The Science of Air Pollution

To better understand the issues surrounding air pollution, we need to dive into the science concerned with studying the atmosphere and human activities.

This will also make us realise how air pollution affects us.

Air pollution is detrimental to human health and well-being, is costly in terms of economic activity, and contributes to global warming.

In simple terms, air quality refers to how clean the air is.

A number of questions arise from this: What does clean air look like? What are the common air pollutants? And where do they come from?

Where does air pollution come from?

Let’s start from scratch.

Some air pollutants are natural. Going outside and feeling the wind against your face is the biggest indicator of how the air is always in motion. In Ireland, the wind predominantly flows from the west and south-west, bringing with it lots of moist air from the ocean. The air literally carries millions of tons of water in the form of droplets from the Atlantic Ocean before it falls as rain, sleet, hail or snow.

Water droplets suspended in air are what we call aerosols. In fact, aerosols refer to any kind of small particulate matter floating in the air. Natural aerosols also include sand particles blown up from the Sahara desert and a wide variety of emitted products from landscape fires and volcanic eruptions. Air pollution from such events can be transported over long distances. During the 2023 wildfire season, smoke from wildfires in Canada reached Ireland. Note: Some landscape fires - such as gorse fires in Ireland - are started by people - and are not strictly natural.

Gases are another form of pollutants and these can be emitted naturally. Our atmosphere is primarily made up of the gases nitrogen and oxygen, as well as other gases, in smaller amounts. These gases vary in concentration and include carbon dioxide, ozone and methane. Once again, some natural phenomena such as volcanic eruptions, wildfires and even plant activity can change the composition of our atmosphere.

Some air pollutants are dissipated and dispersed in a matter of hours or days. Others may linger for hundreds of years.

Which pollutants are we causing?

In addition to the above-mentioned natural sources of pollutants, it has long been evident that human activities are causing significant changes to the atmosphere.

Human activities such as burning of fossil fuels for home heating and energy production, emissions from internal combustion engines of vehicles, ships and planes, emissions from industrial processes as well as agriculture all release pollutants into the atmosphere.

The biggest sources of air pollution in Ireland are from the burning of solid fuels - wood, peat, briquettes and coal - for home heating; as well as emissions from road transport.

What does air pollution look like?

Particles all around us

As mentioned above, small particles from various sources are suspended in the air. These are called particulate matter (PM) which includes soot, dust, ash, sand and liquid droplets. Some particlesare large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.

The largest source of ambient particulate matter in Ireland comes from home heating. When burning peat, coal and wood in fireplaces and stoves, large amounts of particulate matter of different sizes are released. The smallest particles are of the most concern as they can enter our blood stream when inhaled. This can lead to a variety of adverse health effects, such as respiratory damage, stroke and cardiovascular disease, especially if large quantities are inhaled in indoor environments.

Other prominent sources of particulate matter include vehicle tyres. Tyre wear occurs on all road vehicles (even electric vehicles) due to road friction. The material scraped off can range in size from larger flakes of plastic to tiny particles (termed microplastics) that can easily be inhaled and enter the blood stream. Many of the components in car tyres are known carcinogens. There is a lot still to be uncovered about the long-term effects of particulates from car tyres in the environment and their effect on human health.

Gases - more than just hot air

Internal combustion engines from diesel and petrol cars also emit a range of polluting gases which are damaging to our health. These include:

Nitrogen Oxides (NOx), in particular Nitrogen Dioxide (NO2). We are exposed to NO2 when we live near busy traffic routes; when we walk or cycle next to traffic. We are also exposed to NO2 when travelling inside our vehicles. NO2 is damaging to our lungs and exacerbates conditions such as asthma and emphysema. It can also affect the liver and spleen.

Ozone is a gas composed of three oxygen atoms. While Ozone is an important barrier against harmful UV radiation in the upper atmosphere (the stratosphere), ground-level ozone is a harmful air pollutant. Ground-level ozone forms when other air pollutants (Nitrogen Oxides NOx and Volatile Organic Compounds VOCs) in the air react with sun light. Air pollution attributable to Ozone is more common in cities with hotter climates.

Sulphur Oxides (SOx), wich includes Sulphur Dioxide (SO2), are emitted by burning coal and oil, and by the processing of mineral ores which contain sulfur. SOx are damaging to our lungs, and cause acid rain. Fuel regulations have led to significant reductions in SOx emissions and related health and environmental effects.

Other air pollutants which are of greater concern due to their impacts on the environment include:

Methane (CH4) is a powerful greenhouse gas emitted from the decay of organic matter under anaerobic conditions. The largest sources of methane emissions worldwide are agriculture, fossil fuels and the decomposition of waste in landfills. Of natural sources, CH4 is mostly emitted from wetlands.

CO2 is a greenhouse gas emitted in any combustion reactions. The main source of CO2 is the use of fossil fuels - coal, oil, and gas - which account for almost 90% of global carbon dioxide emissions.

The effect also applies to surrounding neighbourhoods as particulate matter is released from chimneys. During cold winter nights, air quality can decrease significantly as many households light their fireplaces and stoves simultaneously. While it can add a certain ambience within the houses and the smell may invoke a sense of nostalgia, it also poses a public health risk.

Source: US EPA - Size comparison for PM particles

How does air pollution affect me?

Air pollution is the single biggest environmental threat to human health, causing 1,400 premature deaths every year in Ireland (European Environment Agency, 2021).

Health conditions related to air pollution include chronic and acute respiratory diseases, lung cancer, stroke and heart disease.

The World Health Organization gives recommendations for maximum levels of air pollutants in the environment based on their health impacts. These are typically lower than legal air quality standards set by the European Union.

Meeting WHO Air Quality guidelines will be a major challenge for society. Ireland and Europe are aiming to move towards achieving the health based WHO Air Quality guidelines (EPA, 2022) in the near future.

  • Fine particulate Matter - PM₂.₅ is the air pollutant most harmful to our health. These particles are small enough to infiltrate deep into the lungs and into our bloodstream, causing respiratory damage, stroke and cardiovascular disease.s here

  • Short-time exposure to NO2 can lead to irritation of airways, leading to symptoms such as choughing, wheezing or difficulty breathing. It also makes respiratory diseases - in particular asthma - worse. Long-term exposure under higher levels of NO2 can lead to development of asthma and possiby make respiratory infections worse.

  • Ground-level ozone can irritate the respiratory system, worsen existing conditions like asthma, and damage lung tissue. It weakens the immune system, making people more prone to respiratory infections and exacerbating heart conditions. Long-term exposure may lead to chronic respiratory diseases and premature death, especially in vulnerable groups. Minimizing exposure by reducing ozone precursors and avoiding outdoor activities during poor air quality periods is crucial for public health.

  • Sulfur oxides (SOx) can cause various health problems, including respiratory issues like coughing, throat irritation, and shortness of breath. They can exacerbate conditions like asthma and bronchitis, and prolonged exposure may lead to decreased lung function and increased susceptibility to respiratory infections. Additionally, SOx emissions can contribute to cardiovascular problems and exacerbate existing heart conditions. Reducing SOx emissions is crucial for protecting public health and improving air quality

What is the connection between air pollution and climate?

Air pollution and climate change are inherently linked in several ways:

Common Sources: Both arise from human activities such as burning fossil fuels for energy, transportation, industrial processes, and agriculture. These activities release pollutants and greenhouse gases into the atmosphere, contributing to both air pollution and climate change.

Greenhouse Gas Emissions: Many air pollutants, such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), are also potent greenhouse gases. These gases trap heat in the Earth's atmosphere, leading to the greenhouse effect and global warming.

Feedback Loops: Climate change can exacerbate air pollution and vice versa. For example, higher temperatures can increase the formation of ground-level ozone, a harmful pollutant. Extreme weather events, such as flooding, can cause damage to buildings, leading to damp and mould in homes. Warmer temperatures can lengthen the pollen season.

Health Impacts: Both air pollution and climate change have significant health effects. Air pollution can cause respiratory and cardiovascular diseases, exacerbate asthma, and increase the risk of premature death. Climate change can worsen air quality, increase the frequency and intensity of heatwaves, storms, and wildfires, leading to heat-related illnesses, injuries, and displacement.

Environmental Consequences: Air pollution and climate change also have environmental impacts. Pollution can harm ecosystems, degrade soil and water quality, and contribute to biodiversity loss. Climate change can disrupt ecosystems, alter habitats, and threaten species survival through changes in temperature, precipitation patterns, and sea levels.

Solutions: Addressing air pollution and climate change requires comprehensive strategies that consider their interconnected nature. The good news is that efforts to reduce greenhouse gas emissions can simultaneously improve air quality, leading to co-benefits for human health and the environment. Additionally, adaptation measures are necessary to mitigate the impacts of climate change on air quality and public health.