VANCOUVER -- Wildfire smoke continues to plague the south coast Wednesday, with air quality advisories for Metro Vancouver and the Fraser Valley extended for the ninth day in a row.

The hazy conditions are largely due to raging wildfires in Washington State and Oregon.

Air quality improved slightly Tuesday night, but ground-level smoke still remains and is expected to remain throughout the week.

Metro Vancouver says a weather system forecast for Friday may bring further improvements in air quality, though the smoke concentrations may vary widely across the region as winds and temperatures change, and as wildfire behaviour changes.

The fine particulate matter advisory that has been in effect since Sept. 8.

Fine particulate matter, also known as PM2.5, refers to airborne solid or liquid droplets with a diameter of 2.5 micrometres or less.

It can easily penetrate indoors because of its small size.

People with chronic underlying medical conditions or acute infections such as COVID-19 should postpone or reduce outdoor physical activity until the advisory is lifted, especially if breathing feels uncomfortable.

Canada Post suspended mail and parcel delivery in several communities Tuesday due to poor air quality.

White Rock, Cloverdale and New Westminster were given a “red alert” and will not receive mail until conditions improve.

Other parts of Metro Vancouver and the Fraser Valley experienced delays to service.

“The safety of our employees is our number one priority,” said Canada Post on its website.

The latest updates on delivery service can be found here.

Southern B.C. has recorded some of the worst air quality readings in the world this past week.