Urban Flux

Scientists have studied the exchange of carbon dioxide between natural ecosystems and the atmosphere in remote rural areas around the globe for many years. Now, with the concern over increasing greenhouse gas emissions and industrial pollutants, many studies have been launched to understand the details surrounding urban carbon fluxes. By comparing the carbon dioxide and water vapor budgets of agricultural or natural ecosystems against those of urban areas, we can gain better insight into turbulent fluxes of heat, H2O, and CO2 in urban areas. This, in turn, will provide insight into the fate of urban air pollutants such as particulate matter, nitrogen oxides, and volatile organic compounds.

Pollution-related health problems for people that live in urban and high traffic areas are well documented, but information regarding the sources, sinks, and chemistry of air pollutants is less well defined. The Eddy Covariance technique has not been used much in this area historically, in part because of the complexity of system designs, implementation, and data processing. With this technology now available, urban CO2 and H2O fluxes, as well as fluxes of common urban air pollutants can be properly characterized. This data can be used to support current and future environmental policies.

The Eddy Covariance method, which is the most direct and defensible way to measure such fluxes, has been used for many years in the micrometeorology community. Modern instruments and powerful computational software are expanding the use of Eddy Covariance to a broad range of scientists including biologists, ecologists, and others who are interested in understanding urban flux. A detailed tutorial describing the Eddy Covariance method can be found here.

Researchers around the world use LI-COR instruments for carbon cycle-related studies. The LI-7500 Open Path CO2/H2O Analyzer is commonly used in Eddy Covariance measurements to determine the vertical carbon dioxide and water vapor fluxes over relatively large areas. LI-7000 Closed Path CO2/H2O Gas Analyzer is also an excellent option for monitoring CO2 fluxes, especially in areas with high precipitation.

An important component in the overall carbon balance of urban areas is the impact that green spaces have on absorbing carbon through photosynthesis. Green roofs are an emerging trend among efforts to increase the beneficial impacts of live plants in urban areas. Green roofs have a positive impact on urban microclimates, but much like overall urban carbon fluxes, scientists have yet to characterize the impact of green roofs. The LI-8100 can be used to help quantify the effects of green roofs and other green spaces by measuring carbon exchange at the soil surface.

Although urban fluxes have been largely ignored until recently, the significant role that they have in the global carbon cycle cannot be ignored. As urban areas continue to expand around the globe, the importance of monitoring urban fluxes will expand as well.