Air pollution is an invisible killer with a stranglehold on many parts of our fragile planet. Nine out of 10 of us breathe air containing levels of pollutants that exceed World Health Organization limits. Every year, around 7 million people die from diseases and infections related to air pollution – that’s more than five times the number of people killed in road collisions and more than the official death toll of COVID-19.
Air pollution is also inextricably linked to climate change because short-lived climate pollutants, like methane, black carbon and ground-level ozone, have an out-sized impact on global warming. Reducing them could cut the current rate of warming in half.
“We have the ability and knowledge to improve air quality and when we do we also mitigate climate change, increase life expectancy, improve human and ecosystem health, increase crop yields and sustain development,” said Valentin Foltescu, a Senior Programme Management Officer with the United Nations Environment Programme. “The countries that are currently most exposed to dangerous air have the most to gain – meaning that improving air quality is also a way to address global inequality.”
Here are five of the most dangerous pollutants in our air.
PM2.5 refers to fine particles that are 2.5 microns or less in diameter. They are invisible to the naked eye, though noticeable as particle smog in highly polluted areas, and present indoors and out. PM2.5 particles come from combusting unclean fuels for cooking or heating, burning waste and agriculture residue, industrial activities, transportation and windblown dust, among other sources. PM2.5 particles penetrate deep into the lungs and bloodstream, increasing the risk of dying from heart and lung disease, stroke and cancer. These particles can either be emitted directly or formed in the atmosphere from several different emitted pollutants, such as ammonia, and volatile organic compounds.
Ground-level ozone, or tropospheric ozone, is a short-lived climate pollutant and although it exists only for a few days to a few weeks, it is a strong greenhouse gas. It forms when pollutants from industry, traffic, waste and energy production interact in the presence of sunlight. It contributes to smog, worsens bronchitis and emphysema, triggers asthma, damages lung tissue and reduces crop productivity. Exposure to ground-level ozone causes an estimated 472,000 premature deaths every year. Because ozone stunts the growth of plants and forests, it also reduces the amount of carbon that can be sequestered.
Nitrogen oxides are a group of air polluting chemical compounds, including nitrogen dioxide (NO2) and nitrogen monoxide. NO2 is the most harmful of these compounds and is generated from the combustion of fuel engines and industry. It can damage the human heart and lungs and it reduces atmospheric visibility at high concentrations. Finally, it is a critical precursor to the formation of ground-level ozone.
Black carbon, or soot, is a component of PM2.5 and is a short-lived climate pollutant. Agricultural burning to clear land, and the wildfires that sometimes result, are the world’s largest sources of black carbon. It also comes from diesel engines, burning trash, and stoves and furnaces that combust fossil and biomass fuels. It causes poor health and premature death and also increases the risk of dementia. Black carbon emissions have been decreasing over the past decades in many developed countries due to stricter air quality regulations. But emissions are high in many developing countries where air quality is poorly regulated. As a result of open biomass burning and residential solid fuel combustion, Asia, Africa and Latin America contribute approximately 88 per cent of global black carbon emissions.
Methane comes mainly from agriculture, particularly livestock, sewage and solid waste, and oil and gas production. It helps create ground-level ozone and hence contributes to chronic respiratory illnesses and premature death. Intergovernmental Panel on Climate Change research shows that methane – a major short-lived climate pollutant – is responsible for at least a quarter of today’s global warming and reducing human-caused methane, which accounts for more than half of all methane emissions, is one of the most effective ways of combatting climate change.