An air quality advisory for Metro Vancouver and the Fraser Valley was expanded on Wednesday.
Metro Vancouver had already issued an advisory due to fine particulate matter, known as PM2.5, due to wildfire smoke coming from Oregon and Washington state.
The regional district expanded the advisory to include ground level ozone, which is formed when pollutants react in sunlight. Ground level ozone is most pervasive in the late afternoon and early evening.
People with chronic medical conditions, infections such as COVID-19, young children and the elderly are advised to avoid outdoor physical activity, according to Metro Vancouver.
Exposure is of particular concern for people with lung or heart disease, chronic obstructive pulmonary disease, asthma or diabetes, it added.