Measuring ammonia fluxes using relaxed eddy accumulation and continuous gas analysis

Emissions of ammonia from areal sources, especially those from agricultural operations, may be a significant portion of the reactive nitrogen inventory. A relaxed eddy accumulation system was developed and tested to measure near-continuous ammonia fluxes from cattle feedlot pens – sites with daytime ammonia fluxes between 50 and 150 micrograms/m2/s. A tower based conditional sampler was used to obtain independent samples of up- (C_up) and down-moving (C_dn) eddies. Samples were routed to a cavity ring down analyzer and an ion mobility spectrometer operating in time-share mode for determining ammonia concentration differences (C_up–C_dn). The sampling and analysis system included adaptive sampling schemes to reduce uncertainty in the 30-min flux estimates. Collocated measurements of CO2, water vapor, and heat flux also were made to parameterize the performance of the conditional sampler. Discussions will include simulation of a synthetic instrument in agricultural and native settings coupled with preliminary results from field testing along the Front Range of Colorado. Results will be compared to other micrometeorological measurement techniques and mass balance studies of feedlot nitrogen transport.