Simulations of ozone distributions in an aircraft cabin using computational fluid dynamics

doi:10.1016/j.atmosenv.2012.02.010

Atmospheric Environment

Volume 54, July 2012, Pages 348-357

https://doi.org/10.1016/j.atmosenv.2012.02.010 Get rights and content

Abstract

Ozone is a major pollutant of indoor air. Many studies have demonstrated the adverse health effect of ozone and the byproducts generated as a result of ozone-initiated reactive chemistry in an indoor environment. This study developed a Computational Fluid Dynamics (CFD) model to predict the ozone distribution in an aircraft cabin. The model was used to simulate the distribution of ozone in an aircraft cabin mockup for the following cases: (1) empty cabin; (2) cabin with seats; (3) cabin with soiled T-shirts; (4) occupied cabin with simple human geometry; and (5) occupied cabin with detailed human geometry. The agreement was generally good between the CFD results and the available experimental data. The ozone removal rate, deposition velocity, retention ratio, and breathing zone levels were well predicted in those cases. The CFD model predicted breathing zone ozone concentration to be 77–99% of the average cabin ozone concentration depending on the seat location. The ozone concentration at the breathing zone in the cabin environment can better assess the health risk to passengers and can be used to develop strategies for a healthier cabin environment.

Highlights

► A CFD model was developed to study the influence of surface reactions on the ozone distributions in an aircraft cabin. ► The CFD model showed reasonable agreement with available experimental data. ► Breathing-zone ozone concentration varies amongst passengers and ranges from 77 to 99% of the bulk air concentration.

Introduction

Aircraft passengers and crew could be exposed to a variety of chemical and biological agents during a flight. Many of the agents are potential health hazards (NRC, 2002). Ozone is one such chemical agent that poses a significant health concern (EPA, 2006, Weschler, 2006). Ozone exposure has been found to be associated with respiratory problems such as asthma, bronchoconstriction, airway hyperresponsiveness, and inflammation (EPA, 2006). There is also suggestive evidence that links ozone to cardiovascular morbidity (EPA, 2006). Exposure to a low level of ambient ozone can increase mortality risk (Bell et al., 2006).

The risk of ozone exposure is high in an aircraft cabin environment because of the high ozone concentration in the air at typical cruise altitudes (500–800 ppb) and the subsequent ozone infiltration in the cabin through the air supply system. Ozone forms a variety of byproducts as a result of chemical reactions with human skin and with surfaces in aircraft cabins (Wisthaler et al., 2005, Weschler et al., 2007, Coleman et al., 2008, Pandrangi and Morrison, 2008, Wisthaler and Weschler, 2010). These chemical reactions can produce even more harmful chemical contaminants than the ozone itself (Weschler, 2004, Wisthaler et al., 2005) or secondary organic aerosols (Weschler and Shields, 1999).

To protect passengers and crew, the U.S. Federal Aviation Regulations (FAR Section 25.832) limit cabin ozone concentration to 250 ppb, sea level equivalent, at any time above flight level 320 (32,000 ft above sea level) or to 100 ppb, sea level equivalent, during any 3-h interval above flight level 270 (27,000 ft above sea level). To meet these regulations, some airlines employ catalytic converters in the air supply system to reduce the ozone level. However, in the absence or malfunctioning of these converters, the ozone level can go substantially higher. Spengler et al. (2004) measured the average ozone concentration in 106 flights and found that the ozone concentration in 20% of the flights exceeded the 100 ppb limit. Bhangar et al. (2008) collected real-time ozone data from 76 flights and found that ozone levels strongly varied with season and the presence or absence of an ozone converter.

In-flight measurements of ozone provide valuable information about the cabin air quality, but they are expensive and tedious. It is also difficult to identify the various factors affecting the ozone removal and byproduct formation through in-flight measurements. To overcome these difficulties, many investigations have used cabin mockups to systematically study ozone initiated reactive chemistry in a cabin environment (Wisthaler et al., 2005, Tamas et al., 2006, Weschler et al., 2007). These investigations have provided valuable information about the various factors that affect the cabin ozone levels and the ozone reactive chemistry. Although experimental studies provide reliable results, they are inflexible to changes in the system configuration and boundary conditions. It is also very difficult to obtain the distribution of ozone and associated byproducts in a cabin environment because of the large number of sensors required. Hence, it is necessary to develop a reliable and accurate method to calculate the ozone distributions and associated byproducts in a realistic cabin environment. The health risks to passengers and crew can then be assessed and possible mitigation strategies can be developed.

In order to understand the health risk to aircraft passengers from ozone, this research had a three-fold objective:

1.
Develop a model to simulate the ozone distributions in an occupied aircraft cabin.
2.
Compare the model results with available experimental data.
3.
Use the model to study the ozone exposure of passengers.

Section snippets

State of the art

Many investigations have studied ozone distributions, the associated byproducts, and exposure assessments. For example, numerous experimental studies have been conducted to characterize ozone exposure and ozone initiated reactive chemistry in buildings and aircraft cabins (Wisthaler et al., 2005, Tamas et al., 2006, Wang and Morrison, 2006, Wang and Morrison, 2010, Weschler et al., 2007, Wisthaler and Weschler, 2010). Wang and Morrison, 2006, Wang and Morrison, 2010 performed field experiments

Case setup

This investigation used CFD to simulate the ozone distributions in an aircraft cabin mockup for which detailed experimental data were available (Tamas et al., 2006). The cabin mockup was a section of Boeing-767 (3 rows, 21 seats) as shown in Fig. 1, which was 4.9 m wide, 3.2 m long, and 2.0 m high in the center with a total volume of 28.5 m³. The experimental setup injected the air containing ozone to the cabin from the two overhead air-supply slots along the longitudinal direction (12 mm × 3200 mm

Evaluation parameters

This section defines some important parameters for evaluating the cabin air quality for the cases designed in the previous section. These parameters help evaluate the CFD results against the available experimental data.

Results

The following section reports how the CFD was used to obtain the evaluation parameters defined in Section 4 and shows the comparison with the experimental data from Tamas et al. (2006).

Discussion

The primary difficulty in computing the ozone distribution was that the γ for the ozone reactive surfaces was unknown. Hence, this investigation obtained the γ from the “measured” v_d and computed v_t by using Eq. (4). The flux model (Eq. (3)) was then used to compute the ozone removal by cabin surfaces. However, in the cases with the T-shirts and passengers, the flux model (Eq. (3)) was not used to compute the surface deposition since the v_d was found to be very close to v_t, and Eq. (4) was not

Conclusions

The investigation developed a CFD model to study the ozone reactions at different cabin and human related surfaces and simulate the ozone distributions in the cabin. The investigation led to the following conclusions:

•
The study identified the individual contributions of cabin and human related surfaces to ozone removal and their deposition velocities. The results concluded that the human related surfaces (T-shirts and passengers) removed much more ozone than the cabin surfaces (carpet and seats).

Acknowledgements

The authors would like to thank Dr. Charles J. Weschler of the University of Medicine and Dentistry of New Jersey for his help in interpreting the experimental data obtained by his group and our CFD results. This study was partially supported by the National Basic Research Program of China (The 973 Program) through grant No. 2012CB720100 and partially funded by the U.S. Federal Aviation Administration (FAA) Office of Aerospace Medicine through the National Air Transportation Center of

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Simulations of ozone distributions in an aircraft cabin using computational fluid dynamics

Abstract

Highlights

Introduction

Section snippets

State of the art

Case setup

Evaluation parameters

Results

Discussion

Conclusions

Acknowledgements

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Building and Environment

The exposure–response curve for ozone and risk of mortality and the adequacy of current ozone regulations

Environmental Health Perspectives

Ozone levels in passenger cabins of commercial aircraft on North American and transoceanic routes

Environmental Science & Technology

Air quality criteria for ozone and related photochemical oxidants (final)

ANSYS FLUENT 12.0 Theory Guide

Ozone decay rates in residences

Journal of the Air & Waste Management Association

Evaluation of the harvard ozone passive sampler on human subjects indoors

Environmental Science & Technology