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/ESRL 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/ESRL 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.