Forest fires don't just endanger people and buildings in the immediate vicinity of the flames. The smoke they produce can affect entire regions for days or weeks. Depending on wind and weather conditions, air quality can deteriorate even far beyond the actual danger zone.
During such smoke incidents, many people retreat to their homes and close the windows and doors. While this is generally a good idea, it does not automatically mean that the air inside is uncontaminated. Smoke particles can enter through drafty windows, doors, ventilation systems, and other openings in the building. The actual level of contamination depends, among other things, on the building, the duration of the incident, and ventilation practices.
Continuous monitoring of indoor air quality helps identify invisible pollutants and tailor protective measures accordingly.
What pollutants are found in wildfire smoke?
Wildfire smoke consists of a complex mixture of gases and particles. The substances produced depend on what vegetation, buildings, vehicles, or materials are burning and how complete the combustion process is.
Fine particles are particularly particulates . Very small particles, in particular, can remain in the air for a long time and penetrate deep into the respiratory tract. The World Health Organization identifies particulates as the greatest health hazard in the mixture of wildfire smoke.
Key metrics include:
- PM1 and PM2.5: very small particles that can penetrate deep into the lungs
- PM10: larger inhalable particles, including ash and resuspended dust
- VOC: volatile organic compounds that can be released during the combustion of various materials
- Carbon monoxide: a toxic combustion gas that can be particularly relevant in situations with heavy smoke and near fires
Other pollutants, such as polycyclic aromatic hydrocarbons, may also be present in wildfire smoke. However, a single indoor air quality monitor cannot analyze the entire mixture of substances or reliably attribute individual compounds to a specific source.
Why is PM2.5 particularly important in wildfire smoke?
PM2.5 refers to particles with an aerodynamic diameter of no more than 2.5 micrometers. Because of their small size, these alveolar-accessible particles can penetrate deep into the lungs. Some of the particularly small particles can even enter the bloodstream.
In the short term, wildfire smoke can irritate the eyes and respiratory tract, among other things, and cause coughing, headaches, or breathing difficulties. Children, older adults, pregnant women, and people with asthma, cardiovascular disease, or other pre-existing conditions are particularly at risk.
How far can wildfire smoke travel?
The extent to which the wind carries particulates contaminated air was evident, for example, at the end of June 2019, when a fire broke out on a former military training area in Lübtheen (Mecklenburg-Western Pomerania). Of the total 6,200 hectares of forest, between 1,200 and 1,300 hectares were engulfed by the fire. Firefighting efforts were severely delayed by overgrown forest trails and the presence of old ammunition. The fire department spent many days working to contain this devastating wildfire. During this time, the concentration of particulate matter in the surrounding area rose to exorbitant levels due to the fire.
On some days, the north wind carried fine particulate matter from the wildfire area far inland. Even in Leipzig, about 300 kilometers from Lübtheen, the smell of smoke was clearly noticeable and led to many concerned calls to the fire department. The high levels of fine particulate matter were also clearly recorded by the air-Q: As early as the early morning hours of July 1, the air-Q recorded PM10 and PM2.5 levels that far exceeded the daily limits of 50 μm/m³ and 25 μm/m³, respectively, set by the Federal Environment Agency (UBA) and the WHO.
particulates and Asthma in Children: What Studies Show
A study by Khreis and other researchers published in the *European Respiratory Journal* demonstrates just how significant the long-term impact of particulates can be on the development of asthma. Using population, air quality, and health data, the study examined the exposure of approximately 63.4 million children in 18 European countries.
The results of the model calculation: If all the countries studied had complied with the WHO guideline value for PM2.5 in effect at the time—an annual average of 10 µg/m³—the researchers estimate that approximately 66,600 new cases of asthma in children could have been prevented each year. This corresponded to about 11 percent of new cases. If concentrations had been reduced to the lowest PM2.5 levels observed in the underlying studies—1.5 µg/m³—the figure would have been approximately 190,900 cases, or 33 percent.
For people with existing asthma, a period of smog therefore poses a particular risk: symptoms may worsen, medication may be needed more frequently, and in severe cases, hospitalization may be required. Children are especially vulnerable because their airways and immune systems are still developing.
Can wildfire smoke get into the house even with the windows closed?
Yes. Even with the windows closed, some outdoor air can enter the building. The U.S. Environmental Protection Agency (EPA) notes that, during a smoke event, indoor PM2.5 concentrations often still reach a significant portion of outdoor levels if the air is not purified. However, the degree of protection a building provides can vary greatly.
Older or drafty buildings generally allow more outside air to enter than well-sealed buildings. Frequent opening of doors, exhaust systems, and ventilation systems that bring in outside air also affect indoor air quality.
Smell and visibility are not reliable indicators in this context: indoor air may already be contaminated before a distinct smell of fire is detected. Conversely, a detectable smell alone does not indicate the exact concentration of particulate matter.
Reducing Wildfire Smoke Indoors
If the relevant authorities determine that it is safe to remain in the building, a room that is kept as clean as possible can help reduce personal exposure. A bedroom or another room where residents can stay for extended periods during the heaviest smoke is suitable for this purpose.
The following measures are recommended:
1. Keep windows and doors closed
When outdoor pollution levels are high, windows and exterior doors should remain closed as much as possible. Doors should be opened only as often and for as short a time as necessary.
Ventilation and air conditioning systems may, provided it is technically feasible and safe to do so, operate in recirculation mode from time to time. The appropriate setting depends on the specific system. The manufacturer’s instructions and the guidelines of the relevant authorities should be followed.
2. Use a suitable air purifier
An air purifier with a HEPA filter can remove a large portion of the fine particles from the air in a room. It is crucial that the unit is appropriate for the size of the room and is operated for a sufficiently long period of time.
HEPA filters remove particles, but they do not automatically remove all gaseous components of smoke. Devices equipped with an additional, adequately sized activated carbon filter can reduce certain gaseous substances. However, even these filters do not remove every possible compound.
3. Avoid additional sources of particles
During a smoke incident, the indoor air should not be contaminated by additional sources. These include, in particular:
- Smoking
- Candles and incense sticks
- Wood-burning stoves and open fireplaces
- high-heat frying or grilling
- Sprays and products with high solvent content
- Vacuuming without a suitable HEPA filter
Frying and burning candles, in particular, can cause particulate matter levels to rise so sharply in the short term that the pollution is mistakenly attributed solely to the wildfire.
4. Wait until the outdoor air quality improves before ventilating
If windows remain closed for an extended period of time, CO₂, humidity, and other indoor air pollutants can build up. That is why it is important to let fresh air back in at an appropriate time.
Follow the guidance provided by local authorities and rely on reliable outdoor air quality data. Once the situation has improved, it may be advisable to ventilate the room thoroughly for a short period. You can then check the indoor air quality readings to see whether the fine particulate matter levels have remained low or have risen again.
How does the air-Q help with wildfire smoke?
The air-Q continuously monitors indoor air quality. Depending on the model, it measures PM1, PM2.5, and PM10, as well as VOCs, carbon monoxide, CO₂, temperature, and humidity, among other things.
This helps answer important questions:
- Is smoke entering the building?
- In which room is the particle concentration the lowest?
- Do the readings go up when windows or doors are opened?
- How quickly does an air purifier reduce the concentration of fine particulate matter?
- Will the indoor air remain protected overnight?
- When is ventilation necessary due to rising CO₂ levels?
The measured values are displayed as a time series. This makes it possible to identify not only individual snapshots but also prolonged exposure and short-term spikes. The air-Q can issue warnings when values are out of the ordinary.
Through a smart home connection, an air purifier, for example, can also be turned on automatically as soon as the fine particulate matter level exceeds a preset threshold. Whether the measure is successful is then immediately visible in the measurement history.
Indoor Air Quality Testing for Homes, Schools, and Businesses
Wildfire smoke doesn't just affect private households. Schools, nursing homes, hotels, offices, and public buildings often need to maintain the safest possible indoor environment for extended periods of time.
Using multiple networked monitoring devices, it is possible to identify which areas of a building are particularly affected and where filtration or sealing needs to be improved. Those in charge can document the effectiveness of ventilation and air purification strategies and respond more quickly should another period of smoke occur.
Conclusion: Take measurements not only outdoors, but also indoors
During a wildfire, staying indoors is often the most effective way to reduce personal exposure to smoke, provided that evacuation is not necessary. However, closed windows alone do not guarantee clean air.
The combination of a room that is as well-protected as possible, appropriate air filtration, reduced indoor sources, and continuous monitoring provides a solid foundation for reducing exposure. The air-Q shows how much smoke actually enters the room and whether the measures taken are effective.
