Metro Vancouver is advising people in eastern areas of Metro Vancouver and the Fraser Valley to avoid strenuous outdoor activities during mid-afternoon because of high levels of air pollution.
The regional district says high concentrations of ground-level ozone are expected to persist until the weather changes sometime in the next few days.
Exposure is particularly a concern for infants, the elderly and those who have underlying medical conditions such as lung or heart disease and asthma.
"If you are experiencing symptoms such as chest discomfort, shortness of breath, cough or wheeze, follow the advice of your health care provider and stay indoors in air conditioned spaces," said the advisory.
The provincial government's Air Quality Health Index is also forecasting pollution levels across the region will range between four and five on a scale of one to ten on Monday before dropping slightly on Tuesday.
While ozone in the earth's upper atmosphere helps block harmful ultraviolet rays from the sun, at ground level it can cause health problems for humans.
Ground-level ozone is formed from several factors including nitrogen from vehicles and other fossil fuel consumption, volatile organic compounds from sources such as paint, and hot weather and sunlight.