Background: More attention is required on the relations between air pollution and exercise characteristics. Aims: This systematic review aims to investigate the combined effects of exercise intensity and duration in ambient air pollution referenced against 2021 WHO Air Quality Guidelines, on lung function and fractional exhaled nitric oxide (FeNO). Methods: A search was conducted using PubMed, Sport Discus, Proquest, and Web of Science databases, up to August 2023, in accordance with the PRISMA guidelines. Results: From 1220 identified articles, 22 were included based on inclusion and exclusion criteria. Exercise intensity and duration were reported as described by authors of the original research. Pollutant concentrations were classified as above or below the 2021 24-h WHO Air Quality Guideline pollutant thresholds. Exercise intensities were inconsistent, ranging from “comfortable pace” walking to 90% maximum heart rate. Exercise duration ranged from 20 min to 8 h of intermittent exercise. Eighteen studies measured pollutants that the WHO provide 24 h thresholds for; 14 of those 18 studies had conditions that exceeded threshold for at least one pollutant, and 11 of the 14 reported significant associations between air pollution, exercise, lung function and/or FeNO. Conclusions: Adverse lung function and FeNO responses were associated with exercise in conditions with pollutant concentrations exceeding the 2021 24 h WHO thresholds. Longer duration exercise (> 2 h) was frequently associated with adverse acute responses, whilst the potential influence of exercise intensity was less clear. Evidence appears to suggest exercise ≥ 120 min in pollution concentrations exceeding WHO thresholds may result in reduced lung function.