The way to monitor the calibration is by mean of Standard Lamp test. In particular the ratio R6 is a measure of ozone but using the internal standard lamp as a light source. In the analysis of the campaign we look at the SL ratios to check the instrument stability. Comparing the SL Ratios with the original configuration and the final one it's a good tool to check the possible change on the instrumental calibration of the instrument (Figure 2).

Figure 2: Evolution of the SL values respect reference values using the initial configuration (upper plot) and final one (lower plot)

The calibration provides a R6 reference value, usually the vale recorded during the calibration. Previous reference values and new ones with the observed values are shown in Table 2.

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Original

Original

Final

Final

Table 2&nbsp;: R6 reference values and mean values during the campaign with the initial and final configuration.

<br> A difference from the reference value more than five units normally indicates the need of SL correction. Looking to the SL data we can conclude the Arosa brewers 040,072,156 and probably 163 needs standard lamp correction for the analysis of the ozone when using the original configuration; whereas for the final configuration no SL is needed for any instrument. (Figure 4)

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Figure 3: SL R6 differences between observations and reference values, also difference between initial and final configuration is showed

<br> Also we can consider also a change in more than 5 units on SL between the original and final instrument calibration is a major change in instrument configuration. So modifications on the instrumental calibration (F) of brewers #017, #156 and #163 will produce a significative change in the ETC calibration.

<br> The temperature range of the instruments during the campaign was very high (from 10º to 40º). The behaviour of the instruments against temperature is plot on figure 4 the calculated slopes of the regression lines are summarized in table 4.

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Table 3: Temperature dependence R6 units/Cº

<br> [File:FigureSL_temp.png]]

Figure 4&nbsp;: Temperature dependence of the instruments during the campaign, original configuration (blue) and final configuration (green).