Air humidity

the air humidity, or briefly humidity, designates the portion of the water vapour of the gas mixture of the terrestrial atmosphere or in areas. Liquid water or ice is not added to the air humidity therefore.

Condensing water vapour as indirect proof for the humidity

table of contents

work on

] general a water-free air mixture dry air. Tables for compositionair usually refer to dry air, since the water vapour portion of damp air with 0 to 4 percent by volume varies comparatively very strongly. The air humidity is affected particularly by the availability by water, the temperature and the degreethe mixing of the atmosphere. Higher air temperatures enable to take up air thereby, more water vapour. With very small concentrations of water vapour in air one calls the air humidity also trace dampness.

physical fundamentals

evaporation andAlways

individual water molecules of the water volume cross condensation at a free water surface, which separates liquid water from the air volume lying over it, into the air volume. In the liquid water the water molecules are comparatively strongly together bound by molecular forces, whereby itself the coherent Liquid group to only train can. Due to their thermal movement the water molecules carry however certain in each case amounts at kinetic energy, which strew around a temperature-dependent average value. A small percentage of water molecules has therefore always sufficient thermal energy, around the binding forcesto overcome the surrounding molecules, leave the water surface to and change over into the air volume to thus evaporate. The evaporation rate depends their kinetic energy the binding energy of the liquid group on the percentage of those molecules, exceeds and becomes therefore among other things onthe dominant temperature determines.

Turned around evaporated water molecules from air also meet the water surface and can depending upon their kinetic energy with a certain probability by the molecule group be caught there, therefore condensed. The condensation rate depends onthe density of the water molecules in air. To consider participate that this model can be only applied to a water surface, condensation procedures in the free atmosphere are often substantially more complex.


regards one an evaporation procedure with more constantTemperature and at the beginning of dry air, then stops itself the temperature appropriate evaporation rate, while the condensation rate is first alike to water molecules for lack of in air zero. The evaporation rate is thus larger than the condensation rate and the number of water molecules inair rises. Thus also the condensation rate and the net evaporation (evaporation rate minus condensation rate) grow begin to sink. The density of the water molecules in air and thus the condensation rate rise so long, until equal to condensation rate and evaporation rate are, perTime unit thus likewise many water molecules of the water into air cross as from air in the water. Then the equilibrium is reached, in which the net evaporation is zero, although a constant particle exchange between air and water takes place. Same applies toSublimation and Resublimation over an ice surface, however with another point of equilibrium.

The concentration of water molecules in air, available in the equilibrium, is the Sättigungskonzentration. If the temperature rises, also a higher Sättigungskonzentration will adjust itself, there now likewise the higherEvaporation rate for the reaching of a new equilibrium by a higher condensation rate to be again compensated must. It can be derived thus from this simple model of the kinetic gas theory, why the Sättigungskonzentration must depend on the temperature.

Becomes however often more substantiallyUnderstanding error committed, whereby it should be noticeable that the characteristics of air did not play a role with the regarded procedures. The Sättigungskonzentration is determined nearly alone by the characteristics and the occurrence of the water vapour, there it to no substantial interaction alsothe other atmosphere gases comes. The colloquially common and mode of expression wide-spread because of the simplicity also in experts, air can take up a certain quantity of water vapour at given temperature maximally, is misleading. Air does not take the humidity similarlyto a sponge up and also the term of the saturation may be understood here also not similarly to a solution. Air consists of independently acting gas particles, which interact essentially only over impacts. Neither oxygen therefore is in nitrogen,still water vapour solved in possibly another gas.


increases one by a supply of water molecules their concentration beyond the Sättigungskonzentration, then the condensation rate rises beyond the evaporation rate because of the larger density temporarily at water moleculeson and the concentration at water molecules sinks afterwards the equilibrium value. It comes to a supersaturation.

Also here it is to be noted that it concerns not an inability of air to hold the surplus water vapour.Rather the water vapour under these conditions uses a darbietende condensation surface, in order to lower its concentration by heterogeneous condensation on the Sättigungskonzentration. If such condensation surfaces, the condensation nuclei are missing, then air can take up durably substantial quantities of water vapour, to itfinally to a homogeneous condensation comes. This is for example in large volumes of pure an air as possible, thus with a small aerosol concentration, and with large distance of any confinement surfaces the case (see cloud chamber). Spontaneous condensation from water vapour to water dropletstakes place without condensation germs only at extreme supersaturation of several hundred per cent of relative dampness. In practice however nearly always a sufficiently large quantity of aerosols is in air present, so that it in the atmosphere hardly to supersaturationsfrom several per cent points comes.

partial saturation

the evaporation rate of the water cannot exceed certain maximum values. It therefore lasts longer time until the equilibrium reset itself after a disturbance. Became by the for example nocturnal coolingPart the humidity content condenses, then air is first insatiated after a heating up and can reach the state of saturation only slowly again. This partial saturation is for our atmosphere because of the frequent variations in temperature the normal case, whereby one usually of insatiatedAir speaks. It is of great importance for numerous procedures, how far air is distant from the state of saturation, why different dampness mass serves to describe this condition quantitatively.

dependence of the saturation quantity on enviromental influences

basesder Thermodynamik

Alle Gasteilchen eines idealen Gases bewegen sich im Rahmen der kinetischen Gastheorie unabhängig voneinander und wechselwirken in diesem Modell ausschließlich durch elastische Stöße, bevorzugen dabei jedoch keine Raumrichtung. The description ideal gases takes place via the general Gasgleichung,the their behavior concerning the variables of state pressure, volume, temperature and amount of material describes. The ideal behavior of air decreases however with increasing steam content. Air and particularly that in it contained water vapour show therefore many material effects,which among other things by the van that Waals equation or the Virialgleichungen approach to be described.

Under natural atmospheric conditions deviating reciprocal effects of the gas particles are to be considered as for example phase transitions, electrostatics and Hygroskopie from the ideal behavior. It comes in particular to oneReciprocal effect of the gaseous water molecules with the firm and liquid components floating in air, the aerosols. In order to be able to understand the dynamics of the steam content in air, thus the air humidity, correctly, it is necessary therefore, both the fundamental processesto understand within an ideal gas (a particle character) and the additional characteristics of a material gas (reciprocal effects of the particles beyond impacts) correctly. Apart from a purely qualitative understanding of the different subprocesses and thus the fundamental dynamics it is however also necessary,to describe these effects in their meaning and their last-finite effect on the air humidity quantitatively. For this exist different thermodynamic basic relations and empirical Näherungsformeln, which are presented in the course of the article apart from a purely qualitative description.


maximumDampness as a function of the temperature

with increase of the temperature increases the portion of water molecules, which possess sufficient kinetic energy, in order the water surface to leave. It stops itself thus a higher evaporation rate, which compensates by a higher condensation ratewill must, which presupposes however a higher concentration of water molecules in air. The water vapour capacity of air increases therefore, as in the illustration right represented, exponential with rising temperature. The water vapour has one for each temperature with given pressureclearly saturation quantity determined. With atmospheric normal print of 0,10135 MPa a cubic meter of air can take up 9.41 gram water with ten degrees Celsius altogether. The same amount of air takes up with 30 degrees Celsius however up to 30,38 gram water. One designates theseSaturation quantity as maximum dampness, which is tabulated in the article saturation. Here also Mollier diagrams are common after smelling pool of broadcasting corporations Mollier (1923) for the representation of the air humidity far.


the water vapour capacity of air is, as stated above, dependent on thatTemperature, not however at the same time also of the pressure. This is because of it that with water vapour satisfied air does not represent ideal gas and an increase in pressure in the condensation of an appropriate quantity of water results, not however in a change of the water vapour capacity. In general formapplies this to the phase transitions other gases, arises however due to for atmospheric temperatures/pressures to rather atypical condensation and boiling points more rarely. A small deviation shows the humidity however nevertheless, why one a Korrekturfaktor (English.: enhancement factor)uses, in order to receive more exact values. This Korrekturfaktor considers molecular reciprocal effects, which increase the Sättigungsdampfdruck of the water vapour. The Korrekturfaktor depends thereby on temperature and pressure, whereby it moves with atmospheric conditions within the range of 0,5% and thereforeusually one neglects (details in the article Sättigungsdampfdruck).

other materials are

solved purity of the water in the water, then they make leaving the water surface to the water molecules more difficult, whereby the evaporation rate sinks and a smaller saturation quantity adjusts itself (so-called. Solution effect).

surface curvature of the water

is the water surface as for example with a drop outward curved, then the water molecules are less strongly bound at the surface and can leave the surface more easily. This curvature effect causes therefore,that the evaporation rate rises. If satisfied air with small nebula droplets stands in the equilibrium, its relative dampness amounts to therefore something over 100%.

If the water surface is inward curved (like for example with the meniscus in a partly water-filled capillary), then are the water molecules bound at the surface more strongly and can leave the surface less easily - the evaporation rate sinks. If satisfied air is located in an aqueous porous material with the menisci in the equilibrium, its relative dampness amounts to less than 100%.

dampness mass

the water content of air can be indicated by different dampness mass so mentioned. Synonymously usable designations are clarified by a diagonal stroke, matching dampness mass are located in the same line.

absolute air humidity

the absolute air humidity, also water vapour density or briefly Dampfdichte (symbol: ρ w, ρD, D or A; not obligatorily fixed), the mass of the water vapour is in a certain air volume, thus its density and/or concentration. It is usually indicated in gram water per cubic meter of air. It is limited upward throughthe maximum dampness ρ w, max, which prevails during a saturation (associated formulas and values see there).

The absolute air humidity is not strongly temperature-dependent and without its indication with values in other temperature ranges comparable due to the change of the volume. In additionvaries it with the height, since with this the air pressure and concomitantly the volume of a given Luftpaketes change, which remain at the same time constant mass of the water however. It has thus no conservative characteristic in the vertical one and changesitself therefore also with up and downward movements of the Luftpaketes. One calls this also shift variance or Instationarität. This effect disappears due to the pressure independent saturation quantity with an increasing approximation to the maximum dampness. There the absolute humidity besides with difficulty toomeasure are become only rarely related they.

The absolute air humidity can be computed by means of the following formulas, whereby the first term arises as a result of the conversion of the equation of state ideal gases:

<math> \ rho_w = \ frac {e} {R_w \ cdot T} = \ frac {m_ {\ mathrm {water vapour}}} {V_ {\ mathrm {entirely}}}< /math>

The individual symbolsstand for the following sizes:

relative air humidity

the relative air humidity (symbol: φ, f, U or rF; ) the proportional relationship between the momentary water vapour pressure and the saturation water vapour pressure is not obligatorily fixed.

  • With a relative air humidity of 50% containsair only half of the water vapour quantity, which could be maximally contained at the appropriate temperature.
  • With 100% of relative air humidity air is completely satisfied with water vapour.
  • If the saturation is exceeded of 100%, then the surplus strikes itselfHumidity as condensation and/or. Fog down.

With rising temperature the water vapour quantity needed for the saturation increases. That has the consequence that the relative air humidity of a given air volume decreases when heating up. Since thus the maximum dampness with the temperature changes,here the indication of the temperature is for the comparability of the values compellingly necessary. Thus it shows up for example that in one as drying appearing desert with an air temperature of 34,4 °C and a relative humidity of 20% altogether 7.6 gramWater vapour in a cubic meter of air are contained, which corresponds to a relative humidity of 100% with an air temperature of 6,8 °C and would thus lead to the condensation. Therefore phenomena are such as vapor or fog a signal for a high relativeAir humidity and at the same time for low temperatures. The perception of air as drying or damp is thus rather because of the temperature as to actually in their contained quantity of water.

The large advantage in relation to the relative air humidity other damp is their comparativelysimple measurability. This has the consequence that the relative humidity is the measure for the air humidity, furthest common with distance. With a not-proportional indication, thus in the range of values 0 to 1, one speaks thereby also of the saturation relationship.

One can the relative air humidity with the following formulas compute:

<math> \ varphi = \ frac {e} {E} \ cdot 100 \ \ % \ approx \ frac {\ mu} {\ mu_s} \ cdot 100 \ \ % \ approx \ frac {\ rho_w} {\ rho_ {w, max}} \ cdot 100 \ \ % \ approx \ frac {s} {S} \ cdot 100 \ \ %< /math>

The individual symbols stand for the following sizes:

with the help of the relative dampness andthe associated temperature level can among other things also the dew point be computed. By a combination of different equations one receives a possibility for the conversion of the relative into the absolute air humidity on basis of the temperature (t - temperature in °C; T - Temperaturein Kelvin):

<math> \ rho_w = \ frac {E_0} {R_w} \ cdot \ frac {\ varphi} {T} \ cdot E (t) \ qquad \ qquad \ mathrm {with} \ qquad \ qquad \ frac {E_0} {R_w} = 1324.34 \; \ frac {\ mathrm {g \ cdot K}} {\ mathrm {m^3}} </math>

specific air humidity

the specific air humidity, also steam content (symbol: s or q) givesthe mass of the water on, which is in a certain mass of damp air.

This size behaves in contrast to the previous damp so long conservatively with vertical movements of a Luftpaketes, as no condensation or evaporation occurs. The reason for thisit lies in the fact that a kilogram of air or water vapour remains always independent of air pressure or air temperature a kilogram. For the indication of the specific air humidity it plays therefore no role, in which height a Luftpaket is. This applies so long, like thoseQuantity of water vapour remains alike, why it may not come again to a change of the state of aggregation. However the difficult measurement of the specific air humidity opposes this advantage, which remains reserving as a rule a laboratory.

The maximum specific air humidity in the state of saturation,the saturation dampness in such a way specified, has the symbol S (also q s).

The specific air humidity s can be computed with the following formulas, whereby the respective size is defined over the first term and all following terms of equivalents or approximationsfor this represent (flat steel bar - air moistens; tl - dry air; W - Water vapour and/or. Water). Of practical importance only the latter terms are, all different serve for to the derivation and didactical comprehensibleness.

<math> s: = \ frac {m_ {\ mathrm {W}}} {m_ {\ mathrm {flat steel bar}}} = \ frac {m_ {\ mathrm {W}}} {m_ {\ mathrm {tl}} + m_ {\ mathrm {W}}} = \ frac {\ frac {m_ {\ mathrm {W}}} {V_ {\ mathrm {G}}}} {\ frac {m_ {\ mathrm {tl}}} {V_ {\ mathrm {G}}}+ \ frac {m_ {\ mathrm {W}}} {V_ {\ mathrm {G}}}} = \ frac {\ rho_ {\ mathrm {W}}} {\ rho_ {\ mathrm {tl}} + \ rho_ {\ mathrm {W}}} = \ frac {\ rho_ {\ mathrm {W}}} {\ rho_ {\ mathrm {flat steel bar}}}< /math>
<math> s = \ frac {\ rho_ {\ mathrm {W}}} {\ rho_ {\ mathrm {tl}} + \ rho_ {\ mathrm {W}}} = \ frac {\ frac {e} {R_W \ cdot T}} {\ frac {p - e} {R_ {tl} \ cdot T} + \ frac {e} {R_W \ cdot T}} = \ frac {\ frac {e} {M_ {\ mathrm {W}}}} {\ frac {p - e} {M_ {\ mathrm {tl}}} + \ frac {e} {M_ {\ mathrm {W}}}} = \ frac {\ frac {M_ {\ mathrm {W}}} {M_ {\ mathrm {tl}}} \ cdot e} {p -\ left (1 - \ frac {M_ {\ mathrm {W}}} {M_ {\ mathrm {tl}}} \ right) \ cdot e} \ approx \ frac {0 {,} 622 \ cdot e} {p - 0 {,} 378 \ cdot e} \ approx 0 {,} 622 \ cdot \ frac {e} {p}< /math>

whereby applies:

<math> \ rho_ {\ mathrm {W}} = \ frac {e} {R_W \ cdot T} \ qquad \ qquad \ mbox {and} \ qquad \ qquad M_ {\ mathrm {W}} = \ frac {R_W} {R}< /math>
<math> \ rho_ {\ mathrm {tl}} = \ frac {p - e} {R_ {tl} \ cdot T} \ qquad \ qquad \ mbox {and} \ qquad \ qquad M_ {\ mathrm {tl}}= \ frac {R_ {tl}} {R}< /math>

The saturation dampness is calculated accordingly after:

<math> S: = \ frac {m_ {\ mathrm {W \ with \ S \ ddot attigung}}} {m_ {\ mathrm {flat steel bar}}} = \ frac {\ rho_ {\ mathrm {W \ with \ S \ ddot attigung}}} {\ rho_ {\ mathrm {flat steel bar}}} \ approx \ frac {0 {,} 622 \ cdot E} {p - 0 {,} 378 \ E cdot} </math>

The individual symbols stand for the following sizes:

mixing proportion

the mixing proportion (symbol: μ, x, m), also dampness degree mentioned, givesthe mass of the water on, which is in a certain mass of dry air. In their characteristics mixing proportion and specific air humidity are identical. As a rule also the numerical value does not differ very strongly, why one can equate both sizes approached.

The mixing proportion can be computed with the following formulas, whereby it is defined over the first term and all following terms represent equivalents or approximations for this (flat steel bar - air moistens; tl - dry air; W - Water vapour and/or. Water):

<math> \ mu: =\ frac {m_ {\ mathrm {W}}} {m_ {\ mathrm {tl}}} = \ frac {\ rho_ {\ mathrm {W}}} {\ rho_ {\ mathrm {tl}}} = \ frac {M_ {\ mathrm {W}}} {M_ {\ mathrm {tl}}} \ cdot \ frac {e} {p - e} \ approx 0 {,} 622 \ cdot \ frac {e} {p - e}< /math>

The individual symbols stand for the following sizes:


hair hygrometer

of measuring instruments for the collection of the air humidity are called hygrometers, in particular as absorption hygrometers (Hair hygrometer), dew-point hygrometers, psychrometers and dampness sensors.


diurnal variation

the air humidity shows a typical diurnal variation, which can be very different depending upon site conditions and also not always must follow a certain sample,exactly this however as a rule does. Thus for instance the following process shows up for summer Berlin in: at the absolute air humidity is to seven o'clock local time on the average at approximately 10.6 g/m ³, then at 14 o'clock at 10,0 g/m ³ andfinally at 21 o'clock again at 10,6 g/m ³. In the winter in the morning 4.5 shows up g/m ³, at noon 4.6 g/m ³ and in the evening again 4.5 g/m ³. The air humidity rises thus in the winter after sunrise and sinks after sunset, exactly against set to the diurnal variationthe air temperature and as one it due to the increased evaporation would expect. In the summer the influence of convection is added, Luftpakete the penetration of drier air masses ascending there from the height causes and therefore to a along-daily to afternoon minimumlead. In the evening hours the absolute humidity with leaving convection rises however again. In the summer therefore two steam pressure maxima, one show up around approximately 8 o'clock and one around approximately 23 o'clock.

yearly variation

in the yearly variation, based on eitherDaily or monthly means as average values of many years, points themselves maxima of the relative air humidity to late autumn and early winter, thus in the period of the largest formation of fog. In contrast to this minimum values stand in the spring and early summer. The steam pressure is smallest in the winter and in the summer tohighest. The determining influences are thereby evaporation and advection of water vapour, some very strong regional and/or. local purchase exhibit.

dependence on the height

the water vapour pressure takes with increasing height and thus removing air temperature first very rapidlyand then starting from three kilometers only slowly off. In ten kilometers height it amounts to then only about a per cent of the land value. The relative air humidity does not show such a clear trend, is in the tropopause, in Central Europe about off11 kilometers height, however usually very small. It amounts to here under normal conditions about 20% and continues to drop with increasing height, which also the reason for it is that the Wolkenbildung is limited to the troposphere almost exclusively.

Work on []

Meaning and ranges of application

the air humidity are in a multiplicity of applications of importance, whereby the meteorology and climatology form here their theoretical, not however for their application orientated center. The role of the water vapour, its characteristics and in particular its technicalApplications outside of the atmospheric conditions are described there. The general characteristics of the water and its natural spreading can be reread separately.

numerous phenomena can everyday life in the everyday life be attributed to the humidity, of which some here exemplaryto be introduced are.

If one observes wet articles or open water surfaces during a longer period, without this from the outside further water one supplies, then their wetness decreases and/or. the water surface drains. Laundry becomes with the time drying, puddlesdisappear, food become hard and ungeniessbar. It comes to the evaporation. This is however only so long possible, how the air is insatiated, which is relative humidity thus below 100%.

With rising air humidity also the heat conductivity and the thermal capacity takes thatAir too, so that at constant temperature of the heater surface the area is faster warmed up.

If one enters a heated area coming from the cooler environment, then one often states that eyeglass lenses begin to fit. Same applies also to windowpanes. Are the disks, for example a car, substantially more coldly than the interior of the vehicle, then fit these much fast and can thereby the field of view of the driver strongly limit. There is the same effect in one of hot steam clouds would fulfill bath, becausehere the mirrors fit within shortest time. Reason for all these effects are the cold surfaces, those air in its direct environment cooling. The higher the relative humidity of the ambient air is, the faster reaches air with the cooling thatDew point and water condense. The higher the temperature difference between surface and ambient air is, the more strongly cools the ambient air down near the surface. For this reason the described cases show up particularly in the winter and in very wet areas. The driver managesby being able to be blown constantly warm air on the disk and thus a sufficient cooling of air there present goes around. The temperature differences are however particularly strongly pronounced at an outside temperature of under 0 °C and the air interchange not particularlylargely, then it can come also to the training of ice flowers.

These effects are responsible also for freezing freezing subjects in a refrigerator when simultaneous drainage not packed cooling commodity. Their water evaporates first, however comparatively slowly, at temperatures between 4 and8 °C. At the cooler freezing subject with temperatures under 0 °C it resublimiert due to the cooling however to ice. Technical use finds this effect during the freezing drying process.

A further effect in this connection is the so-called carburetor icing, like itAnd particularly with carburetors of sport airplanes arises to automobile carburetors. Air is accelerated by the Bernoulliverengung inside a carburetor over a short distance and the air pressure is lowered and in the consequence the temperature. With high air humidity it comesthen to a precipitation of water, which settles at low temperatures as ice in the carburetor.

The change of the maximum humidity one knows also with airplanes or snaps running cars to observe, those pretty often at sharp edges of the bearing areas or e.g.a spoiler form so-called marginal vortices. Also in them the air pressure, the air humidity sinks partially is precipitated and shows up as fog.

The Ausatemluft is substantially damper and warmer with humans, in addition, many animals than the a breathing air. This recognizesone to the fact that these in the winter and/or. at low temperatures becomes apparently visible. The warm-damp Ausatemluft is cooled down thereby under the dew point and it comes to the emergence of steam clouds. Same applies also to the exhaust gases of vehicles and power stations,their winter steam clouds with an additional waste gas emission to be often confounded.

meteorology, climatology and hydrology

with water vapour satisfied air is cooled down under the dew point, then liquid water separates by condensation from air,if the for this necessary condensation nuclei (aerosols) are present. These are present however under natural conditions nearly always in sufficient concentration, so that it comes only in exceptional cases to salient supersaturations of several per cent points. The condensation and starting from temperaturesunder 0 °C also Resublimation of the water vapour among other things clouds -, snow - lead nebulas , rope and hoar frost formation to. Water vapour is therefore no permanent gas of the atmosphere and points with a statistic period spent of approximately ten days onehigh mobility up.

Although the water vapour is represented only with relatively small concentrations in the atmosphere, it carries a large portion of the global water circulation for the associated material conversion under its high mobility and and plays therefore in the Wasserbilanzan important role. Here the humidity is also an important input for formation of precipitation and/or. their computation and also for the determination of the evaporation and/or. the evaporation, transpiration and Interzeptionsverdunstung. This plays a substantial in the context of the climatic Wasserbilanz againRole for different climatic classifications.

From the humidity can besides important meteorological sizes be derived, like for example the condensation level and the virtual temperature. Also is the humidity and/or. the water vapour substantially at the radiation balance of the atmosphere takes part and affectsby the latent warmth the atmospheric temperature gradient stored in its state of aggregation, in particular the damp-adiabatic temperature gradients.

drying process

with the drying process of materials by evaporation is crucial that itself between the water content of the drying property and the air humidityan equilibrium adjusts. At a certain humidity and temperature the drying property can be dried therefore not arbitrarily further, but reached sometime a point of equilibrium characteristic of the respective conditions. It is not sufficient therefore in each case simply to wait tothe desired low water content of the drying property adjusted itself. On the other hand it is aufwändig to constantly exchange or warm up to high temperatures air, so that a high meaning in the drying technology is attached to the accurate computation of this point of equilibrium. In other applications,as in the building industry and in the agriculture, however usually in the effect of the wind one trusts, which near-blows constantly new insatiated air and thus for example the water extracts from hay or the fresh concrete.


in biology and the ecology is particularly the air humidity of of great importance here. It conditionally not only the occurrence of climate zones or certain ecological systems, but plays also with the transpiration over the gap openings of the sheets and intheir intercellular area (inter+cellular) a large role (water vapour partial pressure). The humidity is therefore an important parameter for the water regime of plants and animals (sweat). A special role plays the humidity besides for animals, which breathe mainly over the skin. For thiscount many snails and other soft animals, which possess a small tolerance in the consequence also against drainage.


within the range of the Humanmedizin is recommended a relative air humidity of the ambient air by 45 55%. Particularly in closed,badly ventilated and well heated areas this value however often one falls below, which to a decreased breath achievement and an impairment of the skin and/or. Mucous membrane to lead can. This is particularly in the winter the case, there cold outside air then only onesmall absolute humidity possesses and following warming up to room temperature to be after-moistened should (air moisturizers), in order not to let the relative humidity drop too strongly.

In very cold areas or also cold seasons and/or. at the nighta increased liquid consumption of the human organism often shows up, although due to the missing ullage by sweating rather the opposite would have to be accepted. Justified this lies in the humidification of the dry a breathing air and the associated loss of water. Becomes cold outside airwith the inhalation warms up, then their water vapour capacity rises and lowers thereby also the relative humidity. In contrast for this the Sättigungsdefizit rises and the inclination of the liquid Lungengewebs water to change over into the gaseous state of aggregation increases. In the summer and/or. with warm ambient airthe a breathing air is warmed up hardly still additionally and keeps therefore its usually high relative air humidity. If the additional losses of water are not too here large by sweating, the water requirement of the body is higher therefore with cold site conditions.

A increased air humidity is forthe respiration favorably, since the oxygen arrives over the alveoles then more easily into the bloodstream. The skin needs a high humidity, over not out drying, since this is closely coupled with the skin dampness. Particularly mucous membranes are susceptibly to draining, there themonly a small evaporation protection have and on their high dampness for the preservation of their functions are dependent. So a small dampness of the nose mucous membrane can have a increased occurrence from nose bleeding to the consequence. Thereby also the immune defense of the skin becomes generalweakened (increased cold risk) and their ability lowered to the exchange of material, about which the mouth mucous membrane is concerned particularly. Also susceptibility for skin provoking and/or. - one increases turning red or skin inflammations by a small air humidity.

A high relative humidity obstructs however the regularization thatKörpertemperatur by sweating and is felt therefore fast as stifling. Seen despite relatively higher temperatures to be able therefore very hot deserts by the organism to be borne often substantially easier (presupposed he does not suffer from drainage) than rain forests with a highHumid and comparatively moderate temperatures. This effect, the air humidity on the felt temperature possesses, by the Humidex is described, whereby the fundamental connection between a rising humidity and a rising felt temperature applies also to low values of the humidity andthus for example for the reduction of the room temperature and thus the heating expenditure to be consulted can.

At the time of the execution of Inhalationsnarkosen dampening of the inhalierten gas mixture is very importantly, there otherwise the arising for application coming medical gases water-free to be stored andEvaporation effects in the lung of the patient cooling down features (evaporative cold) and a certain drainage would cause.

land and forestry

of sour countries forest in the fog

in the agriculture exist the danger of a drainage that with a too low humidityArable crops and thus the harvest failure. By the increase steam pressure gradients between sheet surface and atmosphere thereby humidity is extracted from the plants (see section biology), in particular if its gap openings are opened on the day and they have only a small evaporation protection,which with many domestic plants (C-3 plants), the case is.

But also in forestry and the woodworking industry the humidity plays a role. Storing wood has itself a self-dampness, the wood moisture in such a way specified, in the run thatTime to the humidity adapts. This change of the wood moisture affects the composition and the volume of the wood and is thus of large importance for all woodworking trades and industries. Thus for example often fire sprinklers become in sawmillsbegun, in order to keep the wood damp.

Also the typical way, boards, to store square timbers and bars in such a way that they can be flowed around by all sides of air, is to guarantee that these did not forgive themselves or putrefy. Also it must when shifting halls - and parquet floors on the fact consideration to be taken that the wood of the environment dampness adapts (fiber saturation point) and this therefore to pour and shrink can.

storekeeping and production

Ein vorbereiteter Humidor mit Hygrometer
prepare Humidor with hygrometer

in the storekeeping of food is the air humidity very importantly for control the benefit-ripe, particularly with camp fruit. Also corrosion can be favoured by a high air humidity, particularly over the indirect effect of the increased rope formation,and must be considered therefore with the storage, for example by metals. This applies in the same form to all other humid-sensitive materials and goods, like among other things special chemicals, for certain cigars (Humidor right), wines, salami, wood, works of art, Books and integrated circuits. As consequence of it the humidity is a substantial factor with the organization of Raumklimaten in stockrooms, museums, archives, libraries, laboratories, computing centres and industriellen production plants, particularly in microelectronics.Particularly problematic such a storage is here special also with a goods transport over long distances and in an weather-isolated container. Changing environmental influences can lead here to the formation of condensation and cause damage to the cargo in this way.

Work on []

The dew point in

an important role, treated in a separate article, plays external walls of buildings Konidienträger of the mold fungus Penicillium in building physics. By this one understands the temperature surface within the brick-work and/or. the external wall of a building,starting from which it with a further cooling to the formation of a condensate to come can. Background is that warm air can take up more humidity than cold air. Moves warm and air enriched with humidity by diffusion or convection within the external wallfrom the warmer to the colder area (and/or. from the inside outward) along gradients of the water vapour concentration, then it comes to the condensation and thus to the dampness formation, as soon as the dew point is fallen below. From this again an health-endangering fungus growth can result. The effort goestherefore there, the place of the dew point by the purposeful use of building materials and/or. to shift also building methods as far as possible outward and/or. to avoid at all a dew point. An example for this is the thermal insulation, which usually at thatExterior of the wall is attached. It can thereby, contrary to an insulation on the inside, which limit fungus growth in the interiors.

In the winter period - called in this connection often rope period - are the temperature and the water vapour pressure on the insidemore highly than outside. The external wall exhibits therefore for both values a downward gradient outward. This is however even with a homogeneous external wall not equivalent, there their time-dependent memory effect for warmth and water vapour differently is and itself also the temperaturesand steam pressures in timing differently change. With inhomogenous walls it is added that the downward gradient is different in the individual materials. So a steam check foil has for example a large steam pressure gradient, however however hardly a temperature gradient. With insulating materials it often turned around,here the downward gradient of the water vapour pressure is small, but the temperature gradient high. Condensation occurs whenever the water vapour pressure would exceed locally and temporally its value maximally possible at given temperature.

See also: Vapor barrier

air and space travel

In aviation the danger of freezing bearing areas and tail unit exists by the Resublimation of the water vapour contained in air. This effect can limit the airworthyness within shortest time very strongly and is responsible for numerous accidents. One works againstthis procedure by de-icing equipments, which the critical ranges (e.g. Bearing area front edge) heat around ice beginning to prevent. A lower-priced method consists covering of it the bearing area front edge with a skin from rubber and to press stossweise compressed air between the Gummihaut and the bearing area.The skin curves and by the deformation the rigid ice is blown off.

In space travel it comes with rocket starts to similar problems due to low outside temperatures. Starting windows are selected therefore also on the basis of meteorological criteria and broken off starts if necessary. ThoseNeglect of this principle, usually in connection with technical lack, can lead to disasters like the explosion of the Challenger space shuttle.

sources and references


  • Häckel H. (1999): Meteorology.4. Aufl. Ulmer publishing house, Stuttgart; UTB 1338; 448S.ISBN 3-8252-13382
  • Zmarsly E., Kuttler W., Pethe H. (2002): Meteorological-climatological basic knowledge. An introduction with exercises, tasks and solutions. Ulmer publishing house, Stuttgart. S ISBN of 3-8252-22810
  • hops P., Kuttler W. (1998): Weather and climate. Teubner publishing house, Stuttgart/Leipzig. ISBN 3-3220-02551
  • Weischet W.(2002):Introduction to the general climatology. Fount carrier. ISBN 3-4430-71236

Web on the left of

This article was taken up to the list of exzellenter articles.

  > German to English > (Machine translated into English)