Pertubuhan Sains & Kesejahteraan
Science & Wellness Organisation
(PPM-013-05-16022012)
Special Consultative Status with the United Nations Economic and Social Council
Ambient (Outdoor) Air Pollution
A Major Environmental Health Problem
Ambient (outdoor) air pollution is one of the most significant environmental risks to human health. Despite progress in technology and regulation in some regions, air pollution remains pervasive, with the majority of the global population exposed to air quality levels that exceed World Health Organization (WHO) recommendations. This widespread exposure presents a major challenge for public health systems worldwide.
What is Ambient Air Pollution
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Ambient (outdoor) air pollution refers to the presence of harmful substances in the outdoor air environment. These substances originate from a wide range of human activities and natural processes, particularly those involving the combustion of fuels and large-scale industrial operations. Pollutants can remain suspended in the air for extended periods, travel across long distances, and accumulate in populated areas.
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WHO identifies several pollutants that are commonly monitored because of their prevalence in outdoor air and their relevance to air quality management. These pollutants form the basis of air quality assessment and regulatory frameworks at national and international levels.
Global Burden of Ambient Air Pollution
WHO data indicate that ambient (outdoor) air pollution affects nearly the entire global population and remains a leading environmental risk to health.
99%
of the world’s population was living in areas where air quality levels did not meet the WHO air quality guideline levels in 2019
4.2 million
premature deaths in 2019 were attributed to ambient (outdoor) air pollution globally
89%
of these premature deaths occurred in low- and middle-income countries, reflecting substantial global disparities in exposure and health impacts
Source: World Health organization
Types of Pollutants
There are five major pollutants that commonly affect ambient air quality. These pollutants differ in their physical characteristics, sources, and behaviour in the environment.
Particulate Matter (PM)
Particulate matter (PM) consists of inhalable particles composed of substances such as sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust, or water. PM is classified by aerodynamic diameter, with PM2.5 and PM10 being the most widely used indicators in air quality monitoring and regulation.
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PM10
Particles with diameters between 2.5 µm and 10 µm, often referred to as coarse particles, are mainly generated by mechanical and natural processes. Common sources include pollen, sea spray, wind-blown dust from erosion, agricultural activities, roadways, and mining operations.
Image source: Unsplash - Photo by Jacob McGowin
PM2.5
Finer particles arise from direct emissions such as fuel combustion in vehicles, industries, and power generation, as well as from secondary formation through chemical reactions between gases in the atmosphere.
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In outdoor environments, particulate matter sources vary by location but typically include transportation systems, industrial activities, power plants, construction sites, waste burning, fires, and agricultural fields.
Nitrogen Dioxide (NOâ‚‚)
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Nitrogen dioxide (NOâ‚‚) is a reddish-brown gas that is soluble in water and acts as a strong oxidant. In ambient air, NOâ‚‚ is mainly produced through high-temperature combustion of fuels, particularly from transportation, industrial processes, heating systems, and power generation.
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Outdoor NOâ‚‚ concentrations are therefore closely linked to areas with high traffic density and combustion-related activities.
Ozone (O₃)
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Ground-level ozone (O₃) is a major component of smog. Unlike some pollutants, ozone is not emitted directly into the atmosphere. It forms through photochemical reactions involving pollutants such as volatile organic compounds, carbon monoxide, and nitrogen oxides (NOₓ) released from vehicles and industrial sources.
Because its formation depends on sunlight, ozone concentrations are typically higher during periods of sunny weather, especially in urban and suburban environments.
Carbon Monoxide (CO)
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Carbon monoxide (CO) is a colourless and odourless gas produced by the incomplete combustion of carbon-containing fuels such as wood, petrol, charcoal, natural gas, and kerosene.
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In ambient air, motor vehicles represent the predominant source of carbon monoxide, making it particularly common in areas with heavy traffic and congestion.
Sulfur Dioxide (SOâ‚‚)
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Sulfur dioxide (SOâ‚‚) is a colourless gas that dissolves readily in water. It is mainly released through the combustion of fossil fuels used for domestic heating, industrial activities, and power generation.
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Outdoor concentrations of sulfur dioxide are generally higher in regions where sulfur-containing fuels are widely used for energy production.
WHO Air Quality Guidelines
To address the risks posed by ambient air pollution, WHO has established Global Air Quality Guidelines (AQGs). These guidelines provide evidence-based recommendations for concentration levels of key outdoor air pollutants, including PM2.5, PM10, NO₂, O₃, CO, and SO₂.
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The guidelines define guideline values, which are associated with the lowest known risk to human health, alongside interim targets intended to support progressive improvements in air quality where immediate achievement of guideline values is not feasible. WHO emphasises that health risks can occur even at low levels of exposure, underscoring the importance of continuous pollution reduction.
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The AQGs serve as a global reference for governments and public health authorities when developing air quality standards, monitoring systems, and long-term pollution control strategies.
Health Effects of Ambient Air Pollution
According to WHO, exposure to ambient (outdoor) air pollution is associated with a wide range of adverse health outcomes across the life course.
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Cardiovascular Diseases
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Ischaemic heart disease
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Myocardial infarction (heart attacks)
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Stroke
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Hypertension
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Heart failure
Respiratory Diseases
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Chronic obstructive pulmonary disease (COPD)
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Pneumonia
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Asthma
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Reduced lung function
Cancer
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Lung cancer
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Other cancers
Maternal, Fetal, and Birth Outcomes
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Low birth weight
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Preterm birth
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Small for gestational age births
Children’s Health Outcomes
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Acute lower respiratory infections
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Pneumonia
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Impaired lung development
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Reduced lung function
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Asthma
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Childhood cancer (including leukaemia)
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Otitis media
Neurological Effects
Long-term exposure to PMâ‚‚.â‚…, NOâ‚‚ and ozone is linked to neurological effects.
Infectious Diseases
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Pneumonia
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Tuberculosis
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Other acute respiratory infections
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COVID-19 (worsened outcomes)
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Emerging Evidence
WHO recognises a growing body of evidence linking ambient air pollution to additional health outcomes:
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Type 2 diabetes
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Dementia
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Autism spectrum disorders
Other Acute Health Effects of Air Pollution
Short-term exposure to elevated air pollution levels can result in immediate symptoms, including:
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Eye and nose irritation
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Difficulty breathing
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Coughing
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Headaches
Heat Stress and Air Pollution
Heat stress occurs when the body is unable to effectively regulate and eliminate excess heat, leading to a rise in core body temperature and heart rate. It is recognised as the leading cause of weather-related deaths.
According to the World Health Organization, heat stress can worsen existing medical conditions, particularly among vulnerable populations. Health conditions exacerbated by heat stress include:
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Cardiovascular disease
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Respiratory disease
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Acute myocardial infarctions
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Kidney disease
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Asthma
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Mental health conditions
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Diabetes
WHO further highlights that heat stress and air pollution can interact, compounding health risks during periods of extreme heat. When elevated temperatures and high air pollution levels occur together, the risk of illness, hospitalisation, and premature death increases, placing additional strain on health systems.
Policies That Reduce Air Pollution
According to the World Health Organization, air pollution is the second highest risk factor for noncommunicable diseases, making policy action essential for protecting public health. Because most sources of outdoor air pollution lie beyond individual control, effective reduction requires coordinated action at local, national, and regional levels across multiple sectors.
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Industry
Adoption of clean technologies to reduce industrial smokestack emissions, along with improved management of urban and agricultural waste. This includes capturing methane emissions from waste sites for use as biogas instead of open burning or incineration.
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Energy
Expanding access to affordable clean household energy solutions for cooking, heating, and lighting to reduce reliance on polluting fuels.
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Transport
Transitioning to cleaner modes of power generation; prioritising rapid urban transit systems, walking and cycling networks, and rail-based freight and passenger transport; and promoting cleaner heavy-duty diesel vehicles, low-emissions vehicles, and fuels with reduced sulfur content.
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Urban Planning
Improving the energy efficiency of buildings and promoting greener, more compact city designs to reduce energy demand and emissions.
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Power Generation
Increasing the use of low-emissions fuels and renewable, combustion-free power sources such as solar, wind, and hydropower; supporting co-generation of heat and power; and expanding distributed energy generation, including mini-grids and rooftop solar systems.
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Municipal and Agricultural Waste Management
Implementing waste reduction, separation, recycling, reuse, and reprocessing strategies, as well as biological waste treatment methods such as anaerobic digestion to produce biogas. Where incineration is unavoidable, strict emission controls are essential.
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Health-Care Activities
Placing health services on a low-carbon development pathway to improve system resilience, reduce environmental health risks, and support cost-efficient service delivery. The health sector can also demonstrate leadership by supporting climate-friendly policies.
Moving Forward:
From Evidence to Action
Ambient (outdoor) air pollution remains a major environmental health problem, with clear links to cardiovascular, respiratory, neurological, infectious, and developmental health outcomes, as well as millions of premature deaths globally. The evidence presented by the World Health Organization underscores that air pollution is not only an environmental issue, but a preventable public health risk that requires sustained, and coordinated action.
In response to these challenges, the Science & Wellness Organisation (SWO) is advancing its Global Clean Air Campaign, with a strong focus on disease prevention, public education, and evidence-based action. The campaign aims to address health risks associated with air pollution by strengthening awareness of preventive measures, supporting informed decision-making, and reinforcing clean air as a fundamental public health priority.
By translating scientific evidence into accessible knowledge and promoting alignment with international air quality guidelines, SWO seeks to empower communities, institutions, and policymakers to take meaningful action. Improving air quality is not only essential for protecting current populations, but also for safeguarding future generations and building more resilient, and healthier societies.