CO<sub>2</sub>, CO and CH<sub>4</sub> measurements from the NOAA Earth System Research Laboratory's Tall Tower Greenhouse Gas Observing Network: instrumentation, uncertainty analysis and recommendations for future high-accuracy greenhouse gas monitoring efforts

Abstract

A robust in situ CO₂ and CO analysis system has been developed and deployed at eight sites in the NOAA Earth System Research Laboratory's (ESRL) Tall Tower Greenhouse Gas Observing Network. The network uses very tall (> 300 m) television and radio transmitter towers that provide a convenient platform for mid-boundary layer trace gas sampling. Each analyzer has three sample inlets for profile sampling, and a complete vertical profile is obtained every 15 min. The instrument suite at one site has been augmented with a cavity ring-down spectrometer for measuring CO₂ and CH₄. The long-term stability of the systems in the field is typically better than 0.1 ppm for CO₂, 6 ppb for CO, and 0.5 ppb for CH₄, as determined from repeated standard gas measurements. The instrumentation is fully automated and includes sensors for measuring a variety of status parameters, such as temperatures, pressures and flow rates that are inputs for automated alerts and quality control algorithms. These algorithms provide detailed and time-dependent uncertainty estimates for all of the gases and could be adapted to other species or analysis systems. The design emphasizes use of off the shelf parts and modularity to facilitate network operations and ease of maintenance. The systems report high-quality data with > 93% uptime. Recurrent problems and limitations of the current system are discussed along with general recommendations for high accuracy trace-gas monitoring. The network is a key component of the North American Carbon Program and a useful model for future research-grade operational greenhouse gas monitoring efforts

Long-term greenhouse gas measurements from aircraft

“…9b and c) and the CH 4 median offsets in all three years (−0.1, 0.5, and 0.5 ppb, Fig. 10a-c) in situ comparisons at NOAA ground sites as well, and seem to have become more prevalent since 2011 (Andrews et al, 2013). Laboratory tests are currently underway to determine the cause of these high CO 2 flask anomalies, which is currently unknown.…”

“…Laboratory tests done with PFP flasks filled sequentially with a single tank and compared with single glass flasks (typically used in the NOAA ground network) show measurement offsets of −0.09 ± 0.05 ppm for CO 2 (http://www.esrl.noaa.gov/gmd/ccgg/aircraft/qc.html). Recent analysis of wet samples in the laboratory and comparisons with in situ CO 2 measurement systems on towers (Andrews et al, 2013) suggest that the PFP flasks may have uncertainties as high as 1 ppm for CO 2 due to possible surfacewater interactions when sampling wet air (as is done on the C-130) or due to residual water vapor in PFP flasks from insufficient drying prior to sampling. Unlike lower-pressure network flasks, the PFP flasks store air samples at 2700 hPa; effects of off-gassing from any surface area exposed to the sample will therefore be amplified.…”

High accuracy measurements of dry mole fractions of carbon dioxide and methane in humid air

“…These instruments have been shown to require infrequent calibration (less than once per day) to meet WMO/GAW (inter-laboratory compatibility) goals (Richardson et al, 2012;Andrews et al, 2013). In this paper, we will focus on analysers based upon cavity ring down spectroscopy (CRDS) manufactured by Picarro, Inc. (Santa Clara, CA).…”

“…The CRDS instrument (Model G1301, SN CFADS09) was installed for about two months during Fall 2011 at the 300-m tall Boulder Atmospheric Observatory (BAO) tower near Boulder, CO, where routine in-situ measurements are made using a LI-COR NDIR CO 2 analyser on a dried ambient air stream (Andrews et al, 2013). The water vapour correction coefficients were measured in the laboratory using Method #2 several months prior to this deployment.…”

Biological and physical influences on soil <sup>14</sup>CO<sub>2</sub> seasonal dynamics in a temperate hardwood forest

“…Atmospheric samples from the eddy covariance tower were also sampled from just above the forest canopy at 21 m above ground level into glass flasks, using a programmable flask package and compressor (Andrews et al, 2013). These whole-air samples were collected approximately every 6 days at 12:30 a.m. local time, so that they reflected respiration not influenced by photosynthesis.…”