Conference Agenda

Hydrogen (H₂) is expected to become an increasingly important energy carrier during the energy transition. This will likely cause increased levels of atmospheric H₂, due to unavoidable losses during the production, transport, storage, and usage of hydrogen. Multiple studies have shown that through interaction with the hydroxyl radical, global tropospheric and stratospheric composition could be impacted, however a large uncertainty remains due to a lack of understanding of the global hydrogen budget. A key feature of the global hydrogen cycle is the strong kinetic isotope effects due to the large mass difference between H₂ and HD. The resulting large differences in ²H/¹H isotope ratios help constrain constrain the magnitudes of sources and sinks in the global hydrogen budget.

For the first time, we present a comprehensive global hydrogen budget derived using a coupled H₂-HD inversion framework embedded within the three-dimensional chemical transport model TM5. This budget is obtained using a global set of 178,640 H₂ mole fraction measurements and 540 δD(H₂) measurements, which are subsequently supplied to the CarbonTracker data assimilation system. Using its ensemble Kalman filter approach we estimate the magnitude and spatial distribution of monthly global hydrogen emissions, chemical production and losses for the period 2003–2023. To evaluate the robustness of our results, we compare optimized simulated hydrogen mole fractions with independent observational data from aircraft profiles collected during the IAGOS-CARIBIC, NOAA/ESRL, and ATom campaigns. We also compare optimized ²H/¹H isotope ratios with available IAGOS-CARIBIC profiles but note that additional measurements would strengthen our evaluation.

Organic aerosols (OA) account for a large fraction of particulate matter. Throughout their life-time the composition of OA is continually changed by chemical reactions in the atmosphere. Due to the complexity of the organic aerosol, there is no clear chemical tracer of these atmospheric transformations. In this work we investigate in a laboratory study, if stable carbon isotopic signatures can be used as a tracer of certain aging processes.

We produce organic aerosol by the combustion of biomass and coal and expose it to atmospheric aging in a Potential Aerosol Mass (PAM) Oxidation Flow Reactor. We collect organic aerosol on two filters, the primary filter collected directly after the combustion chamber and the second one after the aging reactor. We measure d¹³C in OA desorbed from filter samples at three different temperature steps, which correspond to different volatility fractions of the OA.

Aging in the PAM reactor strongly changes the d¹³C values of the organic aerosol. The aged filters have overall lower d¹³C values than the primary filters, which can be explained by the strong secondary organic aerosol (SOA) formation in the PAM reactor, with the reaction products (low d¹³C) condensing on the primary aerosol. Moreover, we can see that characteristic changes in d13C at the different temperature steps, indicating that reaction products mainly accumulate at most volatile and least volatile OA fractions. The accumulation in the most volatile OA fraction can be explained by the fact that the condensing SOA is quite volatile. The accumulation of reaction products in the least volatile fraction can be explained by photolysis and oxidation reactions on the particles that produce less volatile organic compounds.

The experiments show the strong potential of carbon isotope analysis to unravel aging pathways in the ambient atmosphere.