Although there are more than 200 odor-causing volatile organic compounds (VOCs), phenol and p-cresol are two prominent odor-causing VOCs found downwind from concentrated animal feeding operations (CAFOs). The VOC emissions from cattle and dairy production are difficult to quantify accurately because of their low concentrations, spatial variability, and limitations of available instruments. To quantify VOCs, a protocol following U.S. Environmental Protection Agency (EPA) Method TO-14A has been established based on the isolation flux chamber method and a portable gas chromatograph (GC) coupled with a purge-and-trap system. The general objective of this research was to quantify phenol and p-cresol emission rates (ERs) from different ground-level area sources (GLASs) in a free-stall dairy during summer and winter seasons using this protocol. Two-week-long sampling campaigns were conducted in a dairy operation in central Texas. Twenty-nine air samples were collected during winter and 37 samples were collected during summer from six specifically delineated GLASs (barn, loafing pen, lagoon, settling basin, silage pile, and walkway) at the free-stall dairy. Thirteen VOCs were identified during the sampling period and the GC was calibrated for phenol and p-cresol, the primary odorous VOCs identified. The overall calculated ERs for phenol and p-cresol were 2656 ± 728 and 763 ± 212 mg hd⁻¹ day⁻¹, respectively, during winter. Overall phenol and p-cresol ERs were calculated to be 1183 ± 361 and 551 ± 214 mg hd⁻¹ day⁻¹, respectively, during summer. In general, overall phenol and p-cresol ERs during winter were about 2.3 and 1.4 times, respectively, higher than those during summer.

Enteric methane (CH4) accounts for about 70% of total CH4 emissions from the ruminant animals. Researchers are exploring ways to mitigate enteric CH4 emissions from ruminants. Recently, nano zinc oxide (nZnO) has shown potential in reducing CH4 and hydrogen sulfide (H2S) production from the liquid manure under anaerobic storage conditions. Four different levels of nZnO and two types of feed were mixed with rumen fluid to investigate the efficacy of nZnO in mitigating gaseous production. All experiments with four replicates were conducted in batches in 250 mL glass bottles paired with the ANKOMRF wireless gas production monitoring system. Gas production was monitored continuously for 72 h at a constant temperature of 39 ± 1 °C in a water bath. Headspace gas samples were collected using gas-tight syringes from the Tedlar bags connected to the glass bottles and analyzed for greenhouse gases (CH4 and carbon dioxide-CO2) and H2S concentrations. CH4 and CO2 gas concentrations were analyzed using an SRI-8610 Gas Chromatograph and H2S concentrations were measured using a Jerome 631X meter. At the same time, substrate (i.e. mixed rumen fluid+ NP treatment+ feed composite) samples were collected from the glass bottles at the beginning and at the end of an experiment for bacterial counts, and volatile fatty acids (VFAs) analysis. Compared to the control treatment the H2S and GHGs concentration reduction after 72 h of the tested nZnO levels varied between 4.89 to 53.65%. Additionally, 0.47 to 22.21% microbial population reduction was observed from the applied nZnO treatments. Application of nZnO at a rate of 1000 μg g− 1 have exhibited the highest amount of concentration reductions for all three gases and microbial population. Results suggest that both 500 and 1000 μg g− 1 nZnO application levels have the potential to reduce GHG and H2S concentrations.