This week, millions of Americans are anxiously scanning air quality maps focusing on two colors: red and purple. Red indicates "unhealthy" air quality, and purple? "Very unhealthy." "Red is the color ...

This week, millions of Americans are anxiously scanning air quality maps focusing on two colors: red and purple. Red indicates "unhealthy" air quality, and purple? "Very unhealthy." When did purple ...

This week, millions of Americans are anxiously scanning air quality maps focusing on two colors: red and purple. Red indicates "unhealthy" air quality, and purple? "Very unhealthy." When did purple ...