Chemistry and the Environment, Contributed Talk (15min)

NMVOC, CH4 and NH3 emissions of different silage-based diets for dairy cows at herd level

D. Steger1, S. Schrade2, M. Zähner2, M. Hill1, K. Zeyer1, S. Reimann1, F. Dohme-Meier2*, J. Mohn1*
1Empa, Laboratory for Air Pollution / Environmental Technology, 8600 Dübendorf, Switzerland, 2Agroscope, Ruminants research unit, 8356 Ettenhausen, Switzerland

Agricultural activities, such as dairy cattle farming in perticular, make a substantial contribution to the Swiss methane (CH4) and ammonia (NH3) emissions [1, 2]. In addition, dairy farming is also a relevant source for non-methane volatile organic compounds (NMVOCs) [3]. Since summer 2015, Agroscope and Empa assess CH4, NH3 and CO2 emissions from dairy cows at the experimental housing for emission measurements, Waldegg, Switzerland [4]. The housing consists of two spatially separated compartments, each for 20 cows, which allows comparative quantification of emissions simultaneously. A dual tracer-ratio method with SF6 and SF5CF3 is applied to determine emissions under natural ventilation and detect cross-contamination [5]. For two years, 2018 and 2020, the focus was additionally on NMVOC emissions under different feeding regimes, silage-based vs. silage-free (2018) and different silage types with and without additives (2020). NMVOC emissions were determined using different analytical techniques, such as gas chromatography with flame ionisation detector (GC-FID) and a total hydrocarbon monitor (THC), while C4, CO2 and NH3 concentrations were quantified using cavity ring down spectroscopy. NMVOC emissions in the compartments with the silage-based diet were generally dominated by ethanol followed by methanol and ethyl acetate. Summer measurements showed around 70% lower ethanol emissions in the compartment with the silage-free diet compared to the silage-based diet. In autumn and winter, ethanol emissions in the silage-free compartment were even lower - in the range or below the detection limit. Based on the collected NMVOC emission data, the statistical model and metrological data from MeteoSchweiz we established a model-based calculation to estimate yearly NMVOC emissions for dairy cattle in mountain and plain regions under different feeding regimes.

[1] Federal Office for the Environment FOEN, Switzerland’s Greenhouse Gas Inventory 1990–2019, 2011, 643.
[2] Kupper, T., et al., Ammoniakemissionen in der Schweiz 1990-2010 und Prognose bis 20202013, 110.
[3] Bühler, M., Agricultural emissions of NMVOC and PM, 2018,  51.
[4] Schrade, S., et al., Versuchsstall zur Entwicklung und Quantifizierung von Massnahmen zur Minderung von Emissionen, 2015, 450–455.
[5] Mohn, J., et al., Atmospheric Environment2018, 179, 12–22.