Summer Fires: The Effects on Air Pollution and Health


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Wildfires are common in summer, but can be extremely dangerous when they take place. Image by John McColgan.

Wildfires – such as those in California – can have substantial effects on both air pollution and human health. What are the most common pollutants resulting from the California wildfires, and other fire events – and how dangerous are these chemicals?

Wildfires: A Common Problem in Summer

Wildfires are becoming a common occurrence during summer months in many counties/areas. In the last weeks, for instance, many areas of California have been on fire, with flames expanding quickly to larger and larger areas.

Unfortunately, similar incidents take place every year in many places; in south European countries and in Australia, for example, large wildfires occur every summer.

Although the majority of the fires are caused by human activities, the meteorological conditions can significantly affect these wildfires. Periods of prolonged drought, like those in California for instance, can lead to wildfires, and strong winds can favor the expansion of the flames and make it more difficult to control the fires.

Pollution from Wildfires

Wildfires have a huge impact on the environment, as hundreds/thousands of hectares of forests get burned in each fire, with effects on the flora/fauna of the areas involved. If these fires occur close to inhabited areas, lives and belongings of the local people can also be at risk.

To fully assess the impact of the wildfires, however, pollution has also to be taken into account, as the smoke formed during the fires contains chemical compounds which may be toxic.

Particulate Matter

The expression “particulate matter” (PM) refers to the small particles, both solid and liquid, which can be present in the atmosphere.

The hazard of these particles depends on their size; smaller particles can penetrate more easily into the human respiratory system and, hence, cause more problems (irritations, respiratory difficulties, etc.).

PM10 and PM2.5 are particulates with diameters smaller than 10 and 2.5 micron (mm), respectively; their concentration in the atmosphere is usually monitored, especially in big cities.

Smoke from wildfires always contains PM, which comes from the incomplete combustion of the solid wood and/or from other parts of the trees/bushes.


Smoke from wildfires can contain toxic compounds. Image by MONGO.

Carbon Monoxide and Ozone

Wildfire smoke can also contain some hazardous gaseous compounds such as carbon monoxide (CO) and ozone (O3).

CO, if inhaled in high quantity, can be poisonous.

Ois an irritant for the respiratory system. Moreover, being a very reactive molecule, ozone can react with other species present in the atmosphere and form more toxic compounds.

Wildfires and their Effect on Air Quality

The toxic compounds present in the wildfire smoke can significantly affect the quality of the air; this effect can be considerable not just in the areas of the fires themselves, but also at several miles distance from the fires.

Some data collected by the Climate Center association confirm this. In the city of Salmon (Idaho, US), for instance, in August 2012, PM2.5 concentration was as high as 80 mg/m3, due to the Halstead Fire; this value is eight times higher than the standard safe PM2.5 value. The concentration was extremely high even though the fire occurred more than 100 km – over 62 miles – away from the city.

Similarly, in the city of Reno (Nevada, US), in August 2013 the air quality was not considered safe for 4 days, due to the Rim Fires, taking place almost 250 km, or 155 miles away.

Wildfire Pollution: Risks of Dioxins?

Dioxins are organic molecules which contain chlorine, with very high toxicity; in fact they are teratogenic (i.e. they can cause birth defects) and carcinogenic (can cause cancer).

Dioxins can be formed during combustion if the compounds burnt contain chlorine atoms.

The presence of dioxins in wildfire smoke is not very likely; indeed, some Australian researchers showed that the dioxin emissions from bush fires were lower than originally estimated. However, if fires spread and reach inhabited areas, and if houses/buildings are burnt, there is the risk of dioxin emissions. The chances are especially high if plastic materials catch fire.

This happened for, instance, in Rome Fiumicino airport (Italy) in May 2015. Due to a fire inside the terminal, the dioxin level increased in some parts of the airport. Although the concentration was not considered worrying, some parts of the terminals were shut as a precaution measure, and workers used protective masks.

Long Term Effects on the Climate

In recent years scientists have started to investigate whether the emissions from wildfires can also have a long term effect on the climate.

One of the reasons for this is that carbon dioxide (CO2) is also emitted by wildfires; CO2 is a greenhouse gas whose increasing atmospheric concentration, according to some, is causing global warming and ocean acidification.

Some scientists think that, due to the more frequent and extended wildfires, higher CO2 amounts are emitted, and this can have a significant effect on the climate. As forests act as a carbon sink, the disappearance of large areas due to fires can also be crucial.

Further to this, however, some researchers from the US Forest Service also considered the possible interactions that the particles present in the smoke can have with solar radiation, and the possible long term effects on climate patterns at a local level. The topic is quite complex, and needs more in-depth study.


Smoke from wildfires can cause cardiovascular problems. Image by MONGO.

Wildfire: Effects on Human Health

As mentioned above, wildfire smoke may contain several toxic chemicals, especially for the respiratory system. Recent data, however, seem to show that the exposure to these emissions may also have an effect on cardiovascular health.

Researchers from Monash University (Australia), in fact, published a study in which they correlate the exposure to PM2.5 due to the wildfires in Victoria (2006-2007) and cardiovascular problems. They found that there was an increase in the cases of out-of hospital cardiac arrests and ischemic heart diseases.

According to the authors of the research, more studies like this should be performed, to have a better understanding of the effect particulate matter may have on the health of more vulnerable people (i.e. older people, people with chronic diseases, etc.)

Worrying over Wildfires

As wildfires become more and more common, it is important to be aware of the risks associated with them, not just for the ecosystem and for personal safety, but also for pollution and human health.

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