Wrong Calibration Gas 2017

• This issue is known since March 2019, which was too late for some of the FLUXNET uploads we did at the same time. Affects fluxes by approx. 3%.
• This issue can be corrected with the script CGC Calibration Gain Correction, available on GitLab, or directly with FCT v0.9.5+.

CO2 standards measured by UniBe were off

by PM

The Problem

CO2 standards, measured at 15.07.2016 were off by 10-15 ppm. We measured the flasks at EMPA (CZ) on 07/03/2019 and found roughly 14 ppm difference (see below). After knowing this, I confronted ML and he immediately found the problem: the calibration was done using a cubic calibration function (UniBe1) instead of a linear one (UniBe2). This resulted in approx 12 ppm difference. Considering the “wrong” air matrix of the synthetic air (only 20% O2, no Ar), the EMPA measurements are roughly 1 ppm underestimated. This leads to a difference of approx 1.5 ppm between EMPA and UniBe2.

Conclusions

• UniBe2 are the correct concentrations
• we calibrated with the wrong concentrations (UniBe1) at the dates in the table below

Erroneous flasks

Calibrations with the wrong standards

CH-AWS

• Affected time period: all IRGA72 CO2 concentrations between 2017101207.A00 and 2019112107.A00.
• Affected time periods are also shown in EC Raw Binary Format (CH-AWS).

CH-CHA

• Affected time period: all IRGA75 CO2 concentrations between 2017011114.C57 and 2017031507.C00.
• Due to the replacement of in 15 Mar 2017, only a short time period of approx. 2 months is affected by the wrong calibration gas.
• Affected time periods are also shown in EC Raw Binary Format (CH-CHA).

CH-DAV

• The LI-7200 used for EC at CH-DAV was not affected by the wrong calibration gas.

CH-FRU

• Affected time period: all IRGA75 CO2 concentrations between 2016113012.b47 and 2019112707.X00.
• From the notes, it was not clear if 2016 and 2017 were affected.
• Affected time periods are also shown in EC Raw Binary Format (CH-FRU).

CH-LAE

• Affected time period: all IRGA72 CO2 concentrations between 2017121417.L22 and 2019031523.L20.
• Affected time periods are also shown in EC Raw Binary Format (CH-LAE).

CH-INO

CH-OE2

• Affected time period: all IRGA72 CO2 concentrations between 2018100419.o00 and 2019111313.o00.
• Affected time periods are also shown in EC Raw Binary Format (CH-OE2).

Downloads

• Original info file by PM (.md as .zip)
• Updated info file by PM (.md as .zip) 14 Apr 2020

Last Updated on 15 Feb 2024 21:22