Define the main characteristics of air humidity. Give a definition of the radiation balance and its components
One of the very important indicators in our atmosphere. It can be either absolute or relative. How is absolute humidity measured and what formula should be used for this? You can find out about this by reading our article.
Air humidity - what is it?
What is humidity? This is the amount of water that is contained in any physical body or medium. This indicator directly depends on the very nature of the medium or substance, as well as on the degree of porosity (if we are talking about solids). In this article, we will talk about a specific type of humidity - about the humidity of the air.
From the course of chemistry, we all know very well that atmospheric air consists of nitrogen, oxygen, carbon dioxide and some other gases, which make up no more than 1% of the total mass. But besides these gases, the air also contains water vapor and other impurities.
Air humidity is understood as the amount of water vapor that is currently (and in a given place) contained in the air mass. At the same time, meteorologists distinguish two of its values: these are absolute and relative humidity.
Air humidity is one of the most important characteristics of the Earth's atmosphere, which affects the nature of local weather. It should be noted that the value of atmospheric air humidity is not the same - both in the vertical section and in the horizontal (latitudinal) section. So, if in subpolar latitudes the relative indicators of air humidity (in the lower layer of the atmosphere) are about 0.2-0.5%, then in tropical latitudes - up to 2.5%. Next, we will find out what absolute and relative humidity are. Also consider what difference exists between these two indicators.
Absolute humidity: definition and formula
Translated from Latin, the word absolutus means "full". Based on this, the essence of the concept of "absolute air humidity" becomes obvious. This value, which shows how many grams of water vapor is actually contained in one cubic meter of a particular air mass. As a rule, this indicator is denoted by the Latin letter F.
G/m 3 is the unit of measurement in which absolute humidity is calculated. The formula for its calculation is as follows:
In this formula, the letter m denotes the mass of water vapor, and the letter V denotes the volume of a particular air mass.
The value of absolute humidity depends on several factors. First of all, this is the air temperature and the nature of advection processes.
Relative Humidity
Now consider what relative humidity is. This is a relative value that shows how much moisture is contained in the air in relation to the maximum possible amount of water vapor in this air mass at a particular temperature. The relative humidity of the air is measured as a percentage (%). And it is this percentage that we can often find out in weather forecasts and weather reports.
It is also worth mentioning such an important concept as the dew point. This is the phenomenon of the maximum possible saturation of the air mass with water vapor (the relative humidity of this moment is 100%). In this case, excess moisture condenses, and precipitation, fog or clouds form.
Methods for measuring air humidity
Women know that you can detect the increase in humidity in the atmosphere with the help of your puffy hair. However, there are other, more accurate, methods and technical devices. These are the hygrometer and the psychrometer.
The first hygrometer was created in the 17th century. One of the types of this device is precisely based on the properties of the hair to change its length with changes in the humidity of the environment. Today, however, there are also electronic hygrometers. A psychrometer is a special instrument that has a wet and dry thermometer. By the difference in their indicators and determine the humidity at a particular point in time.
Air humidity as an important environmental indicator
It is believed that the optimum for the human body is a relative humidity of 40-60%. Humidity indicators also greatly affect the perception of air temperature by a person. So, at low humidity it seems to us that the air is much colder than in reality (and vice versa). That is why travelers in the tropical and equatorial latitudes of our planet experience the heat and heat so hard.
Today, there are special humidifiers and dehumidifiers that help a person regulate the humidity of the air in enclosed spaces.
Finally...
Thus, the absolute humidity of the air is the most important indicator that gives us an idea of the state and characteristics of the air masses. In this case, it is necessary to be able to distinguish this value from relative humidity. And if the latter shows the proportion of water vapor (in percent) that is present in the air, then absolute humidity is the actual amount of water vapor in grams in one cubic meter of air.
Air humidity. To characterize air humidity, the following concepts are used: water vapor elasticity, absolute humidity, physiological relative humidity, saturation deficit and dew point.
Vapor pressure in air is the tension of water vapor, expressed in units of pressure (mm Hg, bar, N / m 52 0). The elasticity of water vapor when it is saturated with air is called maximum elasticity, or saturation elasticity at a given temperature. Each temperature corresponds to a certain maximum amount of water vapor, more than which the air cannot absorb. Exceeding this limit causes condensation and precipitation of droplet-liquid water from the air.
Absolute humidity is the content of water vapor, expressed in grams per 1 m 3, in millimeters of mercury column pressure, or in the SI system - in pascals (1 Ra \u003d N / m2).
Relative humidity is the ratio of the actual water vapor pressure in air to the saturation pressure at a given temperature, expressed as a percentage.
The saturation deficit is the difference between the saturation pressure and the actual vapor pressure in air, or between maximum and absolute humidity.
The dew point is the temperature at which the absolute humidity of the air reaches saturation, that is, it becomes maximum.
Physiological relative humidity) - the ratio of the amount of water vapor actually contained in the air to their the maximum number, which can be contained in the air at the surface temperature of the human body and lungs, that is, at 34 and 37 C, respectively (also expressed as a percentage). Evaporation from the surface of the body and respiratory tract at temperatures below these is possible, even if the air is completely saturated, since, heating up in respiratory tract and at the surface of the body up to 34 and 37 5o 0C, it becomes more moisture-intensive.
The humidity of the air affects the release of heat by the evaporation of sweat. The rate of sweat evaporation depends on temperature, relative humidity and air velocity. The greater the saturation deficit and the higher the speed of air movement, the more intense the evaporation of sweat. In this case, such an amount of heat is lost that the moving air (wind) has a beneficial effect even at temperatures significantly higher than body temperature. It has been established that the wind worsens health and reduces performance at a temperature of 37.0 5o 0C only in the case of 100% saturation of the air with water vapor. At an air humidity of 60%, the wind ceases to have a beneficial effect only at temperatures above 43.3 C, and at a humidity of 30% - at temperatures above 60 C.
At low temperatures, air humidity has little effect on heat transfer from the surface of the body due to the fact that in frosty air, due to its low moisture capacity, even when fully saturated, it contains an insignificant amount of water vapor. In hygienic practice, it is customary to normalize relative humidity due to the fact that by its value it is more convenient to judge the influence of humidity, as well as other environmental factors on human heat transfer. It is believed that the optimal value of relative humidity is in the range of 50-60%; the acceptable lower value is 30%, the upper one is 70%, the lower extreme is 10-20%, and the upper extreme is 80-100%. For measurement use: hygrometer, psychrometer.
The speed of air movement. hygienic value. The dependence of human exposure on temperature and air humidity. Methods and means of measurement. Grade.
Air movement. The main factor that determines the movement of air (wind) is the difference in pressure and temperature. Air movement is characterized by speed, direction, shape (laminar, turbulent) and duration. Moving air greatly affects the amount of heat transfer by convection. Convection is understood as the transfer of heat by moving air molecules (and liquids) in a medium with disturbed thermal equilibrium. The higher the air velocity, the higher the heat transfer. The cooling effect of the wind sharply increases at negative air temperatures. The speed of its movement of the order of hundredths of a meter per second is already felt by a person. It should be noted that the wind, exerting pressure on the surface of clothing, facilitates the penetration of cold air into the underwear space and accelerates the overall cooling of the body. As the ambient temperature rises and the temperature difference decreases, the heat loss by convection decreases. If the air temperature becomes equal to the skin temperature (34 C), the heat transfer in this way stops altogether, and if it exceeds it, then a reverse flow of heat from the air to the body is established (convection heating) . However, the warming effect on the body of moving air takes place only if the amount of heat transferred by heated air is greater than its loss due to sweat evaporation. This is observed or very high temperature air (over 60 C) or at lower temperatures, but at 100% humidity, when sweat evaporation stops. In all other cases (that is, when the humidity is less than 100% and the air temperature is below 60 C), the moving air has a cooling effect. The cooling effect of moving air is used to improve habitability in tanks and other objects with sources of thermal radiation. The movement of air removes excess heat falling on the surface of the body, making it possible to work with radiation levels that exceed the maximum tolerated.
At average air temperatures (from 18 to 20 C) in the premises, the optimal value of the air velocity is 0.05 - 0.25 m / s, the permissible value is 0.3 m / s. At low temperatures, the maximum tolerable air velocity is 3-5 m/s. Means for measurement: anemometer, catathermometer.
28. Air of closed inhabited premises. Causes that change its natural composition and pollution level. Prevention of adverse effects on humans. The air in habitable rooms contains the same amount of oxygen, but it is not biologically active. It lacks “something” that the body needs and gives it vitality and health. This “something” is atmospheric electricity, or rather, its carriers, gas ions. The main application of ionizers is the creation in the premises of the optimal concentration of negatively charged air ions, which are necessary for normal life. Air devoid of air ions is "dead", impairs health and leads to diseases. Any disease begins with a metabolic disorder in the cells of the body, a manifestation of which is a decrease in their negative charge, and this changes the colloidal state of the cells, the release of their contents into the bloodstream and intravascular coagulation. The negative charge of cells can be restored medications(heparin) and by inhalation of air, with an excess of negative oxygen air ions. These air ions, entering the lungs, penetrate into the blood and are carried throughout the body, restoring the negative charge of cells, stimulating metabolism and exerting an antithrombotic effect.
AIR HUMIDITY. DEW POINT.
INSTRUMENTS FOR DETERMINING AIR HUMIDITY.
1. Atmosphere.
The atmosphere is the gaseous shell of the Earth, consisting mainly of nitrogen (more than 75%), oxygen (slightly less than 15%) and other gases. About 1% of the atmosphere is water vapor. Where does it come from in the atmosphere?
A large proportion of the earth's area is occupied by seas and oceans, from the surface of which water constantly evaporates at any temperature. The release of water also occurs during the respiration of living organisms.
The amount of water vapor contained in the air affects the weather, human well-being, the conduct of technological processes in production, the safety of exhibits in the museum, the safety of grain in storage. Therefore, it is very important to control the degree of air humidity and the ability, if necessary, to change it in the room.
2. Absolute humidity.
absolute humidity air is called the amount of water vapor contained in 1 m 3 of air (water vapor density).
Or , where
m is the mass of water vapor, V is the volume of air that contains water vapor. P is the partial pressure of water vapor, μ is the molar mass of water vapor, T is its temperature.
Since density is proportional to pressure, absolute humidity can also be characterized by the partial pressure of water vapor.
3.Relative humidity.
The degree of humidity or dryness of air is affected not only by the amount of water vapor contained in it, but also by air temperature. Even if the amount of water vapor is the same, at a lower temperature the air will appear more humid. That is why in a cold room there is a feeling of dampness.
This is because at a higher temperature, the air can contain a higher maximum amount of water vapor, and is present in the air when the vapor is rich. That's why, maximum amount of water vapor, which may contain in 1 m 3 of air at a given temperature is called saturation vapor density at a given temperature.
The dependence of the density and partial pressure of saturated steam on temperature can be found in physical tables.
Considering this dependence, we came to the conclusion that a more objective characteristic of air humidity is relative humidity.
relative humidity called the ratio of the absolute humidity of the air to the amount of steam that is necessary to saturate 1 m 3 of air at a given temperature.
ρ is the vapor density, ρ 0 is the density of saturated vapor at a given temperature, and φ is the relative humidity of the air at a given temperature.
Relative humidity can also be determined through the partial pressure of steam
P is the partial pressure of steam, P 0 is the partial pressure of saturated steam at a given temperature, and φ is the relative humidity of the air at a given temperature.
4. Dew point.
If the air containing water vapor is cooled isobarically, then at a certain temperature the water vapor becomes saturated, since as the temperature decreases, the maximum possible density of water vapor in the air at a given temperature decreases, i.e. vapor density decreases. With a further decrease in temperature, excess water vapor begins to condense.
Temperature at which a given amount of water vapor in the air becomes saturated is called dew point.
This name is associated with a phenomenon observed in nature - dew. Dew is explained as follows. During the day, air, land and water in various reservoirs warm up. Consequently, there is an intensive evaporation of water from the surface of reservoirs and soil. Water vapor in the air is unsaturated at daytime temperatures. At night, and especially in the morning, the temperature of the air and the surface of the earth drops, water vapor becomes saturated, and excess water vapor condenses on various surfaces.
Δρ is the excess moisture that is released when the temperature drops below the dew point. 
Fog has the same nature. Fog is the smallest droplets of water formed as a result of the condensation of steam, but not on the surface of the earth, but in the air. The droplets are so small and light that they can be suspended in the air. On these droplets, light rays are scattered, and the air becomes opaque, i.e. visibility is difficult.
With the rapid cooling of the air, the vapor, becoming saturated, can, bypassing the liquid phase, immediately pass into the solid. This explains the appearance of frost on the trees. Some interesting optical phenomena in the sky (for example, a halo) are caused by the passage of solar or lunar rays through cirrus clouds, consisting of tiny ice crystals.
5.Instruments for determining humidity.
The simplest devices for determining humidity are hygrometers of various designs (condensation, film, hair) and a psychrometer.
Operating principle condensation hygrometer based on measuring the dew point and determining the absolute humidity in the room from it. Knowing the temperature in the room and the density of saturated vapors corresponding to this temperature, we find the relative humidity of the air.
Action film and hair hygrometers associated with a change in the elastic properties of biological materials. With an increase in humidity, their elasticity decreases, and the film or hair is stretched to a greater length.
Psychrometer consists of two thermometers, in one of which the tank with alcohol is wrapped with a damp cloth. Since moisture is constantly evaporating from the fabric and, consequently, heat is removed, the temperature indicated by this thermometer will be lower all the time. The less humid the air in the room, the more intense the evaporation, the thermometer with a wet reservoir cools more and shows a lower temperature. According to the temperature difference between dry and wet thermometers, using the appropriate psychrometric table, determine the relative humidity of the air in a given room.
Actual water vapor pressure -e - the pressure exerted by it is measured in mm Hg. or millibars.
Elasticity V.p. in a state of saturation is called saturation elasticity - E - this is the maximum elasticity of the vp possible for a given t 0 . The saturation elasticity increases with t 0 of air: at a higher t 0, air is able to hold more VP than at a lower one.
For every 10 0 C, the saturation elasticity increases by ≈ 2 times.
If the air contains v.p. less than is needed to saturate it at a given t 0 , one can determine how close the air is to saturation. For this, it is determined relative humidity - r - (it characterizes the degree of saturation of air with water vapor).
r = e / E ∙ 100%
When saturated e = E And r = 100%
Absolute air humidity - water vapor density -but (expressed in grams per 1 m 3 of air).
Humidity deficiency D - difference between saturation elasticity E and actual vapor pressure e at a given t 0 air.
D = E - e
Dew point τ - t 0 at which the ce contained in the air Could saturate the air.
Condensation- the transition of water from a gaseous state to a liquid occurs in atm. in the form of the formation of tiny droplets with a diameter of several microns. Larger droplets form when small ice crystals coalesce or melt.
In air, saturated water vapor when air t 0 drops to the dew point τ or an increase in the number of v.p. going on condensation, at t 0 below 0 0 С, water, bypassing the liquid state, can turn into a solid one, forming ice crystals; this process is called sublimation.
Condensation and sublimation can occur in the air on condensation nuclei, on the earth's surface and various objects. The most important nuclei of condensation are particles of soluble hygroscopic salts, especially sea salt (they enter the air when the sea is rough, when sprayed sea water etc.).
When t 0 of the air cooling from the underlying surface reaches the dew point, dew, hoarfrost, frost, liquid and solid (frost) raids, ice are deposited on the cold surface from it.
4. Clouds and their formation, structure, structure, tiers.
If condensation (sublimation) of water vapor occurs at a certain height above the surface, then clouds.They differ from fogs in their position in the atmosphere, physical structure and variety of forms.
Clouds - accumulation of products of condensation and sublimation, their occurrence is associated with the adiabatic cooling of the rising air. The rising air cools gradually, reaches the boundary, where its t 0 becomes equal to the dew point. This border is called condensation level. Above it, in the presence of condensation nuclei, clouds can form. The lower boundary of the clouds coincides with the level of condensation. Crystallization occurs at t 0 below -10 0 C. Falling below the cond. cloud droplets can evaporate.
Clouds are carried by air currents. If the relative humidity in air containing clouds, decreases then they can evaporate. Under certain conditions, part of the cloud elements is being consolidated, becomes heavier and can fall out from the cloud in the form of precipitation.
According to the structure, clouds are divided into 3 classes:
1) water (drip) - at positive t 0 they consist of drops with a diameter of thousandths and hundredths of a mm, at negative t 0 they consist of supercooled droplets;
2) ice (crystalline) - are formed at sufficiently low t 0;
3) mixed - consist of a mixture of supercooled drops and ice crystals, are formed at moderately negative t 0.
Cloud forms are very diverse. In the modern international classification, they are divided into 10 genera, in which a significant number of species, varieties and additional features are distinguished.
International cloud classification.
Clouds of these genera occur at altitudes between sea level and the tropopause. Conventionally, 3 tiers are separated, the boundaries of the tiers depend on the geographical latitude and t 0 conditions.
The upper layer of clouds: polar latitudes - 3-8 km, temperate - 5-13 km, tropical - 6-18 km.
The middle layer of clouds: polar latitudes - 2-4 km, temperate - 2-7 km, tropical - 2-8 km.
The lower tier of clouds: in all latitudes - up to 2 km.
The main families and types of clouds and the conditions for their formation.
in height and appearance clouds are grouped into 4 families:
IV sem. - clouds of vertical development
The 10 main genera of clouds are grouped into families as follows.
I sem. - clouds of the upper tier
1. pinnate - Cirrus (Ci)
2. cirrocumulus - Cirrocumulus (Cc)
3. cirrostratus - Cirrostatus (Cs)
II cem. - middle tier clouds
4. high - cumulus - Altocumulus (Ac)
5. high - layered - Altoostatus (As) (can penetrate into the upper tier)
III sem. - low level clouds
6. stratocumulus - Stratocumulus (Sc)
7. layered - Stratus (St)
8. layered - rain - Nimbostratus (Ns) (almost always located in the lower tier, but usually penetrate into the overlying tiers)
IV sem. - clouds of vertical development (the bases lie in the lower tier, the tops comprehend the positions of the clouds of the upper tier)
9. cumulus - Cumulus (Cu)
10. cumulonimbus - Cumulonimbus (including thunderstorms and showers)
The nature and shape of clouds are determined by processes that cause air cooling, leading to cloud formation.
There are several genetic types of clouds.
I. Clouds of convection(cumulus) are formed as a result of convection, when an inhomogeneous surface is heated: 1) intramass(associated with processes inside the air masses); 2) frontal(arise due to processes associated with fronts, i.e. at the boundaries between air masses); 3) orographic(formed when air flows onto the slopes of mountains and hills).
II. wavy clouds occur predominantly under the inversion layer (stratus, stratocumulus, altostratus). In stable air masses, the main process of cloud development is a weak turbulent transfer of water vapor together with air from the earth's surface upwards and its subsequent adiabatic cooling.
III. Upslope clouds (stratus)- These are huge cloud systems stretched along warm or cold fronts (especially well-defined in the case of a warm front).
Precipitation
Precipitation is water that has fallen to the surface from the atmosphere in the form of rain, drizzle, grains, snow, hail. Precipitation mainly falls from clouds, but not every cloud gives precipitation.
Forms of precipitation: rain, drizzle, snow pellets, snow, ice pellets, hail.
Precipitation formation. The water droplets and ice crystals in the cloud are very small, they are easily held by the air, even weak ascending currents carry them upward. For precipitation to form, the cloud elements must be enlarged so that they can overcome the ascending currents. Enlargement occurs, 1) as a result of the merging of droplets and the adhesion of crystals; 2) as a result of evaporation of some elements of the cloud, diffuse transfer and condensation of water vapor on other elements (especially in mixed clouds). By origin, precipitation is distinguished: 1) convective (formed in a hot zone, from southern to northern tropic), 2) orographic and 3) frontal (formed when air masses with different t 0 and other physical properties meet, fall out of warm air in the temperate and cold zones).
The nature of precipitation depends on the conditions of their formation: drizzling, torrential and continuous precipitation.
Characteristics of the precipitation regime. The daily course of precipitation (coincides with the daily course of cloudiness) and its types: 1) continental (has 2 maxima - in the morning and in the afternoon, and 2 minima - at night and before noon) and 2) sea (coastal) - 1 maximum (at night) and 1 minimum (day).
The annual course of precipitation, i.e. the change in the amount of precipitation by months in different climatic zones is different. The main types of annual precipitation are: 1) equatorial (precipitations fall evenly throughout the year, max is the equinox period); 2) monsoonal (max - in summer, min - in winter - subequatorial climatic zone and the eastern outskirts of the continents in the dead and subtropical zones, especially in Eurasia and North America); 3) Mediterranean (max - in winter, min - in summer; western outskirts of the continents in the subtropical zone); 4) continental temperate zone (during the warm period it is 2-3 times more; when moving inland, the total amount of precipitation decreases); 5) marine temperate zone (fall evenly over the seasons, small max in autumn and winter).
AIR HUMIDITY - the content of water vapor in the air, characterized by a number of values. Water evaporated from the surface of the continents and oceans when they are heated enters the atmosphere and is concentrated in the lower layers of the troposphere. The temperature at which air reaches saturation with moisture for a given water vapor content and constant pressure is called the dew point.
Humidity is characterized by the following indicators:
Absolute humidity (Latin absolutus - full). It is expressed as the mass of water vapor in 1 m³ of air. It is calculated in grams of water vapor per 1 m³ of air. The higher the air temperature, the greater the absolute humidity, since more water changes from liquid to vapor when heated. During the day, the absolute humidity is higher than at night. The indicator of absolute humidity depends on the geographical location of a given point: in polar latitudes, for example, it is up to 1 g per 1 m³ of water vapor, at the equator up to 30 grams per 1 m³; in Batumi (Georgia, the Black Sea coast), the absolute humidity is 6 g per 1 m³, and in Verkhoyansk (Russia, North-Eastern Siberia) - 0.1 grams per 1 m³. The vegetation cover of the area largely depends on the absolute humidity of the air;
relative humidity. This is the ratio of the amount of moisture in the air to the amount that it can hold at the same temperature. Relative humidity is calculated as a percentage. For example, the relative humidity is 70%. This means that air contains 70% of the amount of vapor that it can hold at a given temperature. If the daily course of absolute humidity is directly proportional to the course of temperatures, then relative humidity is inversely proportional to this course. A person feels good at a relative humidity of 40-75%. Deviation from the norm causes a painful state of the body.
The air in nature is rarely saturated with water vapor, but always contains some amount of it. Nowhere on earth has a relative humidity of 0% been recorded. At meteorological stations, humidity is measured using a hygrometer device, in addition, recorders are used - hygrographs;
The air is saturated and unsaturated. When water evaporates from the surface of the ocean or land, the air cannot hold water vapor indefinitely. This limit depends on the air temperature. Air that can no longer hold moisture is called saturated. From this air, at the slightest cooling, water droplets begin to stand out in the form of dew, fogs. This is because water, when cooled, changes from a gaseous state (steam) to a liquid state. Air above a dry and warm surface usually contains less water vapor than it could contain at a given temperature. Such air is called unsaturated. When it is cooled, water is not always released. The warmer the air, the greater its ability to absorb moisture. For example, at a temperature of -20 ° C, the air contains no more than 1 g / m³ of water; at a temperature of + 10°С - about 9 g/m³, and at +20°С - about 17 g/m³. Therefore, with the apparent high humidity of the air in the tundra and its dryness in the steppe, their absolute humidity can be the same due to their difference in temperature.
The calculation of air humidity is of great importance not only for determining the weather, but also for carrying out many technical measures, in the storage of books and museum paintings, in the treatment of pulmonary diseases, and especially in the irrigation of fields.