Allegheny County: NO2 and Black Carbon

About BC: BC, also known as soot, is formed during high temperature fuel combustion. The major source of BC in the U.S. is diesel vehicles. In Pittsburgh, there are also significant emissions from industrial facilities such as coke ovens and steel mills.

Regulation and attainment: BC is a component of fine particulate matter (PM_2.5). The EPA designates PM_2.5 as a criteria pollutant, and there are two standards: an annual average standard of 12μg/m³ and a 24-hour standard of 35μg/m³. The World Health Organization (WHO) advocates for even lower standards that would better protect health: 10 μg/m³ annual average and 25 μg/m³ daily average. The annual and daily standards reflect the fact that PM_2.5 exposure has both chronic (e.g., death) and short-term (e.g., asthma attacks) health impacts. Allegheny County does not meet either the annual or the 24-hour PM_2.5 standards. BC is not regulated directly by the EPA, but it contributes to the particle problem in Pittsburgh.

Health: Exposure to PM_2.5 is connected to a variety of health impacts: increased asthma attacks, heart attacks, lung cancer, and death. Fetal exposure to PM_2.5 leads to low birth weight and some studies have also linked it to the development of autism. PM_2.5 is a complex mixture of thousands of components, and thus most studies of PM health effects have focused on total PM_2.5 exposure. However there is emerging evidence that certain PM components, including BC, are particularly harmful.

At-risk individuals: At risk individuals can also include those with chronic conditions (heart or lung disease, diabetes, etc), the very young, the elderly, and women of childbearing age. In Pittsburgh, BC concentrations are the elevated near roadways, near industrial areas, and in the river valleys. People who live and/or work in these areas can be exposed to BC concentrations that are a factor of 4-10 higher than the concentrations observed in upland areas located far from major roads or industrial facilities.

What can be done: The benefits to regulating BC emissions are huge. In the United States, the average public health benefits associated with reducing directly emitted PM_2.5 (such as BC) are estimated to range from $290,000 to $1.2 million per ton PM_2.5 in 2030, according to the U.S. EPA. Large industrial sources in Pittsburgh can emit more than 10 tons of BC per year. The cost of the controls necessary to achieve these reductions is generally far lower. Diesel trucks and buses should follow the existing anti-idling laws, which reduce emissions when the vehicles are not in motion. School districts and transit authorities can trade out old buses for newer, cleaner models or retrofit older vehicles with pollution control equipment such as diesel particulate filters. Perhaps most importantly, emissions from industrial facilities can and should be reduced. Mobile sources like cars and trucks are the major source of BC emissions in the U.S., but emissions from this sector have been falling much more rapidly than industrial emissions.

Limitations of this study: (1) The map shows annual average concentrations, and therefore smoothes over shorter plume events that occur periodically and could cause acute health impacts or odor complaints. (2) BC is just one measure of carbon soot particles in the atmosphere. One can also quantify "elemental carbon", or EC, which is measured differently than BC and can therefore produce different concentrations. (3) While there may be limitations or uncertainty in the absolute pollutant concentrations represented by the maps, the gradients and spatial variations are a good representation of reality. Areas colored red have higher concentrations than areas colored blue.

About NO_x: Nitrogen oxides (NO_x) are emitted any time a fuel is burned in air. The major NO_x sources in the U.S. are mobile sources, such as cars and trucks, and stationary sources like power plants and industrial fuel combustion. EPA’s National Ambient Air Quality Standard uses NO₂ as the indicator for the larger group of nitrogen oxides, because the other NO_x species rapidly convert to NO₂ in the atmosphere. NO₂ contributes to the formation of ground-level ozone, fine particle pollution, and a number of adverse effects on the respiratory system.

Regulation and attainment: The EPA sets two NO₂ standards: an annual average standard of 53 parts per billion (ppb) and a 1-hour standard of 100 ppb. The annual and 1-hour standards reflect that NO₂ has adverse health effects associated with both chronic and short-term exposures. Allegheny County is in compliance with the NO₂ standards. However NO₂ concentrations below the EPA-designated standards can still cause respiratory irritation and trigger asthma attacks. NO₂ also contributes to ambient ozone (O₃) and fine particulate matter (PM_2.5), which are both out of attainment for the county and have large social costs associated with exposures.

Health: Exposure to NO₂ causes airway inflammation and can trigger or worsen asthma attacks. Studies show a connection between breathing elevated short-term NO₂ concentrations and increased visits to emergency departments and hospital admissions for respiratory issues, especially asthma. These health impacts can occur well below the EPA designated standards for NO₂.

At-risk individuals: NO₂ concentrations in vehicles and near roadways are appreciably higher than those measured at monitors in the current network. In-vehicle concentrations can be 2-3 times higher than measured at nearby area-wide monitors. Near-roadway (within about 50-100 meters) concentrations of NO₂ have been measured to be approximately 30 to 100% higher than concentrations away from roadways. Individuals who spend time on or near major roadways can experience short-term NO₂ exposures considerably higher than measured by the current network. Approximately 16% of U.S housing units are located within 300 ft of a major highway, railroad, or airport (approximately 48 million people). This population likely includes a higher proportion of non-white and economically disadvantaged people. NO₂ exposure concentrations near roadways are of particular concern for susceptible individuals, including people with asthma, children, and the elderly.

Limitations of these maps: (1) The map shows annual average concentrations, and therefore smoothes over shorter plume events that occur periodically and could cause acute health impacts or odor complaints. (2) While there may be limitations or uncertainty in the absolute pollutant concentrations represented by the maps, the gradients and spatial variations are a good representation of reality. Areas colored red have higher concentrations than areas colored blue.