Air Pollution: A Decreasing Global Threat?

Air pollution is a serious public health threat, with nearly half of Americans breathing in unsafe levels of air pollutants. While fine-particle air pollution has decreased across the US since 1981, overall air pollution is worsening due to factors such as wildfires, industrial emissions, and climate change. During the COVID-19 pandemic, global road travel and commercial flight activity decreased significantly, leading to a notable drop in ultrafine particle concentration. However, the Trump administration's environmental rollbacks and attacks on environmental justice threaten to exacerbate air pollution and disproportionately impact communities of color and low-income neighborhoods.

Ultrafine particles

Despite the risks, UFPs remain largely unregulated. The EPA does not regulate ultrafine particle emissions, and they are not included in the PM10 and PM2.5 particle classes that are regulated. However, the World Health Organization has published good practice statements regarding measuring UFPs. There is also ongoing debate about how the EU should regulate UFPs, and there is a dispute between China and South Korea over the responsibility for ultrafine dust.

UFPs can be intentionally fabricated for use in medicine and technology or can be byproducts of emissions, combustion reactions, or equipment such as automobile exhaust, printer toner, and tire wear and tear. The major source of UFPs in urban outdoor air is motor traffic, and the concentration of UFPs typically follows road traffic patterns. During the COVID-19 pandemic, when global road travel and commercial flight activity decreased significantly, a study found that UFP concentration dropped by nearly 50%.

While the highest air pollution levels typically occur when a site is downwind of an airport, there are policy changes that can help reduce exposures. For example, increasing the adoption of sustainable aviation fuel technology, such as low-sulfur fuel and electric engines, can help to reduce UFP emissions.

COVID lockdowns

The COVID-19 pandemic saw an unprecedented reduction in global travel, with road travel and commercial flight activity decreasing by 50% and 60% respectively. The lockdowns imposed by cities and countries during the initial months of the pandemic saw flight activity almost come to a standstill, decreasing by 96%. This presented a unique opportunity for researchers to study the impact of these mobility changes on air pollution.

A study by the School of Public Health found that ultrafine particle concentration, which are toxic pollutants that can cause inflammation in the lungs, brain, and other organs, dropped by nearly 50% due to reduced aviation and road activity during the first few months of the pandemic. Ultrafine particle concentration decreased by 48% during the state-of-emergency period, coinciding with a 74% reduction in aircraft traffic and a 51% reduction in road traffic.

Another study by UNU-FLORES measured the levels of air pollution in Ulaanbaatar, Mongolia, and found that while Sulphur dioxide increased due to the use of coal briquettes in heating homes, other pollutants such as NO2, PM10, and PM2.5 decreased noticeably during the lockdown period compared to the previous five winter periods.

NASA also conducted a study that mapped PM 2.5 levels across China, Europe, and North America during the early months of the pandemic. They found that the seasonal differences in PM 2.5 were driven primarily by natural variability in meteorology rather than pandemic lockdowns. The most significant lockdown-related differences were detected in China, with a notable reduction over the North China Plain, where the strictest lockdowns were in place.

Despite these reductions, it is important to note that not all pollutants were removed from circulation during the lockdowns. In some cases, such as in London and Paris, PM2.5 concentrations actually increased. Additionally, the decline in NO2 concentrations during the lockdowns was not as large as expected, ranging from 10 to 50%. These findings highlight the need for sophisticated analysis to truly understand the impact of interventions on air quality and to develop effective strategies for reducing air pollution.

Wildfires

Particulate matter, specifically PM2.5, is of great concern when it comes to wildfires. These fine particles, generally 2.5 micrometres in diameter or smaller, can easily penetrate homes and buildings, increasing indoor particle concentrations. During wildfires, PM2.5 concentrations can increase substantially, posing a significant risk to public health. Inhalable PM2.5 can travel deep into the lungs and potentially enter the bloodstream, leading to various health issues, including asthma, lung disease, heart attacks, and premature death. The health impacts of wildfires disproportionately affect individuals with cardiovascular or respiratory diseases, older adults, children, pregnant women, outdoor workers, and those of lower socioeconomic status.

The impact of wildfires on air quality can be long-lasting and far-reaching. Smoke from wildfires can drift for thousands of miles, bringing air pollution to areas far from the fire zones. For example, the 2021 summer fires in North America and Russia led to PM2.5 levels spiking in western North America, reaching several times the level recommended by the World Health Organization. Similarly, the Canadian wildfires in 2025 released more carbon in five months than Russia or Japan emitted from fossil fuels throughout 2022.

To break the vicious cycle between wildfires and air pollution, governments need to adopt a joined-up approach that addresses the interconnectedness of these issues. This includes focusing on planning, prevention, and preparedness, as outlined in the 'Fire Ready Formula'. Additionally, measures to reduce black carbon emissions can help prevent wildfires and improve public health outcomes.

Fossil fuels

The impact of fossil fuel pollution extends beyond human health. It contributes to climate change, with emissions from fossil fuels being the dominant cause of global warming. In 2018, 89% of global CO2 emissions came from fossil fuels and industry. Additionally, fossil fuel extraction, transportation, and refining often result in oil spills that harm wildlife, destroy habitats, and contaminate water sources. The BP Deepwater Horizon spill in 2010, for instance, released 134 million gallons of oil into the Gulf of Mexico, causing extensive damage to marine life and ecosystems.

Furthermore, the production and use of plastics derived from fossil fuels contribute to pollution. Globally, 300 million tons of plastic waste are produced each year, with a significant portion ending up in the ocean. Plastic pollution not only harms marine life but also pollutes the food chain and contributes to greenhouse gas emissions.

However, there is growing awareness of the negative impacts of fossil fuels, and efforts to transition from fossil fuels to renewable energy sources are gaining momentum. For example, China lowered its fossil fuel PM 2.5 emissions by about 44% between 2012 and 2018, resulting in significant health benefits and saving approximately 1.5 million lives annually. Additionally, studies have shown that communicating the health risks associated with air pollution from fossil fuels can effectively decrease support for fossil fuels and increase support for low-carbon energy sources.

Transportation

The US Environmental Protection Agency (EPA) has played a pivotal role in reducing air pollution from transportation in the United States. After Congress passed the Clean Air Act in 1970, the EPA gained the authority to regulate pollution from cars and other transport forms. The EPA, along with the State of California, has since led the national effort to reduce vehicle pollution by implementing increasingly stringent standards. As a result of these standards, new passenger vehicles are now 98-99% cleaner for most tailpipe pollutants compared to those in the 1960s. Fuels are also much cleaner, with lead eliminated and sulfur levels reduced by more than 90%.

The EPA's efforts have had a tangible impact on air quality in US cities, which has improved despite population growth and increased vehicle usage. Between 1980 and 1999, levels of lead in the air decreased by 94%. From 1991 to 2000, concentrations of all six criteria air pollutants declined, including carbon monoxide, nitrogen dioxide, ozone, and particulate matter. For example, carbon monoxide levels dropped by 41%, and coarse particulate matter levels fell by 5%. Since 1992, the number of nonattainment areas, or areas that do not meet air quality standards, has decreased by 46%.

In Europe, targeted policies and measures have also led to a decrease in the emission of most air pollutants from transport in the EU-27. Between 1990 and 2022, emissions of nitrogen oxides from transport across the EU-27 decreased by 51%, sulphur oxides by 82%, carbon monoxide by 90%, methane by 76%, and non-methane volatile organic compounds by 91%. However, emissions of ammonia and nitrous oxide increased by 121% and 35%, respectively, during this period.

The COVID-19 pandemic provided a unique opportunity to study the impact of reduced aviation and road activity on air quality. During the pandemic's first year, global road travel and commercial flight activity decreased by 50% and 60%, respectively. Ultrafine particle concentration, which is particularly harmful to human health, dropped by nearly 50% during this time.

Some cities have successfully reduced transport-related emissions through various initiatives. For example, Copenhagen, known as one of the world's greenest cities, has invested heavily in cycling infrastructure and aims to become carbon-neutral by 2025. London introduced the Ultra Low Emission Zone (ULEZ), charging older, more polluting vehicles to enter the city centre, resulting in reduced nitrogen dioxide levels. Bogotá's TransMilenio bus rapid transit system and the implementation of car-free days have also helped reduce air pollution in the city.

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