Production, Management and the Environment: Environment

The number of dairy cows in Idaho has increased by approximately 80% in the last decade with concentrated dairy production facilities being the norm. The majority of these production facilities are located in southern Idaho, which has generated regional air quality concerns. To determine the potential air quality impacts of these facilities, we determined emissions of ammonia (NH3) and methane (CH4) during four seasons on a 700 cow open-lot dairy (small) using open-path Fourier transform infrared spectrometry (OP/FT-IR) and over a one-year period at a 10,000 cow open-lot dairy (large) using a photoacoustic field gas monitor. Measurements were made at a background location and over the open lots at the small dairy or at the center of the lots at the large dairy. Average NH3 concentrations over the lots at the small dairy were between 0.13 to 0.41 ppmv, while concentrations at the large dairy were between 0.39 and 0.74 ppmv. Average CH4 concentrations over the lots at the small dairy were between 2.2 to 3.0, while concentrations at the large dairy were between 2.1 and 6.6 ppmv. Ammonia emission rates, calculated by the WindTrax model, ranged between 0.04 to 0.25 kg NH3/cow/day for the small dairy and 0.12 to 0.19 kg NH3/cow/day at the large dairy. Methane emission ranged between 0.20 to 0.55 kg CH4/cow/day for the small dairy and 0.33 to 1.23 kg CH4/cow/day for the large dairy. At these average emission rates, farms with greater than approximately 1,650 cows would be required by the State of Idaho to adopt best management practices to reduce ammonia emissions through a permit by rule.