## 4 Conclusions  
Eleven vehicle cabin filters were evaluated to understand their FE in removing PM and BC from vehicular exhaust. All tested filters exhibit an inverted V-shape of FE with sizes (6-520 nm), and the most penetrating particle size was found to be 100-200 nm. Nominal filters generally offer 28-30% FE for 100-200 nm particles, 80% FE for 6 nm particles, and 48% for 520 nm particles. Electrostatic filters provide better FE across all tested sizes, showing 44-46% FE for 100-200 nm particles, 94% for 6 nm particles, and 60% for 520 nm particles. Two filters were found to underperform, showing only 78% for 6 nm particles and 35% for 520 nm particles. These filters only show 10-11% FE for 100-200 nm particles. The FE characteristics of all nominal filters did not change considerably, and the FE (with respect to PN, BC, and PM) remained relatively stable (at 30-40% overall) within the course of the experiment, which can be translated to about 1-2 years of typical filter usage time. Electrostatic filters offer a significant improvement in overall FE with 60% at new state. The FE gradually declined over time and reaches the FE of nominal filters in about 1-2 years. The reduction in FE over time is attributed to the accumulation of dust and BC particles over time, which could shadow the charges on the fibers. The underperforming filters only offer less than 20% FE during the course of its usage, and in one case, the FE slightly improved after one year of usage likely due to the accumulation of dust and BC particles.  
Experiments were also conducted to evaluate two charcoal cabin filters to understand their effect on removing BTEX. Observations demonstrated that charcoal filters were useful in removing BTEX compared to non-charcoal filters. One filter showed 11-17% of removal efficiency for BTEX, while the second filter showed 38-41%. Although not performed, it is expected that similar removal efficiencies could occur for similar VOCs. This study showed that the presence of charcoal extends the function of a cabin filter to provide additional gaseous removal ability in addition to PM removal.  
[PERSON] designed the experiment, constructed the laboratory setup, conducted the experiment, collect all gaseous and particle measurements, and analyzed the particle data and manuscript preparation. [PERSON] prepared the BTEX standard and led the laboratory VOC analysis. [PERSON] contributed to the study design and provided the cabin filters. [PERSON] constructed all the electrical connections. All authors have read and agreed to the published version of the manuscript.  
This work was funded by the Emissions Research and Measurement Section of Environment and Climate Change Canada.  
The data presented in this study are available on request from thecorresponding author.  
The authors would like to acknowledge [PERSON], [PERSON], and [PERSON] from Emissions Research and Measurement Section for providing technical suggestions to this study; [PERSON] from Analysis and Air Quality Section for providing scientific comments and suggestions to the VOC experiment; [PERSON] from Departmental Project Management Office Division for providing access to a Dodge Grand Caravan for used in this project. The analysis, results and conclusion presented are those of the authors alone. The conclusions and views expressed do not necessarily, and should not be taken to, any endorsement from ECCC.  
The authors declare no conflict of interest.