All you need to know about air pollution episodes

On a global scale, we are all impacted by air pollution throughout our daily lives. Air pollution concentrations vary significantly throughout the day (diurnal patterns) and throughout the year (seasonal patterns). It negatively affects the health of anyone who is exposed to it and puts our most vulnerable populations at high risk. Air pollution episodes, more specifically, have social, economical, political, and environmental consequences, including contributing to climate change. What is an air pollution episode? What is their source and how are they caused? How can you protect yourself when it occurs in your area? Read on to learn more.

Skyscrapers covered in smog

Air pollution episodes

What is an air pollution episode?

An air pollution episode occurs when ambient air pollution levels are higher than usual. Air pollution episodes often last up to several days and impact a widespread geographical area. They are experienced everywhere on a global scale, and the air quality episode may pertain to one or multiple air pollutants, posing environmental effects and effects on human health. The most common air pollutants that require alerts when levels are too high include:

Some of the most newsworthy air pollution episodes include the Great London Smog episode of 1952, the Los Angeles smog episode of 1973, the Kuwait Oil Fires of 1991, and the Melbourne Dust Storm of 1983. Of course, these episodes are extreme examples. Seasonal air pollution episodes occur multiple times annually. In Europe and the UK, we have also seen a rise in air pollution episodes due to emissions sourced by wildfires and Sahara desert dust. Scientific research shows that these events are becoming more severe as a result of climate change.

A wildfire burning in a forest

What causes an atmospheric air pollution episode?

Air pollution episodes are usually categorised as ‘winter smog’ or ‘summer smog’ episodes. Both impact human and environmental health and contribute to global climate change.

Winter smog

Also referred to as ‘pea-soupers’, the source of this type of atmospheric air pollution episode was historically the burning of coal (domestic and industrial) during the winter seasons in the 1950s and 1960s. In the UK, the Great London Smog episode of 1952 occurred in December when coal burning was at its peak. However, thanks to the Clean Air Acts of 1956 and 1968 in the UK, the availability of natural gas, and a global effort to use technology to improve air quality and environmental conditions, these air pollution episodes occur less often. Unfortunately, they are still fairly common and are now mostly caused by emissions of particulate matter (PM10 and PM2.5) due to road transport. Research supports PM’s serious impact on both human and environmental health.

How do winter smog events occur? Atmospheric air pollution episodes in winter are caused by an atmospheric phenomenon called ‘temperature inversion’. This is when a thin layer of the atmosphere near the Earth becomes cooler than the layer above it. Environmental air pollutants then become trapped and remain at ground-level. They remain in place until meteorological and weather conditions change.

Winter smog episodes have severe effects on health for everyone who breathes outdoor and indoor air (remember: on average, indoor air is 2 to 5 times more polluted than outdoor air). In addition to environmental degradation, winter air pollution episodes lead to an increase in hospital admissions, respiratory conditions, heart problems, and premature death. Particularly vulnerable are individuals with health conditions like respiratory (asthma or chronic pulmonary obstructive disorder (COPD)) or heart disorders1. These episodes are further impacted by our changing climate.

Summer smog

Summer smog air pollution episodes occur mostly in urban and their surrounding suburban environments. Atmospheric nitrogen dioxide (emitted from road transport and industrial sites) reacts with other environmental air pollutants present when exposed to sunlight. As a result of these chemical reactions, ozone is created. Ozone, as well as fine particles like PM10 and PM2.5 that are released from road traffic, domestic, and industrial sources, accumulate in high quantities.

High concentrations of these air pollutants cause severe health impacts for those with preexisting conditions like respiratory or heart disorders. Severe summer smog episodes even pose problems for healthy people, especially in urban environments, who may experience difficulties breathing, coughing, and nose and throat irritation2.

A city port covered in smog

What does it mean when there is an air pollution alert?

An air pollution alert is issued when hourly or daily concentrations of air pollutants are significantly higher than normal levels (and those advised by WHO guidelines and/or other government standards) and pose danger to human health3. When an alert is issued, those levels are expected to remain high for several days to come, causing air quality and environmental issues.

This system is in place to notify the population of immediate health risks due to sustained levels of air pollution and encourage them to take extra precaution4. Although everyone is impacted by high air pollutant levels, this is particularly important for those whose health is the most at risk including:

What should I do when air pollution levels are hazardous?

Recommendations on a residential scale

The WHO has published a list of suggestions to follow in order to protect human health during atmospheric air pollution episodes. Some of their suggestions are:

  1. Remain indoors. High-risk individuals should protect their health by avoiding going outdoors, especially near heavily-trafficked urban areas and motorways, as much as possible. It also helps to research your local climate conditions regularly to help you understand air quality trends in your area (this service is offered by many local governments throughout Europe and the UK).
  2. Keep windows and doors closed. This will keep high levels of ambient pollution from accessing your indoor spaces.
  3. Avoid heavy and prolonged exertion outside. Breathing in high concentrations of air pollutants especially whilst performing strenuous activity exacerbates air pollution’s effect on health.
  4. Prevent emitting air pollution whilst indoors. Avoid burning anything like candles or wood stoves. Do not smoke indoors (this includes all tobacco products, cannabis, and e-cigarettes). Also refrain from using volatile organic compound (VOC)-releasing products like cleaning products, air fresheners, adhesives, solvents, and paint. In general, avoid products that contribute to environmental pollution.
  5. Keep your home clean. Try to use wet mopping and dusting more than sweeping or hoovering to avoid releasing particles and dust into your indoor air.
  6. Limit unnecessary motor vehicle travel and encourage public transport/carpooling. This will protect you and your health from further exposure and reduce further environmental contributions to ambient air pollution. If you must travel by car, avoid speeding and comply with restrictions put in place. Local authorities may limit driving within the city limits or alternate traffic, for example. Air quality trends aside, this is always a recommended step for the protection of our climate!
  7. Designate a clean room for children and elderly individuals. Ideally, the room should have few, if any, windows (if it has windows, keep them closed). Research and scientific studies recommend installing and running an air purifier in this room and in other rooms of the house.
A person sweeping the floor in their home

Recommendations on an industrial scale

  1. Temporarily cease industrial activities. The less air pollutants that are emitted during atmospheric air pollution episodes, the better.
  2. Reduce air pollution contributions. If industrial activities have been ceased, take extra steps to ensure that any other pollutant emissions are reduced. Again, regardless of air quality trends, this is a step that should be emphasised globally, throughout all phases of industrial processes.

Install an air purifier in homes, offices, and industrial settings

An air purifier provides a much-needed level of protection from air pollution on a daily basis and during environmental air pollution episodes. During air pollution episodes when it is recommended to keep windows closed and to stay indoors, an air purifier helps circulate stale air and clear it of pollutants, protecting your health. Considering that our indoor spaces are significantly more polluted than our outdoor spaces, it is important to invest in clean indoor air quality to protect you and your loved ones from the dangers of air pollution.

Not any air purifier will do, however! The most important air filtration technology to seek out during atmospheric air pollution episodes is a HEPA-certified filter. The WHO recommends at least a HEPA H13 filter or better3. H13 filters are medical-grade (a technology found often in hospitals) and guarantee filtration of 99.97% of pollutants down to a size of 0.01 microns in a single pass. All of Eoleaf’s HEPA-certified filters are H13.

In addition to HEPA-certified filters, all Eoleaf devices contain seven other technologies as part of our proprietary 8-step filtration technology. Our technology removes the following from your indoor air:

Our team of air purification experts is here to answer any questions you may have about using our air filtration technology to safeguard your health from air pollution. Whether we are undergoing an air pollution episode or not, air pollution is one of the most crucial public health issues globally, responsible for 7 million premature deaths annually. Contact us anytime or refer to our in-depth Buying Guide to find the right device for your needs.

Eoleaf's AEROPRO 40 air purifier


1 ERG. (2023). How bad are winter smogs?. London Air Quality Network Guide.

2 ERG. (2023). How bad is summer smog?. London Air Quality Network Guide.

3 What to do when there is an air pollution alert. World Health Organization. (11 November 2023).

4 National Environmental Technology Centre. (n.d.). Air Pollution Episodes. Air Quality in the UK - air pollution episodes. 

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