Wildfires in Canada are sending heavy smoke across the northern U.S., and New Jersey is experiencing some unhealthy air pollution. The air quality has some Northeasterners wondering, what is the AQI, or Air Quality Index? AQI, or Air Quality Index, is the measure of how healthy or unhealthy the air is.

States across the U.S. are feeling the impact of the Canadian wildfires as air quality takes a hit from the smoke, according to a government website that tracks air quality in the United States.

Another air quality alert is in effect Tuesday for NYC, western Long Island, the Hudson Valley, northwest New Jersey and southwest Connecticut.