Overview

Since its inception in 1992, the Global Greenhouse Gas Reference Network’s aircraft program has been dedicated to collecting air samples in vertical profiles over North America. The program's mission is to capture seasonal and inter-annual changes in trace gas mixing ratios throughout the boundary layer and free troposphere (up to 8000m/26,000 ft). At present, most aircraft program flights collect 12 flask samples at different altitudes (up to 13,279 m/43,555 ft). These samples are stored in glass flasks for later analysis of Carbon Dioxide (CO₂), Carbon Monoxide (CO), Nitrous Oxide (N₂O), Methane (CH₄), Molecular Hydrogen (H₂), and Sulfur Hexafluoride (SF₆), as well as isotopes of CO₂ and CH₄, and multiple Halo- and Hydrocarbons.

Data collected by the aircraft program provide a view of how the large-scale horizontal and vertical distribution of the measured trace gases change throughout a given year over the continent. The large-scale, three-dimensional picture of how trace mixing ratios change throughout the year has provided a means to estimate the contribution of the North America continent to the atmospheric concentration of long-lived tracers like carbonyl sulfide and CO₂ (e.g Montzka et al. 2007 and Crevoisier et al. 2010) and an essential benchmark for forward and inverse modeling (i.e. Stephens et al. 2007; Yang et al., 2007; Peters et al. 2007; Maddy et al. 2008; Xiong et al. 2008; Campbell et al. 2008).

Project Goals

To facilitate a broad-scale sampling program across North America it was important to establish a sampling protocol that would not require technical expertise at the sampling sites. This was accomplished by developing a portable, automated system for obtaining air samples that can be quickly shipped back to NOAA/GML for carefully calibrated and quality-controlled measurements. At a predetermined altitude, the sampling system is simply activated by a toggle switch that is easily accessible to the pilot. Time, location and auxiliary variables such as temperature and relative humidity are logged with each sample and downloaded into the NOAA/GML database when the samples are returned to the laboratory.

The aircraft program is actively pursuing alternative sampling strategies. Intensive sampling campaigns are focused on specific processes such as Lagrangian flux experiments or fossil fuel emission validation experiments. Additionally, work is being done to pursue in-situ measurements on commercial aircraft. It is anticipated that data resulting from commercial aircraft will significantly enhance the frequency and spatial distribution of profiles.

Sampling frequency and height distribution varies at each site, but samples are collected from 500 m above ground to 8000 m above sea level at the majority of aircraft sites. While sampling flights have been conducted at some sites as often as two to three times per week, sample flights at most sites are only carried out once every two to three weeks.