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Why are the air quality measurement devices located on the roof (pictures in tge article)? Fresh air is up there, but what people breathe is air closer to the s

Why are the air quality measurement devices located on the roof (pictures in tge article)? Fresh air is up there, but what people breathe is air closer to the surface.

quercusa 3y ago
There's not going to be any significant difference between 2m and 10m. A better question might be why they are measuring temperature there on a hot roof and not over grass. According to NOAA, that's a Class 5 location (the worst): Class 5 (error ≥ 5ºC) – Temperature sensor located next to/above an artificial heating source, such a building, roof top, parking lot, or concrete surface. (Section 2.2.1 of the U. S. Climate Reference Network Site Information Handbook) http://www1.ncdc.noaa.gov/pub/data/uscrn/documentation/program/X030FullDocumentD0.pdf http://www1.ncdc.noaa.gov/pub/data/uscrn/documentation/progr...
- phonon 3y ago
  How do you know those instruments in the photo are measuring temperature?
  - giantg2 3y ago
    I'd assume (maybe wrongly) proper air measurement would require some adjustment for things like density based on altitude, temperature, etc so there's a standard to compare it to.
  - stephen_g 3y ago
    The cylindrical unit half way up the pole and to the right with the louvres is a solar radiation shield that would be typical for containing a thermometer and possibly a humidity sensor - the louvres let the air through without letting direct sunlight hit the thermometer and throw off its reading. But I’m sure they aren’t using it as a calibrated value (obviously they would have guidelines for placement and would know this doesn’t meet them), it’s probably just being used as an indicative reading.
- pbhjpbhj 3y ago
  Edge effects are a massive thing in fluid flow. I'd expect there to be a significant difference between air quality at ground level (human mouth level) and 2nd-storey level. Isn't the turbulent flow around ground obstructions likely to make more pollutants gather in the boundary layer, and the lower flow rate ensure they're not swept away? (I don't know the answer, I'm asking a question to check my intuition)

Why are the air quality measurement devices located on the roof (pictures in tge article)? Fresh air is up there, but what people breathe is air closer to the surface.

quercusa 3y ago

There's not going to be any significant difference between 2m and 10m. A better question might be why they are measuring temperature there on a hot roof and not over grass. According to NOAA, that's a Class 5 location (the worst): Class 5 (error ≥ 5ºC) – Temperature sensor located next to/above an artificial heating source, such a building, roof top, parking lot, or concrete surface. (Section 2.2.1 of the U. S. Climate Reference Network Site Information Handbook) http://www1.ncdc.noaa.gov/pub/data/uscrn/documentation/program/X030FullDocumentD0.pdf http://www1.ncdc.noaa.gov/pub/data/uscrn/documentation/progr...

phonon 3y ago
How do you know those instruments in the photo are measuring temperature?
- giantg2 3y ago
  I'd assume (maybe wrongly) proper air measurement would require some adjustment for things like density based on altitude, temperature, etc so there's a standard to compare it to.
- stephen_g 3y ago
  The cylindrical unit half way up the pole and to the right with the louvres is a solar radiation shield that would be typical for containing a thermometer and possibly a humidity sensor - the louvres let the air through without letting direct sunlight hit the thermometer and throw off its reading. But I’m sure they aren’t using it as a calibrated value (obviously they would have guidelines for placement and would know this doesn’t meet them), it’s probably just being used as an indicative reading.
pbhjpbhj 3y ago
Edge effects are a massive thing in fluid flow. I'd expect there to be a significant difference between air quality at ground level (human mouth level) and 2nd-storey level. Isn't the turbulent flow around ground obstructions likely to make more pollutants gather in the boundary layer, and the lower flow rate ensure they're not swept away? (I don't know the answer, I'm asking a question to check my intuition)