Station News

Return to : Station News Index

Logo Note about our Air Quality Sensor


Posted on 20th Sep 2020

You may have noticed this morning, that our onsite Air Quality Monitor has been reading high, don't worry it's not smoke.

In foggy conditions or Sea Mist/Fog etc., our PurpleAir device may measure fog (aerosols) as particles and therefore overestimate PM2.5 and PM10. High-cost devices are equipped with sample heaters that heat up the air sample and enable the device to differentiate between fog and particulate matter.

However they are a tad too costly for a retiree.

Further investigation during today, has seen that the PM levels have not abaited and we believe due to the fact that the combination of sea salt aerosols ( Sea Mist ) as well local Household Woodfire's ( staying Low Lying ) are the cause, Note our own Fire has not been alight since late last night.

Fog, mist and haze all affect visibility, which is an important part of forecasts affecting many aspects of life, from driving conditions to shipping and aviation.

Fog and mist differ by how far you can see through them. Fog is when you can see less than 1,000 meters away, and if you can see further than 1,000 metres, we call it mist.

In our meteorological glossary fog is defined as 'obscurity in the surface layers of the atmosphere, which is caused by a suspension of water droplets'.

By international agreement (particularly for aviation purposes) fog is the name given to resulting visibility less than 1 km. However, in forecasts for the public, this generally refers to visibility less than 180 m.

Mist is defined as 'when there is such obscurity and the associated visibility is equal to or exceeds 1000 m.' Like fog, mist is still the result of the suspension of water droplets, but simply at a lower density.

Mist typically is quicker to dissipate and can rapidly disappear with even slight winds, it's also what you see when you can see your breath on a cold day.

A third term you might also hear mentioned is haze. This is a slightly different phenomenon which is a suspension of extremely small, dry particles in the air, not water droplets. These particles are invisible to the naked eye, but sufficient to give the air an opalescent appearance.