Costs of GHG sensors

Micro-meteorological are costly from both financially and in their requirements. The use of micrometeorological techniques requires homogenous fields which are not influenced by surrounding infrastructures such as trees or buildings. This techniques is frequently used on flat terrains where homogeneity exists in soil properties, vegetation and land-use such as grasslands, maize or wheat mono-crop systems. The capital costs required to run these measurements are high. This is due to the apparatus involved – 3D fast-response, wind field gas analyzers, auxiliary instruments (such as meteorological stations. For CO2 measurements at a single sight costs can vary between 60,000-80,000 USD. Costs accumulate even further if additional gases are measured (approximately 30,000 – 40,000 depending on the gas). For example, to measure CH4 open gas sensors are required and likewise, N2O emissions require spectroscopy instruments. Chikowo et al. (2014) suggests micro-meteorological techniques for studying GHG exchange are not ideal for smallholder systems as a result of the complexity associated with this techniques for soil and land properties/management.

The cheaper alternative is chamber measurements. Automated systems (which are identical to static chambers in design) can incorporate in-field gas analysers or alternatively gas samples can be stored in vials and examined in the laboratory later. Capital costs vary according to the choice of gas analysis technology, system configuration (for e.g. the use of an in-field gas analyiser or not) and operational costs. According to de Klein and Harvey (2015), a system that employs 12 chambers as well as an in-field gas analyser, gas chromatography is the cheapest option valuing at approximately 100,000 USD. This method facilitates calculating GHG emissions at a fine scale as chambers cover areas of <1m2. This makes them more favourable for smallholder farmers in Ireland than micro-meteorological techniques. Furthermore, chamber measurements provide storage space for gas samples for future analysis and do not need a power supply at the site. In contrast, data collected from micro-meteorological measurements are more prone to disturbances as installation of the chamber influences the surrounding environmental conditions.

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