Surface and Column Variations of CO2 using Weighting Functions for Future Active Remote CO2 sensors and Data from DISCOVER-AQ Field Campaign
Thursday, 18 December 2014
Fast response (1 Hz) and high precision (< 0.1 ppmv) in situ CO2 measurements were recorded onboard the NASA P-3B during the DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) Field Campaign, to investigate the ability of space-based observations to accurately assess near surface conditions related to air quality. The campaign spanned 4 years and took place over four geographically different locations. These included, Washington DC/Baltimore, MD (July 2011), San Joaquin Valley, CA (January – February 2013), Houston, TX (September 2013), and Denver, CO (July-August 2014). With the objective of obtaining better CO2 column calculations, each of these campaigns consisted of missed approaches and approximately two hundred vertical soundings of CO2 (from the surface to about 5 km). In this study, surface and column-averaged CO2 mixing ratio values from the vertical soundings in the four different urban areas are used to examine the temporal and spatial variability of CO2 within the lower troposphere. Tracers such as CO, CH2O, NOx, and NMHCs will be used to identify the source of variations observed in these urban sites. Additionally, we apply nominal CO2 column weighting functions for potential future active remote CO2 sensors operating in the 1.57-mm and 2.05-mm measurement regions to convert the in situ CO2 vertical mixing ratio profiles to variations in CO2 column optical depths, which is what the active remote sensors actually measure. Using statistics calculated from the optical depths at each urban site measured during the DISCOVER-AQ field campaign and for each nominal weighting function, we compare the natural variability of CO2 columns in the lower troposphere; relate the CO2 column variability to surface emissions; and show the measurement requirements for the future ASCENDS (Active Sensing of CO2 Emissions over Nights, Days, and Seasons) in the continental U.S. urban areas.