For dry air, its density at sea level at 59 °F (15 °C) and 14.7 psi (1013.25 hPa) (mean sea-level pressure) is approximately 0.0765 lb/(cu ft) (1.225 kg/(m^3)). If you change the air temperature, humidity, or altitude (and hence the pressure), the air density will change, too.
Dew point is the temperature at which the water vapor contained in the air reaches its saturation state. It is a physical quantity strictly related to the humidity of the air. When the air is further cooled past the dew point, the water vapor will condense to form water — dew.
About 1.204 kg/m³. Since the dry air density can be calculated as ρ = P/(R×T) with R = 287.058 J/(kg·K), at 101325 Pa and 20 °C = 293.15 K, we get: ρ = 101325 / (287.058 × 293.15) = 1.204 kg/m³.
Use this air density calculator to instantly find how tightly packed an object''s molecules are, allowing you to estimate ρ based on the local temperature and pressure conditions. This value is vital for many further calculations, such as determining the aerodynamic drag forces or the performance of wind turbines. Continue reading to get a better understanding of the relationship between the local weather and ρ, and learn what air density levels you can expect in various regions.
The density of air depends on many factors and can vary in different places. It mainly changes with temperature, relative humidity, pressure and hence with altitude (take a look on the air density table below). The air pressure can be related to the weight of the air over a given location. It is easy to imagine that the higher you stand, the less air is above you and the pressure is lower. Therefore, air pressure decreases with increasing altitude. In the following text, you will find out what is the air density at sea level and the standard air density.
The density of air is usually denoted by the Greek letter rho, or ρ, and it measures the mass of air per unit volume (e.g. g/m3). Dry air mostly consists of nitrogen (∼78%) and oxygen (∼21%). The remaining1% contains many different gases, among others, argon, carbon dioxide, neon or helium. However, the air will cease to be dry air when water vapor appears.
As a mixture of gases, air doesn''t have a constant density; this value depends largely on air composition. Most components have similar densities and don''t influence the overall density in a substantial way. One exception is water vapor; the more water vapor in the air, the lower its density.
To find the air density at any given location, you will need some basic weather parameters. You can usually find them on your local weather stations website.
The method of finding the air density is quite simple. You have to divide the pressure exerted by the air into two partial pressures: of the dry air and of the water vapor. Combining these two values gives you the desired parameter.
Subtract the vapor pressure from the total air pressure to find the pressure of dry air:pd=p−pv.
Input the calculated values into the following formula:
The basic definition of air density is very similar to the general definition of density. It tells us how much does a certain volume of air weigh. We can express it with the following density of air formula:
From the above equation, you may suspect that the density of air is a constant value that describes a certain gas property. However, the density of every matter (solids, liquids, gases) depends, stronger or weaker, not only on the chemical composition of the substance but also on the external conditions like pressure and temperature.
Because of these dependencies and the fact that the Earth''s atmosphere contains various gases (mostly nitrogen, oxygen, argon and water vapor) the air density definition needs to be further expanded. A proper modification has been made in our air density calculator with the density of air formula shown in the section called "How to calculate the air density?"
By the way, we would like to bring up an interesting point. What do you think? Is moist air heavier or lighter than dry air? The correct answer may not be as intuitive as you can think at first. In fact, the more water vapor we add to the air, the less dense it becomes! You may find this hard to believe, but we will try to convince with some few logical argumentations.
"Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules."
Imagine that you put dry air into a container of fixed volume, temperature and pressure. The perfectly dry air is composed of:
Note that every molecule listed is heavier that or equal to 18 u. Now, let''s add some water vapor molecules to the gas with the total atomic weight of 18 u (H₂O — two atoms of hydrogen 1 u and one oxygen 16 u). According to Avogadro''s law, the total number of molecules remains the same in the container under the same conditions (volume, pressure, temperature). It means that water vapor molecules have to replace nitrogen, oxygen or argon. Because molecules of H₂O are lighter than the other gases, the total mass of the gas decreases, decreasing the density of the air too.
In the previous sections, we used the term dry air a couple of times. However, what does it actually mean? There are two definitions:
A well-known approximation of dew point is a logarithmic function of relative humidity. As you may know, when the function of a logarithm approaches zero, its value goes to minus infinity. Therefore, a dew point doesn''t exist for the zero relative humidity. However, you can still calculate what is the density of dry air with our air density calculator! Just select dry air in the "air type" field, where we have ignored dew point/relative humidity in the computations.
The opposite effect is achieved with pressure. Imagine that you have a gas cylinder with a constant volume. The increased pressure of the cylinder translates into the increased number of molecules inside - the density of air becomes higher.
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