Water vapor enters the atmosphere mainly by the evaporation of water from the surface of the seas and oceans, a lesser role in this regard is played by lakes, rivers, soil. In inhabited premises, evaporation of moisture by the lungs (about 350 g / day) and skin (about 500-600 g / day), as well as its entry into the air when washing clothes, cooking food, etc., is of great importance.
Humidity is characterized by the following basic concepts:
• Absolute humidity – the elasticity of water vapor presently in the air, expressed in mmHg. Art. (g / m 3 );
• maximum humidity – the elasticity of water vapor when the air is completely saturated with moisture at a given temperature (g / m 3 );
• relative humidity – the ratio of absolute humidity to maximum humidity, expressed as a percentage;
• saturation deficit – the difference between the maximum and absolute humidity;
• physiological moisture deficit – the arithmetic difference between the maximum humidity at 37 ° C (equal to the temperature of the human body) and the absolute humidity at the time of observation.
The mercury cup barometer (Fig. 4A) is a vertical glass tube filled with mercury. The upper end of the tube is soldered, and the lower end is immersed in a cup of mercury. A thermometer is mounted in the case. A mercury barometer is installed in the room on the main wall, away from heating appliances, windows and doors, out of direct sunlight.
Aneroid barometer is a corrugated metal box from which air is drawn .
With an increase in atmospheric pressure, the walls of the aneroid box bend inward, and with a decrease, they straighten. Using a system of levers, these vibrations are transmitted to the arrow, which moves along the dial. The device is installed in a horizontal position and protected from direct sunlight and sudden temperature fluctuations. Before the countdown, you should lightly tap the body or glass of the barometer with your finger to overcome the friction of the metal transmission parts in the mechanism of the device. Aneroid barometer is less accurate than mercury, but it is portable, safe and easy to use.
It indicates the amount of water that every cubic meter of inhaled air can extract from the body.
Under any temperature conditions, a significant increase in relative humidity seems to be an unfavorable factor. Saturation of air with water vapor can contribute to the hypothermia of the body due to the fact that the heat capacity of water (1.0) is much higher than the heat capacity of air (0.237), therefore, moist air always seems colder.
A prolonged stay of people in a room with high humidity and low temperature (15o-10oС and lower) is the cause of hypothermia (general and local) and a decrease in the body’s resistance, as a result of which there is an increase in certain diseases (arthritis, neuralgia, cataracts upper respiratory tract).
Low humidity air (dry) provides a favorable increase in heat transfer at high temperature and helps to reduce heat loss at low temperature. However, a long stay in rooms with low humidity can be one of the reasons for the development of dry catarrh of the upper respiratory tract. In residential premises, the relative humidity is 40–60%, and the acceptable humidity is 30–70%.