A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Spatial variability of carbon dioxide in the urban canopy layer and implications for flux measurements
Abstract This contribution reports CO2 mixing ratios measured in the urban canopy layer (UCL) of a residential neighborhood in Vancouver, BC, Canada and discusses the relevance of UCL CO2 temporal and spatial variability to local-scale eddy covariance (EC) fluxes measured above the UCL. Measurements were conducted from a mobile vehicle-mounted platform over a continuous, 26-h period in the longterm turbulent flux source area of an urban EC tower. Daytime mixing ratios were highest along arterial roads and largely a function of proximity to vehicle traffic CO2 sources. At night, there was a distinct negative correlation between potential air temperature and CO2 mixing ratios. The spatial distribution of CO2 was controlled by topography and micro-scale advective processes (i.e. cold-air pooling). Mobile CO2 measurements were then used to calculate CO2 storage changes (F S) in the UCL volume and compared to single-layer F S estimates calculated from the EC system. In total, five variations of F S were calculated. On average, the choice of F S calculation method affected net measured hourly emissions (F C) by 5.2%. Analysis of F S using a four-year dataset measured at the EC tower show F S was 2.8% of hourly F C for this site on average. At this urban EC location, F S was relatively minor compared to F C and calculation of F S using a single-layer method was adequate, though F S still represents a potentially large uncertainty during individual hours.
Highlights The micro-scale variability of carbon dioxide was mapped in an urban environment. During day, carbon dioxide was mainly a function of proximity to traffic. At night, the distribution was controlled by accumulation due to cold-air pooling. Hourly changes of carbon dioxide storage in the urban canopy layer were calculated. Changes affected measured eddy covariance fluxes on average by 5%, but up to 123%.
Spatial variability of carbon dioxide in the urban canopy layer and implications for flux measurements
Abstract This contribution reports CO2 mixing ratios measured in the urban canopy layer (UCL) of a residential neighborhood in Vancouver, BC, Canada and discusses the relevance of UCL CO2 temporal and spatial variability to local-scale eddy covariance (EC) fluxes measured above the UCL. Measurements were conducted from a mobile vehicle-mounted platform over a continuous, 26-h period in the longterm turbulent flux source area of an urban EC tower. Daytime mixing ratios were highest along arterial roads and largely a function of proximity to vehicle traffic CO2 sources. At night, there was a distinct negative correlation between potential air temperature and CO2 mixing ratios. The spatial distribution of CO2 was controlled by topography and micro-scale advective processes (i.e. cold-air pooling). Mobile CO2 measurements were then used to calculate CO2 storage changes (F S) in the UCL volume and compared to single-layer F S estimates calculated from the EC system. In total, five variations of F S were calculated. On average, the choice of F S calculation method affected net measured hourly emissions (F C) by 5.2%. Analysis of F S using a four-year dataset measured at the EC tower show F S was 2.8% of hourly F C for this site on average. At this urban EC location, F S was relatively minor compared to F C and calculation of F S using a single-layer method was adequate, though F S still represents a potentially large uncertainty during individual hours.
Highlights The micro-scale variability of carbon dioxide was mapped in an urban environment. During day, carbon dioxide was mainly a function of proximity to traffic. At night, the distribution was controlled by accumulation due to cold-air pooling. Hourly changes of carbon dioxide storage in the urban canopy layer were calculated. Changes affected measured eddy covariance fluxes on average by 5%, but up to 123%.
Spatial variability of carbon dioxide in the urban canopy layer and implications for flux measurements
Crawford, B. (author) / Christen, A. (author)
Atmospheric Environment ; 98 ; 308-322
2014-08-22
15 pages
Article (Journal)
Electronic Resource
English
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