Measurements Provided:
Concentration of atmospheric oxygen relative to atmospheric nitrogen, in units of "per meg" (or 0.0001% or 1/1000000) deviation from a reference value, and concentration of atmospheric carbon dioxide as mole fraction in dry air in ppm.
Measurement Characteristics:
- Overall estimate of uncertainty: 5 per meg
- Response time: 0.4 Hz (raw data sampled at 10 Hz) for sensor, but mixing in inlet and trap volumes results in a 20 s smoothing window.
- Precision: 2.5-4.0 per meg (5 s integrated measurement) dependent on aircraft motion.
- Other measurement characteristics (comments on signal/noise, bias limits, etc):
- Measurements are relative to the Scripps O2 Program O2 scale, with zero relative to a stored reference sample of air.
History of Significant Changes:
AO2 flew on the ACME-07, START-08, all 5 HIPPO campaigns, ARISTO-2015, ORCAS, and all 4 ATom campaigns. Mid-way through START-08, the non-pressure-controlled 1/4" Synflex inlet tube was replaced with a pressure-controlled 1/8" stainless tube, which fixed a pressure-dependent inlet surface effect problem. The earlier data have been corrected but have greater uncertainty.