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.