title: Predictive model for vehicle air exchange rates based on a large, representative sample.
abstract: The in-vehicle microenvironment is an important route of exposure to traffic-related pollutants, particularly ultrafine particles. However, significant particle losses can occur under conditions of low air exchange rate (AER) when windows are closed and air is recirculating. AERs are lower for newer vehicles and at lower speeds. Despite the importance of AER in affecting in-vehicle particle exposures, few studies have characterized AER and all have tested only a small number of cars. One reason for this is the difficulty in measuring AER with tracer gases such as SF(6), the most common method. We developed a simplified yet accurate method for determining AER using the occupants' own production of CO(2), a convenient compound to measure. By measuring initial CO(2) build-up rates and equilibrium values of CO(2) at fixed speeds, AER was calculated for 59 vehicles representative of California's fleet. AER measurements correlated and agreed well with the largest other study conducted (R(2) = 0.83). Multivariable models captured 70% of the variability in observed AER using only age, mileage, manufacturer, and speed. These results will be useful to exposure and epidemiological studies since all model variable values are easily obtainable through questionnaire.
authors.affiliation: Keck School of Medicine, Environmental Health Division, University of Southern California , Los Angeles, California 90033, United States.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Fruin
authors.forename: Neelakshi
authors.initials: N
authors.lastname: Hudda
authors.forename: Constantinos
authors.initials: C
authors.lastname: Sioutas
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: Delfino
mesh_terms: D000392:Air Movements; D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data*; D016902:Air Pollution, Indoor / Q000032:analysis / Q000706:statistics & numerical data*; D001336:Automobiles / Q000706:statistics & numerical data; D002245:Carbon Dioxide; D004784:Environmental Monitoring / Q000379:methods; D006801:Humans; D019570:Inhalation Exposure / Q000706:statistics & numerical data*; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D001335:Vehicle Emissions; D002245:Carbon Dioxide