ARS | Publication request: Standardization of flux chamber and wind tunnel flux measurements for quantifying volatile organic compound and ammonia emissions from area sources at animal feeding operations

Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 26, 2012
Publication Date: February 1, 2013
Citation: Parker, D.B., Ham, J., Woodbury, B.L., Cai, L., Spiehs, M.J., Rhoades, M., Trabue, S.L., Casey, K., Todd, R.W., Cole, N.A. 2013. Standardization of flux chamber and wind tunnel flux measurements for quantifying volatile organic compound and ammonia emissions from area sources at animal feeding operations. Atmospheric Environment. 66:72-83.

Interpretive Summary: Environmental regulations enforced by the USEPA now require the reporting of air emissions from animal feeding operations. Portable wind tunnels and flux chambers are one method used to quantify air emissions from large area sources such as pens and lagoons. The flux chamber or wind tunnel is placed over the emitting surface, clean air is passed through the chamber, and the air emissions are measured. There have been many different designs of flux chambers and wind tunnels. One problem with chamber-type measurements is that the emission rate changes depending on the air flow rate passed through the chamber, leading to highly variable and potentially inaccurate emission estimates. Because of this variability, there is a need to standardize flux chamber and wind tunnel measurements so that results can be compared on an ‘apples to apples’ basis. In this paper, we present a simple methodology for standardization and comparison of different chamber types by measuring water evaporation within the chamber. We also demonstrate a field-based method for improving the accuracy of emission estimates with a correction factor that relies on evaporation estimates within and outside of the flux chamber.

Technical Abstract: A variety of wind tunnels and flux chambers have been used to measure fluxes of volatile organic compounds (VOC) and ammonia (NH3) at animal feeding operations (AFO). However, there has been little regard to the extreme variation and potential inaccuracies caused by inappropriate air velocity or sweep air flow rates. There is a need to standardize flux chamber and wind tunnel measurements. In this paper, we present results of evaporative and VOC flux measurements with the EPA flux chamber and a small wind tunnel. In the EPA flux chamber, evaporative flux was positively correlated with sweep air flow rate (SAFR) between 1 and 20 L/min (r2=0.981-0.999) and negatively correlated with sweep air relative humidity between 0 and 80% (r2=0.982-0.992). Emissions of gas-film controlled compounds like NH3 and VOC at AFOs were positively correlated with evaporation rates between 0.6 and 2.8 mm/d. We propose a simple methodology for standardizing and comparing different chamber types by measuring water evaporation within the chamber using a mass balance approach under controlled laboratory conditions. As demonstrated in a case study, an evaporative flux ratio correction factor (EFRCF) improved the accuracy of field-measured chamber flux measurements. In the field study, both the EPA flux chamber (SAFR = 5 L/min) and small wind tunnel (SAFR = 1 L/min) underestimated the true field emissions of VOC, with EFRCFs of 2.42 and 3.84, respectively. EFRCFs are recommended for all but the driest of soil and manure conditions.