Strategies for measurement of atmospheric column means of carbon dioxide from aircraft using discrete sampling

Abstract

[1] Automated flask sampling aboard small charter aircraft has been proposed as a lowcost, reliable method to greatly increase the density of measurements of CO 2 mixing ratios in continental regions in order to provide data for assessment of global and regional CO 2 budgets. We use data from the CO 2 Budget and Rectification-Airborne 2000 campaign over North America to study the feasibility of using discrete (flask) sampling to determine column mean CO 2 in the lowest 4 km of the atmosphere. To simulate flask sampling, data were selected from profiles of CO 2 measured continuously with an onboard (in situ) analyzer. We find that midday column means can be determined without bias relative to true column means measured by the in situ analyzer to within 0.15 and better than 0.10 ppm by using 10 and 20 instantaneously collected flask samples, respectively. More precise results can be obtained by using a flask sampling strategy that linearly integrates over portions of the air column. Using less than 8-10 flasks can lead to significant sampling bias for some common profile shapes. Sampling prior to the breakup of the nocturnal stable layer will generally lead to large sampling bias because of the inability of aircraft to probe large CO 2 gradients that often exist very close to the ground at night and during the early morning.

Variation of CO<sub>2</sub> mole fraction in the lower free troposphere, in the boundary layer and at the surface

“…In accordance with the conclusion of Bakwin et al (2003) our study suggests that few flask air samples are not always sufficient to represent the mean PBL value of the CO 2 mole fraction, especially in winter when occasionally only 1-3 flask samples were taken in the PBL. The estimation of the mean PBL mole fraction by interpolation of flask air sample values may deviate from the real one (as determined by in situ measurements) by as much as 2 µmol mol −1 on average.…”

“…5. It was already discussed by Bakwin et al (2003) that the mean PBL mole fraction usually cannot be estimated free of bias from airborne flask air samples from a small number of levels.…”

Evaluating a 3-D transport model of atmospheric CO<sub>2</sub> using ground-based, aircraft, and space-borne data

“…To help evaluate the model vertical distribution of CO 2 throughout the troposphere we use aircraft data from the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL, Matsueda et al, 2002); Intercontinental Chemical Transport Experiment North America (INTEX-NA, Singh et al, 2006); the COBRA campaign (Bakwin et al, 2003); and Airborne Extensive Regional Observations in Siberia (YAK-AEROSIB, Paris et al, 2008Paris et al, , 2010. Table 1 provides a summary of these campaigns; for the sake of brevity, we refer the reader to the dedicated campaign literature, as cited above, for further details of each dataset.…”

“…We also showed that the model reproduced GLOBALVIEW surface concentration data over North America. A preliminary study using data from the 2003 CO 2 Budget and Rectification Airborne experiment (COBRA) (Bakwin et al, 2003) showed that the model had a positive bias of 2 ± 3.5 ppm throughout the boundary layer, suggesting too weak model vertical mixing; a relatively small model bias in the free troposphere (2-6 km) where surface flux signatures are relatively weak, increasing to a positive bias of 2.3 ± 1.8 ppm at 8-10 km that was attributed to a possible error in describing stratosphere troposphere exchange (Shia et al, 2006).…”

Assessing the regional surface influence through Backward Lagrangian Dispersion Models for aircraft CO<sub>2</sub> vertical profiles observations in NE Spain

“…Bakwin et al, 2003), from aircraft vertical sampling (Wofsy et al, 1988;Lloyd et al, 2001;Font et al, 2010) or by performing Lagrangian boundary layer budget campaigns (Schmitgen et al, 2004;Martins et al, 2009;Sarrat et al, 2009). The estimation of the regional surface fluxes based on a single tall tower is restrained by the influence of local fluxes (of up to 50 km distance) .…”