Outdoor air pollution is a major environmental health problem affecting.
By reducing air pollution levels, we reduce the burden of stroke, heart disease, lung cancer, and chronic and acute respiratory
diseases, including asthma. The lower the levels of air pollution, the better the cardiovascular and respiratory health of
The World Health Organization
Air quality guidelines" provide an assessment of health effects of air pollution and thresholds for health-harmful pollution
In 2014, 92% of the world population lived
in places where the air quality guidelines were not met. Outdoor air pollution in both cities and rural areas was estimated
to cause 3 million premature deaths worldwide in 2012.
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.
Reducing 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 peri-urban
air pollution sources.
Reducing outdoor air pollution reduces emissions
of CO2 and short-lived climate pollutants like black carbon particles and methane, thus contributing to the near- and long-term
mitigation of climate change.
Indoor smoke is
a serious health risk for some 3 billion people who cook and heat their homes with biomass fuels and coal.
Some lung cancer deaths could have been averted by improving ambient air quality, or
by reducing tobacco smoking.
A 2013 assessment
by WHO’s International Agency for Research on Cancer (IARC) found that outdoor air pollution is carcinogenic to humans,
with the particulate matter component of air pollution most closely associated with increased cancer incidence, especially
lung cancer. An association has been observed between outdoor air pollution and increase in cancer of the urinary tract/bladder.
Exposure to small particulate matter causes cardiovascular and respiratory
disease, and cancers.
Most sources of outdoor
air pollution are beyond the control of individuals and demand action by cities and national and international policymakers
in transport, energy waste management, buildings and agriculture.
There are many examples of successful policies in transport, urban planning, power generation and industry that reduce air
Clean technologies that reduce industrial smokestack
emissions; improved management of urban and agricultural waste, including capture of methane gas emitted from waste sites
as an alternative to incineration (for use as biogas).
to clean modes of power generation; prioritizing rapid urban transit, walking and cycling networks and rail interurban freight
and passenger travel, and shifting to cleaner heavy duty diesel vehicles and low-emissions vehicles and fuels, including
fuels with reduced sulfur content.
Improving the energy
efficiency of buildings and making cities more compact, and energy efficient.
Increased use of low-emissions fuels and renewable combustion-free power sources (like solar, wind
or hydropower); co-generation of heat and power; and distributed energy generation ( mini-grids and rooftop solar power generation).
and Agricultural waste management:
Strategies for waste reduction,
waste separation, recycling and reuse or waste reprocessing and improved methods of biological waste management such as anaerobic
waste digestion to produce biogas and low cost alternatives to the open incineration of solid waste. Where incineration is
unavoidable, then combustion technologies with strict emission controls are critical.
The "WHO Air quality guidelines" indicate that by reducing particulate matter (PM10) pollution from
70 to 20 micrograms per cubic metre (μg/m), we can cut air pollution-related deaths by around 15%. The Guidelines apply
worldwide and are based on expert evaluation of current scientific evidence for:
particulate matter (PM)
sulfur dioxide (SO2), in all WHO regions.
Definition and principal sources
Particulate Matter affects more people than any other pollutant. The major components of PM are sulfate, nitrates,
ammonia, sodium chloride, black carbon, mineral dust and water. It consists of a complex mixture of solid and liquid particles
of organic and inorganic substances suspended in the air. Air quality measurements are typically reported in terms of daily
or annual mean concentrations of PM10 particles per cubic meter of air volume (m3). The most health-damaging particles are
those with a diameter of 10 microns or less, (≤ PM10), which can penetrate and lodge deep inside the lungs. Chronic exposure
to particles contributes to the risk of developing cardiovascular and respiratory diseases, as well as of lung cancer.
There is a close, quantitative relationship between exposure
to high concentrations of small particulates and increased mortality or morbidity, daily and over time. Small particulate
pollution has health impacts even at very low concentrations – indeed no threshold has been identified below which no
damage to health is observed.
The effects of PM on health occur at levels of exposure currently being experienced by many people
both in urban and rural areas and in developed and developing countries – although exposures in many fast-developing
cities today are often far higher than in developed cities of comparable size.
"WHO Air Quality Guidelines" estimate that
reducing annual average particulate matter concentrations common in many developing cities, to the guideline could reduce
air pollution-related deaths by around 15%.
are serious risks to health from exposure to ozone (O3), nitrogen dioxide (NO2) and sulfur dioxide (SO2). As with particulate
matter, concentrations are often highest in the urban areas of low and middle - income countries. Ozone is a major factor
in asthma morbidity and mortality, while nitrogen dioxide and sulfur dioxide play a role in asthma, bronchial symptoms, lung
inflammation and reduced lung function.
at ground level – not to be confused with the ozone layer in the upper atmosphere – is one of the major constituents
of photochemical smog. It is formed by the reaction with sunlight (photochemical reaction) of pollutants such as nitrogen
oxides (NOx) from vehicle and industry emissions and volatile organic compounds (VOCs) emitted by vehicles, solvents and industry.
As a result, the highest levels of ozone pollution occur during periods of sunny weather.
Excessive ozone in the air can have a marked effect on human health. It can cause
breathing problems, trigger asthma, reduce lung function and cause lung diseases. In Europe it is one of the air pollutants
of most concern.
Nitrogen dioxide (NO2)
As an air
pollutant, NO2 has several correlated activities. At short-term concentrations, it is a toxic gas which causes significant
inflammation of the airways.
NO2 is the main source of nitrate aerosols,
which form an important fraction of ozone. The major sources of anthropogenic emissions of NO2 are combustion processes (heating,
power generation, and engines in vehicles and ships).
Epidemiological studies have shown that symptoms of bronchitis in asthmatic children increase in association with long-term
exposure to NO2. Reduced lung function growth is linked to NO2 at concentrations currently measured in cities of Europe and
Sulfur dioxide (SO2)
SO2 is a colorless
gas with a sharp odor. It is produced from burning of fossil fuels (coal and oil) and smelting mineral ores that contain sulfur.
The main anthropogenic source of SO2 is the burning of sulfur-containing fossil fuels for domestic heating, power generation
and motor vehicles.
Studies indicate that a proportion of people with asthma experience changes in pulmonary function
and respiratory symptoms after periods of exposure to SO2 as short as 10 minutes. Health effects are now known to be associated
with much lower levels of SO2 than previously believed. Reducing SO2 concentrations is likely to decrease exposure to co-pollutants.
SO2 can affect the respiratory system and the functions of the lungs, and causes irritation of the eyes. Inflammation of the
respiratory tract causes coughing, mucus secretion, aggravation of asthma and chronic bronchitis and makes people more prone
to infections of the respiratory tract. Hospital admissions for cardiac disease and mortality increase on days with higher
SO2 levels. When SO2 combines with water, it forms sulfuric acid; this is the main component of acid rain, a cause of deforestation.
Air Pollution and Health
Understanding and controlling common pollutants indoors can help reduce your risk
of indoor health concerns.
may show up after a single exposure or repeated exposures to a pollutant. These include irritation of the eyes, nose, and
throat, headaches, dizziness, and fatigue. Such immediate effects are usually short-term and treatable.
It is best to eliminate the person's exposure to the source of the pollution, if it
can be identified. After exposure to some indoor air pollutants, symptoms of diseases such as asthma may show up or worsened.
Immediate reactions to indoor air pollutants depends
on age and preexisting medical conditions. Sometimes whether a person reacts to a pollutant depends on individual sensitivity.
Some people can become sensitized to biological or chemical pollutants after repeated or high level exposures. Some effects
may be made worse by an inadequate supply of outdoor air coming indoors or from the heating, cooling or humidity conditions
prevalent indoors or air filters left unchanged..
Health effects may show up years after exposure has occurred or after long or repeated periods of exposure. These effects,
which include respiratory diseases, heart disease and cancer, can be severely debilitating or fatal. It is prudent to try
to improve the indoor air quality in your home even if symptoms are not noticeable.
While pollutants commonly found in indoor air can cause many harmful effects, there is considerable uncertainty
about what concentrations or periods of exposure are necessary to produce specific health problems. People also react very
differently to exposure to indoor air pollutants.
In developing countries, indoor exposure to pollutants from the household combustion of solid fuels on open fires or traditional
stoves increases the risk of acute lower respiratory infections and associated mortality among young children; indoor air
pollution from solid fuel use is also a major risk factor for cardiovascular disease, chronic obstructive pulmonary disease
and lung cancer among adults.
WHO Member States recently adopted
a resolution and a road map for an enhanced global response to the adverse health effects of air pollution.
WHO’s "Health in the green economy" series is assessing the health
co-benefits of climate mitigation and energy efficient measures that reduce air pollution from housing, transport, and other
key economic sectors.
WHO’s work on "Measuring health
gains from sustainable development" has proposed air pollution indicators as a marker of progress for development goals
related to sustainable development in cities and the energy sector.