Methods

 
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Mass Balance

By assuming a constant source emission, transects measuring trace gases upwind and downwind of a source can be used to infer the emission rate of the source. Few assumptions need to be made making this an ideal method to monitor large sources that can be measured with an aircraft.

This technique is suitable for measuring emissions from moderately sized point sources to regional emissions. Currently, we are using this technique to quantify methane and ammonia emissions from the agricultural sector in the TRANS2AM project.

 
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Dispersion Modeling

The dispersion of reactive and non-reactive gases in the atmosphere is necessary for many ground based techniques. The modeled concentration of target species can be related to the actual measurements to infer the emission rate. There can be significant uncertainty when using such methods as dispersion modeling relies upon assumptions and simplifications of a dynamic environment. We work on understanding the best measurement practices for dispersion modeling based measurements.

The most straightforward approach to ground based dispersion modeling is to use the Gaussian plume model.

 

Aircraft Eddy Covariance

The vertical transport of scalars such as heat, water, carbon dioxide and methane is used to quantify the impact of sources that span large areas (in other words, non-point sources). Eddy covariance is the technique of using high resolution (>10 Hz) measurements of scalars and vertical wind to calculate this flux. When used at a stationary site, this results in a time averaged signal. However, as the aircraft travels in time, the value calculated by aircraft is averaged in space. Signal analysis can be used to produce spatially resolved fluxes along the flight path that can provide more spatial information or be used for satellite validation.

 

Instrumentation

The Picarro G2311-f installed in the UW King Air

We use state of art commercially available instrumentation to measure trace gases in the atmosphere. These instruments provide the high precision and/or high frequency necessary for their intended use.

  • Aerodyne Mini Ethane Analyzer

  • Picarro G2311-f 10 Hz CO2/CH4/H2O Analyser

  • Picarro G2401-m CO2/CH4/CO/H2O Analyser

  • Aeris Ultra CH4/C2H6 Analyzer

  • Aeris Ultra CO/N2O Analyser