ARS | Publication request: A BOUNDARY LAYER SAMPLING METHODOLOGY FOR MEASURING GASEOUS EMISSIONS FROM CAFO'S

Submitted to: Proceedings of the Workshop on Agricultural Air Quality: State of the Science
Publication Type: Proceedings
Publication Acceptance Date: April 3, 2006
Publication Date: June 1, 2006
Citation: Marcillac, N.M., Hanan, N.P., Lee, T., Follett, R.F., Johnson, D.E. 2006. A boundary layer sampling methodology for measuring gaseous emissions from CAFO's. Proceedings of the Workshop on Agricultural Air Quality: State of the Science.

Interpretive Summary: The air sampling methodology outlined here has been validated as an effective means of collecting N species (nitric acid, ammonia, and ammonium) with filter packs, as well as trace gases (methane, carbon dioxide, nitrous oxide) with syringe pumps. The use of weather monitoring equipment (tethersondes used here), is vital to the validity of this data, as the wind speed dictates the spread of the plume, the wind direction the collection efficiency, and the temperature, pressure and RH the concentration of the gas or particle species. We have illustrated that the wind direction can pose difficulties in the collection of data, as any shift will change the collection concentration of the gas species. We have made our samplers mobile in order to adjust for this dilemma, but sample times must be compromised if a change in location is necessary. The mobility of the system makes it easy to use over the course of the day by maintaining a downwind location. Additionally, this method gives the concentration of species at five different heights, showing the different vertical profiles. This could prove to be a very valuable tool in selecting monitoring heights of different gas and particle species.

Technical Abstract: Various methodologies have been employed to measure CAFO emissions (e.g. flux chambers, lasers, and stationary towers), but these methods are usually limited in their ability to fully characterize the emission plume from a heterogeneous farm, and thus are limited in their ability to quantify total emissions. We present a whole farm measurement system that overcomes these limitations by sampling concentration and wind speed profiles to characterize the horizontal and vertical extent of the plume at relatively high temporal resolution (30-120 min). The system is designed to measure trace gases (carbon dioxide, methane, and nitrous oxide) using syringe pumps, and N species (nitric acid, ammonia, and ammonium) using specially designed filter packs. The validity of the gas and particle samples obtained by our system needed to be assessed by testing the method and set-up used for recovery of the atmospheric gases. For the trace gas sampling, we conducted a field test using methane gas as a recovery gas. The filter packs, used for N recovery, were tested in the lab for recovery potential, then field validated with URG denuder samplers.