Scheuren, Marie ; Université de Liège - ULiège > DER Sc. et gest. de l'environnement (Arlon Campus Environ.) > Surveillance de l'environnement
Romain, Anne-Claude ; Université de Liège - ULiège > DER Sc. et gest. de l'environnement (Arlon Campus Environ.) > Surveillance de l'environnement
Language :
English
Title :
FIRST DEVELOPMENT OF A GAS SENSOR ARRAY FOR MONITORING AMMONIA SURFACE EMISSION FLUX FROM GRASSLANDS
Publication date :
26 October 2021
Event name :
9th IWA Odour & VOC/Air Emission Conference
Event date :
du 26 octobre au 27 octobre 2021
Audience :
International
Funders :
SPGE - Société Publique de Gestion de l'Eau
Commentary :
Nitrogen is used in agriculture to fertilise croplands. During the spreading of fertilisers,
a substantial part of Nitrogen is lost by volatilisation of ammonia (NH3). These emissions are
responsible for unpleasant odours but are also mainly precursors of particulate matters (PM).
In Europe, agriculture is one of the main source of nitrogen-composed PM. There is a need to
collect more emissions data to understand better this activity impact. Measurement techniques
of NH3, used for ambient air quality monitoring, are expensive and heavy to manage for the
agricultural sector. Other techniques, less expensive, like passive sampling are also used to
estimate ammonia flow but these are not adapted for a continuous monitoring. It’s why we
suggest to customise our usual e-nose devices to ammonia emissions from fertilised
grasslands.
The sensor array is built using six commercial metal oxide semiconductor sensors. The
sensors are inserted radially and evenly into a small size cylindrical PTFE chamber. Four of
the selected sensors are sensitive to ammonia, one is sensitive to VOC and the last one is for
combustible gas. The sensor resistance, the temperature and the humidity are recorded. A
pump is used to suck air out of the sensor chamber, the flow being regulated at 200ml/min.
Ammonia concentration is measured with acid-soaked filters, this methodology is firstly
developed in the lab. In order to determine the NH3 concentration in the atmosphere, we
perform experiments with known NH3 concentration. Ammonia is fed into a system using mass
flow controllers and commercial analytical air cylinder to dilute the gas down to the ppb level.
Synthetic air is humidified at different values. Then, an organic fertilisation experiment was
carried out on a grassland, with cattle slurry. The acid-soaked filters device and the sensor
array were placed on the field at 30 cm over the vegetation. Odour samples are taken in
addition to these two measurements for dynamic olfactometry analysis, also at 30 cm over the
vegetation.
The results show that de acid-soaked filters device effectively traps NH3 and can
therefore be used to determine the NH3 concentration in the air. This first experience of
monitoring a nitrogen fertilisation with a metal oxide sensor array, shows that the instrument is
able to clearly discriminate the change in air composition during the first 2 hours after the
application of slurry. However, these results do not seem to be correlated with the odour
concentration, which is stable during the first day after fertilisation.
