WASHINGTON (AP) — A California company is refusing to recall its ozone generators that federal health authorities believe are unapproved medical devices that could lead to health problems or death.

Generating ozone and negative ions in the air can be done by a corona discharge. For this we can use a sharp tip of negative polarity, acting against a flat metal part of positive or neutral potential ...

Warmer temperatures might be causing plants to emit more chemicals into the atmosphere, adding to one of Phoenix's worst air pollution problems.