Air Quality Improvement Strategies: Reducing Criteria Pollutants

The Clean Air Act requires the United States Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants known as criteria air pollutants. These pollutants are found all over the United States and can cause harm to human health, the environment, and property damage. The six criteria air pollutants include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. To protect public health and welfare, the EPA establishes NAAQS based on the latest scientific information regarding the effects of these pollutants on health and the environment.

Reducing carbon monoxide emissions

Carbon monoxide (CO) is an odorless, colourless, and toxic gas that is harmful to human health. It is a byproduct of the incomplete combustion of carbon fuels. While carbon monoxide does not directly contribute to global climate change, it does react in the atmosphere to produce methane and ozone, which are significant contributors to human-induced climate change.

Stricter Emissions Standards for Vehicles

Motor vehicles, including automobiles, trucks, and buses, are a primary source of carbon monoxide emissions. Implementing stricter emissions standards for new vehicles can help reduce the release of carbon monoxide into the atmosphere. This can include improving fuel efficiency, promoting the use of alternative fuels, and enforcing regular vehicle maintenance to ensure proper combustion and minimise leaks.

Expand Reliance on Mass Transit

Encouraging the use of public transportation, such as buses, trains, and subways, can help reduce carbon monoxide emissions from individual vehicles. By increasing investment in mass transit systems and making them more accessible, convenient, and affordable, more people may be inclined to use them, thereby reducing the number of cars on the road and lowering carbon monoxide emissions.

Improve Industrial Furnaces and Residential Stoves

Inefficient combustion in industrial furnaces and residential stoves can be a significant source of carbon monoxide emissions. Upgrading to more efficient combustion technologies, improving ventilation systems, and ensuring proper maintenance can help reduce the release of carbon monoxide from these sources.

Reduce Deforestation and Encourage Reforestation

Deforestation, particularly through burning, contributes to carbon monoxide emissions. Reducing the rate of deforestation and implementing sustainable forestry practices can help lower emissions. Additionally, reforestation efforts can aid in carbon sequestration, removing carbon monoxide from the atmosphere.

Enhance Ventilation in Enclosed Spaces

Carbon monoxide can quickly build up in enclosed or poorly ventilated areas, such as garages, tunnels, or parking garages. Improving ventilation in these spaces can help dissipate carbon monoxide and reduce the risk of harmful exposure. Proper ventilation is especially important in areas with high traffic volumes or near sources of combustion, such as vehicles or industrial equipment.

Regular Maintenance of Combustion Equipment

Maintaining and properly adjusting combustion equipment, such as boilers, furnaces, and stoves, is crucial in reducing carbon monoxide emissions. Regular inspections, cleaning, and tune-ups by trained professionals can help identify and repair any leaks or malfunctions that may lead to increased emissions.

Lowering sulfur dioxide levels

To lower sulfur dioxide levels, a combination of regulatory measures, fuel transitions, and emission control technologies is necessary. Firstly, governments can play a crucial role in reducing SO2 emissions by implementing and enforcing strict regulations. For example, the Clean Air Act in the United States requires the Environmental Protection Agency (EPA) to establish National Ambient Air Quality Standards (NAAQS) for criteria air pollutants, including SO2. These standards set limits on the acceptable concentration of SO2 in the atmosphere, and non-attainment areas are required to develop State Implementation Plans (SIPs) to improve their air quality.

In addition to regulatory measures, transitioning away from the use of fossil fuels, particularly those with a high sulfur content, is essential for lowering SO2 levels. This can be achieved by encouraging the use of alternative energy sources such as renewables (solar, wind, hydro, etc.) and natural gas, which produce fewer SO2 emissions. Additionally, the removal of sulfur from fuels before burning can prevent the formation of SO2. The Claus process, for instance, is used in refineries to produce sulfur as a byproduct, thus reducing its release into the atmosphere.

Furthermore, emission control technologies can be employed to capture and reduce SO2 emissions from power plants and industrial facilities. Flue-gas desulfurization (FGD) is a technology that enables SO2 to be chemically bound and captured before it is released into the atmosphere. FGD has been instrumental in reducing SO2 emissions and is often required by environmental regulations. Another method is fluidized bed combustion, where limestone is used as a bed material during the burning of coal to remove sulfur from the fuel.

Additionally, the use of fuel additives such as calcium and magnesium carboxylate in marine engines has proven effective in lowering SO2 emissions. These additives react with sulfur oxides, forming compounds that are then removed from the engine exhaust. In vehicles, particularly diesel engines, federal regulations to reduce the sulfur content in fuels have significantly lowered SO2 emissions. This is an example of how regulatory measures and fuel transitions can work together to reduce pollution.

Lastly, natural processes such as volcanic eruptions, which are a significant source of SO2, cannot be controlled. However, by managing and reducing human-caused emissions, the overall levels of SO2 can be lowered, mitigating the impact of these natural events.

Nitrogen dioxide control

Nitrogen dioxide (NO2) is one of a group of highly reactive gases known as nitrogen oxides (NOx). NO2 is a harmful air pollutant that is a product of vehicle, power plant, and off-road equipment emissions caused by fuels burning at high heat. It is one of the six criteria air pollutants that are subject to primary and secondary National Ambient Air Quality Standards under the Federal Clean Air Act.

Reducing Nitrogen Dioxide Control:

• Nitrogen dioxide primarily results from burning fuels in utility and industrial boilers, as well as in automobiles and trucks. Therefore, controlling the emission of nitrogen oxides from these sources is essential.
• NO2 and certain volatile organic compounds react in the presence of strong sunlight to form ozone or "smog". Thus, reducing NO2 emissions can help mitigate the formation of smog.
• NOx reacts with other chemicals in the air to form particulate matter, ozone, and acid rain. Therefore, controlling NO2 emissions can help reduce the formation of these harmful pollutants.
• Nitrogen oxides are formed by various combinations of oxygen and nitrogen at high temperatures during the combustion process. The higher the combustion temperature, the more nitric oxide is generated.
• As road traffic is the principal outdoor source of nitrogen dioxide, implementing measures to reduce emissions from vehicles, such as improving fuel efficiency and promoting the use of electric vehicles, can significantly decrease NO2 levels.
• Indoor sources of nitrogen dioxide include tobacco smoke and gas-, wood-, oil-, kerosene-, and coal-burning appliances, such as stoves, ovens, space heaters, and fireplaces, particularly those that are unflued or poorly maintained. Reducing the use of these appliances or ensuring proper ventilation can help decrease indoor NO2 levels.
• In some regions, diesel- or propane-fuelled ice resurfacing machines in indoor ice arenas contribute significantly to nitrogen dioxide levels. Switching to electric-powered machines or improving ventilation in these facilities can help reduce NO2 concentrations.

Lead removal

The Clean Air Act, enacted in 1970, contains provisions to control common pollutants, including lead. The Act requires the Environmental Protection Agency (EPA) to establish National Ambient Air Quality Standards (NAAQS) for six common air pollutants, including lead. As a result of regulatory efforts by the EPA, including the removal of lead from motor vehicle gasoline, lead levels in the air have significantly decreased.

In Washington, for example, the phase-out of leaded gasoline in 1975 led to a decline in lead levels in the air, and today, all areas of the state meet the air quality standard for lead. However, aircraft that use leaded aviation fuel and metal processing facilities continue to be significant sources of lead emissions.

To address lead pollution, the EPA has implemented various measures, including:

• Funding for community interventions, outreach, education, training, surveillance, and enforcement.
• Accelerated cleanup of lead smelter sites, such as the Colorado Smelter Superfund site.
• Support for water infrastructure improvements, such as the FAST Start program in Flint, Michigan, to identify and replace lead service lines.
• Public outreach for lead-safe renovation, such as in Denver, Colorado, to increase awareness of lead-safe practices and protect vulnerable populations.
• Raising awareness of lead-based paint, such as in St. Joseph, Missouri, where elevated blood-lead levels were detected in children.

The EPA's efforts to reduce childhood lead exposures are overseen by Regional Lead Coordinators in each of its 10 Regions, who collaborate with various stakeholders to address lead poisoning prevention. These measures have helped to reduce lead levels in the air and protect public health, particularly that of children, who are most vulnerable to the harmful effects of lead poisoning.

Ozone reduction

Ozone is a gas composed of three oxygen atoms. While it occurs naturally in the upper atmosphere, where it forms a protective layer that shields the Earth from harmful ultraviolet radiation, ground-level ozone is a harmful air pollutant and the main ingredient in smog.

Tropospheric, or ground-level ozone, is not emitted directly into the air but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs). This occurs when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight.

Ozone is most likely to reach unhealthy levels on hot, sunny days in urban environments, but it can also affect rural areas as it can be transported long distances by wind. People at greatest risk from breathing air containing ozone include those with asthma, children, older adults, and people who are active outdoors, especially outdoor workers.

To reduce ozone pollution, the Environmental Protection Agency (EPA) has implemented national and regional rules to reduce emissions of pollutants that form ground-level ozone. These include vehicle and transportation standards, regional haze and visibility rules, and regular reviews of the National Ambient Air Quality Standards (NAAQS).

State and local governments play a crucial role in improving air quality by developing and implementing state implementation plans (SIPs) for nonattainment areas. These plans outline specific measures to reduce ozone levels and improve overall air quality. Additionally, individuals can take actions to reduce air pollution, such as reducing vehicle emissions, limiting outdoor activities on high-ozone days, and reducing energy usage.

Frequently asked questions