1. Relative humidity
The amount of water vapor contained in the air is expressed in humidity. When the temperature is constant and the relative humidity is low, the corrosion is very slow; when the relative humidity gradually increases and reaches a certain limit, the corrosion rate suddenly increases significantly.

2. Temperature
Under certain humidity conditions, when the metal is corroded, the corrosion rate increases to about 2 times for every 10°C increase in temperature. When the temperature drops greatly, condensation will occur on the metal surface, leading to accelerated corrosion. For example, when the temperature difference between day and night is large, or when the temperature difference between indoors and outdoors is large, condensation will occur. When condensation occurs periodically, rust is most serious. In humid and rainy areas, especially in hot, rainy, or foggy areas or seasons with high relative humidity, metal rust is most likely to occur.

3. Oxygen
Moisture and oxygen are the main factors for the corrosion of metals in the atmosphere. The water film layer adsorbed on the metal surface in the atmosphere is very thin, and oxygen is very easy to dissolve and penetrate into it, which makes the depolarization process of oxygen proceed quite smoothly and plays a major role in atmospheric corrosion.

4. Pollution factors
When there is pollution in the air or the metal surface is unclean, the metal will corrode quickly at a low relative humidity. When the humidity continues to rise above the critical relative humidity, the corrosion rate will gradually increase.

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