Everything You Need To Know About Aerosols & Air Pollution

Fully understanding a concept like pollution can actually be quite tricky. There are multiple types of pollution, all coming from different sources and causing different effects. I decided that this blog would be the perfect place to delve into some of these in more depth, because it’s much easier to change things when we understand them.

So, we’re starting with air pollution, something which affects 91% of the world population. There are a few main pollutants with the strongest evidence of health effects, which are ozone (O₃), nitrogen dioxide (NO₂), sulphur dioxide (SO₂), and particulate matter (PM), however I’m going to pay particular attention to PM, also known as aerosols. Read on for more information.

What are aerosols?

An aerosol is a tiny particle (solid or liquid) in the atmosphere. Some aerosols are so small that they are only made of a few molecules and are invisible, some are visible but still very small. The smaller and lighter a particle is, the longer is stays in the air. Larger particles settle to the ground due to gravity after a few hours, whereas the smallest particles can stay in the atmosphere for weeks.

Aerosols can derive from natural processes, like salt from the sea, dust from dry regions, or particles released by wildfires, but human activities like fossil fuel burning in factories and air pollution from cars also contribute to aerosols in the environment. Some aerosols are released into the atmosphere, while others are made in the atmosphere itself, for example sulfate aerosols are made in the atmosphere from sulfur dioxide released from power plants.

Naming aerosols

When we talk about aerosols most people think of aerosol sprays (like deodorants or cleaning products) which are actually products that contain aerosols, as the word refers to the particles themselves. These particles can also go by different names, which is helpful to know when reading up on them. Toxicologists refer to aerosols as ultrafine, fine, or coarse matter. Regulatory agencies and meteorologists usually call them particulate matter (PM_2.5 or PM₁₀ depending on their size), in engineering fields they’re usually called nanoparticles, and the media will normally use everyday terms such as smoke, ash or soot, that refer to the sources of the aerosol.

Climatologists tend to label aerosols based on their chemical composition. Key groups include: sulfates, organic carbon, black carbon, nitrates, mineral dust, and sea salt. This isn’t a perfect system, as aerosols often clump together and form complex mixtures, but it is helpful because different types of aerosols can cause different effects.

Patterns

When viewed from space, scientists have found multiple patterns emerge from Earth’s aerosols, some natural and some manmade. A thinner and more evenly dispersed veil of aerosols, mainly comprised of salt from whitecaps and sulfates from microalgae, usually covers most of the world’s oceans, while on land large plumes of dust cover deserts. Simultaneously human-populated areas tend to be covered by man made industrial aerosols. For example urban areas will often contain sulfates from power plants, and black and organic carbon from vehicle traffic, while areas with lots of agriculture produce heavy loads of soil dust.

While most aerosols remain in the atmosphere from between four days and a week, they also have the potential to travel great distances in that time, moving thousands of kilometres in a week. Dust from the Sahara desert frequently ends up in the Caribbean, dust from the Gobi desert and pollution from China move East over Japan and toward the central Pacific Ocean, and smoke from wildfires in Siberia and Canada can find its way to the Arctic ice caps.

When it comes to manmade aerosols Asia is also an area that deserves specific focus:

Satellites can detect a visible pall of aerosol clouds over Bangladesh, northern India, and northern Pakistan—an area called the Indo-Gangetic plain, especially during the pre-Monsoon season. The aerosol layer is comprised of complex mixtures of dust blowing from the Thar Desert and pollution from the densely populated plain. In eastern China, fast-growing cities such as Beijing also produce heavy blankets of aerosol.

Over time, aerosol emissions have changed significantly. In Asia, anthropogenic emissions have increased in recent decades as urbanization and industrialization has proceeded at a breakneck pace. By contrast, aerosols have declined in North America and Europe as factories have moved to developing countries and Western nations have adopted more stringent clean air regulations.

The unspoken subtext here is that the long term effects of colonialism and outsourcing of manufacturing (caused by the rampant consumerist, linear economy culture of the west) has directly impacted who deals with the worst of air pollution, as more man made aerosols enter the atmosphere in global south countries and non-western manufacturing hubs.

Aerosols and health

Aerosols are one of the main air pollutants, leading to the premature deaths of millions of people every year as they damage lungs and can even enter the bloodstream. Living within a third of a mile from a motorway has been associated with a 2% reduction in lung capacity, while only last month scientists put the number of early deaths caused worldwide by air pollution at double previous estimates. According to research published in the European Heart Jo urna l the real number sits as 8.8 million a year, meaning toxic air kills more people than smoking.

The smallest particles are linked to the worst health effects, and exposure is key. A London experiment found the difference between walking beside the road on a pavement or walking on the building side of the same pavement, was 163,000 particles per cubic centimetre versus 33,000 particles per cubic centimetre, meaning that people were breathing in five times the number of nanoparticles due to this slight increase in proximity to traffic. As small children and babies in prams are shorter they are also usually closer to exhaust pipes and have smaller lungs, meaning they breathe in pollution more rapidly.

Additionally, scientists have begun to find plastics in the air too. While no one is yet sure of the health impacts of this, microplastics can accumulate toxic chemicals such as mercury or persistent organic pollutants (POPs), including brominated flame retardants and polycyclic aromatic hydrocarbons (PAHs). None of these are good for human health, so it’s not ideal to be breathing them in.

Aerosols and climate

Aerosols affect the climate as strongly as greenhouse gases, but in a completely different way. They are able to scatter sunlight, meaning they actually cool the planet by reflecting about 1/4 of the sun’s rays back to space, with the IPCC concluding that industrial aerosols have acted to significantly slow the increase in global temperature over the last thirty years.

In 1991, the eruption of Mount Pinatubo in the Philippines ejected more than 20 million tons of sulfur dioxide—a gas that reacts with other substances to produce sulfate aerosol—as high as 60 kilometers (37 miles) above the surface, creating particles in the stratosphere. Those bright particles remained above the clouds and didn’t get washed from the sky by rain; they settled only after several years.

Climatologists predicted global temperatures would drop as a result of that global sulfate infusion. They were right: Following the eruption, global temperatures abruptly dipped by about a half-degree (0.6°C) for about two years. And Pinatubo isn’t a unique event. Large, temperature-altering eruptions occur about once per decade.

However other types of aerosol, particularly black carbon or brown carbon/organic matter (depending on the brightness of the underlying ground), will absorb light radiation, adding to warming the atmosphere.

Aerosols’ ability to change the reflectivity of the planet is known as the albedo of the planet. Bright surfaces reflect radiation, cooling the climate, while dark surfaces will absorb radiation and warm the climate. For example, white sheets of sea ice reflect a lot of radiation while dark surfaces, like the ocean, tend to absorb solar radiation and have a net warming effect. Aerosols, especially black carbon, can deposit a layer of dark residue on ice, which both speeds up melting and reduces the amount of radiation being reflected.

Overall, scientists believe the cooling from sulfates and other reflective aerosols overwhelms the warming effect of black carbon and other absorbing aerosols on the planet. Estimates suggest that the cooling effects of aerosols has counteracted about half of the warming caused by the build-up of greenhouse gases since the 1880s. However, unlike many greenhouse gases, aerosols are not distributed evenly around the planet, so their impacts are most strongly felt on a regional scale.

This suggests that, beyond CO2 emissions, we need to reduce fossil fuel use in order to also avoid black carbon aerosols being released into the air, therefore reducing the amount of radiation that is being absorbed.

Aerosols and clouds

Aerosols also have varied effects on weather, particularly when it comes to clouds. Unlike greenhouse gases, which disperse widely and have a fairly consistent impact across the world, aerosol effects can vary more due to how they affect clouds.

We learn that clouds form when enough water evaporates and condenses, however aerosols also lend a hand by serving as tiny ‘seeds’ that helps clouds form, also known as condensation nuclei. Natural aerosols such as sulfates, sea salt or ammonium salts are the most common condensation nuclei in non-polluted areas. Polluted air, however, usually creates clouds that are comprised of more droplets that are smaller in size. These droplets make clouds look brighter than usual, scattering more light and becoming more reflective whilst shading the earth, therefore producing net cooling. This is known as the cloud albedo effect, but scientists have only been able to start quantifying this in recent years.

In general clouds are believed to cool the earth by increasing the reflectivity of the planet and shading 60% of the planet at any one time. Because of this, just a 5% increase in cloud reflectivity could compensate for the entire increase in greenhouse gases from the modern industrial era, while long term decreases in cloudiness could have major adverse impacts. Unfortunately, because aerosols aren’t distributed around the planet in the same consistent way as greenhouse gases, the effects don’t simply cancel each other out; when averaged across the globe, the cooling caused is less than half of the warming caused by greenhouse gases. However on smaller scales the effects can be significant, and so understanding how clouds, and feedback cycles involving clouds, affect regional climate systems is currently a high priority for climatologists.

Of course, the type of aerosol involved is also highly important when it comes to understanding aerosols and clouds. Reflective aerosols tend to brighten clouds and make them last longer, while black carbon can stop cloud formation (which could have disastrous consequences), or warm the surrounding atmosphere and cause droplets to evaporate, turning clouds into a haze that suppresses precipitation.

The details of aerosol effects are still not fully understood, as most instruments can’t yet measure aerosols within clouds, making the role of clouds the “largest single uncertainty in climate prediction” according to climatologists. In fact, less than 1/3 of the models participating in the Fourth Intergovernmental Panel on Climate Change (IPCC) included aerosol effects, and those considered only sulfate aerosols.

As we continue to learn about aerosols, and hopefully remove the more harmful ones such as black carbon from our atmosphere, we may unlock new methods and understandings around mitigating global warming.

Indoor pollution and aerosols

While all of the above has focused on aerosols outside, it’s also important to think about air quality indoors too. Factors such as building materials, how a building is ventilated, how we heat and cook in our homes, and the chemicals we use to clean and room temperature can all affect the quality of air indoors.

While stricter regulations have been imposed on vehicles to reduce traffic emissions, urban air pollution can still come from other sources such as household cleaners, paints and perfumes. Researchers in the US looked a levels of volatile organic compounds (VOCs) in roadside air in Los Angeles and found that as much came from petroleum based industrial/household products as from vehicle exhausts.

These compounds are important to consider because, when they make their way into the atmosphere they react with other chemicals to produce aerosols (PM_2.5,to be specific) that also adversely affect health in urban areas. While these results aren’t exactly the same in the UK/Europe due to more usage of diesel vehicles outside of America, this study still highlighted a lesser discussed source of air pollution.

“This is about all those bottles and containers in your kitchen cabinet below the sink and in the bathroom. It’s things like cleaners, personal products, paints and glues,” said Joost de Gouw, an author on the study at the University of Colorado in Boulder.

“When you think about how much of those products you use in your daily life, it doesn’t compare to how much fuel you put in the car. But for every kilogram of fuel that is burned, only about one gram ends up in the air. For these household and personal products, some compounds evaporate almost completely.”(source)

Just like aerosols, VOCs also occur naturally, predominantly coming from plants and trees. However these are greatly increased by vapours released from things like hairsprays, perfumes, pesticides, deodorants and cleaning products, or from burning fuels like gas and wood.

David Green, who studies air pollution at King’s College London, said: “Organic aerosols, which are produced when these volatile chemicals react in the atmosphere contribute significantly to UK PM2.5 concentrations as they do all over the world. In London, where we measure these routinely, approximately a third of PM2.5s can be attributed to organic aerosols which come from a range of sources including vehicle emissions, wood burning and even cooking. This paper highlights a previously poorly understood source which is currently unregulated.”

(source)

While 85% of raw oil goes into the production of fuels, with only 5% refined for use in chemicals in products like deodorants and pesticides, the way these two products are designed could not be more different. Fuels are designed to be burned, releasing mostly CO2 and water, whilst most household products waft into the air by design, for example with products like hairspray.

So, let’s look at some of the key players when it comes to indoor pollution contributing to manmade aerosols, in order to understand what to avoid in our daily lives.

Cleaning products

Many cleaning supplies and household products contain dangerous chemicals including VOCs (for example acetone, xylene and formaldehyde), ammonia and bleach. These chemicals have been linked with a range of health issues including headaches, chronic respiratory problems, asthma, and allergic reactions. While more research is needed to understand the exact effects of breathing in these chemicals, one study found a correlation between women who clean at home or work and an increased decline in their lung function.

In order to avoid cleaning products that contribute to air pollution, consider some of the following options:

Consider other ways of cleaning: Look at DIY, or using simple ingredients like vinegar, baking soda and water to clean your home. Avoid commercial air fresheners all together, which can release multiple toxic chemicals.
Avoid chemical-heavy products: look for products that are labelled hypoallergenic, as these have lower levels of VOCs, and try to find products with smaller amounts of ingredients that you can understand.
Avoid sprays: when possible use solid or liquid cleaning products rather than sprays, to avoid breathing in any particles, or make sure to check the labels of the products you do spray (or make your own).
Ventilate your home: in general, try to open all of your windows for at least 10 minutes each day to refresh your indoor air, and always open a window when you are cleaning or decorating. Also, look into house plants that naturally purify the air in your home.

Cooking

Cooking with gas or electricity can release aerosols, which is one reason why cookers have chimneys or other ventilation that lets polluted air leave you home. Gas cooking can also produce other emissions, including carbon monoxide, formaldehyde and nitrogen oxides, which aren’t good for health either.

To reduce air pollution risks you can:

Make sure your gas appliances are regularly maintained by a certified engineer.
Make sure extractor fans over your gas stoves and ranges are working, and always use them. Also, open a window when cooking if you can.
Install alarms for both smoke and carbon monoxide (they are separate alarms), and check the batteries regularly.

Candles and incense

Candles and incense sticks can also emit aerosols when burned. Recent scientific research has found that daily exposure to incense burning can lead to impaired lung function, which means that this should be carried out in well ventilated spaces.

Candles have been found to also increase the aerosol concentration in the air while burning, however when looked at in the context of a 24 hour period this increase is minimal. Scented candles can emit small amounts of formaldehyde and VOCs due to fragrances, but if only used occasionally aren’t likely to be a large health risk. In general, aim to avoid paraffin candles as they are made from by-products of petroleum, coal or shale that is then whitened using bleach. Opt for natural soy or beeswax candles, created with natural, non-toxic dyes or perfumes.

Burning wood and coal

Having a wood or coal burning stove/fireplace releases aerosols, and also increases your risk of lung cancer. Smoke from wood heating can also enter neighbouring homes, and UK researchers have suggested that wood burning in densely populated areas may lead to aerosol exposure levels that are comparable to those from traffic sources.

In the UK, this is counteracted with smoke control areas which cover the UK’s largest cities, restricting what you can burn and the types of stove you can use (although many wood burning stoves are currently exempt). Here are some things to consider:

If you must burn coal or wood, make sure your chimneys are inspected and swept regularly by a HETAS qualified sweep.
If you decide to buy a wood-burning stove, choose a modern, lower emission model, and do consider that your choice also affects the quality of air for your neighbours too.
Only burn dry, unpainted and untreated wood (look for wood with the ‘ready to burn’ logo) and don’t burn rubbish or packaging. Ensuring a good air supply in your stove will also reduce the aerosol emissions.
Avoid buying a wood-burning stove or using an open fire if you live in an urban area.
Instead of going for a wood burning fire find alternative options, for example bio-ethanol fires produce no aerosols.
For additional advice, to read the Department for Environment, Food and Rural Affairs’ practical guide on open fires and wood-burning stoves

Building materials

Many of us will be aware of asbestos, which has been banned in the UK since 1999, however many older buildings still contain asbestos in their materials. Before it was known to be dangerous asbestos was used for insulation, flooring, roofing, and spray for ceilings and walls. If asbestos particles are inhaled it can lead to lung diseases decades later. If you find asbestos in your home, it poses very little risk if it remains intact and undisturbed. However, if it’s damaged or deteriorating, you will need to get it removed by professionals.

Fibreglass, which is usually found in attics of homes, can also release fibres when trimmed, cut or sanded. These fibres can irritate the skin, nose and throat. If you discover fibreglass in your home, don’t disturb it, and if you do need to come into contact with it wear a mask and protective clothing.

Paint can also be a large source of VOC’s which can off-gas for months after a room is painted. These fumes can cause headaches, dizziness, nausea, fatigue and allergies. While water based paints are good, these don’t guarantee no VOC’s, so specifically look out for zero VOC paints for your home.

In general, when building or renovating your home, look for building materials that are certified as environmentally friendly, with low VOC emissions and low in pollutants. You can find sustainable products on the website of The Alliance for Sustainable Building Products.

TLDR

This is a lot of information, so to summarise:

There are many types of aerosols; they are tiny particles that can come from natural processes, but are also released due to human activities such as fossil fuel burning and pollution from cars
More manmade industrial aerosols can be found in global south countries and manufacturing hubs
Manmade aerosols cause millions of deaths each year, the smallest particles are linked to the worst health effects
Aerosols also have huge impacts for climate. Many natural aerosols, such as salt particles, reflect light and radiation, cooling the climate and mitigating the effects of global warming. However industrial aerosols, such as black carbon, absorb heat and add to net warming and can coat large reflective surfaces like ice caps, leading to faster melting and more warming.
Aerosols also impact clouds. They can make clouds more reflective, producing net cooling. However black carbon warms the surrounding atmosphere, turning clouds into a haze that suppresses precipitation.
Basically we should work to reduce black carbon emissions, which comes from fossil fuel burning.
Indoor pollution also releases aerosols and can seriously harm our health. We should make considered choices about our cleaning and personal care products, cooking, candles, building materials and heating methods in our homes. Whenever we can opt for non-airborne options (eg. solid deodorant instead of a spray), we should.