Atmospheric pressure is the atmospheric pressure acting on the unit area, that is, the value is equal to that of the unit area and extends upward toUpper bound of atmosphereVertical ofAir column is subjected toThe gravity of.famousMadburg HemisphereExperiments have proved its existence.The SI unit of air pressure is pascal, abbreviated as pascal, and the symbol is Pa[1]。In meteorology, people usually use kilopascals (kPa) or hundred pascals (hpa) as the unit.Other common units are bar (bar, 1bar=100000Pa) and centimeter mercury column (or centimeter mercury column).The pressure varies not only with height, but also with temperature.The change of air pressure is closely related to the change of weather.[2]
Air pressure is the abbreviation of atmospheric pressure, which is the atmospheric pressure acting on the unit area, that is, the weight of the vertical air column extending upward to the upper boundary of the atmosphere per unit area.The pressure is related to altitude, temperature and other conditions.Generally, it decreases with the increase of height.In the horizontal direction, the difference in atmospheric pressure causes air flow.It is a unit of air pressure, usually the height of mercury column.For example, the pressure generated by a standard atmospheric pressure equal to a mercury column 760 mm high is equivalent to the atmospheric pressure of 1.0336 kg on an area of one square centimeter.It is internationally agreed to use "hPa" as the pressure unit.After conversion: one standard atmospheric pressure=1013 hPa (millibar).The annual average pressure in Shenzhen is 1009.8 hPa.[1]
Atmospheric pressure refers to the weight of the atmospheric column per unit area.Meteorologically, it is usually expressed in millimeters of millibar or mercury column height.A standard atmospheric pressure is 1013.2 mbar, or 760 mm high mercury.Since the higher the ground is, the lower the air pressure is, so the height can be measured according to the change of air pressure in the vertical direction.In the horizontal direction, the difference of air pressure can cause air flow, so it is one of the important meteorological elements for analyzing weather forecast.[5]
From the point of view of air molecular motion, it is the result of the combined action of air molecular motion and earth gravity field.Under this combined effect, the impact force exerted by many air molecules on the plane per unit area in each instant is expressed as air pressure.The place where the density of air molecules is high is also the place where the average kinetic energy of air molecules is high, so the impact force is high, so the pressure is also high.[5]
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Standard atmospheric pressure.It is a unit of air pressure, usually the height of mercury column.For example, aStandard atmospheric pressureIt is equal to the weight of a 760mm high mercury column, which is equivalent to the atmospheric pressure of 1.0336kg on an area of one square centimeter.Due to the weight andLength unitDifferent, soBarometric unitIt is also not unified, which is not convenient to compare the global pressureanalysis。Therefore, it is internationally unified to use "hPa" as the pressure unit.
After conversion: one standard atmospheric pressure=1.013 × 10fivePa
1 standard atmospheric pressure=760mm mercury（mercury）Column height
Barogenesis
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Barometric test
fromMolecular kinetic theoryIt can be seen that the pressure of gas isA large number of molecules frequently collide with the vessel wallResulting from.The collision time between a single molecule and the vessel wall is very short, and the effect is discontinuous. However, a large number of molecules frequently collide with the vessel wall, and the force on the vessel wall is continuous and uniform. The ratio of this pressure to the vessel wall area is the pressure.
measuring method
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The commonly used measuring instruments in meteorology include liquid (such as mercury)barometerAnd solid (such as metal empty box) barometer.The barometer is a barometer or barometer installed in an air chamber with less temperature change and sufficient lightmeasureThere are regular air pressure records and continuous air pressure records.The fixed time barometric record of manual visual observation is measured by moving trough or fixed trough mercury barometer. The basic station is observed 4 times a day, and the base station is observed 24 times a day.The metal elastic capsule is used as the sensor to record the timed pressure record of continuous pressure recording and telemetry automatic observation, and the pressure record at any time can be obtained.What is measured with these instruments isAir pressure of the station, according to the altitude of the station and the air pressure, air column temperature, etc. of the stationparameterSea level pressure can be calculated.
The air pressure is expressed in hPa, with one decimal place taken;Some also take the millimeter mercury column height as the unit, taking two decimal places.The conversion relationship between mm and hPa is
1 hPa=0.750069 mm (mercury column height) ≈ 3/4 mm (mercury column height)
1mm=1.333224 hPa ≈ 4/3 hPa
The pressure observation in China was recorded in millimeter mercury column height in 1953 and before, and in hundred pascals in 1954 and after. When the two records are used together, they must be converted to the same unit.
computing method
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Usually, there are balance condition method andNewton's law of motionMethod (The formula is only a rough calculation and sometimes the measured value is inaccurate, everything should be subject to the actual situation).
1. After Torricelli measured the air pressure, people calculated the mass of air per unit area by the formula p=F/S.Then apply the density of air, calculate the volume, and divide by the mass to know the distance from the ground to the top of the atmosphere.
2. When the gas volume, amount of substance and absolute temperature are known, the gas pressure can be calculated by the formula PV=nRT (where R is a constant, R=8.314 Pa · m3/mol · K or R=0.0814 atmospheric pressure · L/mol · K).There are also deformation formulas pV=mRT/M, p=ρRT/M。
Psi（lb/intwo）Pounds/Square inch, commonly used in product parameters in English speaking countries such as Europe and the United States
Generally speaking, "kg" in the industry refers to "bar"
influence factor
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Relationship between air pressure and altitude
The size of air pressure and altitudeAtmospheric temperature、Atmospheric densityIt generally decreases exponentially with height.The air pressure varies daily and annually.In a year,Air pressure in winter compared with that in summerHigh.In a day, the air pressure has a maximum value and a minimum value, which appear respectively at 9~10 o'clock and 15~16 o'clock, and there is a secondary high value and a secondary low value, which appear respectively at 21~22 o'clock and 3~4 o'clock.Daily variation of atmospheric pressureSmall amplitude, generally 0.1~0.4KilopascalAnd decreases with the increase of latitude.
The pressure change is closely related to wind and weather, so it is an important meteorological factor.The commonly used barometric units arePa(Pa)、Mm mercury columnHeight (mm · Hg), millibar (mb).The conversion relationship between them is: 100 Pa=1 mbar ≈ 3/4 mm mercury column height.The commonly used instruments for measuring air pressure in meteorological observation are mercury barometerEmpty box barometer. Barometer.760mm vertical mercury pressure at 0 ℃,Standard atmospheric pressureFirst developed by Italian scientistsTorricelliMeasured
Measuring tools
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The most common instruments for measuring air pressure areMercury barometerAnd empty box barometer.It is also a relatively accurate instrument.
Three centuries ago, GermanMagdeburg The city once openly conducted an experiment. The mayor, Otto Glick, who invented the air extractor, combined two hollow copper hemispheres with a diameter of 37 cm to make them airtight, and then used the air extractor to remove the air from the copper ball.Four strong horses are tied on the ring of each hemisphere and pulled in the opposite direction at the same time. The two hemispheres cannot be separated.Finally, 16 horses were used, and with a loud noise, the copper ball was split in two.This is the famousMagdeburg hemispheres test 。The experiment shows that air is not only pressurized, but also has a great pressure.The body of an adultSurface areaThe average area is 2 square meters, and the atmospheric pressure on his whole body is 200000Newton。
Air pressure is the atmospheric pressure.Air has weight. Air pressure refers to the force exerted by the atmosphere on a unit area.The so-called air pressure of a place means that the unit area of the place extends vertically upward toatmosphereApicalAir columnTotal weight of.In meteorology, the pressure is usually measured in hPa.It is specified as follows: set the temperature to 0 ℃latitudeby45 degreeSea level asStandard situationAir pressure at, called 1Atmospheric pressureAnd its value is 760mm mercury column height, or equivalent to 1013.25 hPa.
Discovery and application
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In October 1640, after a lot of experiments, Torricelli, Torricelli's assistant, realized that the weight of the air in the atmosphere exerted pressure on the mercury in the basin, which pressed the mercury into the glass tube.The weight of mercury in the glass tube should be exactly equal to the weight of mercury in the basin imposed by the atmosphere.When the weight of the atmosphere changes, the pressure it exerts on the basin will increase or decrease, which will cause the mercury column in the glass tube to rise or fall.The change of weather will inevitably cause the change of atmospheric weight.Torricelli discovered the atmospheric pressure and found the method to measure and study the atmospheric pressure.Torricelli's discovery was the beginning of the formal study of weather and atmosphere. It let us begin to understand the atmosphere and laid the foundation for Newton and other scientists to study gravity.At the same time, this new discovery led Torricelli to create the concept of vacuum and invented the barometer, the basic instrument for meteorological research.
Application of atmospheric pressure: press the plastic hook with suction cup on a very flat wall, and you can use it to hang things;Piston and centrifugal pumps can pump water from lower places to higher places;Squeeze out the air in the pen tube, and then let the ink inhale into the pen tube;It is easy to boil food with pressure cooker;A small hole is opened on the lid of the teapot, so that the water can be easily poured out;There are also high-pressure boilersAgricultural sprayer, using straws to suck drinks, syringes to suck liquid medicine, etc., are all related to atmospheric pressure.
Health related
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The impact of air pressure on human health can be summarized into two aspects: physiological and psychological.The effect of low pressure on human physiology is mainly to affect the supply of oxygen in the human body.As the human body, especially the brain, suffers from hypoxia, dizziness, headache, nausea, vomiting, weakness and other symptoms will also occur. Nervous system disorders will also occur, and even pulmonary edema and coma will occur, which is commonly referred to as "mountain sickness".
In the high pressure environment, the tissues of the body are gradually saturated with nitrogen (generally, the human body is saturated with nitrogen after working under high pressure for 5-6 hours). When the human body returns to the standard atmospheric pressure, the excess nitrogen in the body will be discharged with exhalation, but this process is relatively slow. If the body suddenly returns to the standard atmospheric pressure environment from the high pressure environment,Then some of the nitrogen stored in fat may stay in the body, and expand to form small bubbles, blocking blood and tissues, which is easy to form air embolism and cause disease, and even endanger human life in serious cases.
The impact of atmospheric pressure changes on human health is more manifested in the generation, disappearance or movement of the circulation weather situation represented by high pressure or low pressure.Under the situation of low pressure circulation, it is mostly cloudy and rainy, and the wind changes obviously;Under the situation of high pressure circulation, it is mostly sunny and the weather is relatively stable.Under the control of high pressure, the air is dry, the weather is fine and the wind is small, the radiation cooling at night is easy to form a ground inversion layer, and the allergens such as dust, fungi, pollen, spores, etc. are easy to stagnate in the near ground layer, thus inducing the onset of asthma.
At the same time, the change of air pressure will also affect people's psychological changes, resulting in depression and depression.For example, in the rainy and snowy weather under low pressure, especially in the hot and humid weather before the thunderstorm in summer (the pressure is low at this time), people with poor cardiorespiratory function will be extremely uncomfortable, and normal people will also have a feeling of depression and discomfort.This suffocation and depression will make people's vegetative nerves tend to tense, release adrenaline, cause blood pressure to rise, heart rate to speed up, shortness of breath, etc;At the same time, cortisol is broken down, causing increased gastric acid secretion, blood vessel infarction, and blood sugar may also rise sharply.Some scholars conducted a comparative study of the lowest monthly air pressure period and the peak death period, and found that 89% of the peak death occurred during the lowest air pressure period[4]。
