Comparison of urban eddy covariance CO2 and heat fluxes measured at two flux towers in a Mediterranean city

Abstract

Urbanization plays a key role in the steady rise of global CO2 concentration. Urban emissions are primarily from anthropogenic sources, such as the burning of fossil fuel for e.g. heating and cooling needs or vehicular traffic. They vary depending on population density, land cover and land use or morphology, thus it is important to quantify local emissions and their relationship with urban function and form to achieve city-wide budgets. The present study analyses CO2, sensible, and latent heat fluxes from two eddy covariance flux towers in the city of Heraklion, Greece. While located only 1.5 km apart from each other they represent two different land use types: a commercial city center (HECKOR) and a residential area (HECMAS). Despite their spatial proximity, diurnal CO2 fluxes patterns are significantly different, with HECKOR fluxes following commercial and working hours throughout the year and HECMAS capturing major CO emissions from residential heating during winter months and very low fluxes during the rest of the year. Furthermore, there is extreme directionality in CO2 fluxes measured in HECKOR, and thus the estimated diurnal patterns are affected by the seasonality of wind direction patterns. Dynamic flux footprints for both flux towers are analysed to relate CO2 emissions to particular land use and land cover features in both areas. Finally, sensible heat fluxes are higher in HECKOR, most probably due to higher building density and lower vegetation cover in the Heraklion central business district.

Full text

Urban emissions are primarily anthropogenic coming from
the burning of fossil fuels for heating and transport. This
study focuses on 𝐶𝑂2fluxes, sensible and latent heat fluxes measured at two
eddy covariance ICOS flux towers in Heraklion, Greece (Jul 21 –Jun 23).
Comparison of urban eddy covariance 𝐶𝑂2and heat fluxes
measured at two flux towers in a Mediterranean city.
The CoCO2 project has received funding from the European Union’s Horizon 2020 research and innovation
programme under grant agreement No 958927.This poster reflects the views only of the authors, and the
Commission cannot be held responsible for any use which may be made of the information contained therein.
Konstantinos Politakos1,*, Stavros Stagakis1,2, Christian Feigenwinter2, Matthias Roth3, Nektarios Chrysoulakis1
1Remote Sensing Lab, Institute of Applied and Computational Mathematics, Foundation for Research and Technology –Hellas (FORTH), Nikolaou Plastira 100, Vassilika Vouton, GR 700 13, Heraklion, Crete, Greece
2Department of Environmental Sciences, University of Basel, Kingelbergstrasse 27,5046, Basel, Switzerland
3Department of Geography, National University of Singapore, Singapore, Singapore
* Corresponding author: politakos@iacm.forth.gr
Introduction
Two flux towers equipped with IRGASON systems
(Integrated 𝐶𝑂2/𝐻2𝑂Open-Path Gas Analyser, 3D Sonic
Anemometer) and Net Radiometers.
•HECMAS operates since spring 2021 at a residential (left).
•HECKOR operates since autumn 2016 at the city center (right).
Flux Towers
The 𝐶𝑂2fluxes were quality-controlled and filtered using
standard procedures.
•𝐶𝑂2fluxes from HECKOR follow commercial and working
hours pattern year-round and are thus mainly influenced by
traffic emissions.
•HECMAS captures mainly 𝐶𝑂2emissions during winter
months, attributed to residential heating, with very low
fluxes during the hot period.
𝐶𝑂2Fluxes
Similar wind patterns are observed from the two flux towers, in 2021.In the northern part of the
HECKOR footprint, 𝐶𝑂2fluxes follow commercial-business rush hour peaks, while both HECKOR
southern footprint part and HECMAS present lower fluxes attributed to residential activities only.
Sectorial Analysis
Sensible heat fluxes are higher in HECKOR, likely due to its higher
building density and lower vegetation cover in the Heraklion
central business district. HECKOR and HECMAS show similar
Latent heat fluxes.
Heat Fluxes
See Heraklion
fluxes online
real-time
HECKOR HECMAS
𝑇
𝑚𝑒𝑎𝑛 <16𝑜𝐶𝑇
𝑚𝑒𝑎𝑛 <16𝑜𝐶
𝑇
𝑚𝑒𝑎𝑛 >16𝑜𝐶 𝑇
𝑚𝑒𝑎𝑛 >16𝑜𝐶
2021 2022 2023
2021 2022 2023
Land Cover (%)
Flux Tower
A/A 400m r. Footpr. 90% 400m r. Footpr. 90%
High - Low Veg. 10.6 10.1 11.8 23.0
Paved 48.9 49.5 50.2 46.4
Buildings 40.5 40.4 38.0 30.6
Water 0000
HECKOR
HECMAS