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How far does air pollution travel?
Air pollution is spread by wind and weather patterns
Air pollution is spread by wind and weather patterns. This means that any particles in the air – such as pollutants, dust and smoke – will spread with the air wherever it flows.
The air is generally cleaner when it’s further away from sources of pollution
Generally speaking, the further away from sources of air pollution, the cleaner the air. For example, a house next door to a busy road will be more affected by dirty air than a house 1km away. Research has found that levels of pollutants like particulate matter (PM) and nitrogen dioxide decreases significantly within 100-150m of busy roads.
Wind direction and speed matters
However, wind direction can dramatically affect how pollutants spread. Air quality in areas upwind from the road can improve within 100m of the road but can remain bad in downwind areas as far away as 1.5km.
Air pollution travels across countries
Multiple studies have found that air pollution from China has even been spreading as far as the west coast of the United States of America, over 10,000km away. Westerly winds blew pollutants like ozone, sulphur dioxide, nitrogen oxide, carbon monoxide, and PM from China’s industrial areas all the way to US cities like Los Angeles.
Pollutants such smoke from wildfires and dust from dust storms can also travel far distances. Smoke from seasonal wildfires in Indonesia often reaches Singapore and Malaysia, for example, affecting people for days even though they are thousands of kilometres away.
The ten member countries of ASEAN even signed an agreement in 2002 to reduce regional haze caused by wildfires. Indonesia was the last country to ratify this agreement in 2014.
Air circulation patterns change according to season
Natural patterns of air circulation change from season to season, so air quality can vary significantly depending on location, time of year, and weather events like storms. Climate change is also disrupting air flow patterns.
The spread of air pollution shows how important it is to understand air quality standards and how they are measured. Our air may look clean, but is it really?
Wadlow, I, C Paton-Walsh, H Forehead, P Perez, M Amirghasemi, E-A Guérette, O Gendek, dan P Kumar. 2019. ‘Understanding Spatial Variability of Air Quality in Sydney: Part 2—A Roadside Case Study.’ Atmosphere 10:217.
WHO Regional Office for Europe. 2013. Review of evidence on health aspects of air pollution – REVIHAAP Project: Technical Report: Proximity to roads, NO2, other air pollutants and their mixtures. https://www.ncbi.nlm.nih.gov/books/NBK361807/