Eddy Covariance measurements and source partitioning of CO2 emissions in an urban environment: Application for Heraklion, Greece

Cities are now becoming the focus for CO2 emission reduction efforts worldwide and there is a growing need for establishing emission inventories, developing methodologies for improved CO2 monitoring and understanding of the multiple source, sink and storage processes inside the complex urban environment. This study combines Eddy Covariance (EC) measurements of CO2 flux (F-C) during one year period over the city centre of Heraklion with analytical morphological and land cover data to achieve a thorough investigation of the spatiotemporal variability and the controlling factors of F-C in the urban setting. The detailed characterization of the urban land cover and 3D structure was performed using high resolution Earth Observation data. The urban morphological data was used to parameterize a turbulent flux source area model and the land cover data used to analyse the contribution of the source area components to the measured F-C. Heraklion F-C does not present any specific seasonal trend according to the meteorological or vegetation changes throughout the year. Heraklion centre behaves as a net emitter diurnally and throughout the year. The diurnal variability presents a standard pattern in weekdays with a major peak in midday and a secondary in afternoon, clearly following the traffic rush-hour peaks. Space heating emissions during winter remain low, hardly affecting the seasonal and diurnal F-C patterns. The main CO2 sources are the major roads and the intersections, where the heavy traffic is located. The source area analysis revealed that traffic contributes 69% to the estimated annual CO2 emissions. Space heating contributes only 11.6%, while human metabolism is estimated to contribute 19.4%. Vegetation cover of the source area is very low and was assumed to have minor effect to the annual F-C budget. The estimated total annual emissions of Heraklion case study reach 19.4 kg CO2 m(-2) y(-1).