Air pollution in urban areas varies by season due to several factors, including changes in weather patterns, human activities, and natural processes. The key pollutants responsible for adverse health impacts on residents include particulate matter PM , nitrogen oxides NOx , sulfur dioxide SO2 , ozone O3 , and volatile organic compounds VOCs . These pollutants can cause respiratory and cardiovascular problems, as well as other health issues.1. Winter: During winter, air pollution in urban areas tends to be higher due to several factors. Cold temperatures and stable atmospheric conditions can lead to the formation of temperature inversions, where a layer of warm air traps pollutants close to the ground. This results in reduced air circulation and increased pollutant concentrations. Additionally, increased use of heating systems, particularly those that burn fossil fuels, can contribute to higher emissions of PM, NOx, and SO2.2. Spring: As temperatures begin to rise in spring, air pollution levels may decrease due to increased air circulation and dispersion of pollutants. However, this season can also see increased pollen levels, which can exacerbate respiratory issues for some individuals. Furthermore, the transition from winter to spring can lead to increased ground-level ozone formation as sunlight and warmer temperatures promote photochemical reactions between NOx and VOCs.3. Summer: During summer, air pollution levels can vary greatly depending on weather conditions. On one hand, increased sunlight and higher temperatures can lead to the formation of ground-level ozone, which is a major component of smog and can cause respiratory problems. On the other hand, summer storms and increased air circulation can help disperse pollutants and reduce air pollution levels. Additionally, higher temperatures can lead to increased emissions of VOCs from various sources, such as vehicles and industrial processes.4. Autumn: In autumn, air pollution levels may decrease as temperatures begin to cool and atmospheric conditions become more stable. However, this season can also see increased emissions from agricultural activities, such as crop burning, which can contribute to higher levels of PM and other pollutants. Additionally, as temperatures drop, the use of heating systems may begin to increase, leading to higher emissions of NOx and SO2.In summary, air pollution in urban areas varies by season due to changes in weather patterns, human activities, and natural processes. The key pollutants responsible for adverse health impacts on residents include particulate matter, nitrogen oxides, sulfur dioxide, ozone, and volatile organic compounds. Understanding these seasonal variations can help inform strategies to reduce air pollution and protect public health.