Wildfire smoke (WFS) is the leading climate-related risk in Canada and the main source of harmful air pollution. While short-term breathing problems caused by smoke are well known, there is limited knowledge on how repeated exposure contributes to long-term lung disease. This study is a controlled human exposure to varying concentrations of WFS in a safe setting. By comparing the effects of different concentrations, this research will improve understanding of health impacts, identify who may be most vulnerable to exposures, and explore biological changes that could lead to chronic illness.