Insights on estimating urban CO<sub>2</sub> emissions using eddy-covariance flux measurements

Abstract

Abstract. Living in an era of government allocated carbon dioxide (CO2) emissions, knowing the accurate amount of human-induced CO2 becomes very critical. To this end, an in-depth understanding of CO2 emissions in urban areas where human activities are concentrated will be of practical help. With this motivation, we quantify CO2 emission strengths of individual urban activities (i.e. vehicle, industry, heat generation, etc.) based on direct observations of vertical CO2 exchanges at urban-atmosphere interface using Eddy-Covariance (EC) method at Gwangju, Korea (2017.11–2018.08). Day of week difference analysis, together with varying wind sector, grounded from carefully designed measurement set-up, enables us to assess CO2 emission factors (EFs) free from seasonal bias (i.e. heating and urban vegetation); evaluated EFs of traffic from day of week difference was 0.017(±0.011) μmol m-2 s-1 car-1 which is more than 10 times larger than that from simple relation (0.0012 ± 0.0011 μmol m-2 s-1 car-1) between CO2 flux and traffic counts. The CO2 emissions due to the car manufacturing industry within the fetch and heating when air temperatures were lower than 18 °C were quantified as 103.25(±42.18) μmol m-2 s-1 and 2.41(±1.71) μmol m-2 s-1 °C-1, respectively. Urban vegetation uptake was estimated as -1.72 kg C m-2 yr-1 only with EFs traffic inferred from day of week difference indicating possible erroneous estimation in simple relation unless it properly reflects representative seasonal changes in a year. Even though our estimations are conservative EFs due to limitations in corrections of horizontal seepage and vertical storage, we found that both EFs for traffic and heat in latest emission inventory were more than 2.5 times lower than our estimations which indicate the urgency in bottom-up inventory validations.

Spatial and Temporal Variations of Carbon Dioxide Fluxes in Urban Ecosystems of Changsha, China

“…Due to the differences in anthropogenic activities and geography, CO 2 emissions vary greatly even in different wind directions at the same site [17,37,53]. Velasco et al [41] and Crawford et al [42] found that the areas with frequent traffic flow and more exhaust emissions will lead to an increase in carbon dioxide content in the region.…”