Atmospheric pressure It is the weight of a column of air over its cross section per unit area, and its height is equal to the thickness of the atmosphere. Atmospheric pressure = 1 atm or approximately 1 bar. It consists of several gases (78% nitrogen and 21% oxygen, in addition to other gases). Atmospheric pressure decreases with height above sea level, and at sea level it is 1 atm or 1.0132 bar.

Regions with low atmospheric pressure have less atmospheric mass, while regions with high atmospheric pressure have more atmospheric mass than others.

Low atmospheric pressure is formed when the temperature rises, as this causes the air molecules to accelerate and move away from each other, and high atmospheric pressure forms when the temperature decreases, as this leads to the slowness of the air molecules and their approaching each other.

The weight of the column of air, at sea level, has a cross-sectional area of ​​one square meter, and the height of the thickness of the atmosphere, is approximately 10 tons. The higher the altitude above sea level, the lower the atmospheric pressure, and vice versa.

Standard atmospheric pressure[عدل]

Atmospheric pressure is 760 mm Hg = 101 325 Pa = 1.013 bar

• That is, the weight of a column of mercury has a cross-sectional area of ​​1 square centimeter and a height of 760 millimeters. This is equivalent to the weight of a 1 square centimeter column of air and the height of the Earth’s atmosphere.
• If the density of mercury is 13.53 grams / cubic centimeter, then the atmospheric pressure can be calculated through the following law:

$\displaystyle p=\rho gh$

This means that:

Atmospheric pressure = density of mercury x height of the column of mercury x acceleration due to gravity.

Atmospheric pressure = 13.53 x 1000 x 0.76 x 9.81 = 100874.268 N/m²^[1]

And if we want to calculate the weight of the air column of the atmosphere located on 1 square meter in kilograms, we divide the aforementioned result by the value of the earth’s gravitational acceleration, we get:

The weight of the air column in kilograms per square meter = 100874.268 ÷ 9.81 = 10282.8 kilograms / square meter.

No more than 10 tons per square metre.

Atmospheric pressure at sea level[عدل]

It is measured by barometers and is measured at sea level, which is usually mentioned in weather bulletins on radio, television, newspapers and the Internet.

And climatology uses pressure at sea level in order to identify and classify centers of atmospheric pressure on the globe. We find that he knows a group of atmospheric pressure centers that dominate the climate and weather of large areas of the globe. It is classified into two types: highlands and lowlands. Among these heights in the northern hemisphere, we find the Assur High and the Siberian High. One of the most important depressions in the northern hemisphere is the Iceland depression.

The difference in atmospheric pressure when the height is different from the earth’s surface[عدل]

Atmospheric pressure varies at the Earth’s surface up to the mesosphere. Although atmospheric pressure changes with the weather, NASA has averaged all conditions and all regions over the years. Atmospheric pressure can be found through an equation that describes the relationship of height with atmospheric pressure. The higher the height above the Earth’s surface, the lower the atmospheric pressure ^[2] Taking into account the effect of heat and humidity on the accuracy of the result. At lower altitudes, atmospheric pressure decreases by cca 1.2 kPa per 100 metres

For altitudes within the troposphere, we can find the value of atmospheric pressure p for height h By equalizing the barometric formula

$\displaystyle p=p_0\cdot \left(1-\frac L\cdot hT_0\right)^\frac g\cdot MR\cdot L\approx p_0\cdot \exp \left(-\frac g\cdot M\cdot hR\cdot T_0\right),$

Parameter	the description	the value
p0	Standard atmospheric pressure at sea level	101325 Pa
L	temperature lapse rate	0.0065 K/m
T0	Standard temperature at sea level	288.15 K
g	The acceleration of gravity at the Earth’s surface	9.80665 m/s2
M	molar mass of dry air	0.0289644 kg/mol
R	The general gas constant	8.31447 J/(mol•K)

pressure units[عدل]

pressure units

	Pascal (Pa)	Bar (bar)	Technical atmospheric pressure (at)	Pressure (atm)	millimeters of mercury (Torr)	Pounds per square inch (psi)
1 Pa	≡ 1 Newton/m2	10−5	1.0197×10−5	9.8692×10−6	7.5006×10−3	145.04×10−6
1 time	100,000	≡ 106 Dane/cm2	1.0197	0.98692	750.06	14.5037744
1 technical atmospheric pressure	98,066.5	0.980665	≡ 1 kgf/cm2	0.96784	735.56	14.223
1 atm	101,325	1.01325	1.0332	≡ 1 atm	760	14.696
1 millimeter of mercury	133.322	1.3332×10−3	1.3595×10−3	1.3158×10−3	1 millimeters of mercury = 1 Torr	19.337×10−3
1 pound is my weight per square inch	6,894.76	68.948×10−3	70.307×10−3	68.046×10−3	51.715	≡ 1 psi

1 Pascal ≡ 1 Newton/m² ≡ 1 J/m³ ≡ 1 kg/m¹·a second²)≡ 10⁻⁵Load ≡ 10.197×10⁻⁶atmospheric pressure ≡ 9.8692×10⁻⁶Technical atmospheric pressure

The effect of altitude on a person[عدل]

The atmospheric pressure decreases with height above the earth’s surface, and thus the oxygen in the atmosphere decreases, which has an effect on living organisms that breathe air and need oxygen to breathe. The effect of height on a person is as follows:

• Altitude 2400 meters: This is equivalent to the pressure inside passenger planes, and it has no effect
• 2500m Altitude: Some sensitive people start to feel dizzy.
• Altitude 3500 meters: About a third of people who are not used to this experience a feeling of dizziness and fatigue.
• 4000m altitude: 95% of unaccustomed people feel dizzy and tired.
• 5500 Meters Altitude: Some people can live at this altitude. The amount of oxygen at this altitude is about half of the amount at sea level.
• 7,500m: This is where the killer zone begins: mountaineers can’t survive more than a day at that altitude without oxygen tubes.
• 8848 meters high: the highest point on Earth, which is Mount Everest. You can’t survive at that altitude without the oxygen tubes
• Altitude: 12,192 meters: the average flight altitude for commercial aircraft. Here, compressed air is supplied to the aircraft cabin from the outside and its temperature is adjusted.

Atmospheric pressure changes with altitude[عدل]

Atmospheric pressure decreases with increasing altitude above sea level, according to an exponential function. Although the atmosphere also changes due to weather conditions and temperature, NASA has calculated the average pressure change at different altitudes for all regions of the Earth. The following list gives us approximately the change in atmospheric pressure with altitude:

part of 1 atm	Average height
	(Meter)	(Foot)
1	0	0
1/2	5,486	18,000
1/3	8,376	27,480
1/10	16,132	52,926
1/100	30,901	101,381
1/1000	48,467	159,013
1/10000	69,464	227,899
1/100000	86,282	283,076

pressure surface[عدل]

The barometric surface is a surface with one average atmospheric pressure value in all its extensions, as in the barometric surface of 1000 mbar, 850 mbar, 700 mbar, 500 mbar, 300 mbar, 200 mbar, 100 mbar, and the barometric surface is characterized in that it does not extend completely horizontally. Rather, we find it swirling and sometimes wavy, and that is because the rate of pressure decrease with height is not constant, because it depends on the temperature, winds, and air density.

boiling point of water[عدل]

According to the definition, water boils at 100 degrees Celsius. The boiling point is the temperature at which the vapor pressure equals the pressure around water.^[3] Because of this, the boiling point of water decreases under low pressure and rises with high pressure. This is why cooking at the top above sea level needs more times than usual.^[4][5]

This can be determined by knowing the boiling point of water at that altitude. This method was used during the nineteenth century by travelers and explorers to determine the altitude of the areas they were visiting.^[6]

See also[عدل]

• ambient pressure.

the reviewer[عدل]

On Commons, photos and files on: atmospheric pressure

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