One engineer helped develop both leaded gasoline and CFCs.

Two industrial fixes with very different afterlives

In the 1920s, engines often “knocked”: fuel ignited unevenly inside a cylinder, making a damaging metallic rattle and limiting engine performance. Thomas Midgley Jr. and colleagues found that adding tetraethyl lead reduced knocking. The additive was cheap and effective, so it became part of a vast fuel system—cars burned it, and their exhaust carried fine lead particles into streets and neighborhoods.

Lead is a poisonous metal, especially harmful to children’s developing brains. Once released, it does not break down into harmless substances; it can settle into dust and soil and be taken into the body. A solution designed to improve combustion had turned millions of engines into sources of widespread exposure.

Why refrigerants seemed safer

Midgley also helped develop chlorofluorocarbons, or CFCs: chemicals used in refrigerators and air conditioners to carry heat. Earlier refrigerants could be toxic or flammable. CFCs were stable, nonflammable, and relatively safe to handle, making them attractive for appliances and industry.

That stability was the hidden problem. Escaped CFCs could drift into the upper atmosphere, where ultraviolet light broke them apart and released chlorine. A chlorine atom can destroy ozone molecules repeatedly; ozone is the atmospheric shield that absorbs much of the Sun’s harmful ultraviolet radiation. The damage was not obvious where the chemicals were used—it emerged high above the planet, after years of emissions.

The cost of solving the immediate problem

These stories are not simply about one inventor causing two crises. Midgley worked within industrial teams, and companies and consumers adopted products because they addressed urgent, visible problems. The hazards were harder to see: lead traveled with exhaust, while CFCs persisted long enough to reach the stratosphere. In both cases, the benefits appeared quickly and locally; the costs accumulated across populations and, eventually, the planet.

That mismatch is the lasting lesson of Midgley’s career: a chemical can be a remarkably practical fix at the point of use and still create damage far beyond it.