Determination of absolute air humidity. absolute humidity. Methods for measuring air humidity
The following values are used to characterize air humidity: absolute, maximum and relative humidity, saturation deficit, dew point.
absolute humidity called the amount of water vapor in grams contained in given time in 1 m³ of air.
Maximum humidity is the amount of water vapor in grams contained in 1 m³ of air at the moment of full saturation.
relative humidity is the ratio of absolute humidity to the maximum, expressed as a percentage.
Saturation deficiency is the difference between maximum and absolute humidity.
Dew point - the temperature at which the absolute humidity is at its maximum.
When assessing air humidity highest value has a relative humidity value.
Relative humidity can be measured with a hygrometer or psychrometer. basis hygrometer is a defatted human hair connected through a block with an arrow that moves along a scale. The hair lengthens with increasing humidity and becomes shorter when it decreases.
Psychrometers consist of two identical thermometers (mercury or alcohol), the tank of one of them is covered with a cloth, which is pre-moistened with distilled water. As the water evaporates, the tank cools. The temperature difference is used to judge the humidity of the air, since the intensity of evaporation depends on the degree of saturation of the surrounding air with water vapor. Two types of psychrometers are used: stationary (August) and aspiration (Assmann).
August psychrometer used in stationary conditions (on meteorological stations, in hospitals) by placing it in a place where the device is not exposed to heat radiation and wind.
Absolute humidity is calculated using the Regnot formula:
K \u003d f - a (t c - t c) x B,
Where TO- absolute humidity, mm Hg;
f- maximum air humidity at wet bulb temperature (determined according to Table 1.6);
a- psychometric coefficient equal to 0.0001;
t s - dry bulb temperature;
t in - wet bulb temperature;
B- atmospheric pressure at the time of observation, mm Hg
In the Assmann psychrometer thermometer tanks are protected by double metal shields from radiant heat. There are ventilation ducts around the tanks, through which air is sucked in at a constant speed (4 m/s). To measure humidity, a cloth-wrapped thermometer is moistened with distilled water, then the fan spring is wound up and the device is placed at the desired point. Dry and wet thermometer readings are recorded 4–5 minutes after the fan is started.
Absolute humidity
Absolute humidity is the amount of moisture (in grams) contained in one cubic meter of air. Due to the small value, it is usually measured in g / m3. But due to the fact that at a certain air temperature, only a certain amount of moisture can be contained in the air (with an increase in temperature, this maximum possible amount of moisture increases, with a decrease in air temperature, the maximum possible amount of moisture decreases), the concept of Relative Humidity was introduced.
Relative humidity
An equivalent definition is the ratio of the mass fraction of water vapor in air to the maximum possible at a given temperature. It is measured as a percentage and is determined by the formula:
where: - relative humidity of the considered mixture (air); - partial pressure of water vapor in the mixture; - equilibrium pressure of saturated vapor .
The saturation vapor pressure of water increases strongly with increasing temperature (see graph). Therefore, with isobaric (that is, at constant pressure) cooling of air with a constant vapor concentration, there comes a moment (dew point) when the vapor is saturated. In this case, the "extra" vapor condenses in the form of fog or ice crystals. The processes of saturation and condensation of water vapor play a huge role in atmospheric physics: the processes of cloud formation and the formation of atmospheric fronts are largely determined by the processes of saturation and condensation, the heat released during the condensation of atmospheric water vapor provides an energy mechanism for the emergence and development of tropical cyclones (hurricanes).
Relative Humidity Estimation
The relative humidity of a water-air mixture can be estimated if its temperature is known ( T) and dew point temperature ( T d). When T And T d expressed in degrees Celsius, then the expression is true:
Where the partial pressure of water vapor in the mixture is estimated e p :
And the wet vapor pressure of water in the mixture at temperature is estimated e s :
Supersaturated water vapor
In the absence of condensation centers, when the temperature decreases, the formation of a supersaturated state is possible, i.e., the relative humidity becomes more than 100%. Ions or aerosol particles can act as condensation centers, it is on the condensation of supersaturated vapor on ions formed during the passage of a charged particle in such a pair that the principle of operation of a cloud chamber and diffusion chambers is based: water droplets condensing on the formed ions form a visible trace (track) of a charged particles.
Another example of the condensation of supersaturated water vapor is the contrails of aircraft that occur when supersaturated water vapor condenses on soot particles in engine exhaust.
Means and methods of control
To determine the humidity of the air, devices are used that are called psychrometers and hygrometers. August's psychrometer consists of two thermometers - dry and wet. A wet bulb indicates a lower temperature than a dry bulb because its tank is wrapped in a cloth soaked in water, which, evaporating, cools it. The rate of evaporation depends on the relative humidity of the air. According to the testimony of dry and wet thermometers, the relative humidity of the air is found according to psychrometric tables. IN Lately Integral humidity sensors (usually with voltage output) began to be widely used, based on the property of some polymers to change their electrical characteristics (such as the dielectric constant of the medium) under the influence of water vapor contained in the air. To calibrate instruments for measuring humidity, special installations are used - hygrostats.
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 perfectly 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.
Humidity is the amount of water vapor that this moment(and in this place) is 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 forms precipitation, fog or clouds.
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 precise, ways 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 considered optimal for human body is the 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 features 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.
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 perfectly 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.
There are many open reservoirs on Earth, from the surface of which water evaporates: oceans and seas occupy about 80% of the Earth's surface. Therefore, there is always water vapor in the air.
It is lighter than air because the molar mass of water (18 * 10-3 kg mol-1) is less than the molar mass of nitrogen and oxygen, of which air mainly consists. Therefore, water vapor rises. At the same time, it expands, since in the upper layers of the atmosphere the pressure is lower than at the surface of the Earth. This process can be approximately considered adiabatic, because during the time it takes place, the heat exchange of the steam with the surrounding air does not have time to occur.
1. Explain why the steam is cooled in this case.
They do not fall because they soar in ascending air currents, just as hang gliders soar (Fig. 45.1). But when the drops in the clouds get too big, they still start to fall: it's raining (Figure 45.2).
We feel comfortable when the water vapor pressure at room temperature(20 ºС) is about 1.2 kPa.
2. What part (in percent) is the indicated pressure of the saturation vapor pressure at the same temperature?
Clue. Use the table of saturated water vapor pressure values at various temperatures. It was presented in the previous paragraph. Here is a more detailed table.
You have now found the relative humidity of the air. Let's give its definition.
Relative humidity φ is the percentage ratio of the partial pressure p of water vapor to the pressure pn of saturated steam at the same temperature:
φ \u003d (p / pn) * 100%. (1)
Comfortable conditions for a person correspond to a relative humidity of 50-60%. If the relative humidity is significantly less, the air seems dry to us, and if it is more - humid. When relative humidity approaches 100%, the air is perceived as damp. At the same time, puddles do not dry out, because the processes of water evaporation and steam condensation compensate each other.
So, the relative humidity of the air is judged by how close the water vapor in the air is to saturation.
If air with unsaturated water vapor in it is isothermally compressed, both the air pressure and the unsaturated vapor pressure will increase. But the water vapor pressure will only increase until it becomes saturated!
With a further decrease in volume, the air pressure will continue to increase, and the water vapor pressure will be constant - it will remain equal to the saturated vapor pressure at a given temperature. The excess steam will condense, that is, it will turn into water.
3. The vessel under the piston contains air with a relative humidity of 50%. The initial volume under the piston is 6 liters, the air temperature is 20 ºС. The air is compressed isothermally. Assume that the volume of water formed from steam can be neglected compared to the volume of air and steam.
a) What will be the relative humidity of the air when the volume under the piston becomes 4 liters?
b) At what volume under the piston will the steam become saturated?
c) What is the initial mass of the steam?
d) How many times will the mass of steam decrease when the volume under the piston becomes equal to 1 liter?
e) How much water will be condensed?
2. How does relative humidity depend on temperature?
Let us consider how the numerator and denominator in formula (1), which determines the relative air humidity, change with increasing temperature.
The numerator is the pressure of unsaturated water vapor. It is directly proportional absolute temperature(recall that water vapor is well described by the equation of state of an ideal gas).
4. By what percentage does the pressure of unsaturated vapor increase with an increase in temperature from 0 ºС to 40 ºС?
And now let's see how the saturated vapor pressure, which is in the denominator, changes in this case.
5. How many times does the pressure of saturated steam increase with an increase in temperature from 0 ºС to 40 ºС?
The results of these tasks show that as the temperature rises, the saturated vapor pressure increases much faster than the pressure of unsaturated vapor. Therefore, the relative air humidity determined by formula (1) decreases rapidly with increasing temperature. Accordingly, as the temperature decreases, the relative humidity increases. Below we will look at this in more detail.
When performing the following task, the ideal gas equation of state and the table above will help you.
6. At 20 ºС relative air humidity was equal to 100%. The air temperature increased to 40 ºС, and the mass of water vapor remained unchanged.
a) What was the initial pressure of the water vapor?
b) What was the final water vapor pressure?
c) What is the saturation vapor pressure at 40°C?
d) What is the relative humidity of the air in the final state?
e) How will this air be perceived by a person: as dry or as moist?
7. On a wet autumn day, the temperature outside is 0 ºС. The room temperature is 20 ºС, relative humidity is 50%.
a) Where is the partial pressure of water vapor greater: indoors or outdoors?
b) In which direction will water vapor go if the window is opened - into the room or out of the room?
c) What would be the relative humidity in the room if the partial pressure of water vapor in the room became equal to the partial pressure of water vapor outside?
8. Wet objects are usually heavier than dry ones: for example, a wet dress is heavier than a dry one, and damp firewood is heavier than dry ones. This is explained by the fact that the weight of the moisture contained in it is added to the body's own weight. The opposite is true for air. wet air lighter than dry! How to explain it?
3. Dew point
When the temperature drops, the relative humidity of the air increases (although the mass of water vapor in the air does not change).
When the relative humidity of the air reaches 100%, the water vapor becomes saturated. (Under special conditions, supersaturated steam can be obtained. It is used in cloud chambers for detecting traces (tracks) of elementary particles at accelerators.) With a further decrease in temperature, water vapor begins to condense: dew falls. Therefore, the temperature at which a given water vapor becomes saturated is called the dew point for that vapor.
9. Explain why dew (Figure 45.3) usually falls in the early morning hours.
Consider an example of finding the dew point for air of a certain temperature with a given humidity. For this we need the following table.
10. A man with glasses entered the store from the street and found that his glasses were fogged up. We will assume that the temperature of the glass and the layer of air adjacent to them is equal to the temperature of the air outside. The air temperature in the store is 20 ºС, relative humidity 60%.
a) Is the water vapor in the layer of air adjacent to the lenses of the glasses saturated?
b) What is the partial pressure of water vapor in the store?
c) At what temperature is the water vapor pressure equal to the saturated vapor pressure?
d) What is the outside temperature like?
11. In a transparent cylinder under the piston is air with a relative humidity of 21%. The initial air temperature is 60 ºС.
a) To what temperature must the air be cooled at a constant volume in order for dew to fall in the cylinder?
b) By how many times must the volume of air at a constant temperature be reduced in order for dew to fall in the cylinder?
c) Air is first isothermally compressed and then cooled at a constant volume. Dew began to fall when the air temperature dropped to 20 ºС. How many times did the volume of air decrease compared to the initial one?
12. Why is intense heat more difficult to tolerate with high humidity?
4. Humidity measurement
Air humidity is often measured with a psychrometer (Fig. 45.4). (From the Greek "psychros" - cold. This name is due to the fact that the readings of a wet thermometer are lower than dry ones.) It consists of a dry and wet bulbs.
Wet bulb readings are lower than dry bulb readings because the liquid cools as it evaporates. The lower the relative humidity of the air, the more intense the evaporation.
13. Which thermometer in figure 45.4 is located to the left?
So, according to the readings of thermometers, you can determine the relative humidity of the air. For this, a psychrometric table is used, which is often placed on the psychrometer itself.
To determine the relative humidity of the air, it is necessary:
- take readings of thermometers (in this case, 33 ºС and 23 ºС);
- find in the table the row corresponding to the dry thermometer readings, and the column corresponding to the difference in thermometer readings (Fig. 45.5);
- at the intersection of the row and column, read the value of the relative humidity of the air.
14. Using the psychrometric table (Fig. 45.5), determine at what thermometer readings the relative humidity of the air is 50%.
Additional questions and tasks
15. In a greenhouse with a volume of 100 m3, it is necessary to maintain a relative humidity of at least 60%. Early in the morning at a temperature of 15 ºС, dew fell in the greenhouse. The daytime temperature in the greenhouse rose to 30 ºС.
a) What is the partial pressure of water vapor in the greenhouse at 15°C?
b) What is the mass of water vapor in the greenhouse at this temperature?
c) What is the minimum allowable partial pressure of water vapor in a greenhouse at 30°C?
d) What is the mass of water vapor in the greenhouse?
e) What mass of water must be evaporated in the greenhouse in order to maintain the required relative humidity in it?
16. On the psychrometer, both thermometers show the same temperature. What is the relative humidity of the air? Explain your answer.
Word Moisture
The word Moisture in Dahl's dictionary
and. liquid in general: | sputum, dampness; water. Vologa, oil liquid, fat, oil. Without moisture and heat, no vegetation, no life.
What does air humidity depend on?
There is foggy moisture in the air now. Moist, moist, damp, damp, wet, watery. Wet summer. Wet meadows, fingers, air. wet place. Humidity dampness, wetness, sputum, wet condition. Moisten what, moisten, make moist, water or saturate with water. Moisture meter
hygrometer, projectile, showing the degree of humidity in the air.
The word Moisture in the Ozhegov dictionary
MOISTURE, -and, well. Dampness, water contained in something. Air saturated with moisture.
The word Moisture in the Ephraim dictionary
stress: moisture
- Liquid, water or its vapor contained in something
The word Moisture in Max Fasmer's Dictionary
moisture
loans.
from cslav., cf. st.-glor. moisture (Supr.). See Vologa.
The word Moisture in the dictionary of D.N. Ushakov
MOISTURE, moisture, pl. no, female (Books). Dampness, water, evaporation. Plants require a lot of moisture. The air is saturated with moisture.
Word Moisture in the Synonyms Dictionary
alcohol, water, sputum, moisture, liquid, dampness, raw material
The word Moisture in the dictionary Synonyms 4
water, mucus, dampness
The word Moisture in the dictionary Complete accentuated paradigm according to A. A. Zaliznya
moisture,
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisture
August's psychrometer consists of two mercury thermometers mounted on a tripod or placed in a common case.
The bulb of one thermometer is wrapped in a thin cambric cloth, lowered into a glass of distilled water.
When using the August psychrometer, the absolute humidity is calculated using the Rainier formula:
A = f-a(t-t1)H,
where A is absolute humidity; f is the maximum water vapor pressure at the wet bulb temperature (see
table 2); a - psychrometric coefficient, t - dry bulb temperature; t1 - wet bulb temperature; H is the barometric pressure at the moment of determination.
If the air is perfectly still, then a = 0.00128. In the presence of weak air movement (0.4 m/s) a = 0.00110. Maximum and relative humidity are calculated as indicated on page
What is air humidity? What does it depend on?
| Air temperature (°C) | Air temperature (°C) | Water vapor pressure (mm Hg) | Air temperature (°C) | Water vapor pressure (mm Hg) | |
| -20 - 15 -10 -5 -3 -4 0 +1 +2,0 +4,0 +6,0 +8,0 +10,0 +11,0 +12,0 |
0,94 1.44 2.15 3.16 3,67 4,256 4,579 4,926 5,294 6,101 7,103 8.045 9,209 9,844 10,518 |
+13,0 +14,0 +15,0 +16,0 +17,0 +18,0 +19,0 +20,0 +21,0 +22,0 +24,0 +25,0 +27,0 +30,0 +32,0 |
11,231 11,987 12,788 13,634 14,530 15,477 16.477 17,735 18,650 19,827 22,377 23,756 26,739 31,842 35,663 |
+35,0 +37,0 +40,0 +45,0 +55,0 +70,0 +100,0 |
42,175 47,067 55,324 71,88 118,04 233,7 760,0 |
Table 3
Determination of relative humidity according to readings
aspiration psychrometer (in percent) 
Table 4. Determination of the relative humidity of the air according to the readings of dry and wet thermometers in the August psychrometer under normal conditions of calm and uniform air movement in the room at a speed of 0.2 m / s 
To determine the relative humidity, there are special tables (tables 3, 4).
More accurate readings are given by the Assmann psychrometer (Fig. 3). It consists of two thermometers, enclosed in metal tubes, through which air is evenly sucked in by means of a clockwork fan located at the top of the device.
The mercury tank of one of the thermometers is wrapped with a piece of cambric, which is moistened with distilled water before each determination using a special pipette. After wetting the thermometer, turn on the fan with the key and hang the device on a tripod.
After 4-5 minutes, record the readings of dry and wet thermometers. Since moisture evaporates and heat is absorbed from the surface of a mercury ball moistened with a thermometer, it will show more low temperature. Absolute humidity is calculated using the Shprung formula: 
where A is absolute humidity; f is the maximum water vapor pressure at the wet bulb temperature; 0.5 - constant psychrometric coefficient (correction for air velocity); t is the dry bulb temperature; t1 - wet bulb temperature; H - barometric pressure; 755 - average barometric pressure (determined according to table 2).
Maximum humidity (F) is determined using table 2 dry bulb temperature.
Relative humidity (R) is calculated using the formula:
where R is relative humidity; A - absolute humidity; F is the maximum humidity at dry bulb temperature.
A hygrograph is used to determine fluctuations in relative humidity over time.
The device is designed similarly to a thermograph, but the perceiving part of the hygrograph is a fat-free bundle of hair.
Rice. 3. Assmann aspiration psychrometer:
1 - metal tubes;
2 - mercury thermometers;
3 - holes for the outlet of sucked air;
4 - clamp for hanging the psychrometer;
5 - pipette for wetting a wet thermometer.
The weather forecast for tomorrow
Compared to yesterday, it has become a little colder in Moscow, the ambient air temperature has dropped from 17 °C yesterday to 16 °C today.
The weather forecast for tomorrow does not promise significant changes in temperature, it will remain at the same level of 11 to 22 degrees Celsius.
Relative humidity has increased to 75 percent and continues to rise. Atmosphere pressure over the past day has slightly decreased by 2 mm Hg, and became even lower.
Actual weather today
According to 2018-07-04 15:00 it's raining in Moscow, a light wind is blowing
Weather norms and conditions in Moscow
Features of the weather in Moscow are determined, first of all, by the location of the city.
The capital is located on the East European Plain, and warm and cold air masses move freely over the metropolis. The weather in Moscow is influenced by Atlantic and Mediterranean cyclones, which is why the level of precipitation is higher here, and in winter it is warmer than in cities located at this latitude.
The weather in Moscow reflects all the phenomena characteristic of a temperate continental climate. The relative instability of the weather is expressed, for example, in cold winter, with sudden thaws, sharp cooling in summer, loss a large number precipitation. These and other weather events are by no means uncommon. In summer and autumn, fogs are often observed in Moscow, the cause of which lies partly in human activity; thunderstorms even in winter.
In June 1998, a strong squall claimed the lives of eight people, 157 people were injured. In December 2010, heavy freezing rain caused by temperature differences at altitude and on the ground turned the streets into a skating rink, and giant icicles and trees breaking under the weight of ice fell on people, buildings and cars.
The temperature minimum in Moscow was recorded in 1940, it was -42.2°C, the maximum - +38.2°C was recorded in 2010.
The average July temperature in 2010 - 26.1 ° - is close to normal United Arab Emirates and Cairo. And in general, 2010 became the record-breaking year for the number of temperature maximums: 22 daily records were set during the summer.
The weather in the center of Moscow and on the outskirts is not the same.
What determines the relative humidity of the air and how?
The temperature in the central regions is higher, in winter the difference can be up to 5-10 degrees. It is interesting that official weather data in Moscow is provided from the weather station at the All-Russian Exhibition Center located in the north-east of the city, which is several degrees lower than the temperature values of the weather station at Balchug in the center of the metropolis.
Weather in other cities of the Moscow region›
Dry matter and moisture
Water is one of the most common substances on earth, it is a necessary condition for life and is part of all food products and materials.
Water, not being a nutrient itself, is vital as a body temperature stabilizer, nutrient carrier ( nutrients) and digestive waste, a reagent and reaction medium in a number of chemical transformations, a biopolymer conformation stabilizer and, finally, as a substance that facilitates the dynamic behavior of macromolecules, including the manifestation of their catalytic (enzymatic) properties.
Water is the most important component of food.
It is present in a variety of plant and animal products as a cellular and extracellular component, as a dispersing medium and solvent, determining the consistency and structure. Water affects appearance, taste and stability of the product during storage. Through its physical interaction with proteins, polysaccharides, lipids and salts, water contributes significantly to the structure of food.
The total moisture content of a product indicates the amount of moisture in it, but does not characterize its involvement in chemical and biological changes in the product.
The ratio of free and bound moisture plays an important role in ensuring its stability during storage.
bound moisture- this is associated water, strongly associated with various components - proteins, lipids and carbohydrates due to chemical and physical bonds.
Free moisture- this is moisture that is not bound by a polymer and is available for biochemical, chemical and microbiological reactions to occur.
By direct methods, moisture is extracted from the product and its amount is determined; indirect (drying, refractometry, density and electrical conductivity of the solution) - determine the content of solids (dry residue). Indirect methods also include a method based on the interaction of water with certain reagents.
Determination of moisture content drying to constant weight (arbitrage method) is based on the release of hygroscopic moisture from the object under study at a certain temperature.
Drying is carried out to a constant weight or by accelerated methods at an elevated temperature for a specified time.
Drying of samples, sintering into a dense mass, is carried out with calcined sand, the mass of which should be 2-4 times greater than the mass of the sample.
Sand gives the sample porosity, increases the evaporation surface, prevents the formation of a crust on the surface, which makes it difficult to remove moisture. Drying is carried out in porcelain cups, aluminum or glass bottles for 30 minutes, at a certain temperature, depending on the type of product.
The mass fraction of solids (X,%) is calculated by the formula
where m is the weight of the bottle with a glass rod and sand, g;
m1 is the mass of the weighing bottle with a glass rod, sand and
weighed before drying, g;
m2 is the weight of the bottle with a glass rod, sand and sample
after drying,
Drying in the HF apparatus is carried out by means of infrared radiation in an apparatus consisting of two interconnected massive round or rectangular plates (Figure 3.1).
Figure 3.1 - RF apparatus for determining humidity
1 - handle; 2 - top plate; 3 - control unit; 4 - bottom plate; 5 - electrocontact thermometer
In working condition, a gap of 2-3 mm is established between the plates.
The temperature of the heating surface is controlled by two mercury thermometers. To maintain a constant temperature, the device is equipped with a contact thermometer connected in series with the relay. The set temperature is set on the contact thermometer. The device is connected to the network 20 ... 25 minutes before the start of drying to heat up to the desired temperature.
A portion of the product is dried in a rotary paper bag 20x14 cm in size for 3 minutes at a certain temperature, cooled in a desiccator for 2-3 minutes and quickly weighed with an accuracy of 0.01 g.
Humidity (X,%) is calculated by the formula
where m is the mass of the package, g;
m1 is the mass of the package with a sample before drying, g;
m2 is the mass of the package with the dried sample, g.
Refractometric method used for production control in determining the content of dry matter in objects rich in sucrose: sweet dishes, drinks, juices, syrups.
The method is based on the relationship between the refractive index of the object under study or water extract from it and the concentration of sucrose.
Air humidity
The refractive index depends on the temperature, so the measurement is made after thermostating the prisms and the test solution.
The mass of solids (X, g) for drinks with sugar is calculated by the formula
where a - mass for dry substances, determined
refractometric method, %;
P is the volume of the drink, cm3.
for syrups, fruit and berry and milk jelly, etc.
according to the formula
where a is the mass fraction of solids in solution, %;
m1 is the mass of the dissolved sample, g;
m is the sample mass, g.
In addition to these common methods for determining dry matter, a number of methods are used to determine the content of both free and bound moisture.
Differential scanning colorimetry.
If the sample is cooled to a temperature below 0°C, then free moisture will freeze, but bound moisture will not. By heating a frozen sample in a colorimeter, the heat consumed when the ice melts can be measured.
Non-freezing water is defined as the difference between common and freezing water.
Dielectric measurements. The method is based on the fact that at 0°C the dielectric constants of water and ice are approximately equal. But if part of the moisture is bound, then its dielectric properties should be very different from the dielectric properties of bulk water and ice.
Heat capacity measurement.
The heat capacity of water is greater than the heat capacity of ice, because As the water temperature rises, the hydrogen bonds break. This property is used to study the mobility of water molecules.
The value of heat capacity, depending on its content in polymers, gives information about the amount of bound water. If water is specifically bound at low concentrations, then its contribution to the heat capacity is small. In the range of high humidity values, it is mainly determined by free moisture, whose contribution to the heat capacity is about 2 times greater than that of ice.
Nuclear magnetic resonance (NMR). The method consists in studying the mobility of water in a fixed matrix.
In the presence of free and bound moisture, two lines are obtained in the NMR spectrum instead of one for bulk water.
Previous11121314151617181920212223242526Next
VIEW MORE:
Air humidity. Units. Influence on the work of aviation.
Water is a substance that can simultaneously be in various aggregate states at the same temperature: gaseous (water vapor), liquid (water), solid (ice). These states are sometimes called phase state of water.
Under certain conditions, water from one (phase) state can pass into another. So water vapor can go into a liquid state (condensation process), or, bypassing the liquid phase, go into a solid state - ice (sublimation process).
In turn, water and ice can turn into a gaseous state - water vapor (evaporation process).
Humidity refers to one of the phase states - water vapor contained in the air.
It enters the atmosphere by evaporation from water surfaces, soil, snow, and vegetation.
As a result of evaporation, part of the water passes into a gaseous state, forming a vapor layer above the evaporating surface.
Relative Humidity
This vapor is carried by air currents in vertical and horizontal directions.
The evaporation process continues until the amount of water vapor above the evaporating surface reaches full saturation, that is, the maximum amount possible in a given volume at constant air pressure and temperature.
The amount of water vapor in the air is characterized by the following units:
Water vapor pressure.
Like any other gas, water vapor has its own elasticity and exerts pressure, which is measured in mm Hg or hPa. The amount of water vapor in these units is indicated: actual - e, saturating - E. At weather stations, by measuring elasticity in hPa, observations are made of the moisture content of water vapor.
Absolute humidity. It represents the amount of water vapor in grams contained in one cubic meter of air (g/).
letter A- the actual quantity is indicated by the letter A- saturating space. Absolute humidity in its value is close to the elasticity of water vapor, expressed in mm Hg, but not in hPa, at a temperature of 16.5 C e And A are equal to each other.
Specific humidity is the amount of water vapor in grams contained in one kilogram of air (g/kg).
letter q - the actual quantity is indicated by the letter Q- saturating space. Specific humidity is a convenient value for theoretical calculations, since it does not change when air is heated, cooled, compressed and expanded (unless the air condenses). The value of specific humidity is used for all kinds of calculations.
Relative Humidity represents the percentage of the amount of water vapor contained in the air to the amount that would saturate a given space at the same temperature.
Relative humidity is indicated by the letter r.
By definition
r=e/E*100%
The amount of water vapor that saturates the space can be different, and depends on how many vapor molecules can escape from the evaporating surface.
The saturation of air with water vapor depends on the air temperature, the higher the temperature, the greater the amount of water vapor, and the lower the temperature, the less it is.
Dew point- this is the temperature to which it is necessary to cool the air so that the water vapor contained in it reaches full saturation (at r \u003d 100%).
The difference between air temperature and dew point temperature (T-Td) is called dew point deficiency.
It shows how much air must be cooled in order for the water vapor contained in it to reach saturation.
With a small deficit, air saturation occurs much faster than with a large saturation deficit.
The amount of water vapor also depends on state of aggregation evaporating surface, from its curvature.
At the same temperature, the amount of saturating vapor is greater over one and less over ice (ice has strong molecules).
At the same temperature, the amount of vapor will be greater over a convex surface (droplet surface) than over a flat evaporating surface.
All these factors play an important role in the formation of fogs, clouds and precipitation.
A decrease in temperature leads to saturation of the water vapor present in the air, and then to the condensation of this vapor.
Air humidity has a significant impact on the nature of the weather, determining flight conditions. The presence of water vapor leads to the formation of fog, haze, clouds, complicating the flight of thunderstorms, freezing rain.