduced lung function in young adults (Tager et al., 2005), and adult-onset asthma 

in males (McDonnell et al., 1999). Physical activity, as is undertaken by flight attendants, results 

in increased intake. There is no established ―safe‖ level of ozone exposure (Bell et al., 2006).

Real-time measurements made during flights in the 1960s and 1970s revealed that in-cabin 

ozone was commonly above 100 parts per billion by volume (ppb), especially on flight routes 

through high latitudes (Brabets et al., 1967; Bischof, 1973; Nastrom et al., 1980). In 1980, in 

response to these data and to associated health concerns for flight attendants (Reed et al., 1980), 

the Federal Aviation Administration (FAA) established regulations (FAR 25.832 and FAR 

121.578) that are designed to limit levels of ozone in airplane cabins (National Research Council, 

2002). To comply with the regulations, many planes are equipped with ―catalytic converters‖ 

that promote the decomposition of ozone in the ventilation supply air. Alternatively, airlines may 

comply by means of flight-route planning to reduce the probability of encountering elevated 

ozone. Not all planes are equipped with converters. Converters can fail to perform as designed 

owing, for example, to fouling by pollutants that poison the active surface sites. The 

probabilistic planning approach permits, by design, up to 16% of the flights to encounter 

elevated ambient ozone concentrations. Thus, the existence of the regulations, by themselves, do 

not assure that cabin occupants are protected from exposure to elevated ozone levels. 

The ozone level in aircraft cabins is neither routinely monitored, nor has it been the subject of 

much additional research since the ozone standards were established. Spengler et al. (2004) 

presented a survey of flight-integrated ozone levels on 106 segments along with three-hour

average ozone levels measured during the middle of the flight for segments over the Pacific

ocean. The presence or absence of an ozone converter was determined by proxy and was not 

verified. To our knowledge, prior to efforts by ACER/RITE researchers summarized in this 

report, real-time in-cabin ozone data have been reported for just four flights since 1980 (Spicer et 

al., 2004). To address this data gap, the research team made real-time, continuous measurements 

of ozone levels in the passenger cabins of 76 commercial flight segments between February 2006 

and August 2007. 

When ozone is present in an aircraft cabin, ozone-derived reaction products are also present, both 

in the gas phase and on surfaces. The fact that ozone-initiated chemistry could meaningfully 

increase the levels of certain volatile and semivolatile organic compounds in aircraft cabin air 

was first demonstrated in a Boeing-funded study (Wisthaler et al., 2005) conducted in a 

simulated section of a B-767 (3 rows, 21 seats) at the Technical University of Denmark. Given 

the results of this preliminary study, as well as our understanding of ozone chemistry and effects 

observed in various indoor environments, the ACER/RITE research team undertook studies of 

the reaction of ozone with cabin materials, with a pesticide commonly used to disinsect aircraft, 

and with cabin occupants themselves. 

Results from the various tasks that have constituted the ACER/RITE project investigating the 

concentrations and chemistry of ozone in passenger cabins are summarized in the following 

section of this report.
4

RESULTS AND DISCUSSION

Ozone levels in passenger cabins

Ozone levels in airplane cabins, and the factors that influence them, were studied on northernhemisphere commercial passenger flights on domestic US routes as well as on transatlantic and 

transpacific international routes (Bhangar et al., 2008). Real-time data from 76 flights were 

collected during 2006 and 2007 with a battery-powered ozone monitor that works on the 

principle of ultraviolet spectrophotometry. Sampling occurred on flight segments of scheduled 

duration exceeding 3.5 hours. On each flight, ozone levels in the passenger cabin were 

monitored with one-minute time resolution throughout the period that the plane was above 

10,000 feet (such that the use of portable electronic devices was allowed). Figure 1 shows 

representative ozone measurements from four consecutive domestic transcontinental US 

segments monitored within a 6-day interval in April 2006. For these four transcontinental flights 

sampled during spring following a major storm event, ozone levels were high on the three flight 

segments on planes without converters and low on the one segment on a plane equipped with an 

ozone converter. 

Overall, the sample-average ozone level, peak-hour ozone level, and flight-integrated ozone 

exposures varied substantially across the 68 domestic flight segments sampled, with ranges of 

<1.5 to 146 ppb for the flight average, 3-275 ppb for the peak hour, and <1.5 to 488 ppb-hour for 

the flight-integrated exposures, respectively. On planes equipped with ozone catalysts (N = 22 

flight segments), the mean peak-hour ozone level (4.7 ppb) was about a factor of 10 lower than 

on planes not equipped with catalysts (N = 46 flight segments; 47 ppb). Weighted cumulative 

distributions of peak-hour ozone levels for aircraft with and without converters are displayed in 

Figure 2.

The highest levels observed were on one transcontinental US flight on a plane not equipped with 

an ozone converter. The peak (one-minute average) ozone level on this flight was 308 ppb and 

the ozone level exceeded 250 ppb for 22 consecutive minutes. The average ozone level during 

the period sampled (2 hours and 49 minutes) was 132 ppb. We estimate that the average ozone 

level for the entire flight segment (3 hours and 51 minutes) was in the range 99-109 ppb. In all, 

the ozone level exceeded 250 ppb only on this one flight. The ozone level exceeded 100 ppb on 

eight flights, all domestic US routes on planes without ozone converters. The second-highest 

flight-averaged ozone level was 89 ppb. 

Seasonal variation of in-cabin ozone levels on domestic routes without converters is reasonably 

modeled by a sinusoidal curve that predicts peak-hour levels to be approximately 70 ppb higher 

in February and March than in August and September. The temporal trend is broadly consistent 

with expectations, given the seasonal cycle in tropopause height. Episodically elevated (>100 

ppb) ozone levels on domestic flights were associated with winter-spring storms that are linked 

to enhanced exchange between the lower stratosphere and the upper troposphere. All eight of the 

flights with ozone levels exceeding 100 ppb occurred during January-May.

Peak-hour ozone levels on eight transoceanic flight segments, all on planes equipped with ozone 

catalysts, were in the range <1.5 to 58 ppb (Figure 3). Instantaneous peak levels (one-minute 
5

averages) reached 75 ppb on one of these flights and 50 ppb on three others. The highest flightaverage concentration on these eight flights was 25 ppb.

Figure 1. Real-time ozone data from four consecutive domestic transcontinental US flight 

segments monitored within a 6-day interval in April, arranged chronologically in panels A-D. The 

direction (EB: eastbound or WB: westbound) is indicated for each segment. Panel C represents 

data from an aircraft equipped with an ozone converter; the three other flights were aircraft 

without converters. 
6

Figure 2. Weighted cumulative distributions of peak-hour ozone levels sampled in passenger 

cabins on 68 domestic US flight segments. Data are segregated by the presence or absence of 

an ozone converter. The weighted geometric mean and geometric standard deviation (reported 

in box), and the lognormal fits using these parameters (straight lines), are presented for each 

distribution.

Figure 3. Ozone levels sampled on eight transoceanic flights. The shaded bars represent 

peak-hour ozone and the diamonds denote cumulative ozone exposure for each flight segment.
7

Ozone reactions with cabin materials

We measured ozone consumption and byproduct formation on materials commonly found in 

aircraft cabins under flight-relevant conditions (Coleman et al., 2008). Two series of smallchamber experiments were carried out, with most runs at low relative humidity (10%) and high 

air-exchange rate (20 air changes per hour). New and used cabin materials (seat fabric, carpet, 

and plastic) and laundered and worn clothing fabrics (cotton, polyester, and wool) were studied, 

one at a time. We measured ozone deposition to many material samples, and we measured 

primary and secondary emissions of volatile organic compounds (VOCs) from a subset of 

samples. Deposition velocities, reflecting the effective rate of ozone uptake on the fabrics, 

ranged from 0.06 to 0.54 centimeters per second. Emissions of VOCs were higher with ozone 

exposure than without ozone in every case. The most commonly detected secondary emissions 

were saturated aldehydes containing one to ten carbon atoms and also the squalene oxidation 

products 6-methyl-5-hepten-2-one and acetone. For the compounds measured, summed VOC 

emission rates in the presence of 55–128 ppb (residual level) ozone ranged from 1.0 to 8.9 

millimoles per hour per square meter of material surface. Total byproduct yield ranged from 0.07 

to 0.24 moles of volatile product emitted per mole of ozone consumed. Results were used to 

estimate the relative contribution of different materials to ozone deposition and byproduct 

emissions in a typical aircraft cabin. The dominant contributor to both was worn clothing fabric, 

followed by seat fabric. Results indicate that ozone reactions with surfaces substantially reduce 

the ozone levels in cabin air but also generate volatile byproducts of potential concern for the 

health and comfort of passengers and crew.

Ozone reaction with permethrin

Permethrin is commonly used in aircraft cabins for disinsection. Theoretical considerations 

suggested that the reaction of ozone with residual permethrin on cabin surfaces could potentially 

form phosgene. An assessment that was based on already published evidence about ozone levels 

and permethrin surface concentrations in aircraft cabins indicated that significant phosgene 

formation might occur in this setting. Consequently, chamber experiments were designed and 

executed to investigate whether this chemistry could occur with sufficient speed to cause the 

production of phosgene at levels that would raise health concerns. A chemical derivatization 

technique was developed to detect phosgene with a lower limit of detection of 2 ppb. Chamber 

experiments were conducted with permethrin-coated cabin-relevant materials (glass, carpet, seat 

fabric, and plastic) exposed to ozone under cabin-relevant conditions: 150 ppb of ozone, 4.5 air 

changes per hour, <1% relative humidity, and a surface loading of permethrin equivalent to 1.7 

micrograms per square centimeter (Coleman et al., 2010). Phosgene emissions were not detected 

in any of these experiments. The reaction of ozone with permethrin appears to be hindered by the 

electron-withdrawing chlorine atoms adjacent to the double bond in permethrin. Our 

experimental results indicate that the upper limit on the reaction probability of ozone with 

surface-bound permethrin is low, approximately 10-7. This result means that for every ten 

million collisions of an ozone molecule with a permethrin molecule attached to a surface, no 

more than one of those collisions, on average, would produce phosgene. Extrapolation by means 

of material-balance modeling indicates that the upper limit on the phosgene level in aircraft 

cabins resulting from this chemistry is approximately 1 microgram per cubic meter or 0.3 ppb. It 

was thus determined that phosgene formation, if it occurs in aircraft cabins, is not likely to 

exceed relevant, health-based exposure guidelines for this chemical.
8

Ozone removal in a simulated aircraft cabin

As reported in Tamás et al. (2006), a series of experiments was conducted at the Technical 

University of Denmark’s (DTU) simulated cabin facility, a full-scale mock-up of three rows (21 

seats) of a Boeing 767 aircraft (Figure 4). 

Figure 4. Section of the simulated B-767 located at the Technical University of Denmark. The 

facility is equipped with three rows for passengers (21 used seats in all). It also contains used 

carpet, wall sections and HEPA filters recovered from commercial aircraft. The chamber 

volume is 28.5 cubic meters.

In the first set of experiments, ozone concentrations were measured concurrently inside the 

simulated aircraft cabin and in the airstream providing ventilation air to the cabin. Ozone decay 

rates were also measured after cessation of ozone injection into the supply airstream. By 

systematically varying the presence or absence of (a) people, (b) soiled T-shirts, (c) aircraft seats 

and (d) a used HEPA filter, we were able — over the course of 24 experiments — to isolate the 

contributions of these and other factors to the removal of ozone from the cabin air. 

As is apparent from Figure 5, humans are large sinks for ozone. At the same ozone generation 

rates, ozone levels were much lower when passengers were present than when the cabin was 

empty. In the case of this simulated aircraft, people (including their exposed skin, hair and 

clothing) were responsible for almost 60% of the ozone removal occurring within the cabin and 

recirculation system; respiration can only have been responsible for about 4% of this removal; 

the aircraft seats removed about 25% of the ozone; the loaded HEPA filter, 7%; and the other 

surfaces, 10%. (See Figure 6.) Remarkably, a T-shirt that had been slept in overnight and then 

placed over the seat back removed roughly 70% as much ozone as an entire person, indicating 

that skin oils are indeed important factors influencing ozone removal in aircraft cabins. With 

people present, the measured ratio of ozone’s concentration in the cabin to that outside the cabin 
9

was 0.15-0.21, smaller than levels reported in the literature. The results reinforce the conclusion 

that the optimal way to reduce people’s exposure to both ozone and to the byproducts of ozoneinitiated chemistry is to efficiently remove ozone from the aircraft’s air supply system.

Figure 5. Ozone levels with the simulated B-767 when the cabin was empty and when 16 

passengers were present; the ozone generation rate was the same for both conditions.

25%

7%

10%

56%

2%

Seats HEPA Filter

Other Surfaces People

Respiration

Figure 6. Fraction of ozone removed by the various sinks within the simulated section of the 

passenger cabin of a Boeing 767.
10

Ozone reaction with cabin materials and occupants in a simulated aircraft cabin

In a second set of experiments at DTU, we used multiple analytical methods to characterize the 

gas-phase products formed when ozone was added to cabin air during simulated four-hour flights 

that were conducted in the reconstructed section of a B-767 aircraft containing human occupants 

(Weschler et al., 2007). Two separate groups of 16 females were each exposed to four 

conditions: low air exchange (4.4 air changes per hour) and low (< 2 ppb) ozone; low air 

exchange and elevated (61-64 ppb) ozone; high air exchange (8.8 air changes per hour) and low 

(< 2 ppb) ozone; and high air exchange and elevated (73-77 ppb) ozone. The addition of ozone to 

the cabin air increased the levels of identified byproducts from ~70 to 130 ppb at the lower airexchange rate and from ~30 to 70 ppb at the higher air-exchange rate (Figure 7). 

0

20

40

60

80

100

120

140

no ozone, 4.4/h

ozone, 4.4/h

no ozone, 8.8/h

ozone, 8.8/h

average level (ppb) .

acids, aldehydes & ketones other

Figure 7. Sum of the organic compounds detected in the cabin air for the four different 

conditions indicated on the horizontal axis.

Most of the increase was attributable to acetone, nonanal, decanal, 4-oxopentanal (4-OPA), 6-

methyl-5-hepten-2-one (6-MHO), formic acid, and acetic acid, with 0.25-0.30 moles of 

quantified volatile product generated per mole of ozone consumed. Figure 8 shows the yields of 

the major ozone-derived products at both the low and high air exchange rates. Several of these 

compounds reached levels above their reported odor thresholds. A recent study conducted by 

researchers at NIOSH indicates that in vitro exposure of pulmonary epithelial cells to 4-OPA 

results in expression of various inflammatory markers (Anderson et al., 2010). That finding is 

suggestive that exposure to 4-OPA might have associated health risks. Related research has 

further advanced the understanding of ozone’s reactions with human skin lipids (Wisthaler and 
11

Weschler, 2010). In our research, most of the byproducts of ozone-initiated chemistry were 

derived from surface reactions with occupants and their clothing, consistent with the inference 

that occupants were responsible for the removal of more than 55% of the ozone in the cabin. 

The observations made in this study have implications for better understanding the health 

hazards of being exposed to ozone and its byproducts in aircraft cabins and also in other indoor 

settings. Whenever human beings and ozone are simultaneously present, one anticipates 

production of and increased human exposure to acetone, nonanal, decanal, 6-MHO, geranyl 

acetone, and 4-OPA. To the extent that these byproducts pose health risks, being exposed to a 

given level of ozone in a more densely occupied space will tend to pose higher health risks than 

in a less densely occupied space owing to the concomitant increase in exposure to the byproducts 

of ozone-initiated reactive chemistry.

0%

5%

10%

15%

20%

25%

30%

4.4/h 8.8/h yield (mole product per mole ozone)

other C=O

acetic acid

formic acid

6-MHO

4-OPA

decanal

nonanal

acetone

Figure 8. The yields of ozone-derived products were consistent for the experiments conducted 

at two different air exchange rates – 4.4 per hour (4.4/h) and 8.8 per hour (8.8/h).

Impact of ozone and ozone oxidation products on occupants’ self-reported symptoms

In a third set of experiments conducted in DTU’s reconstructed section of a B-767 aircraft cabin, 

Strøm-Tejsen et al. (2008) evaluated human subjects’ symptoms related to air quality and 

comfort during simulated four-hour flights identical to those described in the previous 

subsection. Twenty-nine female subjects, age 19–27 years, were split into two groups. Each 

group was exposed to four conditions: two levels of ozone (less than 2 ppb and 60–80 ppb) were 

utilized at each of two outside air supply rates (4.4 and 8.8 air changes per hour, corresponding 

to 2.4 and 4.7 liters of ventilation air per second per person, respectively). The subjects 

completed questionnaires to provide subjective assessments of air quality and symptoms typical 

of complaints experienced during actual flight. Additionally, the subjects’ visual acuity, nasal 

peak flow and skin dryness were measured. Based on self-recorded responses after 3.25 hours in 

the simulated cabin, the subjects judged the air quality (Figure 9) and eleven symptoms to be 
12

worse for the elevated ozone condition compared to the low ozone condition. Assessments for 

headache, eye achiness, nasal irritation and skin dryness are shown in Figure 10. Not shown, but 

also adversely impacted by exposure to ozone and ozone-derived byproducts, are assessments for 

odor, lip dryness, other eye complaints, dizziness, mental tension, and claustrophobia. Taken 

together, these results indicate that ozone and the products of ozone-initiated chemistry are 

contributing to such complaints. The findings imply that such complaints would be markedly 

reduced in situations where ozone is effectively removed from the ventilation air supplied to an 

aircraft cabin.

-1.0

-0.5

0.0

0.5

1.0

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Indoor Air Quality

Clearly

acceptable

Clearly

unacceptable

P<0.001 0.55

0.26

0.50

0.47

Figure 9. Subjective assessments by cabin occupants of indoor air quality for each of the four 

conditions (low air exchange, low O3; low air exchange, 61 ppb O3; high air exchange, low O3; 

high air exchange; 74 ppb O3) after passengers had been on the simulated flight for 3.25 hours. 

Each box represents the interquartile range, and the horizontal line dividing the box is the 

median, whose value appears to the right; all P-values are one-tail.
13

0

20

40

60

80

100

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Skin Dryness

Skin dry

Skin not dry

P<0.028 P<0.0 43 31 49

29

53

0

10

20

30

40

50

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Nasal Irritation

Overpowering

irritation

Slight

irritation

Moderate

irritation

Strong

irritation

Very Strong

irritation

No

irritation

P<0.0 43

3.6

4.0

5.2

8.7

0

20

40

60

80

100

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Headache

Severe

headache

No headache

P<0.0 09

13

24

11

20

0

20

40

60

80

100

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Eyes Aching

Eyes aching

Eyes not

aching

P<0.013 P<0.0 03 1.8 4.5 1.2

5.3

Figure 10. Subjective assessments by cabin occupants of headache, eye complaints, nasal 

complaints and perceived skin dryness for each of the four conditions, which are defined by 

ozone level and ventilation rate. See Figure 9 for further details.
14

CONCLUSIONS

The research undertaken by the ACER/RITE research team on ozone in aircraft cabins has 

produced an interconnected set of results that significantly advance our understanding about the 

levels of ozone and its reaction byproducts to which passengers and crew are exposed during 

flight along with some important information about the consequences of such exposures. 

Measurements on commercial flights found that ozone levels can be moderate to high on 

domestic flights without ozone converters. We also found that ozone can reach moderate levels 

in the cabin during transoceanic flights even though the planes are equipped with converters.

These levels are compliant with the current requirements of the ozone FARS. However, elevated 

ozone levels in aircraft cabins take on amplified concern given that the US national ambient air 

quality standard for ozone has become more stringent over time. The standard is presently 75 

ppb measured over 8 hrs and a lower standard (down to 60 ppb as the peak hourly average) has 

been recommended (Federal Register, Vol. 75, No. 11, 2938, 19 Jan 2010). Furthermore, in the 

event of high ambient air pollution events, people with respiratory health impairments are 

recommended to take shelter indoors where the ozone is typically only 20-70% of the outdoor 

level (Weschler, 2000). In an aircraft cabin with elevated ozone levels, passengers and crew are 

exposed without any knowledge and there is no place for someone with respiratory health 

impairment to take shelter.

When ozone is present within the cabin, various oxidation reactions occur, mainly on surfaces 

including those associated with the passengers themselves. Laboratory experiments conducted in 

small chambers confirmed that ozone reacts with numerous cabin materials, including clothing, 

yielding acetone, 6-MHO and a series of aldehydes. Simulated flight experiments conducted with 

human subjects in a reconstructed section of a B-767 aircraft cabin identified the same ozone 

derived byproducts as those measured in the laboratory experiments, as well as dicarbonyls, 

organic acids and other oxidation products. Strikingly, in these simulated flights, more than half 

of the net ozone removal within the cabin was attributable to its reactions with cabin occupants. 

The identities of the reaction products indicate that ozone reacts rapidly with skin lipids on 

exposed skin, hair and clothing. The reactions have substantial influence on the levels of these 

byproducts in cabin air. On a positive note, laboratory studies indicate that if phosgene is formed 

via the reaction of ozone with residuals of permethrin (a commonly applied disinsectant), the 

resulting levels of this compound are very likely to be lower than appropriate health-based 

standards. 

Self-assessed symptoms during simulated four-hour flights with and without ozone indicate that 

ozone-oxidation products, in addition to ozone itself, may contribute to the complaints of 

mucous membrane irritation (e.g., irritated eyes and throat) commonly reported by the flying 

public. In addition, certain ozone oxidation products (e.g., formaldehyde, acrolein, and some 

dicarbonyls) are known or suspected of adversely affecting human health at elevated levels. 

Whether and to what extent exposures to the moderate-to-high ozone levels that occur on some 

flights contribute to acute or long-term health effects remains an open question. 

A comparison of ozone levels on domestic flights with and without ozone converters makes clear 

that converters can substantially reduce exposures of passengers and crew to ozone, and, by 

inference, to the byproducts of ozone-initiated chemistry. However, we also found moderate 
15

ozone levels during some transoceanic flights on planes that were equipped with ozone 

converters. This evidence supports a conclusion that while ozone converters can be effective in 

controlling levels in cabin air, their presence alone does not ensure low levels.

IMPLICATIONS

The results derived from the ACER/RITE ozone project have these implications:

• Health and safety evaluations for the aircraft cabin environment should consider the products 

of ozone-initiated chemistry in addition to ozone itself. Exposure to certain ozone-derived 

products may have meaningful consequences for the health and well-being of passengers and 

crewmembers, especially on flights with moderate to high ozone concentrations.

• It would be appropriate for FAA to re-evaluate the FARs for ozone to determine whether they 

are adequately protective of the health of passengers and crew. Concerns arise for the 

following reasons:

- The current FARs do not reflect additional knowledge, accrued since 1980, regarding direct 

adverse health effects of ozone exposure.

- The current FARs do not reflect ozone chemistry and resultant exposures of passengers and 

crew to the byproducts of ozone-intiated chemistry.

- The flying population may include more individuals who are vulnerable to the adverse 

effects of air pollutant exposure than was the case before 1980.

• Adopting as a standard practice the use of ozone converters on all commercial flights may be 

warranted. This practice appears to be common in northern Europe, based on conversations 

with carriers based in this region. 

• A program of random periodic testing of in-service ozone converters could reduce exposures 

that result from degraded or poisoned catalysts.

• Future studies could fruitfully investigate improved technologies for ozone control in aircraft 

cabins. Examples include activated carbon filters to remove ozone and ozone-derived products 

from recirculating air in aircraft cabins and methods to prevent poisoning of in-service 

converters, which would extend their useful life.

PUBLICATIONS DERIVED FROM THIS PROJECT

The following journal articles report on the detailed research investigations conducted as part of 

the ACER/RITE ozone project for the period 2004-2010, as summarized in this technical report. 

Copies of these articles are available on request from WW Nazaroff (nazaroff@ce.berkeley.edu) 

or CJ Weschler (weschlch@umdnj.edu).

Bhangar S, Cowlin SC, Singer BC, Sextro RG, Nazaroff WW, 2008. Ozone levels in passenger 

cabins of commercial aircraft on North American and transoceanic routes. Environmental 

Science & Technology 42, 3938-3943. 

Coleman BK, Destaillats H, Hodgson AT, Nazaroff WW, 2008. Ozone consumption and volatile 

byproduct formation from surface reactions with aircraft cabin materials and clothing fabrics. 

Atmospheric Environment 42, 642-654.
16

Coleman BK, Wells JR, Nazaroff WW, 2010. Investigating ozone-induced decomposition of 

surface-bound permethrin for conditions in aircraft cabins. Indoor Air 20, 61-71.

Strøm-Tejsen P, Weschler CJ, Wargocki P, Myskow D, Zarzycka J, 2008. The influence of 

ozone on self-evaluation of symptoms in a simulated aircraft cabin. Journal of Exposure 

Science and Environmental Epidemiology 18, 272-281.

Tamás G, Weschler CJ, Bako-Biro Z, Wyon DP, Strøm-Tejsen P, 2006. Factors affecting ozone 

removal rates in a simulated aircraft cabin environment. Atmospheric Environment 40, 6122-

6133.

Weschler CJ, Wisthaler A, Cowlin S, Tamás G, Strøm-Tejsen P, Hodgson AT, Destaillats H, 

Herrington J, Zhang JJ, Nazaroff WW, 2007. Ozone-initiated chemistry in an occupied 

simulated aircraft cabin. Environmental Science & Technology 41, 6177-6184.

REFERENCES

Anderson SE, Jackson LG, Franko J, Wells JR, 2010. Evaluation of dicarbonyls generated in a 

simulated indoor air environment using an in vitro exposure system. Toxicological Sciences

115, 453-461.

Bell ML, McDermott A, Zeger SL, Samet JM, Dominici F, 2004. Ozone and short-term 

mortality in 95 US urban communities, 1987–2000. Journal of the American Medical 

Association 292, 2372-2378.

Bell ML, Peng RD, Dominici F, 2006. The exposure-response curve for ozone and risk of 

mortality and the adequacy of current ozone regulations. Environmental Health Perspectives

114, 532-536.

Bhangar S, Cowlin SC, Singer BC, Sextro RG, Nazaroff WW, 2008. Ozone levels in passenger 

cabins of commercial aircraft on North American and transoceanic routes. Environmental 

Science & Technology 42, 3938-3943. 

Bischof W, 1973. Ozone measurements in jet airliner cabin air. Water Air and Soil Pollution 2, 

3-14.

Brabets RI, Hersh CK, Klein MJ, 1967. Ozone measurement survey in commercial jet aircraft. 

Journal of Aircraft 4, 59-64.

Chen C, Arjomandi M, Balmes J, Tager I, Holland N, 2007. Effects of chronic and acute ozone 

exposure on lipid peroxidation and antioxidant capacity in healthy young adults. 

Environmental Health Perspectives 115, 1732-1737.

Coleman BK, Destaillats H, Hodgson AT, Nazaroff WW, 2008. Ozone consumption and volatile 

byproduct formation from surface reactions with aircraft cabin materials and clothing fabrics. 

Atmospheric Environment 42, 642-654.

Coleman BK, Wells JR, Nazaroff WW, 2010. Investigating ozone-induced decomposition of 

surface-bound permethrin for conditions in aircraft cabins. Indoor Air 20, 61-71.

Gent JF, Triche EW, Holford TR, Belanger K, Bracken MB, Beckett WS, Leaderer BP, 2003. 

Association of low-level ozone and fine particles with respiratory symptoms in children with 

asthma. Journal of the American Medical Association 290, 1859-1867.
17

Jerrett M, Burnett RT, Pope III CA, Ito K, Thurston G, Krewski D, Shi Y, Calle E, Thun M, 

2009. Long-term ozone exposure and mortality. The New England Journal of Medicine 360, 

1085-1095.

Levy JI, Carrothers TJ, Tuomisto JT, Hammitt JK, Evans JS, 2001. Assessing the public health 

benefits of reduced ozone concentrations. Environmental Health Perspectives 109, 1215-

1226.

McDonnell WF, Abbey DE, Nishino N, Lebowitz MD, 1999. Long-term ambient ozone 

concentration and the incidence of asthma in nonsmoking adults: The Ahsmog study. 

Environmental Research 80, 110-121.

Nastrom GD, Holdeman JD, Perkins PJ, 1980. Measurements of cabin and ambient ozone on 

B747 airplanes. Journal of Aircraft 17, 246-249.

National Research Council (NRC) Committee on air quality in passenger cabins of commercial 

aircraft. The Airliner Cabin Environment and the Health of Passengers and Crew. National 

Academy Press: Washington, DC, 2002.

Reed D, Glaser S, Kaldor J, 1980. Ozone toxicity symptoms among flight attendants. American 

Journal of Industrial Medicine 1, 43-54.

Spengler JD, Ludwig S, Weker RA, 2004. Ozone exposures during trans-continental and transPacific flights. Indoor Air 14, 67-73.

Spicer CW, Murphy MJ, Holdren MW, Myers JD, MacGregor IC, Holloman C, James RR, 

Tucker K, Zaborski R. Relate Air Quality and Other Factors to Comfort and Health 

Symptoms Reported by Passengers and Crew on Commercial Transport Aircraft (Part I). 

ASHRAE Project 1262-TRP. American Society for Heating, Refrigerating, and Air 

Conditioning Engineers: Atlanta, 2004.

Strøm-Tejsen P, Weschler CJ, Wargocki P, Myskow D, Zarzycka J, 2008. The influence of 

ozone on self-evaluation of symptoms in a simulated aircraft cabin. Journal of Exposure 

Science and Environmental Epidemiology 18, 272-281.

Tager IB, Balmes J, Lurmann F, Ngo L, Alcorn S, Kunzli N, 2005. Chronic exposure to ambient 

ozone and lung function in young adults. Epidemiology 16, 751-759.

Tamás G, Weschler CJ, Bako-Biro Z, Wyon DP, Strøm-Tejsen P, 2006. Factors affecting ozone 

removal rates in a simulated aircraft cabin environment. Atmospheric Environment 40, 6122-

6133.

Weschler CJ, 2000. Ozone in indoor environments: Concentration and chemistry. Indoor Air 10, 

269-288.

Weschler CJ, 2006. Ozone’s impact on public health: Contributions from indoor exposures to 

ozone and products of ozone-initiated chemistry. Environmental Health Perspectives 114, 

1489-1496.

Weschler CJ, Wisthaler A, Cowlin S, Tamás G, Strøm-Tejsen P, Hodgson AT, Destaillats H, 

Herrington J, Zhang JJ, Nazaroff WW, 2007. Ozone-initiated chemistry in an occupied 

simulated aircraft cabin. Environmental Science & Technology 41, 6177-6184.
18

Wisthaler A, Tamás G, Wyon DP, Strøm-Tejsen P, Space D, Beauchamp J, Hansel A, Mark TD, 

Weschler CJ, 2005. Products of ozone-initiated chemistry in a simulated aircraft

environment. Environmental Science & Technology 39, 4823-4832.

Wisthaler A, Weschler CJ, 2010. Reactions of ozone with human skin lipids: Sources of 

carbonyls, dicarbonyls, and hydroxycarbonyls in indoor air. Proceedings of the National 

Academy of Sciences of the United States of America 107, 6568-6575.