Assessing the co-emission of methane and hydrogen from dairy farms in the Netherlands

The atmospheric composition plays a crucial role in the climate through radiative forcing and chemical processes. Although hydrogen (H₂) is not a greenhouse gas itself, it indirectly influences the climate by affecting methane (CH₄) lifetime and atmospheric chemistry. To date, H₂ emissions have not been studied extensively, limiting our ability to detect trends in a changing economy. Recently, efforts have been made towards developing the first European anthropogenic hydrogen budget by combining bottom-up estimates with spatially resolved activity data. Focusing on the correlation between H₂ and carbon monoxide (CO), e.g., fingerprinting, helps further identify H₂ emissions from combustion sources. Even though this technique works well for combustion sources, it does not allow for the inference of fluxes from non-combustion sources.

In this study, we aim to extend the fingerprinting method by examining the correlation between CH₄ and H₂ emissions from dairy farms, following previous studies that showed that H₂ and CH₄ emissions from dairy cows are dynamically linked. To this end, flask samples were collected at different locations on a dairy farm to determine the correlation between the two trace gases for sub-farm-scale sources. Additionally, this study quantified full-farm H₂ and CH₄ emissions by using the active AirCore technique on a UAV platform. The CH₄-H₂ correlations observed at point sources within the farm and those within the full-farm emission plume are found to be consistent with each other. Upscaling based on the well-constrained Dutch national inventory of dairy farming CH₄ emissions, we present an initial estimate of national total H₂ emissions from dairy farming.