Hourly patterns of CO2 in the atmosphere over Boston, MA: An assessment of natural and anthropogenic drivers

Urban areas are playing an increasingly important role in the carbon cycle. Situated on less than 3% of the Earth's landmass, cities are responsible for ~80% of anthropogenic emissions. Yet, our knowledge of carbon exchange in urban areas is limited since we currently cannot parse urban atmospheric CO2 concentrations into useful anthropogenic and biogenic components. Past urban CO2 research efforts have highlighted decreasing levels of atmospheric CO2 across urban to rural gradients - a phenomenon known as an “urban dome” - but have rarely assessed the drivers of observed concentrations. Moreover, most of these studies have been brief in duration (weeks to months) and have not measured concentrations at multiple points across an urbanization gradient. In this analysis, we compare CO2 concentrations over a one and a half year period at three locations across Boston's urbanization gradient in order to better determine the meteorological, anthropogenic, and biogenic drivers of short and long term CO2 trends. Boston, Worcester, and HF, MA were the three sites selected for this analysis and are classified as high density urban, semi-urban adjacent to large tracts of forest, and predominantly rural, respectively. Consequently, the type and magnitude of anthropogenic and biogenic fluxes vary by instrument location. Contrasting the observations across these three sites has enabled a better understanding of how these varying source and sink functions influence surface observations. We also analyzed CO2 concentrations along a vertical gradient at the BU test site in order to 1) better identify urban exchange processes and 2) determine the appropriate instrument height for measuring CO2 concentrations given complex urban micrometeorology. This analysis is a first step in attributing observed CO2 concentrations in urban areas to spatially explicit CO2 emissions.