Metro Vancouver's air quality continues to deteriorate as smoke from dozens of serious wildfires remains over the area.

This afternoon (August 21), the province revised values for the region's Air Quality Health Index, elevating health-risk levels from eight and nine (depending on the specific region) to nine, 10, and 10+.

A 10+ is defined as a "very high" health risk. It's the highest category the B.C. government has.

At the time of writing, the nine, 10, and 10+ health-risk values issued today applied to the City of Vancouver, Burnaby, Richmond, Delta, as well as to cities along the east coast of Vancouver Island.

Slightly lower ratings of seven and eight were recorded in areas covering Surrey, Langley, and Abbotsford.

Things are better around Port Coquitlam, Pitt Meadows, and Maple Ridge, where the Air Quality Health Index stands at four.

Index values for every area of B.C. are available online in the form of a list and an interactive map.

"Metro Vancouver is continuing an Air Quality Advisory for Metro Vancouver and the Fraser Valley because of high concentrations of fine particulate matter due to smoke from wildfires burning in British Columbia and the western United States," reads an August 20 update (issued just prior to risk levels passing 10 today). "Elevated levels of fine particulate matter are expected to persist until there is a change in fire or weather conditions."

For at-risk populations, a 10+ means they should "avoid strenuous activities outdoors. Children and the elderly should also avoid outdoor physical exertion," according to the provincial government.

For the general population, it means people should "reduce or reschedule strenuous activities outdoors, especially if you experience symptoms such as coughing and throat irritation".

The Air Quality Health Index's elevated health-risk warnings come when fine-particulate matter are detected. Fine-particulate matters—about one-thirtieth as thick as a human hair—are of a particular health concern because, when they are inhaled, they are small enough to travel deep into our lungs.

As of August 21, there were more than 50 "wildfires of note" burning across British Columbia. That's an unusually high number, or at least it used to be.

The province declared a state of emergency and requested assistance from the federal government on August 15.

Last year, B.C.'s 2017 wildfire season was the worst in generations. It "dwarfed the historic records for area burned in British Columbia at well over a million hectares, or 12,000 square kilometres," reads a July 2017 government media release. "The effects on people, wildlife and our forest economy will be felt for many years to come.

"Consider also that 2017 was the driest year ever recorded in many parts of B.C.—by a significant margin, according to Environment Canada," it continues.

That July 2017 release from the provincial government notes that year's fires were due, "in large part," to climate change.