Analysis of Anthropogenic CO2 Signal in ICARTT Observations Using a Regional Atmospheric Model

Atmospheric inversion studies of CO2 sources and sinks typically prescribe the anthropogenic component of observations as the result of forward simulations using surface source estimates. The anthropogenic flux is prescribed as a background flux with low uncertainty. Errors in the spatial and temporal estimates of anthropogenic emissions have been shown to result in a bias in regional surface flux estimates. Improved information about the anthropogenic component of atmospheric CO2 observations will reduce the error in such a top-down approach to inferring surface fluxes. In this study, an analysis of the anthropogenic component to atmospheric CO2 measurements is completed using a regional atmospheric chemistry model and its adjoint. Observations of CO2 are made during the ICARTT (International Consortium for Atmospheric Research on Transport) experiment during the summer of 2004 from aircraft platforms. The STEM-2K1 model and its adjoint are applied to characterize the anthropogenic sources influencing the ICARTT observations. Source signatures are obtained using ratios between CO2 and combustion pollutants as well as model derived airmass markers for source region, source types, and airmass age. Model derived influence functions along with assimilated transport model results of anthropogenic tracers are used to characterize the anthropogenic CO2 emissions in the Midwest during the summer 2004 period.