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Daily Air Quality Index - This index is updated daily and can help to inform decisions about whether you or your family should partake in outdoor activities. This is a helpful tool for those who are concerned about their exposure to pollutants, and includes guidelines for those who have respiratory and cardiovascular difficulties.

Days with Exceedences - This metric is comprised of the number of days during which the air quality was worse than the standards deemed acceptable.

Department for Environment, Food & Rural Affairs (DEFRA) - DEFRA is charged with issues related to food, farming, the environment, and more. They are involved with air quality initiatives and produce research. 

Diffusion Tube Samplers - Diffusion tubes can be used to identify areas with high levels of nitrogen dioxides by drawing air in. 

Dioxins - This group of chemicals can be toxic to humans if they are exposed to high levels, and they can remain in the body for a long time. Dioxins are considered “persistent organic pollutants” which means that they are persistently present. Industrial pollution can release dioxins into the air, lessening air quality and jeopardizing human health.

Dispersion model - Air dispersion modelling is one way of measuring air pollution which can be particularly useful for industrial sources of pollution, because they can be a tool for conducting risk assessments and assessing environmental impact. 

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Ecosystem - An ecosystem is an interconnected group of animals, plants, and other organisms which exists in a geographic area. Ecosystems can be incredibly diverse, but they can also be fragile, and disrupting an ecosystem can have major consequences. Processes like deforestation are troublesome from a biodiversity and air quality perspective: as trees are removed, animals lose their homes and their ecosystem may be threatened. Tree removal also causes trees that have been cut down to stop absorbing carbon dioxide from the air and to release their stored carbon, which can lead to increased carbon dioxide levels in the atmosphere which contributes to climate change. 

Electric vehicle - EVs use alternative energy sources in their operations, which may include renewable sources like wind, solar, and water power. Because they can reduce the need to burn fossil fuels, less pollution is emitted which is beneficial for air quality. 

EMEP (Co-operative Programme for Monitoring and Evaluation of the Long-Range Transmission of Air pollutants in Europe) - Also known as the “European Monitoring and Evaluation Programme”, EMEP works on transboundary air pollution issues using science and policy. 

Emissions - Burning fossil fuels or other energy-related activities often results in the production of particles that are subsequently "emitted” into the air. These particles are hence known as emissions.

Emission Factor - An emission factor can help to clarify the greenhouse gas emissions that are associated with the use of a resource.

Emission Inventories - This metric communicates the total quantity of pollutants that have been emitted during a specified period (commonly a year). This can help scientists and policymakers understand the sources of pollution so that they can better create solutions to address air quality concerns. 

Environmental justice - This term refers to environmentalism that is diverse, inclusive, and sensitive to the needs of varied communities. When addressing air quality issues, it is necessary to create solutions that uplift all people and align with the goal of equity for all. One framework for assessing environmental justice is the Three Pillars of Sustainability.

European Union Directives - These legislative acts create goals, and member countries are expected to meet them, but the countries themselves can create the strategy for executing these goals. 

Expert Panel on Air Quality Standards (EPAQS) - Independent panel created to advise the Government on issues related to air quality and pollution. 

Energy efficiency - Can be used to describe the amount of energy that is used to power a certain appliance, home, or other item, and can also refer to the pursuit of reducing the amount of energy necessary to accomplish various energy goals. 

Exceedence - Refers to a time period during which the air quality level barely meets, or fails to meet, acceptable pollution concentration standards. 

Externality - An externality is an effect that is imposed upon a third party by the actions of another individual. For example, when a person decides to drive their car, they are contributing to air pollution and therefore imposing that pollution on others. 

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Filter Dynamics Measurement System (FDMS) - Tool used to measure the composition of particulate matter in order to gauge air quality. 

Fine particles (also known as PM_2.5) - These particles are smaller than coarse particles and larger than ultrafine particles. 

Fluorocarbons - Certain chemicals containing carbon and fluorine which contribute to global warming and can be toxic. 

Formaldehyde - This chemical is used for many purposes, in science, textiles and other materials, and a preservative. In the short term, it can cause coughing, burning sensations, wheezing, skin irritation and more. Though its long term effects are not as well known, there is some evidence that it may be carcinogenic. 

Fossil fuels - These substances are naturally occurring from the fossils of ancient organisms and include natural gas, petroleum, and coal. When burned, they produce carbon dioxides that contribute to global warming and can also pollute the air. 

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Global Action Plan - Global Action Plan is a charity that's working for a green and thriving planet where we can live happily without ruining the Earth we depend on. We do this by making connections between what's good for people and good for the planet. We're the people behind Clean Air Day, the UK's largest air pollution campaign. We work with young people on reducing consumerism and increasing wellbeing - what's good for us is often greener too. And we bring business and young people together to work on a sustainable future - helping young people develop the skills and knowledge to tackle environmental issues is good for the planet and for everyone's future too.

Global Warming - The gradual, long-term increase in the Earth’s temperature. The burning of fossil fuels contributes to this effect, because the carbon dioxide this burning process produces traps heat inside Earth’s atmosphere. Global warming is a component of climate change, which refers to the overall long-term changes in Earth’s climate that have been largely caused by carbon emissions. 

Gravimetric Equivalent PM₁₀ Data - Measurements of particulate matter that have been adjusted so that they can be compared properly.

Greenhouse Gases - Gases (like carbon dioxide, methane, CFCs, NOx, and more) that contribute to the greenhouse effect; these gases form a sort of insulation around the Earth’s atmosphere, and when heat comes in from the sun it is difficult for the heat to escape after reaching Earth to escape. Over time the excess heat trapped in the atmosphere can cause an increase in the overall temperature of Earth to increase, leading to disruptions in our climate (this “Greenhouse Effect” is a major contributor to climate change).  

Greening - The process of transforming something to be more environmentally sustainable. This can include physical entities like buildings and cities, but it can also refer to changes one makes to their lifestyle. 

Ground level ozone - Ozone that occurs near the ground (where people live, walk, and breathe) can be a pollutant because it can cause problems to one’s lungs when inhaled. If continually inhaled over a long period of time, ground level ozone can cause permanent damage to one’s lungs. VOCs and NOx can be transformed into ozone when they are hit by UV light from the sun. 

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Hazard - A potential danger or risk. 

HEPA (high-efficiency particulate air) filter - A standard used to measure the efficiency of an air filtering system. These filters are highly efficient and can be used in hospitals, homes, vehicles and more. 

Hydrocarbons - Composed of hydrogen and carbon, this group includes VOCs (which can contribute to air pollution and cause negative health effects such as cancer). 

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Idling -  Allowing a vehicle’s engine to continue running while the vehicle is not moving. This often occurs in standstill traffic. 

Incineration - Burning, particularly of waste material. This process produces fumes that contribute to air pollution and some, such as dioxin, are serious health hazards. 

Indicators - Metrics that are used to measure the level of air pollution in an area; this could include things like household solid fuels and exposure to particulate matter.

Indoor Air Quality / Indoor Environmental Quality - The quality of air in a building or indoor space. This can be caused by mould, smoke, bacteria, ozone, carbon dioxide, and more, and can be addressed through a variety of methods. Learn more here.

Infrastructure - This refers to the structures used in a society for things like transportation. “Green infrastructure” like efficient public transportation systems can help improve air quality by reducing the number of cars on the road or adding more green spaces in cities and other areas. 

Integrated Environmental Management (IEM) - A holistic approach (from beginning to end) to environmental management that considers all the environmental impacts of a given plan or action and engage stakeholders in the process to discover equitable solutions. 

Inversion - Changes in the atmosphere can cause air pollution to become trapped close to the ground, worsening the quality of air we are breathing.

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Kyoto Protocol - International agreement ( in 1997) of countries across the globe to reduce their carbon emissions through the use of carbon credit trading. 

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Landfill gas - Microorganisms in landfills digest the materials in the landfill, releasing gases such as methane and carbon dioxide. These gases contribute to climate change and can also pose a risk of combustion and groundwater contamination. 

Local Air Quality Action Plan - Plan for local authorities that have established an Air Quality Management Area to meet air quality goals in that area. 

Local Air Quality Management (LAQM) -  A process in which local authorities assess their air quality management practices and performance and estimate what future air quality will be. 

Low Emission Neighbourhoods - A community which has adopted air quality improvement measures which may make transportation easier for pedestrians and bicyclists, incentivize ultra-low emission vehicles, or reduce air and noise pollution. 

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Masks - Though they can help to filter out some pollution, many masks available on the market do not filter out all air pollution (such as smaller particles). It is more effective to take quieter routes and avoid traffic.

Mauna Loa average - Measurements collected in Mauna Loa, Hawaii that are a proxy for the climate conditions as a whole. These metrics measure carbon dioxide concentration, which helps us to understand the changes in carbon molecules in the atmosphere over time.

Maximum hourly average - The maximum hourly average is the highest hourly reading of air pollution obtained during the time period under study.

Mayor's Air Quality Fund - A London fund created to improve London’s air quality across all London boroughs through various projects. This includes measures to closing roads to traffic during school hours, zero emission zones, idling regulations, street cleaning measures, and more.

Methane (CH4) - Containing four hydrogen atoms and one carbon atom, Methane is a greenhouse gas that can be released from natural gas or even from animal agriculture (cows, for example, produce a LOT of methane!). Methane is about 28 times more powerful than carbon dioxide as a contributor to climate change. 

Micrograms per cubic meter (µg/m3) - The concentration of an air pollutant (eg. ozone) is given in micrograms (one-millionth of a gram) per cubic meter air or µg/m3.

Mobile Source -  Sources of air pollution such as vehicles or other methods of transportation. These sources are a major contributor to the greenhouse gases that cause climate change.

Mould - Mould may be present in dark or damp areas and can release spores that can make breathing difficult. Some types of mould (such as black mould) can be highly toxic.

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Natural Environment - Naturally occurring things (organisms and non-living features like rocks, soil and water). 

Nitrogen Oxides (NOx) - A group of pollutants (including nitrogen oxide and nitrogen dioxide) that contribute to smog and acid rain. If inhaled, they can be harmful to one’s health.

Nonattainment area - Used in US law, this term refers to an area which has failed to meet national air quality standards.

Noxious gases - Gases which are harmful to living things.

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Ozone (O₃) - As a molecule, ozone is a molecule composed of 3 atoms of oxygen.

Ozone layer - Composed of ozone, this layer of the stratosphere absorbs a UV radiation from the sun and helps protect our environment from overheating.  

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Particulate matter - Airborne particles that can be composed of a combination of solids and liquids. They vary in size and can be classified based on their diameter. 

Parts per million (PPM) or parts per billion (PPB) - A ratio of particle concentration; this measures the weight of particle units present per million or billion units of air by weight. 

Persistent Organic Pollutants (POPs) - These chemicals (such as DDT, PCBs, and dioxins) can remain in the environment for a long time and harm human and wildlife health because it bio-accumulates in food chains, becoming more concentrated in the bodies of higher-order consumers. They can be transported through the air long distances from their original source.

PM 10 (PM Coarse) - Particulate matter that is equal to or less than 10 micrometers in diameter, which is about a tenth of the diameter of a human hair. 

PM 2.5 (PM Fine) - Particulate matter that is equal to or less than 2.5 micrometers in diameter, which is about a fortieth of the diameter of a human hair. Because they are so light, they can be carried into the air and contribute to poor air quality. 

Point-source pollution - Pollution that can be traced back directly to a source (for example, a pipe releasing toxic chemicals or a factory producing smoke).

Pollution - Harmful materials that are released into the natural environment, such as trash, smoke, ash, or chemical runoff. Pollution threatens the resources that humans and other organisms depend upon to live on Earth. 

Polycyclic Aromatic Hydrocarbons (PAHs) - Particles that can be released from processes like burning coal and other fossil fuels or grilling meat. They can also occur naturally. Humans can encounter PAHs when they breathe in fumes from incineration of fossil fuels, cigarette smoke, and fires, but they can also encounter it from contaminated food or water. In addition to causing eye and respiratory irritation, PAHs are also linked to cancer. 

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Radon - This radioactive gas can cause an increased risk of lung cancer, so it is important for homeowners to be aware of radon levels in their home. Check here to find more information about how to determine the radon risk in your home or neighborhood and what you can do about it. 

Respiration - Also known as “breathing,” this is the process that allows humans and other animals to absorb oxygen from the external environment to use for bodily processes and expel carbon dioxide. When we respirate, we sometimes also breathe in pollutants, and this is a big problem with air pollution! 

Risk - The potential for physical, social, economic, or other types of losses; this is used in planning and environmental management to determine the likelihood and severity of potential outcomes.

Risk factors - Physiologically, risk factors are those characteristics that make an individual more likely to be susceptible to illness, injury, or other health afflictions. For example, asthma or other breathing difficulties may make some individuals more likely to suffer adverse effects when they breathe in polluted air. 

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Secondary fine particles - These particles are formed as a result of chemical reactions (oxidation) of primary particulate matter. They may be formed in the atmosphere. For example, sulfur and nitrogen oxides may transform into sulfuric acid and nitric acid, respectively. 

Sensitive groups (at-risk populations) - In relation to air quality, these groups are more sensitive to air pollution than others. Even though some people may not notice the health effects of air quality, those with asthma, breathing problems, or other risk factors may be more likely to experience adverse health affects. 

Shared Mobility Principles - This set of ten goals is a vision for a society that is both environmentally sustainable and accessible for all people, regardless of level of ability, socioeconomic status, or geographic location. Read more about the goals here. 

Sick Building Syndrome - This is experienced by people who spend time in a building that may have poor indoor air quality or other factors that produce negative health effects. Though scientists don’t fully understand this phenomenon, they do recommend taking steps to address potential causes of SBS by opening windows, getting fresh air outside during breaks, and avoiding smoke, fumes, or checking ventilation systems to make sure everything is working properly.  

Smog - When fog combines with smoke, it can create visible air pollution that may make it hard to breathe outside of the incredibly poor air quality. This can happen because of air pollution from vehicle emissions, incineration, and other sources. Because smog is often toxic, it can cause extremely severe health effects for humans up to and including death. In some parts of the world, smog is such a big problem that some cities issue warnings for people to stay inside, even cancelling work, school, and events! 

Smoke - After incineration (whether natural or man-made), a group of chemicals are released that may contain highly toxic chemicals like carbon monoxide. Long-term or extremely concentrated inhalation of smoke (from smoking, second-hand smoking, wildfires, proximity to incineration, or other sources) can result in eye, throat, and lung irritation and over long periods of time may even be carcinogenic. Those with elevated sensitivity to air pollution should be especially careful to avoid sources of smoke, which could make it harder to breathe.

Socio-economic status (SES) - A measure of an individual’s educational, occupational, financial, or social status. Often, lower socioeconomic status is correlated with greater risk of developing cardiovascular, respiratory, and other problems. 

Spacial planning - The process of determining the ways in which space will be used in urban or other areas. This may include determining where to put certain public facilities, how transportation systems will work, and how the environment will be affected. Spatial planning is important to air quality because designing cities and towns in a way that reduces air pollution and human exposure to it can have a positive impact on health and environmental impact. 

Stationary Source - Unlike a mobile source, a stationary source of pollution is fixed in one place (such as a factory, power plant, or other industrial producer of pollution). 

Sulfur Dioxide (SO₂) - A byproduct of incineration, sulfur dioxide is often present alongside other pollutants. It can cause reduced lung function in individuals with risk-factors (such as those with breathing problems, children, and the elderly.) 

Sustainability - The practice of ensuring that resources available are sufficient to meet the needs of current and future generations; sustainability practices may aim to ensure energy and resources are used efficiently so as not to deplete their availability in the future, and to create a society that is more equitable in its use and distribution of these resources so that they can be used by everyone fairly. 

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Tapered element oscillating microbalance (TEOM) - This instrument is used to detect the concentration of aerosol particles. They have been used in the United States to monitor the levels of coal dust and protect miners from the negative health effects of air pollution. 

Teratogens - Substances which can harm the development of an unborn fetus. Read more about how air pollution can be teratogenic here.

Three pillars of sustainability - Also known colloquially as the “Three Pillars” or the “Triple Bottom Line” or “People, Profit, and Planet,” this term refers to the economic, social, and environmental considerations necessary to ensure a sustainability plan is viable and equitable. The first pillar, economic, means that a given plan or initiative is financially feasible and when used in a business context may mean that the proposed initiative can be undertaken while still benefitting the business in terms of profit. The second pillar, social, requires that plans are equitable for all stakeholders and that they are inclusive and fair. A good sustainability project will take the needs and considerations of multiple groups into account, with a focus on ensuring that the specific needs of each group are met. The third and final pillar, environmental, means that the plan will be environmentally beneficial (for example, improving air or water quality, reducing carbon emissions, protecting wildlife, etc).  

Toxic organic micropollutants (TOMPs) - A group of POPs (toxic chemicals that are long-lasting in the air) including PCBs, dioxins, and other toxins.  

Toxins - Substances that are harmful to health (ranging from minor to fatal effects). "Air toxics” may contain substances such as volatile and semi-volatile organic compounds or heavy metals which can be teratogenic, carcinogenic, and generally harm human or animal health. 

Traffic pollution - Pollution that is a result of vehicles’ tailpipe emissions. Traffic pollution can affect pedestrians, cyclists, and drivers, and is especially harmful to the latter: while sitting in a car, drivers and passengers are inhaling traffic pollution from vehicles around them. 

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Ultrafine particles (PM_0.01) - Particulate matter with a diameter of less than or equal to 0.01 micrometers. These particles are less regulated than particulate matter of PM 2.5 - PM 10 but can be even more harmful when inhaled. They may be produced naturally or artificially and when inhaled are deposited in the lungs and can be absorbed into the bloodstream. This can cause various respiratory and cardiovascular problems. 

Ultra Low Emission Zone (ULEZ) - A standard of emission levels for vehicles, used to reduce overall vehicle pollution. It is currently used across London for most vehicles and those vehicles which violate these standards are subject to a daily fine. 

Urban Outdoor Air Pollution - This kind of pollution is present in cities, and while it may be created outdoors by vehicles or other sources, it can also be present indoors and lower indoor air quality. 

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Ventilation - Can be natural or mechanical, and may include things like opening windows to let outdoor “fresh” air in or using things like air purifiers and filters to remove pollution from the air indoors.

Volatile Organic Compounds (VOC) - Volatile chemicals that can be transformed into gases or vapors. These may also combine with nitrogen oxides to form smog.

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Waste - A byproduct of consumption or production that is no longer useful. This often ends up in landfills or polluting our oceans, but it can also end up in an incinerator; this is especially harmful because incineration of waste can pump large qualities of toxic molecules into the air. 

Wood burning - The incineration of wood products. This can be a big problem in some countries that use wood burning stoves, because the smoke produced by these stoves can lead to extremely poor indoor air quality and harm human health. 

World Health Organisation (WHO) - An international organization that is dedicated to improving health globally and which conducts research and policy analysis on the health impacts of air quality, among other things. 

Wind - The natural movement of air currents. Wind can transport air pollutants, especially long-lasting POPs, to other areas; this is one of the reasons that air pollution is not an issue that can be “contained” in one geographic area. However, wind can also be used as a source of renewable energy that could supplement or replace the burning of fossil fuels. 

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Zero emissions - A standard of energy sources which produce no pollutants. “Net-zero emissions” refers to a target of efficiency in which the amount of carbon emitted is less than or equal to the amount absorbed, effectively meaning that the amount of carbon in the environment is not increasing overall. 

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