Aftertreatment technologies alleviate SOAFP and toxic effects of BTEX in diesel engine exhaust

The emission characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) in diesel exhaust, particularly in relation to typical aftertreatment technologies, remain poorly understood. This study reports the impact of a typical China VI aftertreatment system (ATS) on BTEX emissions from diesel vehicles, along with the associated secondary organic aerosols formation potential (SOAFP) and toxic effects. Although total BTEX concentrations decreased from 787.8 μg/m³ to 77.3 μg/m³ as engine load increased from idle to 75%, benzene consistently accounted for the highest proportion at 47.3%-82.8% across experimental engine loads. The removal efficiency of BTEX in ATS ranged from 1.4% to 8.5% under idle conditions but increased significantly to 96.7% at 75% load, with benzene being removed more efficiently than other species. Among the China VI ATS components, the diesel oxidation catalyst demonstrated the highest BTEX removal efficiency at 73.7%-96.0% under driving conditions, much higher than the selective catalytic reduction and ammonia slip catalyst unit (17.3%-63.4%). In contrast, the diesel particulate filter unexpectedly increased BTEX emissions up to 74.8%. Both SOAFP formation and toxicity effect of BTEX were positively correlated with concentrations, with reductions up to 94.4% and 96.6%, respectively, due to the effect of ATS, and benzene had the highest contribution to toxicity potential. These findings enhance our understanding of BTEX emissions from diesel vehicles, contributing to making diesel emission control policy and optimizing aftertreatment technologies.