- Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia and a major risk factor for ischemic stroke. Previous data showed an effect of nitric dioxide, carbon monoxide, ozone, and particulate matter (PM) smaller than 2.5 μm in diameter on atrial fibrillation development. This study aims to evaluate the effect of air pollution on the new AF onset requiring hospitalization. A case-crossover analysis was performed on a population of patients hospitalized in a large tertiary teaching hospital between 2006 and 2010 with first life occurrence of atrial fibrillation; 1458 patients were admitted to the hospital with new-onset AF. AF onset was associated with an interquartile range elevation of carbon monoxide concentrations during the winter season (odds ratio 1.15, p = 0.040) and sulfur dioxide concentrations during the fall season (odds ratio 1.21, p = 0.028). An interquartile range elevation in nitric dioxide concentration was associated with AF onset only among patients younger than 65 years of age (odds ratio 1.08, p = 0.025). Patients with diabetes mellitus or chronic obstructive pulmonary disorder had higher susceptibility for carbon monoxide-associated AF development. Short-term exposure to carbon monoxide, nitric dioxide, and sulfur dioxide was associated with AF onset, suggesting that these pollutants, originating primarily from traffic, might trigger new AF. This knowledge is essential for understanding a pathophysiology of the disease onset and for the development of recommendations for susceptible patients.