I am working with a sunset RT-4 semi continous EC/OC analyzer. During these days I did some check on this one year old instrument, such as 3 peak calibration test. and it show the instrument underestimate OC about 20%. it seems MnO2 catalyzer need to be changed, and when I call distributor, they even don't know catalyzer need to be changed. Then I am wondering how many Sunset OC/EC RT-4 user use 3 peak calibration to check instrument. then our OC data from RT-4 maybe underestimated even if we calibrate instrument by sucrose.
Have you evaluated your instrument using sucrose? You can compare the calculated and measured carbon concentrations during sucrose experiments to check your instrument. As for the status or the efficiency of the MnO2 catalyzer, we usually use the calibration area (corresponding to the injected CH4) to evaluate. If the calibration area is constant, you don’t need to change the catalyzer. However, the catalyzer should be changed if the calibration area continued to decrease.
By the way, we recently found that the baseline determination method might also be responsible for the underestimation of OC. Refer to Zheng et al., Atmos. Meas. Tech., 7, 1969–1977, 2014 for more information.
Hi, Dr. Cheng. Thanks for your information about multipoint baseline. About 3 peak test, it is asked in DRI2001A operation, and 5% variation is fine, but in RT-4 there is no this requirement.
Since the 1st peak is in inert environment, MnO2-->Mn self-redox reaction, while the 2nd and 3rd peak is in 2% O2 environment, MnO2 works as catalyst. only calibaration peak may not show the whole instrument stability.
So I am asking how many RT-4 user use 3 peak check.
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