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Why is the hydrogen sulfide (H₂S) value so high?

The most likely cause of a high reading, is the presence of hydrogen sulfide (H₂S).

The hydrogen sulphide (H₂S) sensor installed in the air-Q measures based on an electrochemical measuring principle. An abrupt change in temperature or humidity, e.g. by opening a window, can affect the sensor and lead to a positive or negative peak in the sensor readings. Such peaks disappear after a few minutes and do not require any action by the user.

However, various effects, e.g. climatic shocks, can also cause a shift of the zero line here. The air-Q can normally correct incorrect values automatically within a few days (automatic calibration). However, a prerequisite for this is that the air-Q is in a fixed location and in a dynamic / clean environment, i.e. that it is regularly ventilated. One of the indicators used here is the VOC value, which must regularly fall below 700 ppb. If the necessary general conditions cannot be achieved or can only be achieved rarely, the automatic calibration does not work well or fast enough. In this case, manual calibration can help.

See here: How do I perform a manual calibration?

Another reason for very high or abnormal measured values can be the cross-sensitivities of the hydrogen sulfide sensor. For example, it reacts positively to hydrogen sulfide, nitric oxide; negatively to alcohol and ozone(O₃).

All general conditions must therefore be checked and the measured values must also be brought into connection with the measured value of the nitrogen dioxide (NO₂) sensor and ozone (O₃) sensor in the air-Q in order to exclude possible cross-sensitivities as a cause.

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