Ammonia Emissions from a Western Open-Lot Dairy

Abstract

Manure on dairies is the second largest agricultural source of ammonia emissions. Ammonia (NH3) emissions were measured at a 3400-cow open-lot dairy in Texas using a backward Lagrangian Stochastic model in combination with measurements from long-path tunable diode lasers and on-site sonic anemometers. Measurements were made for multiple weeks at a time for most seasons over two years. Both 30-min and daily average emissions were influenced by air temperature consistent with a van ’t Hoff equation. Emissions were also linearly related to saturation vapor density deficit. The influence of temperature on NH3 solubility, expressed by the van ’t Hoff temperature correction function, decreased as the water vapor deficit increased. The mean annual daily NH3 emissions at the farm was estimated at 82 g NH3 d−1 per animal (105 g NH3 AU−1 d−1, 1 AU = 500 kg) with mean emission during the summer of 124 g NH3 d−1 per animal (159 g NH3 AU−1 d−1). A distinct diurnal pattern in NH3 emissions was consistent with diurnal patterns in wind speed, saturation vapor density deficit and air temperature. The mean daytime emissions were twice the mean nighttime emissions. Additional studies are needed to evaluate the frequency of high emission days during the summer.