Objectives/Hypothesis Air pollution has emerged as an important environmental risk factor for chronic rhinosinusitis (CRS) progression. This study assessed exposure to five types of air pollution (PM2.5/10, SO2, NO2, CO, O-3) and explored their effects on CRS with nasal polyps (CRSwNP) severity and endotype. Study Design Retrospective cohort study. Methods Air pollution data from monitoring sites in Beijing were obtained to assess individual air pollution exposure. Outcomes of CRSwNP (n = 282) including Lund-Mackay (L-M) score, Lund-Kennedy (L-K) score, visual analogue scale (VAS) score and nasal patency/airflow resistance and so on were measured to analyze correlations with air pollution and compare groups with different exposure types. Multivariable-adjusted binary logistic regression was used to determine potential air pollution risk factors of the endotype of eosinophilic CRSwNP (ECRSwNP). Results Short-term exposures to PM2.5/10, SO2, CO, NO2, and O-3 were weak but significantly associated with increased L-M scores. Short-term exposures to PM10, CO, and NO2 were correlated with increased VAS headache/facial pain scores. The L-M scores of the group of the highest PM2.5 (>= 150 mu g/m(3)) exposure were significantly higher than those of control group. For each increased unit of the average concentration of PM2.5, there was a 1.047-fold (95% confidence interval, 1.005-1.091) increased risk of the endotype of ECRSwNP. Conclusions Air pollution exposure exacerbated CRSwNP severity and PM2.5 could be a risk factor for endotype of ECRSwNP, suggesting the role of air pollution in CRSwNP pathogenesis. Level of Evidence 4 Laryngoscope, 2021