An Assessment of Radiative, Energy and Carbon Dioxide Fluxes over Three Urban Locations in Dublin

The urban form and function varies across and within cities serving to alter surface-atmosphere exchanges of radiation, turbulent heat and carbon dioxide. To date very few measurements of these exchanges are undertaken in the urban domain despite the growing number of urban dwellers worldwide. This thesis presents the first attempt at investigating these exchanges over an urban surface in Ireland. Radiometer and eddy covariance observations are examined for Dublin at 3 distinctive urban locations (suburban, urban, and urban-compact). The observational period (maximum 33 months) allowed for the investigation of both diurnal and seasonal trends of the turbulent sensible heat (QH), latent heat (QE) and carbon dioxide (FC) fluxes. Net radiation (Q*) was 7.5 and 10% greater in summer and winter at the suburban location when compared to an urban location. Q* was preferentially channelled into the QH in summer and the QE in winter at the suburban location while QH dominates in all seasons at the urban locations. In summer median QH is greater at the urban location (+38 W m-2) while median QE is greater at the suburban location (+30 W m-2). The storage heat flux (ΔQS) was reported as a significant component of the surface energy budget at all locations and is estimated using the Objective Hysteresis Model (OHM). The occurrence of unstable atmospheric conditions increased with increasing built and impervious surface cover fraction however neutral stratification was dominant. Temporal analysis of the CO2 flux indicates photosynthetic uptake in spring, summer and autumn at the well-vegetated suburban location, however the area is a net source of CO2 annually (1.67 kg C m-2 year-1). Temporal and directional analysis of the CO2 flux at an urban location indicates significant contributions from traffic and the emissions are double than the suburban location on an annual basis (3.47 kg C m-2 year-1). Inter-site differences in the mean daily release of carbon are greatest in the summer; the urban location reports values 5 times greater than those reported for the suburban location indicating the role of vegetation in modulating FC (1.4 versus 7.1 g C m-2 day-1)