| Summary: | Statement: Parameters logged by the fCO2 system and ship sensors are quality controlled after each voyage. 1. Data with missing parameters or obvious outliers for the ship or fCO2 system parameters are marked as missing and removed from the calculations. Parameter values are flagged as good (flag=2), questionable (flag=3), or bad (flag=4), depending on the range of values expected. Many of the ship and CO2 system parameters are not reported in the final dataset, but are used to establish that the system is functioning correctly. For example, water flow rates to the equilibrator below 2 LPM are flagged as questionable and the cause investigated with the flag value changed to 4 if the flow has been interrupted or is insufficient. Similar checks are made to ensure the gas flow through the infrared gas analyser is in a suitable range (50 to 120ml/min). The list of parameters checked are: CO2 system data quality controlled: GPS date and Time Latitude and Longitude Water flow rate Gas flow rates through licor analyser Atmospheric pressure Equilibrator pressure Equilibrator water temperature Mole fraction CO2 Water vapour in gas stream Licor NDIR temperature Ship's data quality controlled: GPS date and time Latitude and Longitude Sea surface temperature Sea surface salinity Relative wind speed and direction True wind speed and direction 2. The data sets are next evaluated for excessive warming of the seawater flowing to the equilibrator, and for contamination of the atmospheric measurements by ship stack gas. The fCO2 value in the water is sensitive to warming between the ship intake and equilibrator. The travel time between the ship intake and equilibrator is first checked by comparing the timing of rapid changes in surface water temperature for the intake (SST) and the equilibrator temperatures. The travel time or lag time is usually about 4 minutes, although this can vary due to ship engineers altering the flow rates through the water line and other users removing water. The lag is accounted for in the warming ...
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