Maypearl ISD's superintendent explained the steps the district has taken to solve high levels of carbon dioxide in classrooms, but parents remain concerned.

Her comment drew laughter from the spectators. The display turns green when the CO2 concentration is 1,000 parts per million (ppm) or less, because the figure indicates the air indoors is being ...

Midrange units print in the 40-60 ppm range, with a large jump to high-end printers that print from 150 to more than 1,000 ppm. Color lasers are slower than their monochrome counterparts ...