Globally, air pollution has now become one of the most serious threats to human health. This situation is very dire at roadside areas and poses adverse health outcomes, especially in developing countries experiencing rapid urbanization and industrialization, such as Bangladesh. This study aims to investigate seasonal variation at roadside environments air pollution and its association with traffic volume in an urban area (Gazipur City), Bangladesh. Measurements of air pollutant (PM2.5) and traffic volume were estimated from seven different locations in Gazipur by using Aeroqual sensor and digital devices, respectively, during two distinct seasons (winter and summer) in 2024. Simple linear regression was used to estimate the association between roadside air pollution and traffic volume. Results indicated that the average PM2.5 concentration varied from 192 to 324 µg/m3 during winter and 27 to 72 µg/m3 during summer. Concentrations were highest in the morning, particularly during winter (311 µg/m³), approximately 36% higher than in the afternoon. Results also revealed that there is significant seasonal variation of roadside air pollution. During winter, the average PM2.5 concentration were 4.84 times higher than in the summer season. Additionally, air pollution showed significant association with traffic, explaining up to 92% and 77% of the variance in the winter and summer season, respectively. These findings highlight the importance of tighter control policies (such as proper maintenance of the vehicles, stricter fuel quality standards, phasing out unfit vehicles, proper traffic management etc.) aimed at lowering long-term average roadside air pollution levels and reducing traffic’s contribution to air pollution.