The most likely cause of a high reading, is the presence of Ozone (O₃) in the air.
The ozone (O₃) sensor 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 values. 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. The air-Q can normally correct faulty values automatically within a few days (automatic calibration). A prerequisite for this, however, is that the air-Q is in a dynamic / clean environment, i.e. is regularly ventilated. One indicator used here is the VOC value, which must frequently fall below 700 ppb. If the necessary conditions cannot be achieved or can only be achieved infrequently, the automatic calibration does not work well or fast enough. In this case, manual calibration can be helpful.See here: How do I perform a manual calibration?.
Another cause for selectively very high or deviating measured values can also be the cross-sensitivities, which the ozone sensor has. For example, it reacts positively to Nitrogen dioxide (NO₂), Ethanol (C₂H₅OH) and Chlorine (Cl) and negatively from Hydrogen sulfide (H₂S).
All general conditions must therefore be checked and the measured values must also be brought into connection with the measured value of the ozone (O₃) sensor and the nitrogen dioxide (NO₂) sensor as well as the VOC sensor in the air-Q in order to exclude possible cross-sensitivities as a cause.