Donora, Pennsylvania Smog Event of 1948

J. Ivel


Donora is a town located in Pennsylvania, just south of Pittsburgh, along the Monongahela River. The town was home to many industries, such as steel mills and zinc melting plants (, 2009). The major zinc melting plant, Zinc Works, was owned by the US Steel Corporation (Bryson, 1998). Zinc Works was built on land adjacent to the Monongahela River. It was upwind of the city of Webster, a city beside Donora on the opposite side of the river (Snyder, 1994). The zinc plant contributed a large assortment of heavy metal dust and carbon monoxide into Webster’s atmosphere (Snyder, 1994). Donora is in a valley created by 400 foot cliffs which is poor topography for the dispersion of the smelting plant’s effluent (Snyder, 1994). The topography of the town was concerning because when emissions are released from a plant the flume should be able to disperse and become less dangerous as it dilutes in the atmosphere. In a valley with large surrounding cliffs, the emissions have nowhere to disperse, therefore creating heavily polluted air in a confined space. Figure 1 shows the Google Earth Image of Donora. The town is spread out along the Monongahela River as Figure 1 indicates. This could also influence the collection of pollutants as the air coming off the river could prevent the pollution from expanding past it, trapping the air above the town.

Google Earth Image of Donora
Figure 1. Google Earth Image of Donora. Source: Google Earth

Concerns were brought to these industries by the residents as the pollution was damaging their belongings. Most the residents in Donora were farmers which complained that the smelter effluent was effecting their crops, livestock, topsoil, fences and houses (Snyder, 1994). These residents were paid off for the damages by the owner of the zinc melting plant in the 1920s, as there were little air pollution regulations at the time in Pennsylvania (, 2009).

Zinc and steel were a desired substance during World War 1. This impacted the Pittsburgh area as there were large economic benefits. Due to the financial benefits, Pittsburgh had large amounts of zinc consumption which required large amounts of zinc production (Snyder, 1994). Due to this many neighbouring towns, such as Donora, built steel and zinc plants.

What Happened in Donora?

In late October, 1948, Donora was hit with an environmental disaster that would change the way air pollution was regulated nationwide.

A typical morning in Donora would include the formation of a layer of fog over the town and which would dissipate as the day proceeded (Snyder, 1994). On Tuesday October 26, 1948, this typical morning fog lingered for longer than normal. By Wednesday, the fog was more distinctive and by Thursday none of the fog had burned off, which became a great concern to the town (Snyder, 1994). The superintendent of the zinc melting plant checked on the plant’s operations, however nothing was out of the ordinary (Snyder, 1994). As the weekend began, the residents began flooding to the hospitals and oxygen was administered. The smog became very thick and created little visibility which made evacuation impossible (Snyder, 1994). The smog dispersed due to rain on October 30 and 31, clearing up visibility and creating breathable air (Hefland, Lazarus, & Theerman , 2001). The event was only about 5 days long, but it left the town of Donora in great distress. Figure 2 displays the smoke stacks at a wire mill in Donora. The picture shows the large amounts of smoke that the mills in Donora produced (Dresbach, 1910).

Donora Smoke Stacks of a Wire Mill
Figure 2. Photo of a Wire Mill in Donora. Source: Library of Congress - Dresbach 1910.

Cause of the Smog

The cause of the Donora smog event of 1948 was in debate for a long time. One possible cause was the zinc smelting plant, Zinc Works, because it had been releasing harmful contaminants since it opened. (Bryson, 1998). On October 26, 1948 air movement over the town was sparse which created a temperature inversion. This inversion trapped the pollutants from Zinc Works that saturated the air over Donora, preventing dispersion (Hefland, Lazarus, & Theerman , 2001). The town’s topography limited air movement and the valleys trapped the air within the town. Zinc Works released particulates and industrial contaminants in their emissions during the zinc smelting process (Hefland, Lazarus, & Theerman , 2001). The three dangerous pollutants included hydrofluoric acid, sulfur dioxide and carbon monoxide (Guenther, 2011). The main contaminant of concern that caused many health issues was the gaseous fluoride in the form of hydrofluoric acid (Bryson, 1998). After the incident subsided the US Steel corporation made a deal with US Public Health officials to attempt to hide the fact that Zinc Works was the main contributor to the event (Bryson, 1998). US Steel even took efforts to protect their company by blocking access to their records from the time of the smog event to reporters and investigators (Bass & John, 1990). With further investigations, it was found that the residents who had lost their lives during the event had high levels of fluoride in their system. The fluoride levels were found in the deceased through a postmortem examination which was completed to determine cause of death. The fluoride was found in fatal levels in the tissue of the smog victim’s body (The Observer-Reporter, 2008). Although the fluoride was predicted to be the reason behind the death and sickness in Donora, no conclusion was made. Many authors who have written pieces on the smog event have mentioned industrial contaminants that caused the sickness. Zinc works concealed their records for so many years that it made it difficult to fully explain the Donora smog event.

Fluoride in Industrial Emissions

Fluoride, as a product released through emissions, is common in industrial plants. Airborne fluoride can be a result of volcanic activity; however, the most airborne fluoride comes from industrial sources in urbanized areas (Fluorides, 2000). Out of the 1334 sites that are on clean-up instructions by the US EPA, about 130 contains fluoride compounds on them (Fluorides, 2000). In 1968, about 155,000 tonnes of airborne fluoride was released from industrial sources (Fluorides, 2000). Steel and aluminum production tend to have the largest amounts of fluoride released, however zinc is typically used in the steel production process to protect it from corroding, therefore it also produces fluoride (Facts about Zinc, n.d.). At the time of the smog event in Donora, there were many steel mills that were facing lawsuits for damages occurring from exposure to fluoride compounds (The Observer-Reporter, 2008).

Smog Effects on Donora

Of the town’s population of 14,000, approximately 20 people passed away and between 5000-7000 were estimated to become very ill due to the smog event (Hefland, Lazarus, & Theerman , 2001). The main reason for the sickness and death was due to the high levels of hydrofluoric acid inhaled by the residents. Hydrogen fluoride is another name given for hydrofluoric acid when it is in the gaseous form (Hydrogen Fluoride (HF), 2014). In the form of gas, it is a colourless fume with an intense irritating odor (Hydrogen Fluoride (HF), 2014). The fluoride levels in the deceased and the near-asthmatic breathing of the survivors were 12 to 25 times greater than the normal levels found in the blood (Guenther, 2011). Fluoride is often defined as a chemical that is found in toothpaste to strengthen teeth. However, in the gaseous form it can cause breathing difficulties, sore bones and discoloured teeth (The Observer-Reporter, 2008). One of the symptoms caused by high levels of fluoride in the body is Dyspnea (Bryson, 1998). Dyspnea is when someone has difficulty breathing. It can feel as if one cannot take a deep breath or their chest feels tight (Bass & John, 1990). The fluoride poisoning was the physical effects people felt, but the residents were also affected emotionally. Many wanted justice for the terrible event and wanted the government to set better control over air pollution. Some people lost loved ones during this event and some lives would never be the same.

Humans were not the only living things negatively affected, livestock and plants were also harmed. Immediately after Zinc Works was up and running, the crops and livestock were sickened downwind of the plant (Schroeder, 2011). The slopes of hills were becoming barren and so much erosion occurred that Donora’s cemetery was exposing caskets (Schroeder, 2011). These effects occurred downwind of the plant before the smog event occurred. They should have been indicators that the plant was releasing harmful chemicals to cause such destruction.

Outcomes of the Donora Smog Event

The deadly Donora smog event not only effected the residents within the five-day period that the event occurred, but also affected them long term. A decade later, it was found that Donora’s mortality rate was still notably greater then it was prior to the event and nearby towns (Bryson, 1998). The Donora smog was devastating to the community physically and mentally. The people who were affected by the smog had to live with serious health problems for many years of their lives and will remember those five days that the smog took over their town.

The Donora smog event was one of the many destructive environmental events that led to the Air Pollution Control Act in 1955 (Hefland, Lazarus, & Theerman , 2001). The public had a huge influence with this along with the physically damaging effects created from the events. The act created in 1955 was then further progressed and reinforced by the Clean Air Acts of 1963, 1970 and 1990 which have increased control measures and improved public health immensely (Hefland, Lazarus, & Theerman , 2001). The Donora smog event was devastating to the town, state and country; however, it was an event that great control and regulations came out of it.


Overall, Donora Pennsylvania was greatly impacted by the deadly smog event in 1948. The smog lasted about five days and killed approximately 20 people. About one third of the population was affected by the smog. The smog was caused by the zinc melting plant, Zinc Works, from their effluent containing substantial amounts of fluoride and a temperature inversion that trapped the effluent over the town. The Donora smog event was devastating to the community, however this event helped create the Air Pollution Control Act in 1955 and further developed the Clean Air Acts. The smog may have been an environmental disaster, but in the end, it helped save more people from air pollution.


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