Outdoor Air Pollution: Causes, Sources, Effects & Prevention/Solutions

Outdoor Air Pollution: Causes, Sources, Effects & Solutions

There’s two main types of air pollution – indoor air pollution, and outdoor air pollution.

This guide focuses on outdoor air pollution (also called ‘ambient air pollution’).

We look at what outdoor air pollution is, along with potential causes, sources, examples, effects, and potential ways to prevent, reduce or solve it.

(Note – outdoor air pollution is it’s own atmospheric issue, separate to other issues like greenhouse gases and a changing climate)


Summary – Outdoor Air Pollution

Outdoor air pollution is the release of harmful substances (pollutants) or biological molecules into the outdoor air/atmosphere

The levels of an individual pollutant in the air, the sources they come from, and the impact they each have, differs in each town, city, country and geographic region across the world

Some pollutants are emitted directly (primary pollutants), whilst others form indirectly (secondary pollutants) from primary pollutants interacting or reacting with each other, and other compounds in the atmosphere or environment 

The main human source of outdoor air pollution is the combustion of fossil fuels (coal being one example, as well as natural gas, and oil) – in the generation of electricity, industrial activities, the operation of vehicles/cars, and so on. Waste management and agriculture are two other potential sources. In the US for example, it’s estimated that about one third of all air pollution comes from transport and vehicles

However, air pollutants also come from natural sources. Just a few examples are dust storms from open spaces of land without vegetation (which blow up dust), wild fires and forest fires, and volcanic activity

It’s also possible that air pollutants that originate indoors, may find their way into the outdoor air and become and outdoor air pollution issue. These pollutants come a range of sources such as from burning fuel (wood, kerosene, and other solid ‘dirty’ fuels) in houses for cooking and heating (Cookers, heaters, stoves and open fires) 

Air pollution can particularly be heavy around cities and heavily populated areas 

Vehicles and road transport tends to be the main source of outdoor air pollution in cities

Low to middle income communities of people where air pollution is already at unsafe levels, and groups of people living near highways, industrial sites, power plants, and other pollutant emitting sources, may be at higher risks of suffering from outdoor air pollution. People with existing health conditions, and young children under 5 may also be more heavily affected by air pollution

Some people in some countries may suffer the effects of both indoor and outdoor air pollution

We can measure the levels of outdoor air pollution with an Air Quality Index, amongst other measures. The level of each individual air pollutant on a given day, in a given area or city, can be measured, along with those levels of air quality that might mean for outdoor activity. A general health rating for real time air quality levels may also be given.

Some cities, countries and regions in the world are far more polluted and have much worser air quality than others (for various reasons)

India, Pakistan, China, and parts of Africa feature in the top countries and regions in the world for particulate matter (PM) air pollution levels

Parts of the Middle East and South East Asia also rate poorly for general air pollution levels in some areas

Fine particulate matter (PM2.5) is probably the most harmful air pollutant to human health – even contributing to premature death

Ground-level ozone is another air pollutant that can cause noticeable health issues for human (according to who.int)

Some of the cities with the worst PM2.5 pollution levels are in India

Some organisations highlight air pollution as the greatest environmental risk to human health right now (but a changing climate may be the biggest risk in the future)

Air pollutants have the ability to contribute to premature deaths, and contribute to the development of human health conditions and diseases. But, they can also cause issues for the general environment, wild life, economy, and other sectors of society too

There’s some question over the reporting of deaths attributable to air pollution – air pollution for example exacerbates pre-existing cardiorespiratory illnesses. So, the question might be how much air pollution really contributes to premature death in these people – is it significantly, or not significantly? Additionally, what impact does different concentrations of air pollution really have on healthy people without pre-existing health problems?

Cleaner energy and electricity sources (like renewables), and cleaner vehicle technology (developing electric battery, hybrid, hydrogen and other alternative fuel vehicle types) could go a long way to helping address outdoor air pollution. Anything which decreases the burning ‘dirty’ energy sources and fossil fuels seems a good starting point

There are cities worldwide that have implemented some solutions to outdoor air pollution, and have already experienced a reduction in pollutants.

Air pollution can vary from day to day, and year to year in different geographic location (particularly if air quality measures are implemented in an area). Real time air quality indexes can give an idea of the concentration of a particular air contaminant in a particular geographic area, on a particular day. Weather can play a role in air pollution levels (winds for example can blow pollutants in and out of an area)

Overall, several sources that provide info on air pollution levels over time indicate that air pollution is generally declining globally over the past few decades in many countries. For example the US has seen a decrease in PM 10 and 2.5 from 1980 to 2017. However, in some low to middle income and developing cities and countries, it is increasing

Given that the global population is increasing, the % of the global population experiencing premature death attributable in some way to outdoor air pollution appears to be declining (even if total numbers of premature deaths are staying roughly the same or slightly increasing annually)


What Is Outdoor Air Pollution? 

Outdoor air pollution might be broadly classified as:

  • The release of harmful substances (such as gases), particles (organic and inorganic) and/or biological molecules into the outdoor air

The impact can be on humans and human health, wild life and living organisms, plant life and the environment, and the economy.

Air pollution can also impact aesthetics.


Primary Outdoor Air ‘Pollutants’ (Main Types Of Air Pollutants)

The primary outdoor air pollutants are:

  • particulate matter (PM10, & also PM2.5) (small suspended particles of varying sizes)
  • sulphur dioxide (SO2)
  • nitrogen dioxide (NO2)
  • ozone (O3)
  • carbon monoxide (CO)
  • and volatile organic compounds (VOCs)

These pollutants are usually emitted directly.


Primary vs Secondary Outdoor Air Pollutants

In addition to primary air pollutants, secondary air pollutants can form.

Secondary air pollutants usually form from primary air pollutants reacting or interacting in some way with each other, with atmospheric compounds, or in some other way.


  • Some … [air] pollutants are emitted singularly, but some form when two or more pollutants mix together.
  • For example, SO2 and NOx can react in the Earth’s atmosphere to form particulate matter (PM) compounds

– OurWorldInData


Other examples of secondary pollutants forming are … 

  • Oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain
  • Particulates created from gaseous primary pollutants and compounds in photochemical smog
  • Ground level ozone (O3) formed from NOx and VOCs
  • Peroxyacetyl nitrate (C2H3NO5) – similarly formed from NOx and VOCs

– wikipedia.org


Outdoor Air Pollutants vs Upper Atmosphere Greenhouse Gases

There’s a difference between outdoor air pollutants, and upper atmosphere greenhouse gases from a technical perspective (they deal with separate environmental and scientific issues):

  • Note that carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and synthetic gases, such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs) are more likely to be treated as upper atmosphere/ozone greenhouse gases

– ClimateChangeAustralia.gov.au


Man Made/Human Sources & Causes Of Outdoor Air Pollutants

Human sources may include:

  • Burning of fossil fuels [like coal, oil and natural gas] in electricity generation, transport, industry and households
  • Industrial processes and solvent use, for example in the chemical and mining industries
  • Agriculture
  • Waste treatment

– eea.europa.eu


  • Increased urban power demand, which drives up power plant emissions
  • [increased] use of private motor vehicle transport
  • [energy inefficient] Building heating and cooling systems
  • Industrial emissions
  • … the incineration of solid waste
  • … [the] burning of agricultural waste in peri-urban areas

– who.int


  • Examples [of sources of outdoor air pollution might] include petrol and diesel vehicles … emissions from power generation, factories and business, and agriculture.

– blf.org.uk


  • … most [outdoor air pollutants] are generally linked to human sources like fuel combustion and industrial (factories, business etc.) activities; pollutants are released as by-products of these processes

– OurWorldInData



  • … in towns and cities, the main source of air pollution is road transport

– blf.org.uk


Natural Sources & Causes Of Outdoor Air Pollutants

Natural sources may include:


  • … volcanic eruptions, windblown dust, sea-salt spray and emissions of volatile organic compounds from plants

– eea.europa.eu


  • Other more minor sources [of air pollutants] may include smoke from bushfires, windblown dust, and biogenic emissions from vegetation (pollen and mould spores)

– NSW Government



Different Air Pollutants – Each Have Different Sources, Effects, & So On

Each air pollutant is made up of different chemicals, can come from different activities and sources, and can have different effects on human health.


Particulate Matter (PM10, & PM2.5) As An Air Pollutant

What PM Is, & What’s It Made Of?

  • Particulate matter … is extremely small solid particles and liquid droplets suspended in air.
  • Particulate matter can be made up of a variety of components including nitrates, sulphates, organic chemicals, metals, soil or dust particles, and allergens (such as fragments of pollen or mould spores) (Health.NSW.Gov.Au) 


Where It Comes From (Sources)

  • Particle pollution mainly comes from motor vehicles, wood burning heaters and industry (Health.NSW.Gov.Au)
  • Most particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries and automobiles. Some are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires (EPA.gov)
  • The friction of brakes and tyres on the road also creates particulate matter (blf.org.uk)


Pollution Trends

  • There’s been a 41% decrease in the particulate matter 2.5 national average in the US from 1980 to 2017. There’s also been a 34% decrease in the particulate matter 10 national average in the US from 1980 to 2017 (EPA.gov) 
  • Particle pollution is a major air quality issue in Australia (Environment.gov.au)



  • Studies have linked exposure to particle pollution to a number of health problems including respiratory illnesses (such as asthma and bronchitis), cardiovascular disease [and cancer]. These effects are often more pronounced for vulnerable groups, such as the very young and the elderly. Particle pollution is the major cause of reduced visibility (Environment.gov.au)


Ozone As An Air Pollutant

Where It Comes From (Sources)

  • Tropospheric, or ground level ozone, is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). It is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight (Epa.gov)


Pollution Trends

  • There’s been a 32% decrease in ground level ozone national average in the US from 1980 to 2017 (EPA.gov)



  • Ground level ozone can cause the muscles in the airways to constrict, trapping air in the alveoli. This leads to wheezing and shortness of breath. People with asthma and children, older adults, and people who are active outdoors, especially outdoor workers are most at risk. There are other health issues ground ozone can cause as well (EPA.gov)


Nitrogen Dioxide As An Air Pollutant

Where It Comes From (Sources)

  • Comes from the burning of fossil fuels like coal, oil and gas.
  • Most of the nitrogen dioxide in cities comes from motor vehicle exhaust (about 80%) 
  • Can also come from electrical storms via electrical discharge, and plants, soil and water – although only a very small amount comes from these natural sources.
  • Other sources of nitrogen dioxide are petrol and metal refining, electricity generation from coal-fired power stations, other manufacturing industries and food processing.
  • Unflued gas heaters and cookers are the major sources of nitrogen dioxide in Australian homes 

– Environment.gov.au


Pollution Trends

  • There’s been a 60% decrease in the US national average of nitrogen dioxide from 1980 to 2017 (EPA.gov)
  • In the US, there was 12,412 thousand tons of nitrogen oxide emissions in 2014 ( Statista.com)
  • In Australia, since the early 1990s, even the highest levels of nitrogen dioxide reached in most Australian towns and cities are thought to be acceptable for humans (Environment.gov.au)



  • Causes increased likelihood of respiratory problems. Nitrogen dioxide inflames the lining of the lungs, and it can reduce immunity to lung infections. This can cause problems such as wheezing, coughing, colds, flu and bronchitis. People with asthma, and in particular children and older people are most at risk (Environment.gov.au)


Carbon Monoxide As An Air Pollutant

Where It Comes From (Sources)

  • It is a product of combustion of fuel such as natural gas, coal or wood. Vehicular exhaust contributes to the majority of carbon monoxide let into our atmosphere. In 2013, more than half of the carbon monoxide emitted into our atmosphere was from vehicle traffic and burning one gallon of gas will often emit over 20 pounds of carbon monoxide into the air (Wikipedia/Union Of Concerned Scientists)
  • Is produced in the incomplete combustion of carbon-containing fuels, such as gasoline, natural gas, oil, coal, and wood. The largest anthropogenic source of CO in the United States is vehicle emissions (NAP.edu)


Pollution Trends

  • There’s been a 84% decrease in the carbon monoxide national average in the US from 1980 to 2017 (EPA.gov)
  • In most Australian towns and cities, the levels of carbon monoxide in air are below levels that are hazardous for human health. Only larger cities, like some capital cities, have the potential to have harmful levels of carbon monoxide (Environment.gov.au)



  • Increased levels of carbon monoxide reduce the amount of oxygen carried by haemoglobin around the body in red blood cells. The result is that vital organs … do not receive enough oxygen to work properly.
  • For healthy people  … a small increase in the level of carbon monoxide [has only minor side effects – such as trouble concentrating]
  • People with heart problems are … [are] at greater risk of heart attack.
  • Children and unborn babies are particularly at risk 

– Environment.gov.au


Sulphur Dioxide As An Air Pollutant

Where It Comes From (Sources)

  • About 99% of the sulfur dioxide in air comes from human sources. The main source of sulfur dioxide in the air is industrial activity that processes materials that contain sulfur, e.g. the generation of electricity from coal, oil or gas that contains sulfur. Some mineral ores also contain sulfur, and sulfur dioxide is released when they are processed (Environment.gov.au)
  • Sulphur dioxide can also be produced by volcanoes (Wikipedia.org)


Pollution Trends

  • In the US, sulfur dioxide emissions have been decreasing … (Statista.com)
  • Air quality regarding sulfur dioxide in improving in the US (EPA.gov)
  • In Australia … the highest concentrations of sulfur dioxide in the air are found around petrol refineries, chemical manufacturing industries, mineral ore processing plants and power stations … But, sulfur dioxide levels in air are not generally a problem in Australia (Environment.gov.au)



  • Affects people when it is breathed in. People most at risk [of developing problems] are those with asthma or breathing conditions. It irritates the nose, throat, and airways to cause coughing, wheezing, shortness of breath, or a tight feeling around the chest (Environment.gov.au)


Volatile Organic Compounds As Air Pollutants

What They Are

  • VOCs comprise volatile hydrocarbons and other organic molecules released into the atmosphere (APIS.ac.uk)
  • Common VOCs include acetone, benzene, ethylene glycol, formaldehyde, methylene chloride, perchloroethylene, toluene and xylene (SOE.environment.gov.au)
  • There are different VOC’s such as Butadiene, Dichlorobenzene, Benzene, Chloroform, Methylene Chloride, m,p-Xylene, o-Xylene, and Toluene.


Where They Come From (Sources)

  • VOCs … may have biogenic or anthropogenic sources. In the UK it is estimated that less than 5% of the VOCs (2.3 million tonnes per year, expressed in terms of carbon) emitted into the atmosphere are emitted from vegetation. The rest comes from transport, including distribution and extraction losses (50%), solvent use (30%) and other industrial processes (15%). Road transport alone accounts for 30% of VOC emissions (APIS.ac.uk)
  • Pesticides that are sprayed on to fields and used to fumigate soil can give off chemicals called volatile organic compounds, which can react with other chemicals and form a pollutant called tropospheric ozone. Pesticide use accounts for about 6 percent of total tropospheric ozone levels (wikipedia.org)


Pollution Trends

  • DEC.ny.gov has done some studies on the levels of these VOCs across the NY state. VOCs particularly affect indoor air quality—concentrations of many VOCs are consistently higher indoors (up to 10 times higher) than outdoors ( SOE.environment.gov.au)



  • Different VOCs have different health effects, and range from those that are highly toxic to those with no known health effect. Breathing low levels of VOCs for long periods of time may increase some people’s risk of health problems. Several studies suggest that exposure to VOCs may make symptoms worse in people who have asthma or are particularly sensitive to chemicals (SOE.environment.gov.au)


Impact Of Outdoor Air Pollution On Human Health

There’s two main effects outdoor air pollution can have on human health:

  • Premature deaths 
  • Contribution to health conditions and diseases like respiration conditions, cancers, lung disease, cardiovascular disease, and so on

Fine particulate matter and ozone might be two of the most detrimental air pollutants.


  • The World Health Organisation (WHO) highlights air pollution as the greatest environmental risk to human health [note that this is based on current risk, and that longer-term environmental threats such as climate change may exceed this in the future] 

– OurWorldInData/WHO


  • Some 3.8 million premature deaths annually are attributed to outdoor (ambient) air pollution.
  • About 80% of those deaths are due to heart disease and stroke, while another 20% are from respiratory illnesses and cancers related to exposure to fine particulate matter (PM2.5)
  • … Ground-level ozone … is another health risk, raising rates of asthma and chronic respiratory illness as well as other sorts of breathing problems and reduced lung function.
  • Ozone also reduces crop productivity in peri-urban areas, where ozone levels may often be heaviest.

– who.int


What Is The Most Harmful Outdoor Air Pollutant For Humans & Human Health?

  • … fine particulate matter (PM2.5) [is] the most health-harmful air pollutant [and, a major reason is that it can cause premature death in humans exposed to it via respiratory illnesses and cancers] 
  • Ground-level ozone … is another health risk, raising rates of asthma and chronic respiratory illness as well as other sorts of breathing problems and reduced lung function

– who.int


The three key sources of air pollution deaths are from the indoor burning of solid fuels (indoor air/household pollution), exposure to ambient outdoor ozone (O3), and ambient outdoor particulate matter (PM) pollution.

In 2015, deaths from these 3 pollutants were as follows (as total %’s):

  • Ozone – 3.45%
  • Particulate Matter – 57.54%
  • Indoor Air Pollution/Solid Fuels – 38.72%

– OurWorldInData


Number Of Human Deaths Outdoor Air Pollution Contributes To Per Year

– who.int


  • Some 3.8 million premature deaths annually are attributed to outdoor (ambient) air pollution.

– who.int


  • The World Health Organization estimate that 3 million people die from ambient outdoor pollution every year

– ourworldindata.org


Outdoor Air Pollution vs Indoor Air Pollution: Comparing Contribution To Premature Human Deaths

According to ourworldindata.org:

  • ‘It’s estimated [air pollution contributes to] seven million premature deaths every year (4.3 million from ambient outdoor pollution, and 2.6 from households)


According to who.int:

  • Exposure to outdoor air pollution results in 4.2 million deaths every year
  • Exposure to smoke from dirty cookstoves and fuels in households indoors results in 3.8 million deaths every year 


Challenges In Reporting Deaths Attributable To Outdoor Air Pollution

It is important to emphasize the challenges in reporting on deaths attributable to air pollution:

  • A ‘death’ from air pollution is defined as someone who dies prematurely (could be in the range of months or years) than would be expected in the absence of air pollution] 
  • In many cases, air pollution exacerbates pre-existing cardiorespiratory illnesses—individuals suffering from asthma, for example, are particularly vulnerable.

– OurWorldInData/StateOfGlobalAir.org


Environmental Impact Of Outdoor Air Pollution

  • [In addition to human health] Outdoor air pollution can [also] damage ecosystems, food crops and the built environment 

– OurWorldInData/WHO


It’s also common knowledge that air pollutants like nitrogen dioxide, and sulfur dioxide mix with other pollutants and compounds, and water, to contribute to acid rain, and this contributes to the acidification of natural water sources and soils.


Economic Impact Of Outdoor Air Pollution 

  • Air pollution [as a whole] costs the world economy $5 trillion per year as a result of productivity losses and degraded quality of life

– wikipedia.org


The Relationship Between Air Pollution And Agriculture/Food Production

There is a relationship between food production and air pollution – they both have the ability to contribute to and impact each other. 


  • Agricultural air pollution comes mainly in the form of ammonia (NH3), which enters the air as a gas from heavily fertilized fields and livestock waste. It blows in over cities, reacts with emissions of oxides of nitrogen (NOx) and sulphur (SO2)  from traffic and industry, and leads to the formation of so-called secondary particles

– airclim.org


  • Agriculture is the single largest contributor of ammonia pollution as well as emitting other nitrogen compounds … This affects soil quality and thus the very capacity of the soil to sustain plant and animal productivity
  • … there is increasing evidence that food production is also threatened by air pollution. Ozone precursor emissions (nitrogen oxides and volatile organic compounds) are of particular concern for global food security as these compounds react to form ground-level ozone. This, in turn, penetrates into the plant structure and impairs its ability to develop

– unece.org


  • In India in 2014, it was reported that air pollution by black carbon and ground level ozone had reduced crop yields in the most affected areas by almost half in 2011 when compared to 1980 levels

– wikipedia.org


How Many Cities Worldwide Have Polluted Outdoor Air?

  • [from a survey with a sample size of] 4300+ cities worldwide, only 20% of the urban population surveyed live in areas that comply with WHO air quality guideline levels for PM2.5.
  • Average particulate air pollution levels in many developing cities can be 4-15 times higher than WHO air quality guideline levels, putting many at risk of long-term health problems

– who.int


Which People Might Be Most At Risk From Outdoor Air Pollution?

Some of the people that might be most affected might be:

  • People living in areas close to air pollutant emitting sources
  • People in developing cities
  • People in low to middle income areas
  • People with pre existing health conditions (particularly respiratory conditions)
  • Children
  • Possibly the elderly


  • [ … neighbourhoods, cities and people might be at more risk if they are] sited near environmental hazards, such as highways, power plants, and industrial complexes

– who.int


Lower income and developing areas, as well as children might be most at risk:

  • The problem is even more acute in the developing world … Children under age 5 in lower-income countries are more than 60 times as likely to die from exposure to air pollution as children in high-income countries

– wikipedia.org


Countries, Cities & Regions With The Most Outdoor Air Pollution

  • Regions with the highest particulate matter pollution include cities in India, Pakistan, China, and parts of Africa feature in the top regions
  • 11 of the 12 cities with the worst PM2.5 pollution are in India
  • China, and parts of the Middle East, Africa & South East Asia also have cities with poor outdoor air pollution levels

You can read more about countries, cities and regions where outdoor and indoor air pollution might be the worst in this guide.


According to OurWorldInData are:

  • … majority of pollution-related deaths are in Asia – South, Southeast and East Asia alone accounted for nearly 3 million in 2016.

You can read more about air pollution related deaths by type, country and more here (ourworldindata.org)


  • The most polluted city in a 2016 report, Zabol in Iran, has had its pollution level cut fourfold in the latest version of the database, and now appears to be cleaner than Australia’s capital Canberra
  • Based on the amount of particulate matter under 2.5 micrograms found in every cubic metre of air, Indian regions and cities are the most polluted in the world in 2018, followed by China. Some places in Saudi Arabia are also highly polluted

– WeForum.org


  • Egypt, Mauritania, Libya, Niger, Cameroon and Pakistan also show high mean annual averages of migrograms per cubic meter of PM 2.5 air pollution in 2015 
  • Some of the least polluted countries in the world in terms of mean annual averages of migrograms per cubic meter of PM 2.5 air pollution in 2015 are Kirbati, Samoa, Brunei, Solomon Islands, Sweden, Finland, Australia, Canada, United States, New Zealand, Norway, Spain, and Iceland. 
  • It’s important to note that there is an additional key factor at play, which has some impact on pollution concentrations over time and space: the weather. Local weather conditions, and seasonal and weather patterns have an important influence on the year-round fluctuations in exposure levels reported in each place

– OurWorldInData


How To Measure Outdoor Air Pollution (Air Quality Index), & What Level Of Air Quality Is Safe?

The air quality in a particular geographic location gives an indication of how safe the air is to breathe in that area.

An Air Quality Index is a common measure of air quality in several countries.

The AQI usually monitors and reports on the levels of individual air pollutants in the air, and provides up to date health ratings of air pollutant levels. 

There are large online global sites that keep track of the Air Quality Index (such as WAQI, Airnow and AQICN), and individual governments in countries and cities also have their own tracking programs.

The NSW Government in Australia for example has their own air monitoring networks where they measure particles (PM10, PM2.5), sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2) and visibility. 

The major pollutants that are measured in the air in the US are ozone, particulate matter (PM2.5 and PM10), carbon monoxide, and sulfur dioxide.

Other countries may use other air quality/air pollutant indexes to measure air quality, such as the Air Quality Health Index (Canada), the Air Pollution Index (Malaysia), and the Pollutant Standards Index (Singapore) + others. Some of these other countries measure nitrogen dioxide as well.

Air Quality sites usually list key indicators such as main air pollutants of concern, what to do in the event of certain levels of air pollution, and more.

Read more about air pollution and air quality in this guide.


How To Reduce Outdoor Air Pollution (Potential Solutions)

There are cities worldwide that have implemented solutions to air pollution, and have already seen a reduction in air pollutants.

Cities in Spain, Portugal, Canada, Colombia and South Korea are some of the locations that have seen some sizable reductions.

Some of the solutions that have enabled these cities to achieve these reductions involve:

  • Adding plantlife, tree cover and greenery
  • Reducing the use of personal vehicles (especially those that use fossil fuel like petrol and diesel)
  • Substituting some fossil fuel vehicles with electric vehicles
  • Introducing better public transit systems
  • Encouraging the use of bikes and car sharing
  • Retrofitting buildings with more energy efficient designs and equipment
  • Introducing programs to encourage the saving of energy


Other potential solutions may include:

  • Using clean energy for electricity generation, households, business and industrial activity, and so on
  • Reducing emissions from the agricultural sector
  • Reducing emissions from the waste management sector
  • Reducing the total number of vehicles used in cities, or the per capita number of vehicles
  • Increasing the fuel efficiency of vehicles, and reducing emission rates
  • Using air pollution control devices in industry and transport – particulate control (precipitators, baghouses, scrubbers, collectors), scrubbers, NOx control, VOC abatement, Acid gas control, mercury control, dioxin control and so on


Where it is hard to reduce emissions significantly from or in any one activity, process or geographic locations, people may look to move to areas where the air is cleaner and better quality for breathing in. For lower income and poorer neighborhoods and groups of people, this is obviously a major issue they may not be able to address themselves, and they will need some type of external (government assistance, private project funding, or something else) to help them with a viable solution to air pollution problems that could be a threat to their health if they stay where they are.


Solutions Specifically To Reduce Air Pollution From Transport

Some specific solutions for transport pollution might involve:

  • Focus on cities and heavily populated areas, or areas dense with people as places where the biggest improvement in pollution reduction could take place (as this is where a lot of transport pollution happens)
  • Focus on the main polluting sources of transport – which tend to be road transport such as cars and trucks. But, in addition to road, look at reductions air, water, rail, and so on
  • Consider the impact of freight/shipping transport pollution, and not just personal transport [when looking at greenhouse gas emissions, freight transport can make up as much as 41% of emissions in some countries – so, it’s likely air pollution numbers could be similar]
  • Consider cutting down consumption of fossil fuels and consumption related to car usage as the main strategy, compared to simply trying to convert to electric transport and alternative fuel transport. Reducing the total number of vehicles, reducing distance travelled, and reducing the amount of fuel being used per year will all likely lower emissions more significantly than switching to alternate fuel sources
  • One way the above could be achieved is with more focus on walking, riding and other human powered forms of transport
  • Focus on pollution rates per passenger mile travelled as another key statistic – different modes and models of transport have different rates to be aware of (fuel and passenger efficiency of transport is important in this regard)
  • Consider how hybrid, electric vehicles, hydrogen vehicles and other alternative fuel vehicles can be used most effectively, and how they can become more feasible to use long term
  • Consider how effective redesigns and new features like regenerative braking and fuel efficiency can be
  • Encourage better city planning – re-designing inner city and urban area for less congestion, less built up traffic, more efficient driving without as much stopping, starting, braking and acceleration
  • Consider how urban and CBD areas can be more friendly to walking, biking and public transport
  • Focus on the operation/use stage of transport, as this is where a significant portion of pollution occurs. But, also look for opportunities to reduce pollution at the other stages such as mining and sourcing of materials, fabrication and manufacture, disposal and recycling etc. for opportunities for pollution reduction
  • Maintain and improve vehicle emission and air quality standards, policies, regulations and legislation 
  • Look outside of the transport sector for more effective ways to reduce pollution – for example, is it better or more cost effective to focus on reducing pollution from stationary power plants that run on fossil fuels than cars and vehicles? Some scientists and researchers think so
  • Inform and educate the public on how they can personally reduce pollution and emissions buy using cars less, driving less, maintaining their vehicles, buying ‘greener’ cars and knowing what to look for etc. And, have some way for governments or third party organisations to relay to the public progress of transport pollution over time


Other options and solutions might include …


  • Pollution control technology (on cars and trucks)…
  • Regulations require technology that reduces the amount of smog-forming pollution and carbon monoxide coming from a vehicle’s tailpipe in both petrol and diesel cars
  • Burning less fuel/fuel efficiency…
  • Car fuel efficiency must meet the fuel economy standard for a particular country or state
  • Other technology contributes to more efficiency such as efficient engines and transmissions, improved aerodynamics, better tires, and high strength steel and aluminum
  • Zero emission vehicles…
  • In addition to renewables, there’s also cleaner fuels than traditional gasoline such as natural gas, methanol, ethanol etc.
  • Keeping a car maintained

– pollutionissues.com


  • Strong federal and state policies also help. Vehicle emission standards have helped cut pollution from cars and trucks by about 90 percent since 1998, with further improvements coming from the Tier 3 standards.
  • Future emissions reductions from trucks and other freight sources are essential for meeting air quality standards and protecting the health of those who live and work close to ports, rail yards, and freight corridors.

– ucsusa.org


  • In Melbourne, air quality has been getting better
  • Regulations help with this
  • Modifications to vehicle exhausts help because they decrease emissions and air contaminants

– epa.vic.gov.au


  • Building major railway transportation projects along major highways and transferring people from car travel to train travel could have huge savings on air pollution and emissions

– wikipedia.org


  • Reduce the number of old, poorly designed and not maintained vehicles on the road

– sciencing.com


General Air Pollution Trends

As a % of the overall global population, death rates attributable to air pollution look to have decreased over the last few decades.

However, it does also look like in some low to middle income countries, air pollution levels have become worse in the last few years as well. 


  • Death rates from air pollution—across countries of all income levels—have shown a general decline over the last few decades … [usually] by more than 50 percent.
  • Globally, it’s estimated that outdoor air pollution resulted in 4.2 million deaths in 2016; this represents an increase from 3.4 million in 1990 [however, it should be considered that the global population has increased in that time]

– ourworldindata.org


  • [in some] low to middle income cities … air pollution has become worse over the past several years

– who.int


OurWorldInData also shows levels of the different levels of different air pollutants over the years. You can see that there was a huge increase up until 1970/1980 for most regions, followed by a steady decline (ourworldindata.org)

Although some pollutants have decreased since 1980, there has been small increases or flatlines in progress in the years before 2017. Particulate matter 10 levels are one example of this – with minimal progress being made since 2004.


These People Are Perhaps Most Impacted By Outdoor Air Pollution …

  • Some 25% of households in less-developed cities are reliant on solid fuels for cooking. Those households face a double air pollution burden – polluted air outdoors as well as the polluted air inside the home.

– who.int



1. Hannah Ritchie and Max Roser (2018) – “Air Pollution”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/air-pollution’ [Online Resource]

2. http://www.health.nsw.gov.au/environment/air/Pages/outdoor-air-pollution.aspx

3. https://www.blf.org.uk/support-for-you/air-pollution/where-does-it-come-from

4. https://www.environment.nsw.gov.au/topics/air/monitoring-air-quality

5. http://www.environment.gov.au/protection/publications/factsheet-sulfur-dioxide-so2

6. http://www.environment.gov.au/protection/publications/factsheet-nitrogen-dioxide-no2

7. https://en.wikipedia.org/wiki/Air_pollution

8. https://archive.epa.gov/ozonedesignations/web/html/faq.html#whatisozone

9. https://www.climatechangeinaustralia.gov.au/en/climate-campus/climate-system/greenhouse-gases/

10. http://www.health.nsw.gov.au/environment/air/Pages/particulate-matter.aspx

11. https://www.epa.gov/pm-pollution/particulate-matter-pm-basics#PM

12. https://www.nap.edu/read/10378/chapter/3

13. http://www.apis.ac.uk/overview/pollutants/overview_VOCs.htm

14. https://www.statista.com/statistics/501303/volume-of-sulfur-dioxide-emissions-us/

15. https://www.epa.gov/air-trends/sulfur-dioxide-trends

16. https://www.epa.gov/air-trends/nitrogen-dioxide-trends

17. https://www.statista.com/statistics/501284/volume-of-nitrogen-oxides-emissions-us/

18. https://www.epa.gov/air-trends/ozone-trends

19. https://www.epa.gov/air-trends/carbon-monoxide-trends

20. https://www.epa.gov/air-trends/particulate-matter-pm25-trends

21. https://www.epa.gov/air-trends/particulate-matter-pm10-trends

22. https://www.dec.ny.gov/chemical/66472.html

23. https://www.epa.gov/ozone-pollution/health-effects-ozone-pollution

24. http://www.environment.gov.au/protection/publications/factsheet-carbon-monoxide-co

25. https://soe.environment.gov.au/theme/ambient-air-quality/topic/2016/volatile-organic-compounds

26. https://www.weforum.org/agenda/2018/05/these-are-the-worlds-most-polluted-cities

27. https://www.who.int/sustainable-development/cities/health-risks/air-pollution/en/

28. https://www.eea.europa.eu/themes/air/air-pollution-sources

29. https://www.bettermeetsreality.com/how-to-reduce-solve-air-pollution-with-examples-of-cities-that-have-already-done-it/

30. https://www.bettermeetsreality.com/countries-cities-with-the-worst-ambient-outdoor-air-pollution-household-indoor-air-pollution/

31. https://www.who.int/airpollution/en/

32. https://www.bettermeetsreality.com/what-level-of-air-quality-pollution-is-safe-for-us-to-breathe-live-in/

33. https://www.unece.org/environmental-policy/conventions/envlrtapwelcome/cross-sectoral-linkages/air-pollution-and-food-production.html

34. http://www.airclim.org/acidnews/agriculture-major-cause-air-pollution

35. https://www.bettermeetsreality.com/impact-of-transport-vehicles-on-the-environment/

36. https://en.wikipedia.org/wiki/Environmental_impact_of_pesticides#Air

37. http://www.pollutionissues.com/Ve-Z/Vehicular-Pollution.html

38. https://en.wikipedia.org/wiki/Environmental_impact_of_transport

39. https://www.ucsusa.org/clean-vehicles/vehicles-air-pollution-and-human-health#.XGIFv-IzbR0

40. https://www.epa.vic.gov.au/your-environment/air/vehicle-emissions-and-air-quality

41. https://sciencing.com/effects-car-pollutants-environment-23581.html

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