Traffic reduction alters BTEX profiles and environmental effect in near-road atmosphere: Prolonged effects of benzene.

Benzene, toluene, ethylbenzene, and xylenes (BTEX) are key reactive volatile organic compounds (VOCs) that contribute significantly to tropospheric ozone formation and secondary organic aerosol production. Despite their environmental importance, the environmental effect of BTEX remains underexplored, especially in near-road atmosphere, as most studies have focused on particulate matter and nitrogen oxides. This study continuous observed the variations in BTEX at four roadside sites under different traffic emission scenarios before and after the Spring Festival in near-road atmosphere in Shanghai, which purpose to better understand their environmental dynamics. Results indicated that BTEX and NMHCs concentrations declined substantially (41-63 % and ∼60 %, respectively) during the Spring Festival with reduced traffic, while source apportionment using ternary diagrams and B/T ratios revealed distinct shifts from traffic-dominated to non-traffic contributions during the holiday period. However, Benzene remained at a high level and the corresponding estimated carcinogenic risk remained above the acceptable threshold in both periods. This study demonstrated that short-term traffic emission reductions not only lower VOCs levels but also significantly alter BTEX composition, but benzene still had prolonged effects, which explained that identifying BTEX from different sources is crucial for developing effective strategies to control urban environmental ozone and secondary aerosols.