Air pollution trends across the seasons

While air pollution is an issue all year round, different seasons see an increase in certain pollutants due to various factors such as temperature, climate, and human activities. Read on to find out more.


Ammonia (NH3) concentrations increase drastically in spring due to agricultural activities. It is released from the fertilizer and manure that is spread on fields for planting, which then reacts with other existing compounds in the atmosphere to create secondary particulate matter (PM2.5). In fact, up to 58% of particulate matter in European cities is from ammonia used in farming. 


Ground-level ozone (O3) levels periodically peak during the summer as it is formed through a combination of heat and sunlight reacting with nitrogen oxides (NOx) and volatile organic compounds (VOCs). This is particularly concerning when it comes to ozone’s effects on health, especially since more than 98% of the European Union (EU) population is exposed to ozone levels higher than those recommended by the World Health Organization (WHO).


Certain volatile organic compounds such as methanol and acetaldehyde emit from deciduous trees due to falling and decaying leaves. Plants produce VOCs for various purposes, including adapting to environmental stress, communicating to other plants, and defending against insects. VOCs pose a threat to human health through its ability to form ground-level ozone by reacting with nitrogen oxides in the presence of sunlight.


Smog is a significant issue during winter due to what is known as temperature inversion. Under normal circumstances, air temperature decreases at higher altitudes. However in winter, the atmospheric layer closest to the ground can be cooler than the air above it. High atmospheric pressure is caused by the presence of cold air. It allows solar radiation to reach the earth, thus warming it up. The accumulated heat is lost at night due to lack of cloud clover, causing it to rise and subsequently trap the now-cool air at the ground. As a result, pollutants such as carbon monoxide (CO), nitrogen oxides, particulate matter, and volatile organic compounds are trapped at the ground level until the temperature changes. 

Nitrogen dioxide (NO2) concentrations were found to be higher indoors during the winter than in the summer. This is attributed to fuel-burning (wood, oil, natural gas, coal) heating systems for the winter months. 

Seasonal air pollution where you live

Are you curious about the level changes in air pollution across the seasons? Breeze Technologies’ citizen portal provides comprehensive and hyperlocal information on air pollutants at cities all over the world. This is an initiative run by cities, corporations, and individuals like you. Become a sensor host today and help improve the air you breathe! If you’d like to know more, contact us here.