Characteristics influencing the variability of urban CO2 fluxes in Melbourne, Australia

Urban areas are significant contributors to global carbon dioxide emissions. Vehicle emissions and other anthropogenic related activities are a frequent source of CO2 to the atmosphere, contributing to global warming. Micrometeorological techniques used for observations in Northern Hemisphere cities have found that urban CO2 fluxes are consistently a source. This study investigates CO2 fluxes in an Australian city, adding to the global database of CO2 fluxes in a bid to aid in future development of planning policies concerning reductions in CO2 emissions. Using the eddy covariance approach, fluxes of CO2 were measured at a suburban site (Preston) in Melbourne, Australia from February 2004 to June 2005 to investigate temporal variability. A second site (Surrey Hills) with differing surface characteristics (in particular, greater vegetation cover) was also established in Melbourne and ran simultaneously for 6 months (February 2004–July 2004). Results showed that both sites were a net source of CO2 to the atmosphere. Diurnal patterns of fluxes were largely influenced by traffic volumes, with two distinct peaks occurring at the morning and evening traffic peak hours, with the winter morning peak averaging 10.9 μmol m−2 s−1 at Preston. Summer time fluxes were lower than during winter due to greater vegetative influence and reduced natural gas combustion. Vegetation limited the source of CO2 in the afternoon, yet was not enough to combat the strong local anthropogenic emissions. Surrey Hills showed higher fluxes of CO2 despite greater vegetation cover because of higher local traffic volumes. Annual emissions from Preston were estimated at 84.9 t CO2 ha−1 yr−1. Magnitudes and patterns of suburban CO2 fluxes in Melbourne were similar to those observed in Northern Hemisphere suburban areas.