Air pollution is often viewed as a direct consequence of human activity. However, weather conditions such as temperature, humidity and wind can strongly influence how pollutants accumulate or disperse. Using observations from many cities worldwide, this story explores the hidden relationship between weather and air quality.
How polluted are cities around the world?
The distribution of PM2.5 pollution is highly uneven across the dataset. Most observations fall within the lower to moderate pollution range, with concentrations generally below 100 PM2.5. However, the distribution is strongly skewed to the right, indicating that a smaller number of cities experience much higher pollution levels. Several extreme observations exceed 200 PM2.5, demonstrating that while severe pollution events are relatively uncommon, they can reach dangerously high levels in certain locations. This suggests that air pollution is not a uniform global problem but is instead concentrated in specific cities and regions.
The relationship between temperature and PM2.5 pollution appears positive but not strictly linear. Cities with warmer average temperatures often exhibit higher PM2.5 concentrations, particularly within the range of 20°C to 30°C. However, substantial variation exists at nearly every temperature level, indicating that temperature alone cannot fully explain differences in air quality. The varying bubble sizes, representing humidity, suggest that additional meteorological factors may influence pollution levels. Overall, the chart highlights that temperature is associated with PM2.5 concentrations, but the relationship is shaped by a combination of environmental conditions.
Humidity appears to have a different relationship with PM2.5 pollution than temperature. Higher pollution levels are most commonly observed at moderate humidity levels, while cities with very high humidity generally show lower PM2.5 concentrations. One possible explanation is that moisture in the atmosphere can help remove airborne particles through rainfall and other deposition processes. Although the relationship is not perfectly consistent, the overall pattern suggests that highly humid environments may experience lower levels of particulate pollution than drier locations.
Ozone formation depends on multiple atmospheric conditions.
Ozone pollution displays a noticeable relationship with temperature, although the pattern is more complex than a simple increase or decrease. Ozone levels tend to rise from lower temperatures and reach their highest values at moderate temperatures before declining in some warmer locations. This suggests that ozone formation is influenced by a combination of atmospheric conditions rather than temperature alone. The varying bubble sizes indicate that humidity may also play a role in shaping ozone concentrations. Together, these patterns highlight the complexity of atmospheric chemistry and the influence of weather on air quality outcomes.
Significant differences in average PM2.5 concentrations can be observed between countries. India records the highest average PM2.5 level among the countries shown, followed by Nepal and China. Several European countries also appear within the ranking, although their average pollution levels are notably lower. These findings suggest that air pollution is influenced by a combination of factors, including population density, industrial activity, energy use, transportation systems, and environmental conditions. The variation between countries demonstrates that air quality challenges are not evenly distributed across the globe and that some regions face a much greater pollution burden than others.
The analysis reveals that air pollution is shaped by both environmental and geographic factors. While most cities experience relatively moderate PM2.5 levels, a smaller number face severe pollution episodes that can significantly affect public health and environmental quality. Temperature, humidity, and ozone all display meaningful relationships with pollution levels, illustrating how weather conditions can influence the formation, accumulation, and dispersal of pollutants. At the same time, substantial differences between countries highlight the importance of local economic, industrial, and environmental contexts. Together, these findings demonstrate that understanding air pollution requires considering both human activities and the natural atmospheric processes that shape air quality around the world.
The dataset is from World Air Quality Index project.
Source: https://aqicn.org/data-platform/covid19/verify/8263d3a8-5e73-4327-829d-82b72da83ca6