UCLA

Taxi drivers and passengers are exposed to traffic related air pollutants (TRAPs), but their exposures and mitigation strategies were rarely explored. In passenger vehicles, the particulate matter (PM) concentrations can be 10 times higher than those in the general ambient environment, and the taxi vehicles are usually leakier than regular passenger vehicles due to their more frequent use and greater wear and tear.

This study investigated fine (PM2.5) and ultrafine particle (UFP) levels outside and inside taxis, and their in-cabin to on-road (I/O) ratios under four different ventilation and mitigation conditions. The taxi drivers’ pre- and post-test urine samples were collected and their urinary hydroxylated-polycyclic aromatic hydrocarbons (OH-PAHs) and malondialdehyde (MDA) were analyzed, as biomarkers for their PAH exposures and lipid peroxidation levels.

The four driving test conditions include realistic working (no mitigation; NM) condition, window closed (WC) condition, window closed and high efficiency cabin air (WC+HECA) filter condition, and HECA filter (HECA) condition. The results show that the average UFP and PM2.5 levels inside taxis were 2.57 x 104 particles / cm3 and 26 �g / m3 under NM. The most stringent WC+HECA condition effectively reduced the in-cabin UFP and PM2.5 and UFP by 47%, 37%, respectively, from the NM condition. Under the NM, the average in-cabin to on-roadway (I/O) ratios for UFP and PM2.5 were 0.60 and 0.75 respectively. But when they were driven under WC+HECA, the average I/O ratios for UFP and PM2.5 were significantly reduced to 0.47 and 0.52 respectively. Although reductions in PAH exposures were not significant, the post-test MDA concentrations were found to be significantly associated with the in-cabin PM2.5 and UFP concentrations, suggesting the reduction of the drivers’ lipid peroxidation can be at least partially attributed to the PM2.5 and UFP reduction by WC+HECA. Overall, these results suggest using HECA filters has the potential to reduce vehicle in-cabin particulate matter (PM) levels and protect drivers’ health.