Ammonia Radiometer

About

Ammonia is a pollutant which damages sensitive natural habitats and contributes to particulate pollution in urban areas. In its 2019 Clean Air Strategy, the UK government pledged to regulate to reduce ammonia emissions, nearly 90% of which come from farming. Conventional approaches of measuring ammonia emissions require samples to be taken back to a laboratory, which is a highly laborious process that does not offer real-time measurements. Optical based point sensors suffer from memory effects due to the sticky nature of ammonia and only offer a limited view of concentration profiles. Remote optical sensors overcome this issue but require precision alignment and are cumbersome to set up and maintain. STFC has developed a radiometer concept which will provide truly remote ammonia measurements using millimetre wave technology. This is achieved by detecting and spectrally analysing the microwave radiation that is naturally emitted by ammonia molecules. This is already an established technique in astronomy. The passive microwave/millimetre wave signal detection system builds upon state-of-the-art hardware developed by RAL Space at STFC. The radiometer is intended for use in the agricultural industry to carry out real-time remote monitoring of ammonia levels. An early warning system will flag rising ammonia levels, allowing mitigating measures to be taken. The effectiveness of these measures can then be evaluated. A concept system for radio frequency detection has been demonstrated in the lab. The next stage is to build on this design and develop an instrument specifically tailored for ammonia sensing. Expected detectability thresholds for various atmospheric scenarios have been studied using radiative transfer simulations.