Atmospheric Stability Measurements at a Swine Facility and An Adjacent Corn Field in Iowa.

Atmospheric stability conditions at the surface layer can determine direction and momentum transport of air contaminants. Near confined animal facilities, these transport processes can significantly impact air quality as these sites typically act as net point source of dust and odor constituents; however, little information is available on this respect. This study was conducted to assess year-round temporal patterns of atmospheric stability at a swine facility (S) compared with an adjacent commercial corn field (C) in the US Midwest. Two towers of 20 and 10 m heights for continuous micrometeorological measurements were respectively deployed in S (between buildings) and in C. Each tower was equipped with an eddy-covariance system at 6.8 m height, infrared thermometers (IRT), and 6 cup anemometers and 6 thermocouples installed at log-distributed heights. A complete weather station was deployed between S and C. Overall results from Richardson bulk number and Monin-Obukhov Length (z/L) calculations revealed predominant unstable conditions for S compared to C. During the August-March period, unstable cases (z/L ranging from -1 to -0.01) occurred 1.4 times more frequently for S than C (51 vs. 36%, respectively), while stable cases (0.01-1) were complementarily 2.2 times more frequent for C than S (40 vs. 18%, respectively). These patterns were partly associated with higher surface IRT values for S. Relatively greater diurnal heat capture at S (ground and roof surfaces) and a cooling off effect in C through active canopy transpiration may contribute to explain these z/L and IRT results. Prevalent atmospheric instability at S can suggest enhanced ascendant vertical transport of air pollutants perhaps causing their greater mixing/dilution with the atmospheric layer and/or their facilitated transport sorbed onto particles over farther distances from S. An enhanced understanding of these spatio-temporal atmospheric stability patterns can aid to identify effective odor mitigation strategies near commercial animal facilities.