POSTER 5: UCP - Flux observations
On the anthropogenic heat release due to vehicle traffic determination in Mexico City: a preliminary study
1Instituto de Ecología, UNAM, Mexico; 2Centro de Ciencias de la Atmósfera, UNAM, Mexico
The accelerated growth in population and urban area has resulted in the need to meet increased demand for goods and services, which has become a priority in strengthening the provision of infrastructure and equipment. As a result of this demand, urban areas are subjected to an additional source of energy produced by human activity, as anthropogenic heat release (QF), which depends on the consumption of energy in an area. Accurate estimation of QF is of primary importance in research of local circulation, local thermal environment, and contamination problems associated with it. The objective of this work was to quantify the heat release by vehicle traffic in Mexico City. This was done by determining the traffic flow in a busy avenue by taking videos during the day and calculating the inversion in fuel and heat delivered to the atmosphere. There were 192 vehicles/min from 7:00 to 21:00 local hour (lh) in average, whereas from 7:00 to 13:00 lh, transit flow was 60, and from 13:00 to 21:00 lh, it was 90 vehicles/min in average. This is a heat release of 0.0021 MJ/m2 every 15 min when vehicle traffic is about 100 vehicle/min. This heat release is very small compared to solar radiation (0.04%) being not significant in the energy balance at midday in this area of Mexico City. However, it is necessary to determine the flow of vehicles in other areas of the city where traffic is higher.
Measurements of the Green Roof Energy Balance in Three Canadian Cities
Western University, Canada
Green roofs are a modification to the built environment that replace traditional building roof materials with a vegetated cover. Through alterations of the surface energy and water balance, they modify the microclimate and hydrology of roof surfaces. These alterations may lead to improved environmental conditions at both the building and urban scale and thus make them potentially attractive as measures to reduce the impact of urban areas on the environment. While the thermal performance of green roofs has been extensively studied, assessment of the green roof energy balance is rare. In this presentation we provide results of the energy balance and roof microclimate from green roof test arrays built in in three Canadian cities of varying climates, Calgary AB, London ON, and Halifax NS. The arrays are built from individual 30.5 x 30.5 cm modules that contain the growing medium and plants. Custom built lysimeters are used to monitor the evapotranspiration, heat flux plates and soil thermometry assess the conductive heat flux and net radiometers monitor the surface radiative forcing. Measurements are made over modules with a mature cover of sedum, a succulent, that have a 15 cm growing medium depth. Additional instrumentation, including rain gauges and specially constructed drainage units, is used to document the water balance. The full experimental setup includes four plant types, two medium depths and four slopes.
Here we report results from the summer and fall seasons for the three sites including the temporal evolution of green roof energy balances, case studies during extreme wet and dry periods, seasonal and event specific energy balance flux totals, thermal differences between the green roof and adjacent bare roof and differences between test cities at the seasonal scale. Results are sensitive to the moisture availability with the fraction of latent heat varying from 0.1 – 0.6 depending on module moisture with sensible heat dominating the remainder.
Longterm measurments of the urban energy and CO2 flux in Dublin, Ireland
1UCD, Ireland; 2Maynooth University, Ireland
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 work will present a long-term investigation of these exchanges over the urban surface of Dublin. 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).
The hourly profile of the anthropogenic component of the surface energy balance for the urban region of the Mexico City
National Institute of Ecology and Climate Change, Mexico
In Mexico City has been measured on several occasions the surface energy balance, allowing only an indirect estimate of the anthropogenic component (the latter study was conducted in 1998). This study proposes the estimation of the hourly profile for this component, breaking it in its different subcomponents. Each subcomponent was modeled using time distribution curves of emissions or daily electricity demand curves, depending on the heat sources. For some subcomponents a methodological approach bottom-up was achieved, since more detailed activity data were obtained. However, the methodology of modeling from emission curves or electricity demand curves only allows to disaggregate anthropogenic activity temporarily, but not at lower geographical level. The results obtained for this component show variations close to 300% during the day. Considering the net surface energy balance, the anthropogenic component can represent up to 25%, also, this component reaches its maximum within three periods of the day where has been observed the formation of the phenomenon of Urban Heat Island. From these results it is concluded that this component should be studied in deep to determine its relevance in the urban climatology of the Mexico City.
GHG EMISSIONS ESTIMATION OVER A MEDITERRANEAN CITY THROUGH DIRECT MEASUREMENTS AND INVENTORY APPROACH
1DipNET, University of Sassari, Italy; 2CMCC, Euro-Mediterranean Centre on Climate Change, Italy; 3CNR IBIMET, Institute of Biometeorology, National Research Council, Sassari, Italy
Anthropic areas, such as cities, are recognized to constitute the major source of the CO2 emitted into the atmosphere, and Greenhouse Gases Emissions (GHG) in urban environment derive from different sources (human respiration, domestic heating/cooling, transportation, etc.). Cities, therefore, can affect the global carbon cycle, the atmosphere, and the climate. The link between urbanization and global climate change is complex, and since the urbanization process is increasing worldwide, it becomes crucial to better understand the role of cities in the global warming phenomenon, the interaction between natural and anthropogenic processes, and quantify the urban carbon exchanges.
As part of a Regional Project, in the city of Sassari (Sardinia, Italy) a research activity has been carried out with the general aim to quantify urban fluxes and identify the main GHG emissions sources. A combined methodology is used for this purpose: (1) direct measurements and (2) an inventory approach.
An Eddy Covariance tower is to be set up in the Sassari city center to constantly monitor energy, water, and carbon fluxes at about 24 m above the ground. In addition, a meteorological station and radiometers are to be installed to analyze the environmental characteristics affecting urban fluxes.
A local simplified GHG emissions inventory, developed through standardized procedure guidelines, is also compiled and city emissions were quantified and classified by type of greenhouse gas, manufacturing activity, and source emissive. The inventory tool also allowed a spatio-temporal analysis of the emissions and the temporal disaggregation of the collected annually emissions to produce data on a monthly, and/or daily, and/or hourly time scale.
The combined methodology is able to provide information on the current status of emissions and removals of CO2, through direct measurements and the local inventory, which will help local stakeholders to identify low carbon emissions options for the future planning strategy.
The projects activities, methodologies applied, as well as the preliminary results will be reported here.