Ozone Levels in Passenger Cabins of Commercial Aircraft on North American and Transoceanic Routes SEEMA BHANGAR, † SHANNON C. COWLIN, † BRETT C. SINGER, § RICHARD G. SEXTRO, § AND WILLIAM W. NAZAROFF* ,†,§ Civil & Environmental Engineering Department, University of California, Berkeley, California 94720-1710, Indoor Environment and Atmospheric Sciences Departments, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 Received November 28, 2007. Revised manuscript received March 9, 2008. Accepted March 13, 2008. Ozone levels in airplane cabins, and factors that influence them, were studied on northern hemisphere commercial passenger flights on domestic U.S., transatlantic, and transpacific routes. Real-time data from 76 flights were collected in 2006–2007 with a battery-powered UV photometric monitor. Sample mean ozone level, peak-hour ozone level, and flight-integrated ozone exposures were highly variable across domestic segments ( N ) 68), with ranges of <1.5 to 146 parts per billion by volume (ppbv), 3-275 ppbv, and <1.5 to 488 ppbv- hour, respectively. On planes equipped with ozone catalysts, the mean peak-hour ozone level (4.7 ppbv, N ) 22) was substantially lower than on planes not equipped with catalysts (47 ppbv, N ) 46). Peak-hour ozone levels on eight transoceanic flight segments, all on planes equipped with ozone catalysts, were in the range <1.5 to 58 ppbv. Seasonal variation on domestic routes without converters is reasonably modeled by a sinusoidal curve that predicts peak-hour levels to be approximately 70 ppbv higher in Feb-March than in Aug-Sept. The temporal trend is broadly consistent with expectations, given the seasonal cycle in tropopause height. Episodically elevated ( >100 ppbv) 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. Introduction Passengers in aircraft cabins may be exposed to elevated ozone that naturally originates in the stratosphere. In-cabin ozone depends on ambient levels, the presence or absence of a control device, the rate of outdoor air supply, and the rate of ozone loss through within-cabin transformation processes, such as reactions with interior surfaces. Ozone levels outside the aircraft depend on flight altitude, tropo- pause 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 more sensitive to respiratory health effects, such as infants and adults with cardiopulmonary conditions. Ozone and its reaction byproducts are associated with adverse respiratory and cardiovascular effects (1–3). Acute effects from short- term exposure range from breathing discomfort, respiratory irritation, and headache for healthy adults (4) to asthma- exacerbation and premature mortality for vulnerable popu- lations (5, 6). Chronic exposure effects may include enhanced oxidative stress (7), reduced lung function in young adults (8), and adult-onset asthma in males (9). Physical activity, as is undertaken by flight attendants, results in increased intake. There is no established “safe” level of exposure (2). 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 (ppbv), especially on flight routes through high latitudes (10–12). In 1980, in response to these data and to associated health concerns for flight attendants (13), the Federal Aviation Administration (FAA) established standards (FAR 25.832 and FAR 121.578) limiting levels of ozone in airplane cabins (14). To comply with the regulations, many planes are equipped with “converters” that promote the decomposition of ozone in the ventilation 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, and the probabilistic planning approach permits, by design, up to 16% of the flights to exceed the concentration standard. The ozone level in aircraft cabins is neither routinely monitored, nor has it been the subject of many research papers since the ozone standards were established. Spengler et al. (15) present a survey of flight-integrated ozone levels on 106 segments. The authors also report 3 h ozone levels measured during the middle of the flight for Pacific segments. The presence or absence of an ozone converter was deter- mined by proxy and was not verified. To our knowledge, real-time in-cabin ozone data that indicate variation over time during a flight have been reported for just four flights since 1980 (16). To address this data gap, we continuously monitored ozone levels in the passenger cabins of 76 commercial flight segments between February 2006 and August 2007. Time- resolved (1-min) measurements were made using a portable UV-photometric monitor on many flights across the United States and on several transatlantic and transpacific flights. A range of narrow- and wide-body aircraft, with or without ozone converters, were sampled. Flight selection was sub- stantially opportunistic, with some flights intentionally chosen to augment seasons or flight routes not otherwise well-represented. Real-time sampling was chosen to capture temporal trends within single flights, and because short- term elevated levels, which may be significant for public health, would be masked by flight-averaged sampling. The airlines operating the flights on which we sampled reported to us whether or not the plane was equipped with an ozone- control device. We estimated by direct observation the fractional occupancy of the cabin by passengers. Occupancy is of interest because chamber (17) and simulated-cabin studies (18–20) indicate that recently worn clothing consti- tutes a significant sink for ozone, owing to the apparent reaction of ozone with chemicals in skin oil. Our study objective was to assess the distribution of in-cabin ozone levels and factors that influence them, and to discuss possible consequences, on northern hemisphere commercial pas- * Corresponding author e-mail: nazaroff@ce.berkeley.edu; phone: (510) 642 1040. † Civil & Environmental Engineering Department, University of California. § Lawrence Berkeley National Laboratory. Environ. Sci. Technol. 2008, 42, 3938–3943 3938 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 11, 2008 10.1021/es702967k CCC: $40.75  2008 American Chemical Society Published on Web 04/19/2008