Experts say the haze, which has blocked mountain views and creates spectacular sunsets, is mostly from fires burning in Siberia.
Ken Reid, Metro Vancouver's superintendent of environmental sampling and monitoring, says the smoke is drifting across the Pacific at several thousand metres before being forced to lower altitudes as it approaches B.C.
Meteorologist Eric Taylor, from the B.C. Ministry of Environment, says he has never seen ozone levels as high in B.C.'s central Interior as he has seen the last few days.
He says the Environment Ministry's objective is to keep ozone levels below 82 parts per billion and the level in the Williams Lake areas has reached 84 parts per billion.
Taylor says the Siberian smoke also carries a lot of other pollutants, but the ozone levels had dropped by Tuesday, and a cold front should clear out the haze over the next few days.
According to the air quality index, the air is worst in Kamloops, and the North and Central Okanagan, where it is forecast to be five out of 10 on Wednesday, partially because of a forest fire near Merritt.
Air quality advisories have been issued for Quesnel, Williams Lake, Prince George, Kamloops, Merritt, Smithers, Burns Lake and Houston in recent days and remain in effect according to the provincial website.
But the advisories for Prince George, Smithers, Burns Lake and Houston were lifted on Tuesday, according to Steve Sakiyama, an air science specialist with the Environment Ministry.