AirCore Atmospheric Sampling System
The AirCore is an innovative atmospheric sampling system that consists
of a long tubing, usually in the shape of a coil, that can sample the
surrounding atmosphere and preserve a profile of the trace gas of
interest. The narrow diameter and long length are designed to
minimize the diffusive mixing occuring inside the tubing between
sampling and analysis.
The AirCore, invented and patented by Pieter Tans (the head of the Carbon Cycle Group
at NOAA/ESRL), has been rigorously evaluated and has been shown to provide measurement
precisions better or equal to silicate glass flasks for CO2 and CH4 in the following publication:
For more information, contact Anna Karion.
Sampling On A Balloon
The tubing is initially filled with a standard gas of known concentration (blue). Upon elevation to height H while open on one end, the fill gas evacuates to the minimum ambient pressure encountered (PH). While descending, the tubing equalizes with ambient pressure, filling slowly with surrounding air (rainbow colors). It is sealed when it lands, preserving the sample.
Post-Flight Analysis in Laboratory
The sample is pushed through the tube by opening both ends and running through a continuous analyzer. The air recovered from position xsample in the tubing can be related directly to the ambient pressure during sampling (Pa, sample) by the relationship below, assuming constant temperature in the tubing:
Aircraft Flight Validation
The AirCore was validated by carrying it on-board a light aircraft along with flasks and a Picarro CRDS CO2/CH4 analyzer. The three systems pulled in air through their own separate inlet systems. Results show no overall bias with respect to flasks; 66% of offsets between the systems were within 0.3 ppm of CO2 and 5 ppb of CH4.
Balloon Flights (September 2011)
On September 10, 2011, NOAA and CIRES scientists and engineers teamed up with Edge of Space Sciences (www.eoss.org) to launch three separate balloons with AirCore payloads. The main objective of these launches was to determine the level of agreement between the trace gas profiles for the three AirCores, and whether any differences were due to real atmospheric variability or due to differences in the AirCore samplers. The balloons had different burst altitudes ranging from 25 to 30 km and varied in their descent locations by between 5 and 10 km. The AirCores themselves also varied in their coating material and overall size. The figures show the profiles for CO2, CH4, and CO, as measured post-flight with a Picarro 4-species analyzer (model G2401). The second objective of the launches was to demonstrate the capability of the AirCore to sample the full column of the atmosphere and obtain accurate and precise measurements that can be compared and used for validation of satellite products, such as CO2 column means retrieved from NASA's Orbiting Carbon Observatory, to be launched in 2013.
