11.5: Clean Air
While air pollution is certainly a contributor to climate change via GHGs, it also harms human health in other ways. Air pollution is generated both by natural (biogenic) and human (anthropogenic) sources. Wildfires and volcanoes can spew particulate matter into the air, while vehicle emissions and industrial pollutants produce smog and other gasses. Some air pollutants also undergo chemical reactions when exposed to sunlight which create harmful ground level ozone. Wind currents and water vapor can carry pollutants miles away from their original source. The WHO asserts that both ambient (outdoor) and indoor air pollution contribute to over 7 million deaths around the world each year (WHO, 2019).
The Clean Air Act of 1970 regulates air pollution by empowering the Environmental Protection Agency (EPA) to set and enforce air quality standards. There are six pollutants for which the EPA sets National Ambient Air Quality Standards (NAAQS) for, which are called criteria pollutants. These include carbon monoxide, sulfur dioxide, nitrogen oxide, particulate matter, ozone, and lead. In 1990 the Clean Air Act was amended to include another category of hazardous air pollutants , such as volatile organic compounds (VOCs), pesticides, herbicides, and radionuclides (Frumkin, 2016). The Agency for Toxic Substances and Disease Registry (ATSDR), an agency of the U.S. Department of Health and Human Services, responds to potential toxic emergencies, assists local public health departments, conducts research, and maintains a registry with toxicological profiles of the health effects of natural and man-made hazardous substances that affect our soil, water, and air (ATSDR, 2024).
Primary air pollution is released straight from its source. For example, carbon monoxide is released from motor vehicle exhaust and the combustion of fossil fuels in power plants. It is also released in smoke from forest fires, and is present in environmental (or “second-hand”) tobacco smoke. When other compounds like nitrogen oxides and sulfur dioxide are exposed to sunlight, they can undergo chemical reactions that create ozone and particulate matter. These subsequent pollutants are called secondary air pollution. Thus, air quality is often worse on warm, sunny, summer days than on colder, winter days (Frumkin, 2016, Seabert et al., 2021).
Ozone is both beneficial and hazardous to human health depending on where it exists. In the stratosphere (upper layer of Earth’s atmosphere), ozone blocks harmful UV rays from the sun and protects humans, plants, and animals below - preventing things like skin cancer and cataracts. Compounds called chlorofluorocarbons (CFCs) were used extensively in the mid-20th century to make aerosol propellants, for refrigerators, and in building materials, but these and other pollutants were found to be depleting the ozone layer. Fortunately, in 1987, the Montreal Protocol was signed and countries began phasing out production of ozone depleting substances. Scientists predict that it will be completely repaired by the middle of the 21st century (EPA, 2023). Ground level ozone (in the troposphere) on the other hand, is quite harmful to humans, plants and animals. It can damage the heart and lungs and lead to a variety of chronic diseases (USGCRP, 2023a). Ozone can also be worse in the summer months as a layer of warm air called an inversion layer will trap pollution closer to ground level instead of letting it disperse upward into the stratosphere (Seabert et al., 2021).
Particulate matter is made up of very fine particles of dust, soot, and other solids or liquids of varying sizes. When breathing through the nose, larger particles are typically caught in the nose and upper respiratory system, trapped in mucus and expelled in coughs and sneezes. However, fine particulate matter, or PM2.5 (particulate matter smaller than 2.5 micrometers) can get inhaled much deeper into the lungs and cause damage to lung tissue, as well as increasing the risks of cardiovascular and neurological issues (USGCRP, 2023a). Particulate matter comes from dust, smoke, industrial pollution, vehicle emissions, pollen, and even sea-spray (Frumkin, 2016). We often see particulate matter in the air as smog or brownish haze, hovering over a city-scape on a sunny day.
Air pollution disparately affects minoritized communities including people of color and those of lower socioeconomic status, both in urban and rural areas. This can often be connected to policies and practices such as redlining, as well as industrial zoning. Exhaust from diesel trucks and industrial facilities can be much higher in urban areas, whereas rural areas may be more exposed to pollution from agricultural practices - such as dust and pesticides from crops, or emissions from concentrated animal feeding operations (aka “factory farms). Power plants also release air pollution as well as GHGs. Air quality is made worse by climate change, particularly during heat waves, which may create more secondary air pollution (USGCRP, 2023a).
While the EPA monitors and regulates ambient air pollution, it does not have the same oversight of indoor air pollution. Indoor air pollution can come from building materials, insulation, environmental tobacco smoke, and burning wood, coal, kerosene and even natural gas for cooking or warmth. Mold, mildew, pet dander and dust can also cause respiratory problems. Household cleaning products can release VOCs, which can be particularly harmful to the respiratory system if certain compounds are mixed and then inhaled. Improperly vented combustion for cooking or heating releases carbon monoxide, nitrogen oxides, and particulate matter into the household air. Radon is a radioactive gas that is released from uranium-rich rocks, and can seep into cracks in a home’s foundation and cause lung cancer. Switching to cleaner fuel sources for cooking (such as electricity), removing sources of pollution (such as environmental tobacco smoke), using appropriate ventilation when using cleaners or solvents, and using central ventilation and air conditioning (HVAC) filters or portable air filters are all ways to reduce indoor air pollutants. Additionally, any home improvement projects done on old houses should first be tested for asbestos and lead - as these were commonly used in building materials in the 20th century (EPA, 2014). According to the WHO, 2.3 billion people around the world still use solid fuel for cooking (such as wood, charcoal, and dung), exposing mostly women and children to high levels of air pollution and increasing the risk of respiratory and cardiovascular diseases, cancers, and some infectious diseases as well. In low and middle-income countries, efforts can be made to move toward cleaner fuel sources, such as natural gas and electricity, which would improve air quality, reduce GHGs, and improve health equity (WHO, 2023).
This home’s interior, though beautiful, houses a potential hazard on many levels, therefore, special care need be taken in order to safely operate this wood-burning stove, for not only does it generate a terrific amount of heat, it does so using flame, rather than electricity, which is much more difficult to control. This woman was about to place what appears to be a piece of treated lumber (which can also release harmful pollutants) into the stove as fuel.