Direct measurement and analysis of urban carbon dioxide CO2 flux in Gwangju, Korea

Abstract

To quantify anthropogenic influenced on carbon dioxide (CO2) exchanges between atmosphere-urban interface, direct flux measurements of CO2 and H2O as well as heat were taken place using Eddy-Covariance (EC) method at Gwangju, Korea from November 2017 to August 2018. For the representative measurement of fluxes in an urban setting to cover the various activities taken place, the EC system has been installed on the helideck of the city hall with the total heights of 88 m, above ground level, to secure large enough fetches to fully enclose the urban characteristics (mean building height: 12.33 m , displacement height: 9.1 m). Footprint analysis suggests that our EC measurement setup provides high possibilities of quantifying the emission rate of CO2 from traffic and industrial area. In this research, the lowest possible limits of emission factors of various activities are estimated due to the lack of spatial concentration gradient observations to quantify the degree of vertical storage and horizontal seepage. To estimate the CO2 emission from traffic and industrial area, with the minimized effect of seasonal and diurnal bias due to biogenic activities and/or space heating, a new method relied on CO2 flux and traffic volume Correlation in Day of Week Difference (CiDoWD) is suggested with varying different wind sectors based on land use type. Emission owing to space heating in low temperature condition were calculated trough the relationship between CO2 flux and temperature with Heating Degree Days (HDD) estimation. Finally, carbon uptake by plant (8 – 49 kgC/m2/year) was evaluated from the balance between the observed total CO2 flux (mean: 10 kgC/m2/yr) and assessed CO2 emission rates, such as traffic (9.3 – 20.5 kgC/m2/yr), industrial area (29 – 90.3 kgC/m2/yr) and space heating (2 – 3.3 kgC/m2/yr). The evaluated emission strengths of traffic, industrial area as well as space heating fall in the ranges of previously reported values, but the amount of carbons sequestered by plants which is one to two orders of magnitude higher. Longer period of observations, spatial concentration gradient measurements, in along with simultaneous traffic volume monitoring will reduce uncertainties in our estimations. In addition, more works on carbon capturing potential of urban biosphere are necessary.