ozone

Pinatubo's eruption disrupted the Indian monsoon system, reduced rainfall across South Asia, and contributed to ozone depletion.

Inside the planet's polar vortex, temperatures drop dramatically -- much colder than the air outside -- and the continuous darkness of the long Martian winter allows ozone levels in the atmosphere to rise sharply.

There are holes in the ozone layer, in our ceilings and in our hearts.

City Hall said strong sunshine and hot weather are expected to trigger high ozone levels, with airflow from mainland Europe likely to worsen the situation.

California is home to five of the country’s 10 smoggiest places, as defined by levels of ozone pollution, and also to five of the worst 10 cities by particle pollution, according to the report.