The first major recorded episode of air pollution that produced human casualties occurred in:

The first major recorded episode of air pollution that resulted in human casualties is attributed to the incident that occurred in Donora, Pennsylvania, in 1948. This event is significant because it marked a turning point in public awareness about the dangers of air pollution and its potential impact on health.

In Donora, a temperature inversion trapped industrial smoke containing sulfur dioxide and other pollutants close to the ground, leading to a smog that lasted several days. This situation resulted in over 6,000 individuals suffering from respiratory issues, and there were at least 20 recorded deaths. The severe health effects experienced by the residents underscored the critical need for environmental regulations and raised awareness about the connection between air quality and public health.

This historical context explains why the Donora incident is recognized as a pivotal moment in environmental health history. It serves as an example of how unchecked industrial emissions can dramatically affect air quality and human health. The consequences of the Donora smog spurred government action and led to increased efforts to monitor and regulate air pollution in the United States and beyond.