New Delhi, July 17 -- According to advisories compiled by the National Weather Service (NWS), several states have issued Code Orange, Code Red and Code Purple air quality alerts as elevated levels of fine particulate matter (PM2.5) push air pollution into unhealthy and, in some places, hazardous ranges.

From New York and Pennsylvania to Michigan, Illinois, Ohio, Maryland and Virginia, deteriorating air quality has triggered health warnings affecting millions of people.

The poor air quality is being driven by smoke from ongoing Canadian wildfires, which has been carried south by prevailing winds into large parts of the Great Lakes, Northeast, Mid-Atlantic and Midwest, according to National Weather Service advisories.

The smoke contains ...