Ambient air pollution: Health impacts

Nicolò Lazzati

Ambient (outdoor air pollution) is a major cause of death and disease globally. The health effects range from increased hospital admissions and emergency room visits, to increased risk of premature death.

An estimated 4.2 million premature deaths globally are linked to ambient air pollution, mainly from heart disease, stroke, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections in children.

Worldwide ambient air pollution accounts for:

• 29% of all deaths and disease from lung cancer
• 17% of all deaths and disease from acute lower respiratory infection
• 24% of all deaths from stroke
• 25% of all deaths and disease from ischaemic heart disease
• 43% of all deaths and disease from chronic obstructive pulmonary disease

Pollutants with the strongest evidence for public health concern, include particulate matter (PM), ozone (O₃), nitrogen dioxide (NO₂) and sulphur dioxide (SO₂).

The health risks associated with particulate matter of less than 10 and 2.5 microns in diameter (PM₁₀ and PM_2.5) are especially well documented. PM is capable of penetrating deep into lung passageways and entering the bloodstream causing cardiovascular, cerebrovascular and respiratory impacts. In 2013, it was classified as a cause of lung cancer by WHO’s International Agency for Research on Cancer (IARC). It is also the most widely used indicator to assess the health effects from exposure to ambient air pollution.

In children and adults, both short- and long-term exposure to ambient air pollution can lead to reduced lung function, respiratory infections and aggravated asthma. Maternal exposure to ambient air pollution is associated with adverse birth outcomes, such as low birth weight, pre-term birth and small gestational age births. Emerging evidence also suggests ambient air pollution may affect diabetes and neurological development in children. Considering the precise death and disability toll from many of the conditions mentioned are not currently quantified in current estimates, with growing evidence, the burden of disease from ambient air pollution is expected to greatly increase.

Jonathan McIntosh

Even though all populations are affected by air pollution, the burden of ill-health is inequitable within and across countries. Most of the disease burden is borne by low- and middle-income countries, as well as poor and marginalized populations who tend to live near busy roads and industrial sites characterized by high levels of ambient air pollution. Nearly 90% of the 4.2 million premature deaths due to ambient air pollution occurred in low- and middle-income countries, with the greatest burden in the WHO Western Pacific and South-East Asia regions.

Other susceptible groups include those with pre-existing lung or heart disease, as well as elderly people and children. In children with developing lungs, air pollution exposure can cause both short- and long-term deficits in lung function, as well as long-term reductions in lung growth rate.

Improving air quality is, therefore, among the measures with the greatest potential impact on health equity. Large health benefits would occur for lower income groups, as well as children and the elderly, who bear the brunt of exposure to ambient air pollution or are most susceptible.

Arun Ganesh

Pollutants not only severely impact health, but also the earth’s climate and ecosystems globally.

Air pollutants, such as methane and black carbon, are powerful short-lived climate pollutants (SLCPs) that contribute to climate change and affect agricultural productivity. Although SLCPs persist in the atmosphere for short lifetimes, their global warming potential is often much greater than carbon dioxide. Black carbon, a component of particulate matter, is one of the largest contributors to global warming after CO₂. Black carbon warms the earth’s atmosphere by absorbing sunlight, thereby accelerating the melting of snow and ice. Methane, another SLCP, is a potent greenhouse gas that is 84 times more powerful than CO₂, and is a precursor to the air pollutant ozone. Ozone and black carbon affect weather processes and decrease agricultural yields, thus threatening food security.

Many of the sources of outdoor air pollution, are also sources of high CO₂ emissions. Fossil fuel burning by the energy and transport sectors is a major source of both particulate matter and carbon dioxide. In regions where temperature and precipitation patterns are projected to change due to climate change, it is likely that the frequency and severity of forest fires will also increase, releasing more air pollutants.

Policies to reduce air pollution offer a “win-win” strategy for both health and climate. Lower levels of air pollution result in better cardiovascular and respiratory health of populations in both the long- and short-term. Reducing outdoor air pollution can also reduce emissions of CO₂ and short-lived climate pollutants, such as black carbon particles and methane, therefore contributing to the near- and long-term mitigation of climate change.