A review into the procedures for checking equipment in the Upper Hunter Air Quality Monitoring Network is underway, following a false reading that sparked a health warning.
The Muswellbrook PM2.5 monitor posted a high reading over the weekend and is currently being investigated by the Department of Environment, Climate Change and Water (DECCW).
A public air quality alert was issued, saying the very pine particles had exceeded national health standards.
However there was not an increase in the PM10 results, which would have been expected if smoke was present in the area.
According to the DECWW, the cause of the reading was an instrument malfunction and technicians were called to recalibrate the machine.
Foreign matter had entered the sample line after instruments were checked last Friday and data for the period has now been invalidated because no occurrence of exceeding PM 2.5.
A public apology has been issued and the department says it is reviewing procedures to ensure no similar occurrences happen again.
In December, the DECWW launched the Upper Hunter Air Quality Network, allowing residents to check current air quality online 24 hours a day.
Image: Muswellbrook Council