Land atmosphere interactions in a rapidly urbanizing environment

The majority of greenhouse gases and other atmospheric pollutants originate in cities, yet the interactions between human activities, vegetation, and the atmosphere are poorly understood in urbanizing environments. The Urban Trace-gas Emissions Study (UTES) in the Salt Lake Valley is a multidisciplinary study of the interactions between land cover types and atmospheric processes in a rapidly urbanizing, semi-arid ecosystem. Our goal is to: 1) determine the major local sources of trace gases and quantify their temporal and spatial variability in a variety of land cover types; 2) study the underlying and interacting social-environmental processes controlling emissions and concentrations of pollutants, and 3) use a collaborative process with decision-makers to evaluate scenarios for managing air quality and greenhouse gas emissions as the population of the valley rapidly increases. Our major emphasis is on carbon dioxide, water vapor, and volatile organic compounds (VOC's), all of which influence climate and air quality, and have both anthropogenic and biogenic components. Here we report preliminary results from a pilot study combining measurements of eddy covariance, CO2 concentrations and isotopes, aerosols, VOC's, meteorology, traffic flow, and natural gas combustion in a residential neighborhood. Natural gas usage was fairly constant during the study, which was conducted in the winter, while traffic flow had the characteristic rush hour diurnal pattern. Source identification of CO2 concentrations with stable isotopes showed that only 60% of CO2 sources were attributable to traffic emissions, with the remainder attributed to residential natural gas combustion. Diurnal pollutant concentrations were strongly influenced by local scale near-slope flow patterns, while on a longer scale daily patterns were determined by meso-scale climatic conditions such as the build-up and mix-out of atmospheric inversions. These results showed that an understanding of patterns and influences on human activities, aspects of urban form, and natural processes all contribute to our ability to quantify urban land-atmosphere interactions. The results are being applied to an urban systems model in order to improve our understanding of interactions and feedbacks between social and natural parameters, scale the results to other land cover types, and develop an urban airshed management tool for decision-makers. The model is currently being validated with additional data collection in other land cover types including a pre-urban area and two residential neighborhoods of varying ages, urban structure, and urban forest cover.