Climate Change and the Air We Breathe: Part 1

Title Image: Mexico City smog, 1981  G Lamson/CC BY-NC-SA2.0

Air Quality and Human Health

As a result air pollution is now estimated to be a global health risk on the same level as unhealthy diets and cigarette smoking.

Figure 1 - the global impact of air pollution           Credit: State of Global Air 2024

In the rest of this post we will review the history of outdoor air pollution that triggered government action; how air pollution is harmful; and how Air Quality is defined, measured and managed. In Part 2 we will discuss the tools and government services that can alert you to air pollution threats; and the air pollution impacts of climate change, including rising heat and wildfires.

How Did We Get Here?

By the mid-twentieth century, it became evident that burning fossil fuels, first coal, and later oil and gas, to power cities and industries had created an air quality crisis. In London, England, the catastrophic Great Smog of 1952 led to the deaths of 12,000 people. Faced with an undeniable cause and effect, the government passed the British Clean Air Act in 1956.

Figure 2 - Dense Los Angeles smog helped spark the Clean Air Act    Credit: EPA Archive

  Prior to the passage of the Clean Air Act, control of air pollution was the responsibility of state and local authorities. The Clean Air Act put the federal government in charge, establishing a common regulatory framework across the country.

Air Pollution and Human Health

Figure 3 - Impacts of air pollution on human health   Credit: EPA

Although smog triggered the formation of  the EPA in the 1970's, at that time smog was thought of as mostly ground-level ozone and particulate pollutants were considered to be a less important nuisance. It was not until the 1990fs that research linked small particles to a range of health effects, including asthma symptoms, emergency room visits and premature mortality.

Defining and Managing Air Quality

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Accurately monitoring each of the pollutants is crucial to tracking efforts to reduce pollution at source, with the goal of attaining levels below the current NAAQS for each pollutant.

The U.S. Air Quality Index (AQI) is EPA's tool for communicating day to day outdoor air quality and health risks to the public. AQI reports focus on data for the two most widely distributed pollutants - particulate matter (PM) and ozone (O3). While monitored, Sulfur dioxide is not included in the AQI because its concentrations tend to be very localized, typically near emissions sources, making it less meaningful at regional scales. Similarly, ground level ozone is strongly correlated with both carbon monoxide and nitrogen dioxide levels. The AQI includes six color-coded health risk categories, each corresponding to a range of index values (Figure 4.) The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good outdoor air quality, while an AQI value over 300 represents air quality that is hazardous for everyone.

Figure 4 - EPA Air Quality Index indicates overall air pollution health risk     Credit: EPA

Particle Pollution

Atmospheric particulate matter (PM) comprises microscopic solids or liquid droplets so small that they can be inhaled. Particles smaller than 10 microns in diameter (roughly 0.0004 inches) can be inhaled deeply into the lungs. The smallest particulates can pass through the lungs into the bloodstream, where they can reach every organ in the body.

Figure 5 below shows the size of PM relative to the width of a human hair or a grain of fine sand.  

Figure 5 - Scale of various forms of particulate matter    Credit: EPA

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Ultrafine particles are most commonly emitted through combustion from natural or human sources. Human activity is believed to be responsible for the largest share of UFPs due to the prevalence of UFPs in cities, where global industrialization and population growth have had the most notable impact on air pollution

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Ozone

Figure 6 - Heavy smog in New York City, 1973      Credit: EPA Archive

  Figure 6 shows New York City engulfed in absolutely epic smog in May, 1973, the result of stagnant air and unconstrained air pollution from vehicle exhaust emissions, oil and coal fueled power stations, garbage and waste incinerators, and factory and building furnaces fueled by oil and coal.

Although ozone is typically generated in cities, wind can transport ozone long distances, potentially causing high ozone levels even in rural areas.

What is the State of U.S. Air Quality?

The graphic below is an encouraging summary of the positive changes in key air pollutants over the past 30 years.

Figure 7 - An EPA success story - steady reduction in major pollutants over the last 30 years.        Credit: EPA

  The graph shows the level of each variable as a percentage over or under that pollutant's NAAQS. Thus national average levels of ozone in 2022 (light green line) near 0% are roughly equal to the current ozone NAAQS, while the annual average PM2.5 level has tracked within a few percent of the PM2.5 NAAQS since 2012. The bright blue line shows the dramatic reduction in Sulfur Dioxide emissions that followed requirements for the installation of air pollution controls at coal-fired power plants, and power plants' shift from coal to comparatively clean "natural" gas. In Part 2 of this post we will discuss the EPA's tools and services that can alert you to air pollution threats in near-real time. We will also review the growing impact of climate change on air pollution, including rising heat, the increasing frequency, size and intensity of wildfires, and a changing allergy season.