"SAN FRANCISCO — The threats from climate change are many: extreme weather, shrinking snowpack, altered ecosystems and rising and more acidic seas, to name a few. Another lesser-known issue may hit especially close to home for city dwellers. In the world’s already smoggy metropolises, pollution is likely to grow worse, a phenomenon scientists have taken to calling the climate penalty.
Ozone is a key culprit. This lung-damaging compound, often formed from chemical reactions involving sunlight and automobile exhaust and other pollution, plagues major cities around the globe. As the climate heats up, it is projected that more ozone will form in polluted areas on sweltering days.
'You have a hot summer, you’re going to get a lot of ozone,' said Daniel Jacob, a professor of atmospheric chemistry and environmental engineering at Harvard."