Urban-rural comparison of carbon dioxide fluxes and concentrations in a coastal urban environment

In recent years, numerous flux-towers for CO₂-exchange have been established in cities around the world. These relatively recent measurement campaigns - based on the eddy covariance (EC) technique - are continuously monitoring the turbulent fluxes of CO₂ between urban surfaces and the atmosphere. They are not only valuable in complementing carbon emission inventories on the city scale but also promise new insights into the spatial and temporal variability of CO₂-fluxes and concentrations in urban environments.

In contrast to other parameters or processes of interest in urban climatology (energy balance, temperature, precipitation) a comparison of urban CO₂ to a non-urban 'reference' situation has been rarely reported in literature. The approach to separate the large-scale climate forcing from urban modifications with respect to CO₂ concentrations and fluxes is challenging and strongly biased by the choice and definition of the 'undisturbed reference' site and the 'urban site'. Nevertheless, it is worth to extend urban CO₂-measurements beyond the analysis of single urban flux towers and analyze data in the context of simultaneous measurements over different land-cover patches in an urban landscape.

We present a recently started long-term campaign in Vancouver, BC, Canada. A suburban – rural pair of EC-sites measuring CO₂-exchange is the backbone of the Vancouver instrumentation. The suburban site is operated in a residential neighborhood with intensive irrigation during summer. The rural 'reference' is sited over non-managed and non-irrigated grassland without near-field influence of traffic or other human sources. These sites will be supplemented with short-term flux and concentration measurements. A mobile tower on a moving trailer is used to address the spatial variability of fluxes and concentrations in the city.

The presentation highlights the scientific framework, the instrumental setup and features first results from summer 2007. It will further outline opportunities for collaborations during intensive operation periods in 2008.