HUMIDITY AND DEW POINT

Humidity amount of water vapor in the air

Specific Humidity Saturated Air ACTUAL amount of water vapor in the air at a given time and place Units - g of water vapor / Kg of air Saturated Air At a steady temperature the amount of water vapor is at it’s peak (maximum) Rate of condensation = Rate of evaporation Dependent on air temperature Higher the air temp. - greater the amount of water vapor in the air Water vapor in air doubles every 10°C

Dew Point The temperature at which air is cooled to become saturated and condensation begins More water vapor in the air Less the air has to cool Higher the Dew Point weather.stives-town.info

Relative Humidity Comparison of the specific humidity and the maximum amount of water vapor that the air can hold at a given temperature and pressure UNIT - % Relative humidity = specific humidity X 100% maximum capacity 100% Rel. Hum. – saturated air 0% Rel. Hum. – dry air

Psychrometer Instrument to measure humidity Dry bulb – measures air temp. Wet bulb – has a water soak wick around the bulb – water evaporates – cools the air

Evaporation is a cooling process

Psychrometer Dry air - greater evaporation - greater cooling - greater the difference in the 2 temperatures High humidity – no evaporation (saturated air) - temperatures of the 2 bulbs will be the same or very close

Evaporation question Why do you feel so hot and sticky on hot, humid days in the summertime?

Answer High humidity means air has a lot of water vapor in it. Your body sweats but the water has no where to go so it stays on your body and you feel sticky and aren’t cooled by the evaporation of the sweat.