Direct measurement of greenhouse gas exchange in urban ecosystems

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This research program will develop methods to measure, quantify and analyze emissions of greenhouse-gases (GHG) in cities. We will directly quantify emissions of carbon-dioxide (CO2), methane (CH4) and nitrous oxide (N2O) at scales of neighborhoods or land-use zones. At those scales, where most planning decisions are made, estimated emissions (from consumption statistics or aggregated by modeling) are associated with large uncertainties. There is a lack of in-situ methods and data to independently validate modelled emissions. We will use (i) mass flux measurements of GHGs on towers above urban surfaces, (ii) sample GHG emissions using closed-chambers over urban green-space, and (iii) use stable isotopes to partition selected emission and concentration measurements. We will quantify the contribution of uncertain diffuse sources (and sinks), in particular exchange by urban soils and vegetation. The program will use an existing 30 m research tower in Vancouver, BC, an existing laser spectroscopy system, and remotely sensed data of surface characteristics to address the following limitations and knowledge gaps: (A) Currently, direct measurements of CO2 emissions are limited to the net-exchange from all sources and sinks in an urban area (i.e. building emissions + transportation emissions + respiration - photosynthesis). Hence, a validation of sector-specific models is not possible. We will use direct flux and concentration measurements of stable isotopologues of CO2 to separate net-exchange into individual emission profiles of various sources (isotopic signatures differ for natural gas, gasoline and respiration). (B) We will quantify whether diffuse GHG sources and sinks related to urban land-use are relevant or not in Canadian cities. Specifically, the IPCC Guidelines for National Greenhouse Gas Inventories identify the lack of a methodology for estimating emissions of CH4 and N2O from settlements as an 'obvious' knowledge gap. We will measure CH4 and N2O emissions (and uptake) caused by primarily land-cover (lawns, soils), but also combustion. We will quantify emissions, attribute sources and determine controls.