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Weather Station Hardware => Air Quality Sensors => Topic started by: hmderek on October 23, 2020, 08:43:15 AM

Title: How does fog affect air quality?
Post by: hmderek on October 23, 2020, 08:43:15 AM
Been looking at my Davis AirLink data for a week or so. We've been having some morning with quite a lot of fog. It seems that when the fog lifts, PM level drop.

I've been searching a bit on the relation between fog and air quality, but can't make too much sense of it yet.

Bottom line, I am wondering if the fog is causing the AirLink to show increased PM values, or of the fog correlates with actual decreased air quality. There doesn't seem to be a clear relation between humidity levels and PM values showing by the AirLink, so I'm assuming that it's not just the sensor being affected by humidity.

I'm assuming that the fog isn't actually caused by bad air quality.

Title: Re: How does fog affect air quality?
Post by: miraculon on October 23, 2020, 08:45:44 AM
I would guess that the airborne fog droplets are sensed as "particles".

Greg H.
Title: Re: How does fog affect air quality?
Post by: hmderek on October 23, 2020, 09:26:36 AM
Just stumbled upon this:

'The influence of humidity on the performance of a low-cost air particle mass sensor and the effect of atmospheric fog'

https://amt.copernicus.org/articles/11/4883/2018/amt-11-4883-2018.pdf
Title: Re: How does fog affect air quality?
Post by: Jai Soone on October 23, 2020, 01:11:25 PM
The conclusions of yet another detailed analysis:

Data from these devices are precious and extremely informative;

They can be used reasonably confidently in fair weather conditions and with low time resolution;

Careful data treatment and evaluation are required in two main cases: airsheds affected by mineral dust, and more generally, during relatively high humidity conditions, rain and fog are observed.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7309006/
Title: Re: How does fog affect air quality?
Post by: galfert on October 23, 2020, 02:01:06 PM
TL;DR
Expensive professional air quality sensors use a heater to rid the air of moisture so that it isn't read by the sensor as particles.
Title: Re: How does fog affect air quality?
Post by: waiukuweather on October 23, 2020, 03:46:51 PM
fog affects my readings too (Davis sensor)
good way to see when the fog developed though
Title: Re: How does fog affect air quality?
Post by: the beteljuice on October 23, 2020, 04:35:58 PM
These optical devices go silly when T - DP <= 2C

That equates to RH approx. > 88%

I keep posting in various places that these 'home' devices are nice toys, and give an appreciation of (only) Particulate Matter size within your locale.

Further, the AQI is modelled on what someone thinks the 'normal' pollutant levels / constituents are.

Many of you in the US may have purchased these with all the recent fire activity ...
1/ Yes, they make a good smoke detector.
2/ Anything serious will go 'over scale' and close down the readings.
3/ Shortens the useful life of the sensor (usually < 5yr)
4/ Actual AQI value is meaningless - it is expecting dust / grit particles.