Variability in Lower Tropospheric CO2 over the DC/Baltimore Metro Area: Insight for Remote CO2 Sensors

High-resolution in-situ CO2 measurements were recently recorded onboard the NASA P-3B during the July 2011 DISCOVER-AQ field campaign; a mission designed to investigate the ability of space-based observations to accurately assess near surface conditions relating to air quality. DISCOVER-AQ provided a unique opportunity to examine CO2 distributions over the Baltimore/DC metropolitan region via the execution of a repetitive circuitous flight pattern over six ground measurement sites. The flight route included vertical soundings (0.3 to 4.7 km) over each surface site, and low-level runs (0.3 km) over the Baltimore-Washington Parkway, I-95, and the Chesapeake Bay. In this paper, data from 250 vertical soundings are presented highlighting the remarkable diurnal and spatial variability CO2 exhibits within the lower troposphere, a region of maximum sensitivity for both the GOSAT and OCO remote CO2 sensors. Horizontal gradients in CO2 observed at 0.3 km around each surface site (~ 4 km diameter loop) as well as over the entire flight track are also examined to evaluate the scales of variability influencing GOSAT and OCO footprints (spatial resolutions at nadir of 0.5 km and ~1.29 km × 2.25 km, respectively). These data provide insight into the ability of these space-based observations to fully capture the observed variability given their respective 3 and 16-day ground track repeat cycles and inevitably accurately constrain CO2 surface fluxes. Additionally, we investigate influences on the CO2 distributions using recorded meteorological variables, the HYSPLIT model, in concert with other simultaneously measured trace gases such as acetonitrile and isoprene to explore contributions from biogenic and anthropogenic emissions.