Carbon dioxide uptake of a forested region in southwest France derived from airborne CO2 and CO measurements in a quasi-Lagrangian experiment

International audienceThis paper presents a Lagrangian budgeting approach to quantify the uptake of CO2 by vegetation at horizontal scales of several tens of kilometers. For this purpose, CO2 and meteorological parameters were measured from a small aircraft during four flights in June 2001 over a flat homogeneous and productive temperate forest in the Landes region ( southwestern France). Additional CO measurements were made in order to identify and quantify the potential influence of anthropogenic emissions on the net CO2 flux derived from the measurements. For one of four flights, Lagrangian conditions were nearly perfectly fulfilled. On average, the CO2 mixing ratio in the boundary layer decreased at a rate of 0.11 ppm km(-1), yielding an average CO2 uptake by the forest of 16 +/- 2.5 mumol m(-2) s(-1) between 1230 and 1430 UT. Our result is about 15% smaller than the local net ecosystem exchange measured by eddy covariance at a tower north of the flight domain and about 12% higher than a regional estimate based on remote sensing data for the whole experimental area. The contribution of anthropogenic emissions to the regional CO2 budget was estimated from the CO measurements to be to <0.5 mu mol m(-2) s(-1)

An improved fast-response vacuum-UV resonance fluorescence CO instrument

The fast-response resonance fluorescence instrument for the airborne measurement of carbon monoxide described by Gerbig er al. [1996] was modified by implementing an improved optical filter with more efficient optics and an optimized resonance lamp. Besides reductions in size and weight, the new instrument achieves a sensitivity 10 times higher, a lower background (65 ppb compared with 250 ppb), and a faster time response (<0.1s) than the original instrument. The precision is +/-1.5 ppb at an atmospheric mixing ratio of 100 ppb CO, and the detection limit is 3 ppb (2 sigma) for an integration time of 1 s. First results from the North Atlantic Regional Aerosol Characterization Experiment (ACE-2) campaign during July 1997, when the new instrument was deployed aboard the U.K. Meteorological Office C-130 aircraft, are used to demonstrate the performance of the new instrument

Airborne intercomparison of vacuum ultraviolet fluorescence and tunable diode laser adsorption measurements of tropospheric carbon monoxide

During the fall 1997 North Atlantic Regional Experiment (NARE 97), two separate intercomparisons of aircraft-based carbon monoxide measurement instrumentation were conducted. On September 2, CO measurements were simultaneously made aboard the National Oceanic and Atmospheric Administration (NOAA) WP-3 by vacuum ultraviolet (VUV) fluorescence and by tunable diode laser absorption spectroscopy (TDLAS), On September 18, an intercomparison flight was conducted between two separate instruments, both employing the VUV fluorescence method, on the NOAA WP-3 and the U,K. Meteorological Office C-130 Hercules. The results indicate that both of the VUV fluorescence instruments and the TDLAS system are capable of measuring ambient CO accurately and precisely with no apparent interferences in 5 s. The accuracy of the measurements, based upon three independent calibration systems, is indicated by the agreement to within 11% with systematic offsets of less than 1 ppbv. In addition, one of the groups participated in the Measurement of Air Pollution From Satellite (MAPS) intercomparison [Novelli ef at., 1998] with a different measurement technique but very similar calibration system, and agreed with the accepted analysis to within 5%. The precision of the measurements is indicated by the variability of the ratio of simultaneous measurements from the separate instruments, This variability is consistent with the estimated precisions of 1.5 ppbv and 2.2 ppbv for the 5 s average results of the C-130 and the WP-3 instruments, respectively, and indicates a precision of approximately 3.6% for the TDLAS instrument. The excellent agreement of the instruments in both intercomparisons demonstrates that significant interferences in the measurements are absent in air masses that ranged from 7 km in the midtroposphere to boundary layer conditions including subtropical marine air and continental outflow with embedded urban plumes. The intercomparison of the two VUV instruments that differed widely in their design indicates that the VUV fluorescence technique for CO measurements is not particularly sensitive to the details of its implementation. These intercomparisons help to establish the reliability of ambient CO measurements by the VUV fluorescence technique