Impact of Oporto Metropolitan Area Carbon Dioxide Emissions over the Adjacent Coastal Zone

Concerns about global warming over the last years have stimulated a large number of studies regarding atmospheric and oceanic carbon dioxide (CO2) concentration and its consequences. In spite of the available data on global atmospheric CO2 there is only limited knowledge on CO2 variability at regional scales. Moreover, there is an important gap in our understanding of the contribution of high CO2 emission regions, such as metropolitan areas, to CO2 concentrations over nearby coastal areas-considered by several authors as an important CO2 sink. A possible working hypothesis is that, large littoral metropolitan areas may have a significant influence on CO2 atmospheric concentrations over those areas and exert an important influence on sea-air CO2 exchanges. Therefore, the main objective of this study is to estimate CO2 concentration at a regional scale, under the influence of Oporto Metropolitan Area (OMA) emissions as a first test of this hypothesis. To fulfil this objective, an emission database was built and used to force, together with meteorological synoptic data, a mesoscale atmospheric dispersion model. The model was used to simulate several weather scenarios and estimate CO2 concentrations along a ca. 90 km stretch of the Portuguese northern shore. The results obtained suggest that emissions from OMA have an important influence on CO2 atmospheric concentrations up to 6-12 km offshore, particularly in autumn and winter. However, this CO2 increase does not seem to have the potential to significantly affect sea-air CO2 exchanges, although this is just a preliminary conclusion that has to be tested by field work.