Human and natural influences on carbon dioxide in Salt Lake City: Investigating observed concentrations with a multiple box model

Growing urban environments represent centers of concentrated anthropogenic greenhouse gas emissions. Many studies have been dedicated to understanding and modeling various ecosystem carbon cycles; yet understanding the fine-scale climate processes of the atmosphere-ecosystem carbon cycle in urban areas has received comparatively little attention, particularly in regions of complex mountainous terrain. This study quantifies factors determining CO2 variations in the Salt Lake City valley for all four seasons using a multiple box model sensitive to meteorological conditions and spatial variations in land use, vegetation type, and traffic. Model output is compared to several years of hourly mean measurement at six sites within the valley. Controlling factors quantified include advection, mixed layer growth, biogenic fluxes, and anthropogenic fluxes. The relative importance of these factors is shown to vary diurnally and seasonally.