title: Vehicle and driving characteristics that influence in-cabin particle number concentrations.
abstract: In-transit microenvironments experience elevated levels of vehicle-related pollutants such as ultrafine particles. However, in-vehicle particle number concentrations are frequently lower than on-road concentrations due to particle losses inside vehicles. Particle concentration reduction occurs due to a complicated interplay between a vehicle's air-exchange rate (AER), which determines particle influx rate, and particle losses due to surfaces and the in-cabin air filter. Accurate determination of inside-to-outside particle concentration ratios is best made under realistic aerodynamic and AER conditions because these ratios and AER are determined by vehicle speed and ventilation preference, in addition to vehicle characteristics such as age. In this study, 6 vehicles were tested at 76 combinations of driving speeds, ventilation conditions (i.e., outside air or recirculation), and fan settings. Under recirculation conditions, particle number attenuation (number reduction for 10-1000 nm particles) averaged 0.83 ± 0.13 and was strongly negatively correlated with increasing AER, which in turn depended on speed and the age of the vehicle. Under outside air conditions, attenuation averaged 0.33 ± 0.10 and primarily decreased at higher fan settings that increased AER. In general, in-cabin particle number reductions did not vary strongly with particle size, and cabin filters exhibited low removal efficiencies.
authors.affiliation: Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, California 90089, USA.
authors.forename: Neelakshi
authors.initials: N
authors.lastname: Hudda
authors.forename: Evangelia
authors.initials: E
authors.lastname: Kostenidou
authors.forename: Constantinos
authors.initials: C
authors.lastname: Sioutas
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: Delfino
authors.forename: Scott A
authors.initials: SA
authors.lastname: Fruin
mesh_terms: D000392:Air Movements; D016902:Air Pollution, Indoor / Q000032:analysis*; D001336:Automobiles; D004784:Environmental Monitoring / Q000379:methods*; D005374:Filtration; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis; D001335:Vehicle Emissions; D014691:Ventilation
chemical_list: D052638:Particulate Matter; D001335:Vehicle Emissions