General information

Humidity depends on the nature of the substance, and in solids, in addition, on the degree of fineness or porosity. The content of chemically bound, so-called constitutional water, for example, hydroxides, which are released only during chemical decomposition, as well as crystalline hydrate water is not included in the concept of humidity.

Units of measurement and features of the definition of the concept of “humidity”

• Humidity is usually characterized by the amount of water in a substance, expressed as a percentage (%) of the original mass of the wet substance ( mass humidity) or its volume ( volumetric humidity).

• Humidity can also be characterized by moisture content, or absolute humidity- the amount of water per unit mass of the dry part of the material. This determination of moisture content is widely used to assess the quality of wood.

This value cannot always be accurately measured, since in some cases it is impossible to remove all non-condensed water and weigh the object before and after this operation.

• Relative humidity characterizes the moisture content compared to the maximum amount of moisture that a substance can contain in a state of thermodynamic equilibrium. Relative humidity is usually measured as a percentage of maximum.

Determination methods

Karl Fischer titrator

Establishing the moisture content of many foods, materials, etc. is important. Only at a certain humidity are many bodies (grain, cement, etc.) suitable for the purpose for which they are intended. The life activity of animals and plant organisms is possible only in certain ranges of humidity and relative air humidity. Humidity can introduce a significant error in the weight of an item. A kilogram of sugar or grain with a moisture content of 5% and 10% will contain different amounts of dry sugar or grain.

Humidity measurement is determined by drying the moisture and Karl Fischer titration of the moisture. These methods are primary. In addition to them, many others have been developed, which are calibrated based on the results of moisture measurements using primary methods and standard humidity samples.

Air humidity

Air humidity is a value characterizing the content of water vapor in the Earth's atmosphere - one of the most significant characteristics of weather and climate.

Relative humidity is usually expressed as a percentage.

Relative humidity is very high in the equatorial zone (the annual average is up to 85% or more), as well as in the polar latitudes and in winter inside the mid-latitude continents. In summer, high relative humidity is characteristic of monsoon regions. Low relative humidity values ​​are observed in subtropical and tropical deserts and in winter in monsoon regions (up to 50% and below).

Humidity decreases quickly with altitude. At an altitude of 1.5-2 km, vapor pressure is on average half that of the earth's surface. The troposphere accounts for 99% of the atmospheric water vapor. On average, there is about 28.5 kg of water vapor in the air above each square meter of the earth's surface.

Gas moisture measurement values

The following quantities are used to indicate the moisture content in the air:

absolute air humidity is the mass of water vapor contained in a unit volume of air, that is, the density of water vapor contained in the air, [g/m³]; in the atmosphere ranges from 0.1-1.0 g/m³ (in winter over the continents) to 30 g/m³ or more (in the equatorial zone); maximum air humidity (saturation limit) is the amount of water vapor that can be contained in the air at a certain temperature in thermodynamic equilibrium (the maximum value of air humidity at a given temperature), [g/m³]. As air temperature rises, its maximum humidity increases; vapor pressure, vapor pressure the partial pressure exerted by water vapor contained in the air (water vapor pressure as a fraction of atmospheric pressure). Unit of measurement - Pa. humidity deficit is the difference between the maximum possible and actual water vapor pressure [Pa] (under given conditions: temperature and air pressure), that is, between the saturation elasticity and the actual vapor elasticity; relative air humidity is the ratio of vapor pressure to saturated vapor pressure, that is, absolute air humidity to maximum [% relative humidity]; dew point temperature at which the gas is saturated with water vapor °C. The relative humidity of the gas is 100%. With a further influx of water vapor or when air (gas) is cooled, condensation appears. Thus, although dew does not fall at a temperature of −10 or −50 °C, frost, hoarfrost, ice or snow does fall, a dew point of −10 or −50 °C exists and corresponds to 2.361 and 0.063 g of water per 1 m³ of air or other gas under pressure one atmosphere; specific humidity is the mass of water vapor in grams per kilogram of humidified air [g/kg], that is, the ratio of the masses of water vapor and humidified air; wet bulb temperature is the temperature at which a gas is saturated with water vapor at a constant enthalpy of air. The relative humidity of the gas is 100%, the moisture content increases, and the enthalpy is equal to the initial one. ratio of mixture components (water vapor content) mass of water vapor in grams per kilogram of dry air [g/kg], that is, the ratio of the masses of water vapor and dry air.

Notes

Literature

• Usoltsev V. A. Air humidity measurement. - L.: Gidrometeoizdat, 1959.
• Berliner M. A. Humidity measurements. - Ed. 2nd, revised and additional - M.: Energy, 1973.

see also

Weather
Seasons	Winter spring Summer Autumn
Precipitation	Rain Drizzle Hail Snow Groats Dew Frost Hoarfrost Ice
Forecast and Clouds Humidity (absolute And

Radiation balance of the atmosphere and the underlying surface, the sum of the inflow and outflow of radiant energy absorbed and emitted by the atmosphere and the underlying surface. For the atmosphere, the radiation balance consists of an incoming part - absorbed direct and scattered solar radiation, as well as absorbed long-wave (infrared) radiation from the earth's surface, and an outgoing part - heat loss due to long-wave radiation of the atmosphere towards the earth's surface (the so-called counter-radiation of the atmosphere ) and into outer space.

The incoming part of the radiation balance of the underlying surface consists of: direct and diffuse solar radiation absorbed by the underlying surface, as well as absorbed counter-radiation of the atmosphere; the consumable part consists of heat loss by the underlying surface due to its own thermal radiation. The radiation balance is an integral part of the thermal balance of the atmosphere and the underlying surface.

Define the characteristics of air humidity

The Earth's atmosphere contains about 14 thousand km3 of water vapor. Water enters the atmosphere as a result of evaporation from the underlying surface. In the atmosphere, moisture condenses, moves with air currents and falls again in the form of various precipitation on the surface of the Earth, thus completing a constant water cycle. The water cycle is possible thanks to the ability of water to be in three states (liquid, solid, gaseous (vapor)) and easily move from one state to another. Moisture circulation is one of the most important climate formation cycles.

To quantify the content of water vapor in the atmosphere, various characteristics of air humidity are used. The main characteristics of air humidity are water vapor pressure and relative humidity.

Elasticity (actual) of water vapor (e) - the pressure of water vapor in the atmosphere is expressed in mm. rt. Art. or in millibars (mb). Numerically, it almost coincides with absolute humidity (the content of water vapor in the air in g/m3), which is why elasticity is often called absolute humidity. Saturation elasticity (maximum elasticity) (E) is the limit of water vapor content in the air at a given temperature. The value of saturation elasticity depends on the air temperature; the higher the temperature, the more water vapor it can contain.

If the air contains less water vapor than is needed to saturate it at a given temperature, you can determine how close the air is to the saturation state. To do this, calculate relative humidity.

Relative humidity (r) is the ratio of the actual water vapor pressure to the saturation pressure, expressed as a percentage.

There are other important characteristics of humidity, such as humidity deficit and dew point.

Moisture deficit (D) - the difference between saturation elasticity and actual elasticity:

The dew point fє is the temperature at which the water vapor contained in the air could saturate it. For example, air at a temperature of 27°C has e = 27.4 mb. It will be saturated at a temperature of 20°C, which will be the dew point.

In this lesson, the concept of absolute and relative air humidity will be introduced, terms and quantities associated with these concepts will be discussed: saturated steam, dew point, instruments for measuring humidity. During the lesson we will get acquainted with the tables of density and saturated vapor pressure and the psychrometric table.

For humans, the humidity level is a very important environmental parameter, since our body reacts very actively to its changes. For example, a mechanism for regulating the functioning of the body, such as sweating, is directly related to the temperature and humidity of the environment. At high humidity, the processes of evaporation of moisture from the surface of the skin are practically compensated by the processes of its condensation and the removal of heat from the body is disrupted, which leads to disturbances in thermoregulation. At low humidity, moisture evaporation processes prevail over condensation processes and the body loses too much fluid, which can lead to dehydration.

The amount of humidity is important not only for humans and other living organisms, but also for the flow of technological processes. For example, due to the known property of water to conduct electric current, its content in the air can seriously affect the correct operation of most electrical appliances.

In addition, the concept of humidity is the most important criterion for assessing weather conditions, which everyone knows from weather forecasts. It is worth noting that if we compare humidity at different times of the year in our usual climatic conditions, it is higher in summer and lower in winter, which is associated, in particular, with the intensity of evaporation processes at different temperatures.

The main characteristics of humid air are:

1. water vapor density in the air;
2. relative humidity.

Air is a composite gas and contains many different gases, including water vapor. To estimate its amount in the air, it is necessary to determine what mass water vapor has in a certain allocated volume - this value is characterized by density. The density of water vapor in the air is called absolute humidity.

Definition.Absolute air humidity- the amount of moisture contained in one cubic meter of air.

Designationabsolute humidity: (as is the usual designation for density).

Unitsabsolute humidity: (in SI) or (for the convenience of measuring small amounts of water vapor in the air).

Formula calculations absolute humidity:

Designations:

Mass of steam (water) in air, kg (in SI) or g;

The volume of air containing the indicated mass of steam is .

On the one hand, absolute air humidity is an understandable and convenient value, since it gives an idea of ​​the specific water content in the air by mass; on the other hand, this value is inconvenient from the point of view of the susceptibility of humidity by living organisms. It turns out that, for example, a person does not feel the mass content of water in the air, but rather its content relative to the maximum possible value.

To describe such perception, the following quantity was introduced: relative humidity.

Definition.Relative humidity– a value indicating how far the steam is from saturation.

That is, the value of relative humidity, in simple words, shows the following: if the steam is far from saturation, then the humidity is low, if it is close, it is high.

Designationrelative humidity: .

Unitsrelative humidity: %.

Formula calculations relative humidity:

Designations:

Water vapor density (absolute humidity), (in SI) or ;

Density of saturated water vapor at a given temperature, (in SI) or .

As can be seen from the formula, it includes absolute humidity, with which we are already familiar, and saturated vapor density at the same temperature. The question arises: how to determine the latter value? There are special devices for this. We'll consider condensinghygrometer(Fig. 4) - a device that is used to determine the dew point.

Definition.Dew point- the temperature at which steam becomes saturated.

Rice. 4. Condensation hygrometer ()

An easily evaporating liquid, for example, ether, is poured into the container of the device, a thermometer (6) is inserted, and air is pumped through the container using a bulb (5). As a result of increased air circulation, intense evaporation of ether begins, the temperature of the container decreases because of this, and dew (droplets of condensed steam) appears on the mirror (4). At the moment dew appears on the mirror, the temperature is measured using a thermometer; this temperature is the dew point.

What to do with the obtained temperature value (dew point)? There is a special table in which data is entered - what density of saturated water vapor corresponds to each specific dew point. It is worth noting a useful fact that as the dew point increases, the value of the corresponding saturated vapor density also increases. In other words, the warmer the air, the greater the amount of moisture it can contain, and vice versa, the colder the air, the lower the maximum vapor content in it.

Let us now consider the principle of operation of other types of hygrometers, devices for measuring humidity characteristics (from the Greek hygros - “wet” and metreo - “I measure”).

Hair hygrometer(Fig. 5) - a device for measuring relative humidity, in which hair, for example human hair, acts as an active element.

The action of a hair hygrometer is based on the property of defatted hair to change its length when air humidity changes (with increasing humidity, the length of the hair increases, with decreasing - it decreases), which makes it possible to measure relative humidity. The hair is stretched over a metal frame. The change in hair length is transmitted to the arrow moving along the scale. It should be remembered that a hair hygrometer does not give accurate relative humidity values, and is used primarily for domestic purposes.

A more convenient and accurate device for measuring relative humidity is a psychrometer (from the ancient Greek ψυχρός - “cold”) (Fig. 6).

A psychrometer consists of two thermometers, which are fixed on a common scale. One of the thermometers is called a wet thermometer because it is wrapped in cambric fabric, which is immersed in a reservoir of water located on the back of the device. Water evaporates from the wet fabric, which leads to cooling of the thermometer, the process of reducing its temperature continues until the stage is reached until the steam near the wet fabric reaches saturation and the thermometer begins to show the dew point temperature. Thus, the wet bulb thermometer shows a temperature less than or equal to the actual ambient temperature. The second thermometer is called a dry thermometer and shows the real temperature.

On the body of the device, as a rule, there is also a so-called psychrometric table (Table 2). Using this table, you can determine the relative humidity of the surrounding air from the temperature value shown by the dry bulb thermometer and from the temperature difference between the dry and wet bulb bulbs.

However, even without such a table at hand, you can approximately determine the amount of humidity using the following principle. If the readings of both thermometers are close to each other, then the evaporation of water from the humid one is almost completely compensated by condensation, i.e., the air humidity is high. If, on the contrary, the difference in thermometer readings is large, then evaporation from the wet fabric prevails over condensation and the air is dry and humidity is low.

Let us turn to the tables that allow us to determine the characteristics of air humidity.

Temperature,	Pressure, mm. rt. Art.	Vapor density

Table 1. Density and pressure of saturated water vapor

Let us note once again that, as stated earlier, the value of the density of saturated steam increases with its temperature, the same applies to the pressure of saturated steam.

Table 2. Psychometric table

Let us recall that relative humidity is determined by the value of the dry bulb readings (first column) and the difference between the dry and wet readings (first row).

In today's lesson we learned about an important characteristic of air - its humidity. As we have already said, humidity decreases in the cold season (winter) and increases in the warm season (summer). It is important to be able to regulate these phenomena, for example, if it is necessary to increase humidity, place several reservoirs of water indoors in winter in order to enhance evaporation processes, however, this method will only be effective at the appropriate temperature, which is higher than outside.

In the next lesson we will look at what gas work is and the principle of operation of an internal combustion engine.

Bibliography

1. Gendenshtein L.E., Kaidalov A.B., Kozhevnikov V.B. / Ed. Orlova V.A., Roizena I.I. Physics 8. - M.: Mnemosyne.
2. Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
3. Fadeeva A.A., Zasov A.V., Kiselev D.F. Physics 8. - M.: Enlightenment.

1. Internet portal “dic.academic.ru” ()
2. Internet portal “baroma.ru” ()
3. Internet portal “femto.com.ua” ()
4. Internet portal “youtube.com” ()

Homework

To quantitatively characterize air humidity, the following characteristics are used: water vapor pressure, absolute humidity, mass fraction of water vapor, relative humidity, humidity deficit, dew point and dew point deficit.

Water vapor pressure ( e) is the partial pressure of water vapor contained in the air in millimeters of mercury (mm Hg) or hectopascals (hPa). The maximum possible water vapor pressure at a given temperature is called saturation elasticity or maximum elasticity(E) . When the elasticity of water vapor corresponds to the elasticity of saturation, the air becomes saturated with water vapor and the process of condensation or sublimation begins with the formation of water droplets or ice crystals.

Humidity deficiency or lack of saturation(d) – this is the difference between the elasticity of saturation at a given temperature and the actual elasticity of water vapor

d=E-e

Absolute humidity ( a) is the mass of water vapor in grams contained in

1 m3 of air (g/m3). For a saturated space, absolute humidity is called

saturating water vapor or extreme humidity(A) .

Actual elasticity and absolute humidity are directly dependent on

temperature of the evaporating surface, and saturation elasticity and maximum humidity depend on the air temperature (Table 2.3).

Table 2.3. Dependence of saturation elasticity and maximum humidity on air temperature

The relationship between water vapor pressure and absolute humidity has the form:

(e- mmHg), (2.13)

A=0,8 e

(e- hPa), (2.14)

Air volumetric expansion coefficient;

t− air temperature in °C.

Mass fraction of water vapor ( s) - amount of water vapor in grams per

1 kilogram of humid air (g/kg). It is related to the water vapor pressure by the following relationship:

Where: R-air pressure.

s=622 e , (2.15)

Until recently, this characteristic was called specific humidity . If condensation of water vapor or additional evaporation does not occur, then the mass fraction of water vapor does not change with heating, cooling, compression and expansion of air.

Relative humidity ( f) is the ratio of the amount of water vapor actually contained in the air to the maximum possible at a given temperature, expressed as a percentage.

f=a 100% , (2.16)

f= 100% , (2.17)

Relative humidity characterizes the degree of saturation of air with water vapor at a given temperature. It is inversely related to air temperature.

Dew point(td) - this is the temperature to which it is necessary to cool the air so that the water vapor contained in it, at constant values ​​of pressure and mass fraction of water vapor (specific humidity), reaches a state of saturation. When the air temperature is equal to the dew point, the relative humidity is 100% ( t = td, f= 100%). The dew point is always lower than or equal to the air temperature. On weather maps, the dew point is plotted in degrees Celsius, to the nearest tenth, as follows:

Td Td Td 125

td= 12.5°C

td= -2.8 °C

Dew point deficit ( ∆td) is the difference between the air temperature and the dew point.

∆td = t- td(2.18)

The dew point deficit shows how many degrees the air must be cooled so that the water vapor contained in it reaches a saturation state. With sufficient accuracy we can assume that when ∆td£ 4°C the air is humid, and at ∆td> 4°C - dry.

Water vapor pressure - partial (partial) pressure of water vapor in air

Absolute air humidity - the amount of water vapor in grams per 1 m 3

Specific humidity –

Relative humidity (R) is the ratio of water elasticity. Steam at the same temperature in %.

Condensation is the process of transition from gas to liquid

Sublimation - from gaseous to solid (bypassing the liquid state)

Sublimation and condensation conditions:

The presence of water vapor in the atmosphere at saturation levels

Presence of crystallization centers

The structure of the atmosphere. List the layers that make it up, indicating their heights.

Layer name	Layers	By height	Notes
Troposphere		up to 8(18) km (mid latitudes) up to 10(12) km (in polar latitudes) up to 16(18) km (in tropical latitudes)
Bottom (friction layer)	1-2 km	Low clouds and fogs
Average	up to 6 km (above the lower one)	Mid-level clouds
Upper	From 6 to 10(11)	Form upper level clouds and the tops of powerful cumulonimbus
Tropopause		1-2 km (between troposph and stratosph)
Stratosphere		up to 80-85 km
lower (isothermal)	Up to 30-35 km	t is constant and like in the tropopause
middle (warm layer)	From 30(35)-55(60) km	t increases with altitude reaching 50-70° (absorption of ultraviolet solar radiation by ozone)
Top (mixing layer)	55(60) – 80(85) km	t decreases with altitude -50(-70°)
Ionosphere		80(85)-1000km	0.5 of the total mass of the atmosphere
Scattering Sphere		Above the ionosphere	Molecules can overcome gravity
Mesosphere		Up to 80 km
Thermosphere		80-800 km
Exosphere		Up to 3000

Define an atmospheric front and give their classification.

Atmospheric front is a transition zone between air masses, characterized by sharp changes in the values ​​of metrological elements in the horizon. direction.

Classification:

Warm front – moving towards a retreating cold air mass (like a wedge of cold air, warm air rises to 6-7 km).

Cold front – moving towards a retreating warm air mass. Types:

1st type invasion of cold air along the entire surface of the upward movement of warm air

Type 2 – warm air is unstable and contains reserves of moisture. Cold air displaces warm air (ascending vertical movements appear in the warm air mass, which leads to the formation of nomadic nimbus clouds, the upper boundary reaches the tropopause)

Baric topography maps. Characteristic.

Maps of baric topography - based on aerological observations are made for areas (AT850 height 1.5 km above the ground) (AT700 height 3 km), (AT500 - 5 km) (AT300 - 9 km)

List pressure systems. Give them a brief description.

Cyclone (H) is a baric system in the form of closed isobars, with low pressure in the center. The area of ​​convergence of surface winds blows at an angle of 30-40° to the center of the cyclone, counterclockwise.

A trough is an elongated strip of low pressure between 2 anticyclones, which has an axis near which the isobars have maximum curvature

Axis – line of min pressure, line of convergence of surface winds

Anticyclone (B) is a baric system in the form of closed isobars with high pressure in the center, the area of ​​divergence is near the surface. winds. The wind is clockwise, deviates from the isobar towards low pressure by 30°

A ridge is an elongated strip of low pressure between two cyclones, with a pronounced axis in the axis near which the isobars have max curvature. The ridge axis is the max pressure line, the divergence line of surface winds

Baric saddles are an intermediate baric si-ma, between 2 cyclones and 2 anticyclones. The weather is determined by the light of the air mass where it was formed. Winds are weak and unstable. In winter there are radial fogs and wavy clouds on land. In the summer - a powerful bunch. and cumulonimbus clouds with rain and thunder.

Define a thunderstorm and provide a diagram of a thundercloud.

Thunderstorm is the process of condensation of water vapor in the atmosphere, accompanying. Lightning and thunder.

Frontal thunderstorms - when two air masses interact (warm and cold), stretch in a long chain and cover large areas.

Define the order of battle. List what it should provide.

The order of battle is the relative arrangement of aircraft units and subunits in the air to jointly carry out a combat mission.

BP provides:

Successfully overcoming air defense

Full use of the combat capabilities of units and subunits

The best conditions for searching and reaching targets

The best conditions for observing airspace

Freedom of maneuver and piloting

Convenience and continuity of control

Aircraft safety from mid-air collision

Safety from being hit by your own ammunition

Definition of BP collection. List the steps. The essence of BP.

Gathering is a maneuver of single (groups) of aircraft in order to build a given BP at a designated time at a designated altitude in an approved area

BP stages:

Takeoff and climb to altitude of BP formation

Exit to the starting point for starting maneuvering

Maneuvering to occupy a given BP

The essence of BP = BP provides

Describe the method of gaining altitude at safe distances.

It is used when taking off as a pair (link) and can be used in cases where the take-off interval is less than the safe time distance for breaking through clouds at safe distances

Describe the method of gaining altitude at safe altitude differences (along different glide paths).

The RBZ monitors the accuracy of maintaining a given direction and the maintenance of safe altitude differences by the crews using the ONI, the PRV operator and the reports of the pilots