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Measurements of carbon dioxide fluxes and concentrations at multiple scales in Vancouver, Canada Crawford, Benjamin R.

Abstract

Global carbon dioxide (CO₂) atmospheric mixing ratios and near-surface air temperatures are projected to rise for the foreseeable future. Given that human populations and activity are concentrated in urban areas, knowledge and quantification of CO₂ emissions and uptake processes is important for urban sustainable development applications and emission reduction efforts. Atmospheric measurements of CO₂ in Vancouver, BC were conducted from 2008-2012 to improve spatial resolution of emissions monitoring techniques and advance understanding of urban CO₂ atmospheric transport processes. Three datasets representative of three urban climate scales were collected. At the neighborhood-scale, four years (2008-2012) of eddy covariance (EC) net CO₂ emissions measurements were analyzed with spatial turbulent flux source area models. This allowed high-resolution spatial attribution of the net flux to individual source/sink processes and reduced spatial bias in EC-measured annual net emissions totals. Empirical models developed from three years of hourly EC data (2008-2011) were used to predict net emissions for a fourth year (2011-2012) with errors of 6.7% compared to direct EC measurements on daily timescales. At the micro-scale, high-resolution spatial variations in CO₂ mixing ratios measured at 2 m height from a mobile, vehicle-mounted platform were observed. Nighttime CO₂ mixing ratio patterns were correlated with potential air temperature, suggesting micro-scale advective processes are an important determinant of UCL pollutant transport. Micro-scale observations are linked to local-scale EC flux measurements through consideration of the EC storage flux term (FS). Uncertainties in hourly FS calculated from a single observation height at EC level are caused by flushing of CO₂ from the UCL shortly after sunrise and from CO₂ buildup in the UCL shortly after sunset. CO₂ mixing ratios representative of the city-scale were measured in the urban boundary layer (UBL) using a tethered-balloon system. The net CO₂ flux representative of the city-scale is inferred from hourly changes in UBL CO₂ together with UBL height measurements from a ceilometer. The surface flux calculated using this method is comparable to local-scale urban EC measurements during the same period, however there is uncertainty in the horizontal advective flux resulting from sensitivity to parameterization of CO₂ mixing ratios in upwind, non-urban areas.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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