DNA methylation changes are potential pathways of environmentally induced health effects. We investigated whether exposure to ambient concentrations of NO 2 , PM 10 , PM 2.5 and O 3 and traffic parameters were associated with global DNA methylation in blood of healthy adults.48 non-smoking adults (25 males) with a median age of 39years were sampled in winter and summer. Global DNA methylation in whole blood (% 5-methyl-2′-deoxycytidine, %5mdC) was analyzed with HPLC. Exposure to air pollutants at the home address was assessed using interpolated NO 2 , PM 10 , PM 2.5 and O 3 concentrations for various exposure windows (60- to 1-day moving average exposures and yearly averages) and GIS-based traffic parameters. Associations between pollutants and %5mdC were tested with multiple mixed effects regression models.Average %5mdC (SD) was 4.30 (0.08) in winter and 4.29 (0.08) in summer. Men had higher %5mdC compared to women both in winter (4.32 vs. 4.26) and summer (4.31 vs. 4.27). When winter and summer data were analyzed together, various NO 2 , PM 10 and PM 2.5 moving average exposures were associated with changes in %5mdC (95% CI) ranging from −0.04 (−0.09 to 0.00) to −0.14 (−0.28 to 0.00) per IQR increase in pollutant. NO 2 , PM 10 , PM 2.5 and O 3 moving average exposures were associated with decreased %5mdC (95% CI) varying between −0.01 (−0.03 to 0.00) and −0.17 (−0.27 to −0.06) per IQR increase in pollutant in summer but not in winter.Decreased global DNA methylation in whole blood was associated with exposure to NO 2 , PM 10 , PM 2.5 and O 3 at the home addresses of non- adults. Most effects were observed for the 5- to 30-day moving average exposures.