Air Pollution's Downward Trend: Reasons And Repercussions

Air pollution is a pressing issue that affects people globally. While some cities have seen a decrease in air pollution, such as Paris, which has restricted car traffic and implemented green policies, other major cities like Chicago have been ranked among the most polluted in their respective countries. Climate change, with heat, drought, and increased wildfire smoke, is a significant contributor to worsening air quality. The push for cleaner air is a continuous effort, with organizations like the American Lung Association and governments striving to implement regulations and policies to combat air pollution and protect public health.

Air pollution in the US

Air pollution is a pressing issue in the US, with nearly half of Americans (approximately 156 million people) breathing in unsafe levels of air pollutants. This figure marks a concerning rise compared to the previous year and is expected to further increase due to the climate crisis and rollbacks in environmental regulations. The American Lung Association's annual "State of the Air" report for 2025 highlights the severity of the situation, with a significant increase in individuals exposed to unhealthy air since the previous year's report.

The report reveals that about 43 million people reside in areas with failing grades for ground-level ozone pollution (smog) and short-term and year-round spikes in fine particle pollution (soot). These pollutants originate from sources such as wildfires, wood-burning stoves, coal-fired power plants, and diesel engines. The impact of air pollution is disproportionately felt by communities of color, with people of color constituting 50.2% of those living in counties with failing grades for air quality. Latino Americans are particularly affected, being three times more likely to breathe toxic air pollutants.

The Environmental Protection Agency (EPA), established in 1970, has played a pivotal role in addressing air pollution. Despite overall progress in reducing emissions, the changing climate has made maintaining air quality increasingly challenging. Weather conditions, such as extreme heat, drought, and wildfires, contribute to worsening air pollution. Chicago, for instance, experienced a public health emergency due to toxic chemicals in the air, with air quality maps indicating hazardous levels of pollution.

To combat air pollution, individuals can make conscious choices regarding transportation, energy sources, and food procurement. Supporting leaders who prioritize clean air and responsible climate action is also crucial. However, the Trump administration's rollbacks of environmental regulations and attacks on environmental justice have hindered progress. The EPA itself has faced staffing and funding cuts, impacting its ability to address air pollution effectively.

Climate change and air quality

Secondly, air quality can also influence climate change. Emissions of pollutants, including greenhouse gases, act as climate forcers, with ozone and black carbon contributing to warming the Earth's atmosphere. Conversely, particulate sulfates have a cooling effect on the atmosphere. The complex relationship between air quality and climate change means that interventions to address one can often have implications for the other. For example, vehicle electrification reduces CO2 and NOx emissions but may still result in particulate matter (PM) emissions from tyre and brake friction. Similarly, the use of low-carbon biofuels can reduce net greenhouse gas emissions but may simultaneously contribute to air pollution, especially PM and NOx.

The effects of climate change on air quality are already being observed in various regions. For instance, in April 2025, Chicago experienced a public health emergency due to a cloud of toxic chemicals, with air quality readings reaching 500 on the Air Quality Index (AQI) – the worst possible score. This hazardous air quality was attributed to a combination of industrial emissions and wildfire smoke. Similarly, a 2025 report by the American Lung Association revealed that nearly half of Americans (approximately 156 million people) lived in areas with unhealthy air quality, earning "F" grades for ozone or particle pollution. This marked a concerning increase compared to the previous year's survey, with climate change-driven heat, drought, and wildfire smoke contributing to worsening air quality.

To address these pressing issues, research and interventions are vital. The Environmental Protection Agency (EPA) in the United States has developed various tools, such as the GLIMPSE modeling tool, to assist states with energy and environmental planning. Additionally, the EPA's Community Multi-scale Air Quality Model (CMAQ) is a comprehensive system for studying air pollution across different scales. Multidisciplinary collaboration among professionals from various fields, such as architecture, engineering, climatology, and public health, will be crucial in devising innovative solutions to improve air quality, adapt to climate change, and ensure health equity.

Clean Air Act and its impact

The Clean Air Act (CAA) of 1970 was a landmark piece of legislation that significantly shifted the responsibility for air quality regulation from state to federal government, under the purview of the newly created Environmental Protection Agency (EPA). The EPA was tasked with enforcing the CAA in partnership with state, local, and tribal authorities, and was given the authority to regulate pollution from cars and other forms of transportation, as well as stationary sources such as power plants.

The CAA established the National Ambient Air Quality Standards (NAAQS), setting maximum allowable concentrations of particulate matter and other pollutants, such as lead, carbon monoxide, ozone, sulfur dioxide, and nitrogen dioxide. These standards have been updated several times to reflect technological advancements and an evolving understanding of safe pollutant levels.

The impact of the CAA has been significant. In the 50 years since its passage, air pollution has dropped dramatically, even as gross domestic product has quadrupled. The Act has also had a positive impact on the economy, with cleaner air leading to better health and productivity for workers, as well as savings on medical expenses for air pollution-related health problems. According to a 2011 EPA study, in 2020 alone, the reductions in fine particle pollution and ozone pollution achieved by the Clean Air Act Amendments of 1990 avoided more than 2,300,000 premature deaths, 200,000 heart attacks, millions of cases of respiratory problems, and 135,000 hospital admissions. The amendments also substantially reduced sulfur dioxide and nitrogen dioxide emissions through the Acid Rain Program's cap-and-trade program.

The CAA has also stimulated innovation in cleaner technologies, with the United States becoming a global market leader in this field. It has empowered citizens to take legal action against the government when it fails to perform its duties and hold companies accountable for violating emissions standards. Overall, the Clean Air Act has been a successful and impactful piece of legislation, improving air quality, public health, and the economy in the United States.

Air pollution health effects

Air pollution is a growing threat to public health, with a range of negative health effects. It is caused by the presence of contaminants in the atmosphere, such as dust, fumes, gases, mist, odour, smoke, or vapour, in quantities that can be harmful to human health. The health effects of air pollution depend on the types, sources, and concentrations of pollutants in the air, as well as the levels and duration of exposure.

Short-term exposure to high levels of particulate matter can lead to reduced lung function, respiratory infections, and aggravated asthma. Long-term exposure to fine particulate matter, on the other hand, increases the risk of more serious diseases, including stroke, heart disease, chronic obstructive pulmonary disease, and cancer. Children, the elderly, and pregnant women are especially susceptible to the adverse effects of air pollution. Maternal exposure to air pollution has been linked to adverse birth outcomes, such as low birth weight, pre-term birth, and small gestational age births. Evidence also suggests that air pollution may impact children's neurological development and increase their risk of developing asthma.

In addition to respiratory issues, air pollution can cause inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body, impacting organs such as the lungs, heart, and brain. Fine particulate matter can impair blood vessel function and accelerate calcification in arteries. This can lead to an increased risk of cardiovascular diseases, such as heart attacks and stroke.

Air pollution has also been linked to an increased risk of certain types of cancer. Studies have found associations between air pollution exposure and lung cancer, breast cancer, and colorectal and prostate cancers.

It is important to note that the effects of air pollution are not limited to physical health. There is growing evidence that psychosocial stress, such as poverty, racial/ethnic discrimination, and residency status, can amplify the harmful effects of air pollution. People of colour and low-income communities are more likely to be exposed to air pollution and suffer more significant health consequences.

Strategies to reduce air pollution

According to a global report, Chicago was the seventh most polluted major city in the US in 2024, down from second place the previous year. This decrease in air pollution levels could be attributed to the warmest winter on record, reducing smoke from wood-burning fireplaces. However, a concerning air quality report in 2025 revealed hazardous air quality in Chicago, with an Air Quality Index (AQI) score of 500, indicating a potential acute event such as wildfire smoke.

To address air pollution and improve air quality, the following strategies can be implemented:

• Determine Priority Pollutants: Identify the specific pollutants of concern for each location based on their health and environmental impacts and the severity of the air quality problem.
• Source Control: Identify and implement measures to control and reduce pollution at its source. This includes using less toxic raw materials and fuels, adopting less polluting industrial processes, and improving process efficiency.
• Control Strategy and Planning: Develop a comprehensive control strategy and plan that incorporates the identified control measures. This plan should include implementation timelines and clearly outline the requirements for owners and operators of emission sources to reduce their contribution to air pollution.
• Public Involvement: Engage with the regulated community, the general public, and stakeholders when developing and implementing the control strategy. This early consultation helps to streamline the process and reduce potential challenges.
• Compliance and Enforcement: Establish compliance and enforcement programs to ensure that emission sources adhere to the requirements set out in the control strategy and plan.
• Economic Incentives: Implement economic incentives such as emissions trading, banking, and emissions caps to encourage pollution reduction.
• Transportation Emissions Control: Control transportation-related emissions by implementing emission controls on vehicles and encouraging the use of cleaner fuels.
• Clean Air Technologies: Utilize resources like the Clean Air Technology Center to access information on air pollution prevention and control technologies, including mechanical collectors, fabric filters, combustion systems, and biological degradation methods.
• Meteorological and Environmental Factors: Consider ambient air quality, meteorological conditions, emission source locations, noise levels, and ancillary pollution from control systems to develop effective control strategies.
• Engineering Factors: Take into account pollutant characteristics, gas stream characteristics, control system performance, and the availability of necessary utilities when designing and implementing control measures.
• Cost Analysis: Utilize cost analysis models and tools to assess the emission reductions and engineering costs associated with air pollution control strategies.

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