Net carbon dioxide emissions from central London

Carbon dioxide (CO2) emissions from cities drive increased global atmospheric CO2 concentrations and associated climate change. Urban CO2 emissions can be evaluated using an inventory approach (summing all know emissions and sequestrations of CO2 within a defined area), and/or a micrometeorological approach (summing the exchanges of CO2 through the sides of a defined volume of air, and the change in the total stored within the volume). Generally the micrometeorological approach, with the assumption that only the net turbulent vertical flux of CO2 is significant on annual timescales, is preferred. This study evaluates that assumption with respect to storage and vertical advection of CO2, and calculates net CO2 emissions in central London using both methods for June 2012 to May 2013. Data sources include an eddy covariance system, switched horizontal and vertical CO2 profiles, traffic counts and vegetation surveys. Annual total emissions were 51.4 and 53.5 kg CO2 m− 2 y− 1 (micrometeorological and inventory methods, respectively) i.e., within 4% (1.3% with the assumption that the net vertical turbulent flux is the only non-negligible micrometeorological term). This study supports the use of vertical fluxes calculated from eddy covariance measurements at a single location to estimate total emissions from high density urban environments.