Greenhouse gas emissions from naturally ventilated freestall dairy barns

Abstract Greenhouse gas (GHG) emissions from two naturally-ventilated dairy freestall barns measured for a total of 21 d, one week each in May, July, and September 2009, are presented in this article. The holding capacity of Barn 1 (B1) was 400 Holstein cows, while that for Barn 2 (B2) was 850 cows. Air samples were taken from inlets and outlets of the barns via a custom made multiplexer gas sampling system for measurement of gas concentrations using a photoacoustic infrared multigas analyzer. Barn ventilation rates were based on air velocity measured with arrays of 3-D ultrasonic anemometers at inlets and outlets. Gas concentrations (10 min means) in the barns ranged from: 443–789 ppm for CO 2 , 0.0–39.4 ppm for CH 4 , and 0.25–0.39 ppm for N 2 O; with mean concentrations ranging from 6 to 20%, 0 to 4%, and 26 to 180% above the average background concentrations for CO 2 , N 2 O, and CH 4 , respectively. The correlations between CO 2 and CH 4 enhanced concentrations were relatively stronger ( R of 0.67–0.74) than between CO 2 and N 2 O enhanced concentrations ( R of 0.10–0.20). Environmental conditions did not significantly ( p  = 0.46) impact the enhanced concentrations of N 2 O in the barns. All three parameters ( T , RH , and v ) had significant ( p 2 enhanced concentrations; while only T ( p v ( p 4 enhanced concentrations. Enhanced concentrations of CO 2 and CH 4 correlated negatively with all three parameters. The influence of the temperature-humidity index ( THI ) on CO 2 enhanced concentrations was higher than that of v ; while the effect v had on CH 4 enhanced concentrations was slightly higher than that of the temperature-humidity index. The average emissions, based on hourly means, ranged from 5.3 to 10.7 kg d −1  AU −1 for CO 2 ; 0.3 to 2.5 g d −1  AU −1 for N 2 O; and between 67 and 252 g d −1  AU −1 for CH 4 . Nitrous oxide emissions from the smaller barn, B1 (0.4–2.5 g d −1  AU −1 ), were significantly higher than from the larger barn, B2 (0.3–0.5 g d −1  AU −1 ) most probably because 50% of B1 was open (no stalls) loose dirt floor.