Carbon monoxide fluxes measured using the eddy covariance method from an intensively managed grassland in Ireland

Abstract

Carbon monoxide (CO) is classed as a secondary greenhouse gas (GHG) as it can extend the lifetime of GHGs such as methane and ozone by reacting with hydroxyl (OH) radicals and thus controlling the oxidizing capacity of the atmosphere. CO fluxes were measured from a fertilized and grazed temperate grassland in south-east Ireland using a high frequency quantum cascade laser (QCL) and the eddy covariance method. Measurements were carried out in 2019 (12 months) and 2020 (10 months). In both datasets, a diurnal pattern was observed where CO fluxes peaked between 8 am and 6 pm, and between 8 pm and 2 am during the colder months of the year. Quality controlled CO flux data was gap-filled using a general additive model (GAM) that incorporated photosynthetic photon flux density (PPFD), air temperature, water-filled pore space (WFPS) and month of the year. Modelled CO emissions showed less divergence with measured CO fluxes in 2020 compared to 2019, suggesting that the environmental variables in the GAM were the predominant driver of CO emissions in 2020 but not in 2019. Cumulative CO emissions in 2019 and 2020 were 39.7 ± 147.1 mg_CO–C per m² per month and 31.5 ± 75.2 mg_CO–C per m² per month, respectively. While soils are typically considered a sink of CO, our results show that managed pastures can act as a source of CO and thus warrant further investigation into the implications CO may have on GHG dynamics from agricultural landscapes.