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Development of VOCs and ozone Micro-analysers based on microfluidic devices for Aircraft Cabin Air mOnitoring (MACAO)

Periodic Reporting for period 4 - MACAO (Development of VOCs and ozone Micro-analysers based on microfluidic devices for Aircraft Cabin Air mOnitoring (MACAO))

Période du rapport: 2020-03-01 au 2020-12-31

CONTEXT

In a typical commercial cabin air recirculation system, the air supplied into the cabin consists of a mixture of approximately 50% of outdoor air and approximately 50% of filtered, recirculated air. Various origins of ozone (O3) and Volatile Organic Compounds (VOC) exist in such environments. Some of them come from outside, particularly ozone when the aircraft is flying at high altitudes near the stratospheric ozone layer. Ozone can then react with interior surfaces (materials, occupants) to produce VOCs in the aircraft cabin.
Furthermore, other VOCs are released inside the cabin coming from combustion engines, materials or alcoholic beverages leading to a further degradation of air quality.

OBJECTIVES

The MACAO objectives are in line with those of the Clean Sky2 program. This concerns the development of devices enabling to remove air pollutants generated in the cabin or entering in the cabin through the air conditioning system. These devices will have to be associated to analysers able to monitor pollutants concentrations in the cabin. This project aimed at developing two analytical instruments based on microfluidic devices for the measurement of major indoor air pollutants concentrations in airplanes. The first micro-analyser will measure concentrations of various VOC whereas the second one will measure the ozone concentrations.

CONCLUSIONS OF THE ACTIONS

For ozone, the development has been successful, the consortium being able to find an alternative methodology to the standard colorimetric detection to quantify ozone in air. The ozone microanalyser is based on the measurement performed by an electrochemical ozone sensor coupled to an electrochemical NO2 sensor to eliminate the possible interferences caused by the presence of airborne nitrogen dioxide (NO2). The ozone microanalyser exhibits a fast and linear response to airborne ozone concentrations in the range of interest, i.e. 0 – 1 000 ppb, either in controlled laboratory conditions or at topic manager facilities.
Concerning the VOC analyser, a microfluidic preconcentration unit had to be integrated into an existing BTEX analyser to improve the sensitivity of the device, as well as a second detector to increase the number of detectable molecules. These two tasks were carried out successfully leading to a rudimentary laboratory prototype. Unfortunately, the final demonstrator of the VOC analyser was not completed by the industrial partner because of the COVID-19 health crisis.
First, the specifications for both ozone and VOC analyser were described and detailed in agreement with the Topic Manager.

VOC ANALYSER

Regarding the VOC analyser, a laboratory prototype was developed from an existing instrument able to quantify Benzene and its derivative and already developed by CNRS in collaboration with an industrial partner before the beginning of MACAO Project. To enlarge the number of detectable species, a second “universal” detector was added and placed in series with the PhotoIonisation Detector (PID). To improve its sensitivity, a preconcentrator was successfully developed to concentrate the airborne VOC samples. In fact, 6 versions of preconcentrator were implemented successively until satisfactory results were obtained. The final preconcentrator finalized was tested under controlled conditions, demonstrating that it meets the requirements established in the objectives of this project in terms of sensitivity, energy consumption, analysis duration, repeatability, and reproducibility. The benzene Limit Of Quantification (LOQ) achieved (0.191 ppb which is equivalent to about 5 pg) with an air sample of only 20 mL was found to be lower than the threshold value established in the recent French legislation concerning indoor air quality (0.6 ppb).

OZONE ANALYSER

Concerning the ozone analyser, the first technological solutions considered were abandoned either because of the lack of sensitivity obtained or because of the need for dangerous gases which was incompatible with use in an airplane. A laboratory prototype was first developed based on differential measurements obtained with sensors. Indeed, nitric dioxide (NO2) being an interferent for the ozone sensor, its concentration must be measured to correct the ozone measurement. Finally, an ozone analyser demonstrator was then developed at ICPEES to monitor airborne ozone concentrations in real-time. It included the mechanical design using Computer Aids Design, the development and manufacturing of electronic boards, the realization of a custom case using 3D printing. An embedded software for this instrument was also developed through the Arduino development environment.

EXPLOITATION AND DISSEMINATION

Numbers of published papers and oral communications during the whole duration of the project:
- 1 PhD Thesis
- 7 papers in international journals
- 12 oral communications in international conferences or workshops
- 1 oral communication in a national workshop
A patent related to the preconcentrator was submitted by ICPEES (CNRS, partner 1) in March, 2020.
The two products, i.e. the ozone and VOC analysers, developed in MACAO project had initially a TRL equal to 2 and 3, respectively.

Concerning the VOC analyser, its analytical performances were drastically improved to obtain a laboratory prototype with a TRL 4. The stability of the measurements altogether with the extraordinary sensitivity and an acceptable analysis time make this GC prototype a good candidate for air quality monitoring applications. Nevertheless, this instrument should be tested in real conditions to evaluate the possible influence of interfering compounds and other issues derived from the use in real environments. Such tests imply the need of a VOC analyser demonstrator reaching the TRL 5 integrating an efficient embedded software for the full management of this complex instrument. In addition, the patent submitted in the framework of the MACAO project could be used and integrated into measuring instruments for aeronautics or even the standard monitoring of indoor or outdoor air quality.

Regarding the ozone analyser demonstrator, there is a clear and satisfactory capacity of the ozone sensor to respond fast and linearly to airborne O3 concentrations in the range of interest, i.e. 0 – 1 000 ppb. Since the O3 sensor responds also to NO2, a data treatment and correction method has been established. Absence of cross-sensitivity of the NO2 sensor to O3 concentration in the range of 50 – 400 ppb has been demonstrated, thus ensuring that the data treatment and correction method based on the NO2 sensor's measurements is reliable. An experimental comparison with the reference instrument was also successfully performed at topic manager facilities. This instrument has therefore reached a TRL 5 and has been triplicated for further tests in real conditions, i.e. during real flight.

The air quality sensors developed in the project could guarantee the long-term monitoring of cabin air quality and therefore optimise health and safety of crew members and passengers from potentially harmful molecules.
Illutration on the development of the VOC analyser
Illutration on the development of the ozone analyser