Empa - Air Pollution / Environmental Technology

Emissions and Isotopes

The Group for Emissions and Isotopes provides analytical tools and technical know-how for the characterization and quantification of air pollution. We serve the industry, policy makers and the public with a thorough understanding of anthropogenic and natural emissions. Our main activities focus on the analysis of trace gases and their isotopes to quantify emissions, identify precursors and trace transformation pathways. An overview of ongoing project activities can be found below.

Stable isotopes (H, C, N, O)

We research the naturally occurring variations of hydrogen, carbon, nitrogen and oxygen isotopes in changing environmental settings. Many of our projects center around potent non-CO2 greenhouse gases: nitrous oxide (N2O) and methane (CH4), their emissions from different processes and driving parameters. The relative abundance of nitrogen and oxygen isotopes in a N2O molecule or carbon and hydrogen isotopes in a CH₄ molecule is different depending on its origin (see Figure).

Isotopic signatures of nitrous oxide liberated from aerated (blue) and anoxic (red) zones of a wastewater reactor (Gruber et al., WRX, 2022).

Clumped isotopes

In recent years, we extended our isotope “toolbox” for the study of very rare doubly substituted isotopic species of N₂O and CH₄, which we expect to improve our understanding for a wide range of processes - from the microbial scale to the tectonics history.

Radiocarbon

Radiocarbon analysis in carbon dioxide (CO₂) is the most direct tool to distinguish between renewable sources and fossil fuel combustion, and to support mitigation efforts towards carbon neutrality. We are establishing the first analytical tool for continuous radiocarbon analysis in atmospheric CO₂. The instrumental setup will comprise a SCAR radiocarbon spectrometer and a home-built QCLAS spectrometer for ¹³CO₂/¹²CO₂, both coupled to an automated preconcentration device to separate and purify CO₂ from air.

Analytics: Preconcentration - Laser spectroscopy

Central to most of our work is laser spectroscopy. We run customized and off-the-shelf spectrometers tuned for various singly or doubly isotopically substituted greenhouse gases. If very rare isotopic species or high precision measurements are targeted we interface our spectrometers with custom-built, automated preconcentration devices.

Simplified depiction of the CleanEx flow layout for methane preconcentration and introduction into a QCLAS device (Prokhorov and Mohn, Analytical Chemistry, 2022).

Diffuse emissions / tracers

Many emission sources we are studying are not point sources or ducted but fugitive. Important examples are agricultural emissions from soils and animal housings. In collaboration with our research partner Agroscope, we implemented a tracer ratio method in a naturally ventilated experimental dairy housing in Tänikon. Analyzing the diluted tracer gases together with the target gases of our study, e.g. ammonia, methane, VOCs, we can estimate their mass emissions.

Experimental dairy housing for emission measurements of Agroscope near Tänikon and schematics of the dual tracer dosing and analytics. The design of the housing allows to evaluate the mitigation efficiency for different construction and feeding (Mohn et al., Atmospheric Environment, 2018).

Ongoing projects

IM4CA: Investigating Methane for Climate Action 2025-2028
MetHIR: Metrology for harmonisation of field isotope ratio measurements 2025-2028
MetCTG: Metrology for comparable and trustworthy greenhouse gas remote sensing datasets 2025-2028
CITRA: Clumped isotopes: a transformative tool for understanding aquatic nitrous oxide cycling 2025-2026
isoMET: Metrology for European emissions verification on methane isotopes 2022 - 2025
PARIS: Process attribution of regional emissions 2023 - 2027
quantiAGREMI: On farm quantification of ammonia and greenhouse gas emissions from livestock production 2022 - 2025
graziQ-house: Quantification and modelling of housing-based emissions 2023 - 2027
SCENE: Swiss Center of Excellence on Net-Zero Emissions 2023 - 2026
7up: Exploiting the potential of simultaneous analysis of seven singly and doubly substituted N₂O isotopocules to disentangle production pathways 2022 - 2026
CLUMPME: Clumped isotopes of methane and dolomite to assess the thermal history of orogens and the origin of thermogenic methane 2021 - 2025

Recently ended projects

STELLAR: Stable isotope metrology to enable climate action and regulation 2020 - 2023
AERCOW: Experimental dairy housing for quantifying methane and ammonia emission abatement strategies under entire herd conditions 2018 - 2022
ISOMOL: Advanced understanding of autotrophic nitrogen removal and associated N2O emissions in mixed nitritation-anammox systems through combined stable ISOtopic and MOLecular constraints 2017 - 2022