Concentrations of NOx (NO þ NO2) were monitored downwind from a Central California dairy facility
during 2011 and 2012. NOx concentrations at the dairy were significantly higher than the background
levels during August 2011 primarily due to the presence of elevated NO, but were indistinguishable from
background concentrations during January and April 2012. A Gaussian plume model (AERMOD) and
a Lagrangian back trajectory model (Wind Trax) were used to estimate the flux of NO from the dairy
during August 2011 with the assumption that emissions were primarily from animal feed. NO emissions
from silage were also directly measured from feed to provide additional insight into the sources. Isolation
flux chamber measurements imply an NO flux from the feed of about 1.3 103 g m2 h1
, but these
relatively low fluxes are inconsistent with the elevated NO concentrations observed during August 2011.
This implies that either the flux chamber method grossly underestimates the true NO emissions from
feed, or that most of the ambient NO measured at the dairy is from other sources. Emissions from farm
machinery may account for the NO concentrations observed. Animal feed thus appears to be a small
contributor to NOx emissions within Central California.