Airborne eddy covariance measurements of agricultural nitrous oxide and methane emissions in the Netherlands
In June 2023, DLR scientists from the Institute of Atmospheric Physics together with the DLR facility Flight Experiments successfully conducted an airborne measurement campaign to determine agricultural nitrous oxide (N2O) and methane (CH4) emissions in the Netherlands. This campaign is part of the DLR internal Greenhouse Gas Monitoring Project (GHGMon), which aims to develop and evaluate new measurement systems (in situ and remote sensing) and model solutions for the analysis of industrial N2O and CH4 emissions - especially from area sources such as agriculture.
After carbon dioxide (CO2), CH4 and N2O are the second and third most important long-lived greenhouse gases emitted by humans. Anthropogenic emissions of N2O and CH4 have led to a strong increase in atmospheric concentrations since the beginning of industrialisation and thus to a warming of the atmosphere. To mitigate this warming and thus still meet the 1.5°C target of the Paris Climate Agreement, anthropogenic emissions must be drastically reduced. Agriculture plays a central role in this (see Chapter 5.2 in IPCC AR6 WG1). It is by far the most important anthropogenic source of N2O, especially through the use of synthetic nitrogen fertiliser. But also for CH4, agriculture (particularly livestock and rice cultivation) is the largest anthropogenic emission sector. However, the development of effective emission reduction strategies is complicated by the fact that emissions are poorly understood on a regional scale. For one thing, the underlying processes are complex. For another, they are area sources that are very challenging to measure. The aim of the GHGMon aircraft measurement campaign is to test and apply new methodologies to measure area sources and thus better understand regional N2O and CH4 emissions from agriculture.
The Netherlands was selected as the study area for our aircraft measurement campaign. The Netherlands hosts one of the most intensive agricultural systems in the world and is therefore a hotspot of agricultural N2O and CH4 emissions, not only in European comparison, but globally. To investigate these, a measurement system for airborne eddy-covariance measurements of N2O and CH4 was modified for the measurement campaign. The eddy covariance approach allows the calculation of emission fluxes from measurements of trace gas mixing ratios and associated vertical winds. The method is widely used and established in ground-based measurement systems. Its use in aircraft should now enable emission measurements of agricultural land sources on a regional scale.
As part of our measurement campaign, 15 research flights were carried out with the DLR Cessna in the Netherlands. The team was stationed in Lelystad for three weeks. Using the latest in situ measuring systems, which were specially optimised for use on an aircraft, 45 hours of scientific data were collected. The focus was on concentration and flux measurements of N2O and CH4. But also other trace gases (e.g. CO, C2H6) and isotopologues (13CH4) were measured to better characterise sources and to better understand underlying processes. In the coming months, the DLR scientists will process, evaluate and publish the data. The focus will be on evaluating the new eddy covariance measurement system and quantifying agricultural emissions in the sampled areas. Finally, with the help of local partners, our results will be evaluated and set into context.