Reductions in Aerosol Exposure Afforded by Indoor Air Cleaning Systems

Abstract

P-317 Introduction: In this paper, we report the efficacy of a variety of in-duct and portable air cleaners for control of PM exposure indoors based on trials conducted under controlled conditions in a fully characterized test home. Methods: Aerosol challenge trials were test conducted inside a 120 m2 test home equipped with a typical forced air ventilation system. In-duct air cleaners included a conventional filter (F1), a pleated fabric filter (F5), a conventional electronic air cleaner (EAC), and a new electrostatics technology (ifD) that relies upon an annular field charger and collection flutes coated with a dielectric material. Portable air cleaners (PAC) included a 6.2 m3/min (220 cfm) unit with a HEPA filter and an ionic unit that operates without a fan (IB). Continuous size-resolved particle number concentrations from multiple rooms in the test home were used to ascertain particle decay rates, whole house particle concentrations, and steady-state particle concentrations following emission of a standard polydisperse fine test dust. Results: Particle decay rates and concentrations in the test home varied substantially among the in-duct and portable air cleaners evaluated. Decay rates for 0.3 to 0.5 μ m particles ranged from less than 0.1 per hour (h-1) when neither the air handling unit (AHU) nor an air cleaner (AC) were operated to 7.2 h-1 during operation of the ifD. Performance of five PAC (3.9 h-1) approached the EAC (4.6 h-1), while tests with one PAC and three IB both resulted in removal rates of approximately 1.4 and 0 h-1, respectively. Similar results were obtained for larger particle sizes including those that contribute most to PM2.5 mass concentrations, except that removal rates were greater overall because of particle deposition to surfaces within the home (Table 1).Table 1: Whole House Removal Rates for 1- 3 μm Particles Measured in a Central Room of the Test HomeSteady-state concentrations achieved by the various systems tested were inversely related to decay rate. For example, steady-state indoor levels for the ifD were 2% of outdoor concentrations, 4% for the EAC, 19% for the 1″ filter, 10% for 1 PAC, and 28% for three IB. Discussion and Conclusions: These experiments carried out under simulated real-world conditions indicate that particle removal rates and whole house particle number concentrations indoors can vary by a factor of 10 or more depending upon the use of in-duct and portable air cleaning systems in a home. These results indicate that the greatest reduction in exposure is achieved by high efficiency, high airflow in-duct air cleaning systems. Use of indoor air cleaners could be an important modifier of PM-health relationships observed in epidemiological studies.