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Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. [2] Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depends on the temperature and pressure of the system of interest.
30 sty 2023 · Here is a table with the volume percent of different gases found in air. Volume percent means that for 100 L of air, there are 78.084 L Nitrogen, 20.946 L Oxygen, 0.934 L Argon and so on; Volume percent mass is different from the composition by mass or composition by amount of moles.
It is sometimes convenient to quote water vapour concentration as kg/kg of dry air. This is used in air conditioning calculations and is quoted on psychrometric charts. The following calculations for water vapour concentration in air apply at ground level.
The unit of absolute humidity is g.m^-3 expressed as grams of moisture per cubic meter of air. Consider the example: a maximum of about 30 grams of water vapour can be present in a cubic meter volume of air with a temperature in the middle 80s.
A related measure of concentration is the mass concentration ρX, representing the mass of X per unit volume of air (we will also use ρX to denote the mass density of a body, i.e., its mass per unit volume; the proper definition should be clear from the context). ρX and nX are related by the molecular weight MX (kg mol-1)ofthe gas: (1.8)
The mixing ratio of water vapour in air is the weight of water vapour mixed into a given weight of dry air. The unit is kg/kg. This is the vertical axis of the psychrometric chart.
Relative humidity tells us how much water vapor is in the air compared with the maximum possible. At its maximum, denoted as saturation, the relative humidity is 100%, and evaporation is inhibited. The amount of water vapor in the air depends on temperature.
