Context

Cities are hot spots of anthropogenic greenhouse gas (GHG) emissions. Recognizing this, cities across the world, including Vienna, have announced ambitious net zero targets. However, the efficacy of mitigation may be compromised by uncertainties in municipal GHG inventories. Observations and atmospheric modeling can provide powerful solutions to independently monitor progress of urban climate mitigation policy and enhance transparency. Constraining Vienna’s Carbon Footprint (CVCF) will build upon the infrastructure, partnership and findings of the Vienna Urban Carbon Laboratory (VUCL), which established a tall-tower research station measuring CO2 and CH4 fluxes, concentrations and stable isotopes in Vienna’s city center. In addition to continuing these measurements, CVCF will establish a peri-urban observation station in the Vienna Woods and develop a new clumped-isotope method to better distinguish traffic emissions from biogenic sources of CO2. To unlock the full potential of these measurements for quantifying Vienna’s CO2 and CH4 emissions, CVCF will use atmospheric transport modelling. The project will develop a completely novel isotope-enabled inverse modelling framework that will combine the information contained in the various measurements. The foreseen system will take advantage of both the highly resolved but spatially limited information contained in the flux footprints as well as the less resolved yet spatially more extensive concentration footprints. This approach will set new standards for urban-scale inverse modelling, to make best use of tall-tower observations of both GHG fluxes and concentrations. The resulting multi-scale inversion system will also be able to constrain urban GHG emissions simultaneously and fully consistently with the GHG emissions on larger scales (e.g., national or European)  

Objectives:

CVCF aims to make a substantial scientific contribution to the international research and development on top-down urban emissions monitoring. CVCF has the following concrete objectives:

• To continue concentration, flux and isotope measurements of CO2 and CH4 at the tall-tower station in Vienna’s city centre. The continuation will yield a 10-year CO2 flux time series that began in 2017.
• To establish and operate a similarly equipped peri-urban station on a tower in the Vienna Woods, close to the city border.
• To establish clumped isotope measurements of atmospheric CO2 to distinguish traffic emissions from net biogenic respiration (soil, plants, animals, humans).
• To design and test a novel flux footprint model based on a Lagrangian particle dispersion model with skewed turbulence statistics that will be constrained by the measured momentum fluxes and other meteorological data.
• To develop a completely novel inverse modeling framework for quantifying Vienna’s CO2 and CH4 fluxes that can utilize both flux as well as concentration measurement data.
• To include stable isotope ratios of CO2 into the inversion framework, which would not only allow for determining spatially-resolved net emissions but also separating source types.

Structure