Atmos. Chem. Phys. Discuss., 13, 7267-7310, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The role of vegetation in the CO2 flux from a tropical urban neighbourhood
E. Velasco1, M. Roth2, S. H. Tan2, M. Quak2, S. D. A. Nabarro3, and L. Norford1
1Singapore-MIT Alliance for Research and Technology (SMART), Center for Environmental Sensing and Modeling (CENSAM), Singapore
2Department of Geography, National University of Singapore (NUS), Singapore
3Department of Physics, Imperial College, London, UK

Abstract. Urban surfaces are usually net sources of CO2. Vegetation can potentially have an important role in reducing the CO2 emitted by anthropogenic activities in cities, particularly when vegetation is extensive and/or evergreen. Negative daytime CO2 fluxes, for example have been observed during the growing season at suburban sites characterized by abundant vegetation and low population density. A direct and accurate estimation of carbon uptake by urban vegetation is difficult due to the particular characteristics of the urban ecosystem and high variability in tree distribution and species. Here, we investigate the role of urban vegetation in the CO2 flux from a residential neighbourhood in Singapore using two different approaches. CO2 fluxes measured directly by eddy covariance are compared with emissions estimated from emissions factors and activity data. The latter includes contributions from vehicular traffic, household combustion, soil respiration and human breathing. The difference between estimated emissions and measured fluxes should approximate the biogenic flux. In addition, a tree survey was conducted to estimate the annual CO2 sequestration using allometric equations and an alternative model of the metabolic theory of ecology for tropical forests. Palm trees, banana plants and turfgrass were also included in the survey with their annual CO2 uptake obtained from published growth rates. Both approaches agree within 2% and suggest that vegetation captures 8% of the total emitted CO2 in the residential neighbourhood studied. A net uptake of 1.4 ton km−2 day−1 (510 ton km−2 yr−1 ) was estimated from the difference between the daily CO2 uptake by photosynthesis (3.95 ton km−2 ) and release by respiration (2.55 ton km−2). The study shows the importance of urban vegetation at the local scale for climate change mitigation in the tropics.

Citation: Velasco, E., Roth, M., Tan, S. H., Quak, M., Nabarro, S. D. A., and Norford, L.: The role of vegetation in the CO2 flux from a tropical urban neighbourhood, Atmos. Chem. Phys. Discuss., 13, 7267-7310, doi:10.5194/acpd-13-7267-2013, 2013.
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