Precipitation affects air quality in a variety of ways, which are analysed in detail below:
Removes pollutants:
Rain is a natural cleansing agent that effectively adsorbs and carries away dust, pollutants and harmful substances from the atmosphere through the moisture in the raindrops. This removal effect is particularly significant in urban areas, where the air, which has been polluted for a long time by industrial emissions and traffic exhaust, can be effectively purified under the action of rainwater.
By coming into contact with pollutants in the atmosphere, raindrops combine with particulate matter, sulphur dioxide and nitrogen oxides and then condense to form precipitation, which in turn reduces the concentration of pollutants in the air. This dilution effect is more pronounced in summer thunderstorms and plays an important role in improving air quality.
Wet deposition:
The wet deposition effect during precipitation helps to reduce the concentration of particulate matter in the air. Atmospheric particulate matter combines with water vapour to form larger particles, which in turn settle to the ground by gravity, effectively removing particulate matter from the air and thus improving air quality.
Reduces temperature:
When rain falls, it causes the surrounding temperature to drop due to the effects of evaporation and evaporative cooling. This cooling effect is particularly noticeable in the summer months, breaking up the sweltering heat of hot weather and providing a more comfortable and pleasant environment. At the same time, low temperatures also help to inhibit the generation and dispersion of certain pollutants, further improving air quality.
Inhibit ozone generation:
During precipitation, the intensity of solar radiation decreases, which inhibits the production of ozone during photochemical reactions. Ozone is an important indicator of air pollution and can be harmful to human health. Therefore, precipitation also has a positive effect on suppressing ozone production and improving air quality.
However, it should be noted that the effect of precipitation on air quality is not absolute. Under certain circumstances, such as low precipitation intensity, high relative atmospheric humidity, accompanied by light winds and low-pressure environments, there may be elevated PM2.5 concentrations and a relative deterioration of air quality. In addition, if the precipitation itself is not clean enough (e.g. acid rain), then pollutants such as sulphur dioxide in the air may be dissolved during the precipitation process, resulting in secondary pollution.
In summary, the impacts of precipitation on air quality are multi-faceted, including both positive cleansing, dilution and cooling effects as well as potential negative impacts. In assessing the impact of precipitation on air quality, it is necessary to take into account a number of factors and adopt corresponding measures to reduce pollutant emissions and improve air quality.