Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey
Speaker 1: brain Stuff, I'm Lauren vocal Bam. And if you've ever
Speaker 1: been in the American South on a hot August day,
Speaker 1: you're familiar with the incredible mugginess of borderline hallucinatory experience,
Speaker 1: where you feel like you're walking in a stew of
Speaker 1: your own perspiration. But there's more to understanding that clammy
Speaker 1: gross feeling than simply glancing at a weather forecaster's humidity reading.
Speaker 1: To really get a grasp on how humidity affects your health,
Speaker 1: your home, and your sanity, you need insights on the
Speaker 1: types of humidity, as well as the concept of dew point.
Speaker 1: Humidity can be measured in several ways, but relative humidity
Speaker 1: is the most common. But in order to understand relative humidity,
Speaker 1: it's helpful to first understand absolute humidity. Absolute humidity is
Speaker 1: the mass of the water vapor divided by the mass
Speaker 1: of the dry air in a given volume of air
Speaker 1: at a given temperature. The hotter the air is, the
Speaker 1: more water it can contain, which is why it's never
Speaker 1: quite so humid during cold winters. Relative humidity is the
Speaker 1: ratio of the current absolute humidity to the highest possible
Speaker 1: absolute humidity at the given air temperature. A reading of
Speaker 1: one percent relative humidity means that the air is totally
Speaker 1: saturated with water vapor and cannot hold anymore, creating the
Speaker 1: possibility of rain. This doesn't mean that the relative humidity
Speaker 1: must be one in order for it to rain. It
Speaker 1: must be one percent where the clouds are forming, but
Speaker 1: the relative humidity near the ground could be much lower.
Speaker 1: Humans are very sensitive to humidity, as our skin relies
Speaker 1: on the air to get rid of moisture. The process
Speaker 1: of sweating is your body's attempt to keep cool and
Speaker 1: maintain its current temperature because evaporation uses some of the
Speaker 1: thermal energy in the air to drive the transition of
Speaker 1: liquid sweat to water vapor, making it cooler around you.
Speaker 1: But if the air is already totally saturated at one
Speaker 1: percent relative humidity, sweat will not evaporate into the air.
Speaker 1: As a result, we feel much hotter than the actual temperature.
Speaker 1: When the relative humidity is high, your clothes may become
Speaker 1: saturated with perspiration that can't go anywhere, prompting the feeling
Speaker 1: of being a swampy bog monster of revolting proportions. If
Speaker 1: the relative humidity is low, However, we can feel much
Speaker 1: cooler than the actual temperature because our sweat evaporates, easily,
Speaker 1: cooling us off. For example, if the air temperature is
Speaker 1: seventy five degrees fahrenheit, that's twenty four celsius and the
Speaker 1: relative humidity is zero percent, the air temperature will feel
Speaker 1: like sixty nine fahrenheit or twenty one celsius to our bodies.
Speaker 1: But if the air temperature is seventy five degrees fahrenheit
Speaker 1: and the relative humidity is one, we feel like it's
Speaker 1: eighty degrees fahrenheit or twenty seven celsius. People tend to
Speaker 1: feel most comfortable at a relative humidity between thirty and fifty.
Speaker 1: Humidifiers and de humidifiers helped to keep indoor humidity at
Speaker 1: a comfortable level. They also vitally helped dry interior structures
Speaker 1: like drywall and lumber to prevent them from deteriorating due
Speaker 1: to moisture and subsequent mold. If you and out doorsy person,
Speaker 1: or just particularly sensitive to that clammy damp feeling you
Speaker 1: detect outside, it's vitally important to understand the difference between
Speaker 1: relative humidity and dew point, because the latter will actually
Speaker 1: give you a better idea of just how quickly you'll
Speaker 1: become uncomfortable with any exertion, and it's perhaps more often
Speaker 1: reported in weather forecasts. The dew point is, in short,
Speaker 1: the point at which dew droplets form on objects like grass.
Speaker 1: In other words, the temperature which a relative humidity of
Speaker 1: one is achieved. The higher the dew point, the muggier
Speaker 1: it will be, and the more uncomfortable you'll become. A
Speaker 1: dew point around fifty five is pretty comfortable, but higher
Speaker 1: than sixty five and you'll quickly realize how oppressive the
Speaker 1: situation really is. For example, a temperature of eighty degrees
Speaker 1: fahrenheit that's twenty seven celsius and a dew point of
Speaker 1: sixty degrees fahrenheit or fifteen celsius would mean a relative
Speaker 1: humidity of fifty percent. Humidity is calculated using a formula
Speaker 1: combining vapor pressure, temperature, dew point, and other factors. That
Speaker 1: relative is a level that most people won't enjoy unless
Speaker 1: they have easy access to a nice cool air conditioner.
Speaker 1: So when you hear a weather forecasters say it's eighty
Speaker 1: five degrees outside, but with the humidity it feels like
Speaker 1: ninety two degrees, that ninety two is a combination of
Speaker 1: the temperature and the dew point, also known as the
Speaker 1: heat index. As a rule of thumb, the closer the
Speaker 1: dew point is to the actual air temperature, the more
Speaker 1: likely it is that you'll feel like the air is
Speaker 1: uncomfortably humid. Today's episode was written by Nathan Chandler and
Speaker 1: produced by Tyler Clang. Brain Stuff is a production of
Speaker 1: iHeart Radio's How Stuff Works. For more on this and
Speaker 1: lots of other dewey topics, visit our home planet, how
Speaker 1: stuff Works dot com. And for more podcasts for my
Speaker 1: heart Radio, visit the iHeart Radio app, Apple Podcasts, or
Speaker 1: wherever you listen to your favorite shows.