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Question about measuring moisture content in air using Relative Humidity

  • 03-02-2020 1:37am
    Registered Users Posts: 219 ✭✭

    Hi there,

    I have a question about understanding "relative humidity" that I hope you could kindly help me with?

    I have asthma and I'm trying to figure out whether the humid climate in Ireland would affect my condition in any way. For example I've noticed in the past my symptoms tend to worsen during the winter months but actually improve when I'm on holiday in the south of Spain during the summer months.

    I was thinking that my symptoms are affected in the way I've described above because the Irish winter months have high relative humidity(November has RH of 80%) and the summer months in Spain have relatively low humidity(Spain in June has RH of 60%).

    However I'm struggling to understand how "relative humidity" measures the actual moisture content in the air considering that RH changes based on how warm the air is at a particular time? I've read that the warmer the air is the more moisture it can hold. If the RH in my home is 50 percent at the moment when my central heating is turned off and then becomes 40 percent after I have turned the heating on, am I right in saying that the moisture level in my home hasn't changed at all? The only thing that has changed is the air in my home has a greater capacity for holding moisture than it did before I turned on the heating?

    Any helpful information that you could kindly provide on relative humidity would be greatly appreciated!


  • Registered Users Posts: 3,593 ✭✭✭Pa ElGrande

    RH is an issue for me monitoring data centers that's why I'm posting this diagram. Hope it makes sense I don't have time to write a full explanation now.

    My brother used to have asthma as a child, factors like temperature and other pollutants or particles (mould, dust, smoke) tend to hang around with higher humidity.


    Net Zero means we are paying for the destruction of our economy and society in pursuit of an unachievable and pointless policy.

  • Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir

    Dewpoint, rather than relative humidity, is the true indicator of moisture content of the air (i.e. the mixing ratio, in g of water vapour per kg air). As dewpoint increases, so does mixing ratio, but the relationship is not linear, as shown below.

    Pressure: 1013 hPa

    Dewpoint (°C)|Mixing ratio (g/kg)

  • Registered Users Posts: 219 ✭✭segosego89

    I didn't get a chance to look back over this thread until now. Thanks to both of you for your helpful replies to my original post.