Aerosol Pollution

When aerosols create harmful impact on the environment or people, aerosol pollution has occurred. This section looks at an aerosol definition, aerosol pollution causes, aerosol pollution effects, aerosol pollution solutions and aerosol pollution facts. The latest aerosol pollution news is included at the foot of the page.

Aerosol definition: microscopic solid or liquid particles combined with a gas, often air, that enter the Earth's atmosphere through man-made or natural processes. An aerosol is defined as a colloidal system. 'Colloidal' means a solution that has particles ranging between 1 and 1000 nanometers in diameter with particles able to be dispersed evenly within a suspending solution. The resulting aerosol causes harm to the environment. Terms of measurement: 1 millimeter = 1/1000th of  a metre. 1 micrometer = 1/1000th of a millimeter. 1 nanometer = 1/1000th of micrometer.

Aerosol pollution causes

Natural causes of aerosol pollution

Most aerosols released into the atmosphere are naturally generated - about 90% according to NASA.

 

Volcanic activity emits massive volumes of ash into the atmosphere along with a cocktail of gases including sulphur dioxide. Volcanic aerosols have been a feature of the planet's ecosystem for billions of years.

 

In the world's aquatic systems, some types of microalgae produce a sulfurous gas that can be converted into sulphates in the atmopshere. Sulphates increase the acidity of the atmosphere and form acid rain.

 

Forest fires contribute large quantities of organic carbon and dust from sandstorms and sea salt from ocean spray also provide a continual supply of aerosols into the atmosphere.

 

Some types of vegetation create gases which react with other airborne elements to create aerosols.

Man-made causes of aerosol pollution

Man-made activity contributes to aerosol pollution through fossil fuel combustion, agricultural sources, the release of by-products from industrial processes and interactions with the natural surface of the earth through activities such as construction and mining. 

 

Fossil fuel combustion produces sulfur dioxide in large quantities whilst biomass burning, a method used to clear land, releases organic carbon and black carbon.

 

Forest fires are a natural cause of aerosol release but up to 90% of all forest fires are thought to be started by humans.

 

Automotive vehicles, smelters, incinerators and power plants produce sulphates, carbon, nitrates and numerous less well known particles on a large scale.

 

Within a domestic setting, fireplaces, cookers, cigarettes and candles will all produce an aerosol footprint.

 

 

Stunning NASA imagery mapping global aerosol distribution and composition: images taken between August 2006 and April 2007

Aerosols under the microscope

Sky blue image shows a salt crystal, blade-like image shows volcanic ash, spikey balls image shows pollen grains. Pictures not at same scale.

Aerosol pollution effects

Impact of aerosols on the climate

Aerosols have a major impact on the climate but the relationship is a highly complex one - scientists are working to better understand this complex relationship.

 

Atmospheric aerosols can be either solid or liquid and can be classified into 'primary aerosols' (generated as solid particles like sea salt, dust or soot) or 'secondary aerosols' (formed by chemical reactions in the atmosphere).

 

Aerosols can have direct and indirect impacts.

 

The direct impact is from the aerosols themselves both on air quality and through their interaction with sunlight and the impact this has on global temperatures.

 

Aerosols can absorb sunlight or reflect it back into space via a process known as light scattering. Light scattering depends on the size of the aerosol particle - smaller particles tend to create more random scattering patterns whereas larger particles tend to reflect light energy back in the direction it came from. Returning light energy back into space acts to cool the earth's temperatures. Large volcanic emmissions have long been associated with climate cooling.

 

Indirectly, aerosols have the ability to influence rain fall and cloud formation (aerosols can act to 'seed' cloud droplets leading to the condensation of water and formation of rainfall).

 

There is an irony that measures to reduce aerosol emissions and improve air quality may actually be contributing to global warming.

Impact of aerosols on human health

The World Health Organisation (WHO) estimates that outdoor air pollution contributes to 3 million premature deaths per year.

 

Studies have shown clear links between particulates and the following health problems:

 

Lung cancer

Decreased lung function

Acute and chronic respiratory diseases including asthma

Prematured death in those with lung and heart disease

Irregular heartbeat

Heart attacks and strokes

Decreased lung function

 

The size of aerosol particulate impacts on how the human body deals with the pollutant (refer to top of page for scale measurements).

 

Particles greater than 100 micometers (1/10th of a millimeter) are usually too large to be inhaled. Particles ranging in size from 10-100 micrometers usually get processed by the body's in-built defence mechanisms - mucus membranes in the respiratory system.

 

Particles less than 2.5 micrometers in size have a good chance of making it deep into the lungs penetrating the trachea, bronchioles and alveoli (the tiny air sacs of the lungs) although particles between 2.5 and 10 micrometers are most frequently deposited in the nose, pharynx (the membrane-lined cavity joining the wind pipe to the nose and throat) and larynx (voicebox). 

 

The smallest particles are carried in smog and smoke which is why highly-urbanised areas suffering high levels of smog and air pollution have the worst health statistics.

Aerosol global distribution patterns

The NASA map shown depicts global aerosol distribution and aerosol thickness. The map is taken from the NASA Earth Observatory site. The Earth Observatory’s mission is to share with the public the images, stories, and discoveries about the environment, Earth systems, and climate that emerge from NASA research, including its satellite missions, in-the-field research, and models. A truly great scientific resource.

 

Aerosol distribution patterns have natural and man-made explanations.

 

A heavy band of airborne salt, aided by the strong winds of the 'roaring forties' latitudes is shown as a strip nestled above the north of Antarctica. A lighter and more evenly dispersed aerosol footprint is seen on the oceans generally and is caused by salt from 'whitecap' waves and sulphates through the actions of microalgae.

 

Huge plumes of dust are shown around the world's major deserts. Industrial aerosols show up around the eastern United States and urbanised hotspots across Europe - particularly sulphates from fossil fuel emissions and black and organic carbon from vehicles.

 

However, the densest concentrations of aerosols are to be found around Bangladesh, northern India, northern Pakistan and eastern China. In China, fast-growing cities such as Beijing currently produce heavy concentrations of aerosol.

 

Aerosol distribution is greatly affected by seasonal and local weather conditions.

Aerosol pollution solutions

Government actions to reduce aerosol pollution

Governments are taking active steps to reduce aerosol production. Are they doing enough?

 

The 2016 voluntary 'Paris Agreement' has been ratified by 144 countries with the aim of reducing carbon dioxide and other greenhouse gases - the ultimate goal being to keep the post-industrial global temperature rise to below 2 degrees Celcius.

 

Government taxes and subsidies can be used to disincentivise polluting energies and incentivise clean energies like wind and solar. Policies and investments supporting cleaner transport, energy-efficient housing, power generation, industry and better municipal waste management would reduce key sources of urban outdoor air pollution.

 

Clean air measures and pollutant levels are set in legislature by governments. Levels are recorded and monitored but what are governments doing with the data?

 

A quick delve into recent media headlines suggests governments are struggling to make the targets stick.

Personal actions to reduce aerosol pollution

Fossil fuel emissions are an obvious target given the frequency of personal interactions and the environmental severity of vehicle-derived pollution.

 

Driving less, switching from diesel to non-diesel transport modes like electric, flying less, use of public transport, car pool or car-sharing, recycling and energy conservation all help reduce the personal 'carbon footprint'.

 

Airplanes have a particularly high environmental impact. A typical flight across the United States on a full plane produces 3 tons of carbon dioxide per passenger (rising substantially higher if the plane is not full). By comparison, the same journey by car doubles the figure of 3 tons but take the train and plane stats are reduced by 50%.

 

Cycling or walking not only reduces harmful emissions, it's great for your health - assuming you're not doing this in heavy traffic!

 

On a larger social scale, outdoor emissions from household coal and biomass energy systems, agricultural waste incineration, forest fires and certain agro-forestry activities (e.g. charcoal production) would reduce key rural and urban air pollution sources in developing regions.

 

Aerosol pollution news             

For the latest aerosol pollution news stories and other environmental news, check out our news page

 

The UK 'Independent' newspaper recently reported that, according to campaign groups, diesel exhaust fumes are casuing the biggest health catastrophe since the black death.

 

Nitrogen dioxide annual safe limits set by the EU were exceeded in Oxford Street, London in just two days in 2015. Again in 2016, the safe annual limits were exceeded within a couple of days.

 

A sample of other headlines claims: 'aerosol pollution kills 3.3 million a year worldwide', 'air pollution in China killing 4,000 people every day' and 'air pollution causes early death of 9,500 Londoners every year'.

 

Looking ahead to the future, a $20 million Harvard-led research project is looking at sending aerosol injections 20km up into the stratosphere to see if the predicted global-cooling effect can be geo-engineered. The aim is to establish the method as a possible solution to address future climate change. 

 

Some scientists claim the geo-engineering approach to be short-sighted and foolish. Buying time rather than addressing the underlying problem.

Aerosol pollution facts

Only 10% of aerosol pollution (by mass) is man-made

The other 90% is created through natural processes such as volcanic activity, forest fires, sandstorms and even oceanic microalgae - these organisms produce dimethylsulfide which can be transformed into sulphates in the atmosphere. 

Uusually 4 to 7 days but sometimes 20 - 100 years

The average time that most aerosols spend in the atmosphere. However, aerosols making it to the stratosphere can remain in this atmospheric layer for several years and at the extreme end of the spectrum, Chloroflourocarbons (CFS) can remain in the atmosphere for between 20 - 100 years.

3,000 kilometers

An aerosol particle travelling in the atmosphere at 5 metres/second will cover this distance in a week.

88%

A 2010 atmospheric study of North America estimated that dust from Asia accounted for 88% of total aerosol composition.

200 sensors

NASA co-sponsors a global network of over 200 ground sensors called the Aerosol Robotic Network (AERONET). These sensors are positioned all around the world and measure the amount and type of aerosols in the atmosphere.

3 million deaths per year

Aerosol pollution is accountable for 3 million premature deaths per year globally according to the World Health Organisation.

64 million tons

The annual amount of dust, pollutants and other aerosol particles circulating over North America according to the first measurement-based estimate performed between NASA and University researchers.

Air Quality News -- ScienceDaily

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