Note 26: Volatile Organics Present in Recycled Air Aboard a Commercial Airliner

INTRODUCTION

There has been much publicity as of late on the health effects of biological contaminants and the transmission of viral infections on board commercial airliners due to ineffective air replacement and inadequate filtering. None of these studies however made any attempt at the identification of volatile organic compounds (VOC's) that are also present in this same confined space. Health risks due to Sick buildings have been documented and have caused concern in government and industry due to both time lost by sick employees and the costs involved with remediation. Analytical techniques are needed to identify and quantitate VOC's in airplane cabins to protect both airline employees and the flying public.

For this study, air samples were collected at one hour intervals on flights originating in Newark NJ, London England, Edinburgh Scotland, and Munich Germany. Three different types of aircraft were sampled in coach, business and first class cabins. All samples were collected by trapping on an adsorbent resin and analyzed by thermal desorption-gas chromatography-mass spectrometry.

Experimental

Fourteen air samples from five different flights were analyzed to identify and compare the volatile organics in commercial aircraft cabins. All samples were collected using a Gilian model LSF-113 low flow air sampling pump (Fig.1). This unit maintains a constant flow over variable back pressure within ±5 per cent of the set point. All samples were collected for 50 min. at 100 ml/min.(5.0 L total) through preconditioned 4.0mm i.d. glass-lined stainless steel desorption tubes packed with 200 mg of Tenax® TA. During the two Newark/London flights, five samples were collected over five hours to measure the effectiveness of air filtering/replacement systems over time. Before analysis, each sample was spiked with 50ng each of d-8 toluene and d-8 naphthalene internal standard by injecting 1µl of 50ng/µl stock solution in methanol directly into the Tenax matrix.

All experiments were conducted using a Scientific Instrument Services model TD-2 Short Path Thermal Desorption System accessory connected to the injection port of an HP 5890 Series II GC interfaced to an HP 5971 Mass Selective Detector (1,2). The mass spectrometer was operated in the electron impact mode (EI) at 70eV and scanned from 35 to 400 daltons during the GC run for the total ion chromatogram.

Figure 1 - Personal Air Sampling Pump For the Collection of Volatiles From Air

A short 0.5 meter by 0.53mm diameter fused silica precolumn was attached to the injection port end of a 60 meter x 0.25mm i.d. DB-5MS capillary column containing a 0.25µm film thickness. The GC injection port was set to 250 degrees C and direct splitless analysis was used. The oven was maintained at -40 degrees C during the desorption and extraction process after which the oven was temperature programmed from 35 degrees C to 250 degrees C at a rate of 10 degrees/min.

Results and Discussion

The air samples from five different flights (Figures 2-5) sampled were analyzed to identify and compare the volatile organics present. The VOC's detected can be grouped into three different categories: flavors and fragrances, cleaning and lubricating oils, and aviation fuel by-products.

Figure 2 - Boeing 737 Flight - Edinburgh To London

Figure 3 - Boeing 757 Flight - Munich To London

First of all the expected flavor and fragrance compounds such as benzaldehyde, nonenal, decanal and limonene were detected. Also found were some common fragrance/perfume VOC's such as octanal and 1-phenyl ethanone along with camphor, iso-menthone (from peppermint) and menthol. The next category were compounds related to cleaning and lubricating compounds. Siloxanes are used as a basis for silicone lubricating oils, phthalates and BHT are common in treatments (such as Armour All) for leather and vinyl while tetrachloroethene, once commonly used in dry cleaning and now used to clean metal parts before assembly, was found in noticeable quantities, but primarily on flights originating in the U.S.

Figure 4 - Boeing 747 Flight - London To Newark (first hour on the airplane)

Figure 5 - Boeing 747 Flight - London To Newark (after four hours on the airplane)

The last category of VOC's were toluene and octane and the alkanes from tridecane to heptadecane. These compounds are common by-products of aviation fuel and its associated exhaust fumes. One compound, 1-propene, 2-methyl trimer, was found in significant quantities, but only in flights originating in Europe. This compound may be an anti-knock additive used in European jet fuels. These VOC's were all present in the 1 to 3 ppb (part per billion) range at the onset of all flights. At what concentration these compounds become harmful has not been determined. One bright spot however was that the air replacement system of the Newark/London flights did bring the concentration of these compounds down to .01 ppb or less within three hours after taking off. The shorter flights of two hours and less maintained 1 ppb levels throughout, suggesting that either three hours are needed to completely replace cabin air, or that air replacement isn't a priority on shorter flights.

One interesting result was that while toluene and alkanes disappeared over the course of the flight, the flavor and fragrance compounds associated with foods, perfumes and pharmaceuticals maintained their levels throughout, and the plasticizer related compounds actually increased in concentration (Figures 6-9). This suggests that the source of fuel VOC's ended when the doors were closed, flavors and fragrances persisted due to the constant availability of foods and colognes worn by passengers, and the warm bodies on the leather and vinyl seats apparently caused an increase in VOC's related to their treatment due to a rise in temperature over time. As a side note, no significant difference was seen in the air quality in coach, business and first class cabins.

Figure 6 - Boeing 747 Flight - London To Newark (concentration of decanes in ng/l of air)

Figure 7 - Boeing 757 Flight - Munich To London (concentration of decanes in ng/l of air)

Figure 8 - Flavor & Fragrance Compounds In Cabin Air (average reading over duration of flight)

Figure 9 - Flavor & Fragrance Compounds In Cabin Air

Conclusion

The Short Path Thermal Desorption System used in conjunction with a high quality air sampling pump permits the identification and quantification of a broad range of volatile organics present in enclosed areas. This technique permits quick analysis of samples without the need for difficult, time consuming and environmentally unfriendly solvent extractions. The exposure of the public to the compounds that were identified should be of concern to both airline companies and health officials. These air samples show that the public is constantly in contact with a wide variety of potentially harmful VOC's due to cleaning supplies, lubricants and fuel by-products. These are an unwelcome addition to the flavor and fragrance compounds one expects to encounter around foods. In addition to the levels of biologicals trapped in closed-in areas such as airline cabins, it is apparent that organic compounds should also be of concern. Perhaps it is time for the airlines to do a better job on the quality of air found inside their aircraft.

References

1. Manura JJ, Overton SV, Baker CW, Manos JN. Short path thermal desorption-design and theory. The Mass Spec Source 1990; XIII (4):22-8.

2. Manura JJ, Hartman TG. Applications of a short path thermal desorption GC accessory. Am Lab 1992; 24(8):46-52.