Indirect methods are widely used for determining air exchange rates (AER) in naturally ventilated barns because they are relatively easier and cheaper than direct methods, which measure actual airflow in and out of the barns. The main goal of this study was to evaluate a common indirect method (CO 2 mass balance) against a direct method, and identify factors influencing this indirect method. The mean AER based on 24-h averaging, irrespective of method, ranged from 13 to 39 h −1 during the study-periods. The CO 2-balance method tended to overestimate barn AER. The cows' CO 2 production rate, in the current study, was estimated at 0.178 m 3 h −1 hpu −1 based on 24-h averaging. The CO 2-balance method with 24-h data averaging yielded more reliable barn AER than with shorter averaging times (i.e., 1, 2, and 12 h). The 1-h averaging, however, was chosen to analyze the effects of other pertinent factors on the CO 2balance method to capture diurnal variations of AER. Both wind speed and wind direction had significant effects on barn AER as well as the difference between the CO 2-balance method and direct method. Barn AER, in general, increased with wind speed. The CO 2-balance method was unreliable during milking times, and when indoor-outdoor CO 2 concentration and temperature differences were less than 70 ppm and 0°C, respectively.

This research examined the potential mitigation of NH3 emissions from dairy manure via an enhanced aerobic bio-treatment with bacterium Alcaligenes faecalis strain No. 4. The studies were conducted in aerated batch reactors using air and pure oxygen. Aeration with air and oxygen removed approximately 40% and 100% total ammoniacal nitrogen (TAN), respectively. Intermittent oxygenation (every 2 or 4 h) reduced oxygen consumption by 95%, while attaining nearly identical TAN removal to continuous aeration. The results revealed that adequate oxygen supply and supplementing dairy wastewater with carbon are essential for this bioprocess. Based on the nitrogen mass balance, only 4% of TAN was released as NH3 gas, while the majority was retained in either the microbial biomass (58%) or converted to nitrogen gas (36%). The mass balance results reveal high potential for environmentally friendly bio-treatment of dairy wastewater using A. faecalis strain No. 4 with respect to NH3 emissions.

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