Atmospheric measurements of CO₂ concentration have a key role in climate science, climate change detection, and climate policy.  It is likely that greenhouse gas (GHG) concentration and flux measurements will grow in importance as GHG management policies are implemented at state, national and international levels.  Furthermore, it is likely that many of the GHG control and sequestration technologies will be developed and implemented by chemical engineers. 

Top-down verification of CO₂ emission estimates is an important activity.  In locations with inaccurate inventories, top-down flux estimates are the most reliable source of emissions data.  Even in North America, there remains significant scientific uncertainty regarding the net CO₂ flux, as well as a lack of agreement between bottom up inventory-based flux estimates, predictive biosphere models, and top down (tracer-transport inversion) approaches to carbon flux estimation.   The problem is illustrated by the recent studies with biogenic sequestration estimates of 0.3-1.8 Gt C yr^-1 (top down) and  0.3-0.7 Gt C yr^-1 (bottom up).   These biogenic sinks and associated uncertainties are large, even when compared to the annual U.S. anthropogenic emission of ~5.8 Gt C yr^-1. 

Efforts to narrow the gap between top-down and bottom-up inventories are advancing under the guidance of the interagency North American Carbon Plan.  One key activity is the establishment by the National Oceanic and Atmospheric Administration (NOAA) of a high accuracy CO₂ monitoring program.  The expanded “tall tower” monitoring program is being tested in the Midwest in 2007-2008.  CO₂ monitoring from a 400 m+ television transmitter tower located 10 km from the University of Iowa is scheduled to begin in July 2007. 

Researchers at the Center for Global and Environmental Research at the University of Iowa have recently developed and implemented forward (using the University of Iowa STEM model) and inverse models for CO₂, CO, and carbonyl sulfide, and tested them on the aircraft sampling data from the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign over the Eastern U.S. during summer 2004.  The inverse methodologies include 4dvar using the STEM adjoint.

We will present an overview of our carbon measurement and modeling activities at the Iowa Center for Global and Environmental Research.  Results will include: (1) overview of the tall tower measurement program and initial results from the Iowa CO₂ tall tower; (2) example results from the forward model demonstrating the use of SO₂ as a tracer for coal-fired power; (3) a tracer method that uses CO/CO₂ ratios to determine the anthropogenic fraction of CO₂; (4) corrections to (3) for forest fire and photochemical CO influences; (4) a method for using carbonyl sulfide as a tracer of photosynthetic drawdown of CO₂; and (5) implications of the upcoming launch of NASA’s orbiting carbon observatory and other space-based tropospheric CO₂ measurements. 

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