The lower mainland of British Columbia is a geographic region that comprises the districts of Metro Vancouver and the Lower Fraser Valley. It is situated in a complex topographical and coastal location in southwestern British Columbia. Metro Vancouver is Canada's third largest population center. Accessing the Canadian National Air Pollution Surveillance Program (NAPS) database we calculated air pollutant statistics using the Canadian Ambient Air Quality Standards (CAAQS) averaging times, numerical forms, and numerical levels for the years 2001to 2020. Man Kendall and Sen statistical methods were used to test for the presence of trends and the slope of those trends in fine particulate matter (PM 2.5 ), ozone (O 3 ), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), and volatile organic compound (VOC) ambient air concentrations. We did not determine a significant trend in 98 th percentile of the daily 24-hr average PM 2.5 concentrations. We did determine significant negative trends in the annual average of the daily 24-hr average PM 2.5 concentrations at 6 of the 9 locations. Episodic, multi-day duration elevated PM 2.5 concentrations related to forest fires were a significant influence on PM 2.5 ambient concentrations. Annual 4 th highest daily maximum 8-hr average O 3 concentrations showed no trend at 14 of 18 locations, declined at 3 locations, and increased at one location. We determined statistically significant declines in peak and average NO 2 and SO 2 concentrations, and in time-integrated annual VOC concentrations. Implications : This non-parametric, statistical analysis determines 20-year trends in British Columbia lower mainland ambient air quality for PM 2.5 , O 3 , NO 2 , SO 2 and VOC, assesses air quality against Canadian Ambient Air Quality Standards, and highlights the importance of event-based wildfire-sourced PM 2.5 .