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AQHI and fog

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  1. #1

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    AQHI and fog

    Anyone else noticed how the AQHI index always seems low when there is a lot of fog (of the meteorological kind)?

    Is this coincidence or is there something about fog which traps the air pollution? Worse still, could it be that the roadside sensors don't work accurately when it's foggy?!Name:  ImageUploadedByGeoClicks1427851009.875768.jpg
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  2. #2

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    Difference between fog and smog (the latter known as "haze" to the observatory).

    The real fogs normally happen when the wind shifts offshore, and our pollution gets blown away north and west.

    We get the big smogs when the wind is coming from those directions (or there's not much wind) - combination of home-grown pollution and stuff from our Northern Neighbour (I'm sure others will also remember the sandstorm a few years back that came off the Gobi Desert and some days later sent HK's pollution index off the charts).

    pb1234 likes this.

  3. #3

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    So do you think the pollution readings are correctly showing low pollution in foggy days, because the winds have blown in the fog and blown away the smog?


  4. #4

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    AQHI and fog

    Interesting question.

    How do you determine what you are seeing is real fog and not some other sh*te?

    With the reported temp/dew point spread?

    Last edited by 100LL; 01-04-2015 at 02:30 PM.

  5. #5

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    According to a SCMP article, breathing in fog is not a good idea either...think the article was summat to do with mould busters...


  6. #6

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    Ultimately if we can confirm that the AQHI readings are accurately measuring the bad stuff, and that the measurements aren't distorted by the presence of meteorological fog, then I'd be happy to assume the fog on a day when AQHI is low, is real vapour fog, ignoring for now whether or not that is any better / worse than the bad stuff.

    So for me it comes down to whether or not the AQHI is still accurate (for the bad stuff) when there is meteorological fog around.


  7. #7

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    Lets clarify the HKO's use of "haze" first. They seem to be spot-on with their usage actually. So in the future, whenever they say its hazy, its actually very "dusty"

    http://en.m.wikipedia.org/wiki/Haze

    Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand and snow.[1] Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires.
    and

    Haze often occurs when dust and smoke particles accumulate in relatively dry air. When weather conditions block the dispersal of smoke and other pollutants they concentrate and form a usually low-hanging shroud that impairs visibility and may become a respiratory health threat. Industrial pollution can result in dense haze, which is known as smog.
    So in order to be "hazy", it actually has to be dry. I usually look at the temperature/dew point spread to understand if we have "visible moisture" (in form of fog etc) or not. Knowing that "haze" actually means the air is crap, saves me this step.

    In your case, it will also let you focus on the really foggy days to answer your question. My guess, the particle pollution actually functions as nucleus for the moisture, and less will get trapped in the HKO's sensors, hence resulting in lower reading (theory to be confirmed).

  8. #8

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    Quote Originally Posted by pb1234:
    Ultimately if we can confirm that the AQHI readings are accurately measuring the bad stuff, and that the measurements aren't distorted by the presence of meteorological fog, then I'd be happy to assume the fog on a day when AQHI is low, is real vapour fog, ignoring for now whether or not that is any better / worse than the bad stuff.

    So for me it comes down to whether or not the AQHI is still accurate (for the bad stuff) when there is meteorological fog around.
    I suggest the best bet is to call the EPD. They could give you the answer from the horse's mouth.

    2827 8541

  9. #9

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    Also, check this link (last paragraph and first of next page):

    https://books.google.com.hk/books?id...tput=html_text

    (Sorry, I am on my mobile phone)