1. Project goals Evaluate the accuracy and precision of the CO2 DIAL system, in particular its ability to measure: –Typical atmospheric boundary layer - free troposphere CO2 difference. –Typical synoptic variability in CO2 in both the free troposphere and the atmospheric boundary layer. Collect observations that have the potential to be merged into the broader context of the North American Carbon Program (NACP) Midcontinental Intensive (MCI) regional study.

2. Motivation A gap exists in our ability to continuously measure atmospheric CO2 profiles. –Airborne profiling is infrequent in time and space –Tower-based measurements are continuous, but are limited to the atmospheric boundary layer. –Nearly all remote sensing of CO2 to date is limited to atmospheric column measurements. Knowledge of the vertical distribution of CO2 in the atmoshpere is critically important to inferring accurately terrestrial sources and sink of CO2 using atmospheric inversions (e.g. Stephens et al, 2007, Science). Ground-based, airborne, or space-borne DIAL CO2 has the potential to fill this gap in our ability to describe the atmospheric space-time distribution of CO2.

3. Approach 2.5 week field deployment at the center of a domain rich in complementary CO2 measurements: –Co-located 400 m NOAA tall tower –Co-located NOAA airborne CO2 profiling –Rawinsondes for atmospheric temperature and water vapor profiles at the site –Surrounding mesonet (PSU “ring of towers” and synoptic network of highly calibrated CO2 sensors (densest sampling network in the world) –Center of the NACP MCI domain, last year of intensive field observations.

4. Approach, continued Essential lidar operations –Emphasis on daytime measurements to sense the well-mixed atmospheric boundary layer and overlying troposphere. –Operations on most days to ensure sound documentation of the atmosphere before and after synoptic events. –Operations on all days where airborne profiling will take place (2x/week). Additional desirable lidar operations –Night observations if possible to capture any nocturnal synoptic events (frontal passages). –Occasional nocturnal or early morning observations during calm conditions to attempt to measure CO2 mixing ratio differences within the atmospheric boundary layer.

5. West Branch, Iowa tall tower Continuous CO2 measurements at 31, 99 and 379 m above ground level. Photo below is actually NOAA tall tower site in Texas - shown to illustrate the type of observing platform. Photo at left is from the Iowa tall tower. Photos courtesy of NOAA’s Global Monitoring Division.

6. Seasonal pattern of CO 2 vertical and horizontal gradients Monthly mean CO 2 mixing ratios for continental boundary layer (CBL, sub- sampled for convective afternoon hours at the WLEF tall tower, WI), free troposphere (FT, from aircraft flights at Carr, CO), and marine boundary layer (MBL, at 44.4N). Also shown is cumulative net ecosystem-atmosphere exchange (NEE) of CO 2 at WLEF. FT, MBL and CBL CO2 data from NOAA Global Monitoring Division. NEE measurements from Penn State. Free troposphere Continental boundary layer Ten to 15 ppm FT- CBL CO2 difference is typical during time of campaign.

7. NOAA airborne vertical [CO 2 ] profile at WLEF, Wisconsin. profiles taken in mid-day, May – Sep, 1998, 1999, 2002 [CO 2 ]-depeleted boundary layer due to photosynthesis, high boundary layer top NOAA data, available at ftp://140.172.192.211/ccg/vp/ Examples of spring through fall midday airborne flask samples of the FT-CBL vertical difference in CO2 mixing ratio. CBL FT

8. Synoptic variability in boundary layer CO 2 mixing ratios September, 1997 time series of CO 2 measured on the WLEF-TV tower, WI (upper curve and crosses). It shows the variability of CO2 in the atmospheric boundary layer. Temperature is also plotted (lower curve) to show the correlation with synoptic weather. Changes in CBL CO2 of 10-20 ppm are common during frontal passages. FT CO2 changes are not well known.

9. http://www.amerifluxco2.psu.edu/ Iowa tower is surrounded by a 2007-2008 mesonet (light blue), and a growing long- term continental network

10. Enhanced mesoscale sampling of CO2 surrounding the Iowa tall tower provided by Penn State “ring of tower” sites Large variability in CBL CO2 is evident. Associated changes in FT CO2 are unknown. DIAL CO2 can fill this knowledge gap.