How is the air humidity expressed?

As the name implies, "air humidity" refers to the size of water vapor contained in the air. The greater the humidity, the wetter the air and the closer the water vapor is to saturation. Usually we use relative humidity to express air humidity. At a certain temperature, the smaller the relative humidity of the air, the faster the sweat evaporates and the cooler people feel. In winter and spring in Beijing, the humidity is about 20% during the day and about 70% at night. Because the humidity is too low in winter and spring, people often feel uncomfortable, sometimes their lips are chapped, their nostrils are bleeding, and their throats are dry and itchy. However, in midsummer, when the air humidity reaches more than 80%, people will feel unbearable heat because of the slow evaporation of sweat, and sometimes they will suffer from heatstroke or cause diseases such as kidney disease, tuberculosis and arthritis.

Indoor comfortable meteorological conditions are: when the room temperature reaches 25℃, the relative humidity should be controlled at 40-50%, and when the room temperature reaches 18℃, the relative humidity should be controlled at 30-40%. Families with humidifiers should always adjust the indoor humidity in order to fully serve your health.