OZONE INTERACTIONS WITH HVAC FILTERS Ping Zhao, Jeffrey Siegel, Richard Corsi The University of Texas at Austin

Motivation Mendell and Smith, American Journal of Public Health ,1990 Indoor air pollution: greatest health risks (EPA) People spend more than 90% inside Robinson and Nelson, EPA, 1995 HVAC: more sick-building syndrome symptoms Mendell and Smith, American Journal of Public Health ,1990

Central Question Why are HVAC systems implicated in sick building syndrome? Hypothesis: Ozone reactions on HVAC filters are part of the answer

Ozone Chemistry Ozone reacts with carbon-carbon double bonds Products: ketones, hydroxyl radicals, aldehydes, and carboxylic acids

Evidence Aldehydes, organic acids, other carbonyls Weschler et al., Environmental Science & Technology, 1992 Commercial: 8 to 26% ozone consumption Hyttinen et al., Indoor and Built Environment, 2003 90% dissatisfied with air downstream of filters after exposure to ozone Regeneration of ozone removal Halás and Beko, Masters Thesis, DTU, 2003 Emission of formaldehyde, acetaldehyde and acetone Schleibinger and Rüden, Atmospheric Environment, 1999

Ozone/Filter Interaction CO3(up) CO3(down) O3 Byproducts O3 Regeneration

Experimental System Pump O3 Generator Mixing Fan Top Chamber O3 Analyzer HVAC Filter Bottom Chamber Flow Controller Bubble Flow Meter

Experimental System

Experiments Filters: 8 residential and 7 commercial In field: 4 - 12 weeks MERV rating: 4 or < 4

1. Clean 2. Residential 3. Commercial 4. Residential

Results to Date: Clean

Results to Date: Residential

Results to Date: Commercial

Ozone Removal Efficiency

Summary Ozone is removed by HVAC filters Removal: reaction with particles Removal: commercial > residential Regeneration during periods of low ozone

So What? Do we have a problem? Ozone reduction is good Production of byproducts Dissatisfied occupants Irony: Remove pollutants and then introduce all air for building across those pollutants

Strategies to Minimize Ozone Reactions 1) Change filters frequently Obvious cost consequences Even lightly soiled filters can react

Strategies to Minimize Ozone Reactions 2) Expose and vent filters to high levels of ozone Technique called passivation Some byproducts can persist for a long time Possibility of secondary reactions Continuous particle deposition New ability to react with ozone

Strategies to Minimize Ozone Reactions 3) Scrub ozone from incoming air Can be done with activated carbon Removes other pollutants Expensive, particularly to get complete removal

Strategies to Minimize Ozone Reactions 4) Scrub VOCs after filter Can be done with activated carbon Removes other pollutants Expensive, particularly to get complete removal Potentially more complex than ozone removal

Proposed Strategies Filter industry has a challenge Opportunity for innovation Ideas include Embedding activated carbon (or other sorbent) in filters Coating filters with reactant that causes benign byproducts Line ducts with disposable liner Strongly advocate more research on nature and extent of problem

Research Questions What by-products are emitted from HVAC filters? What are the impacts of ozone concentration, relative humidity, and air flow rate? How to model ozone removal process? What are HVAC filter impacts on occupant exposure to ozone and byproducts? What is effect of varying ozone exposure? What is effect of continuous particle deposition? What is influence of particle composition? To what degree do HVAC filters lower indoor concentrations of O3 in residential and commercial buildings? What species and quantity of by-products are emitted from HVAC filters during and after exposure to O3? To what degree do O3 concentration, relative humidity, and air flow rate affect O3 removal and production of reaction products? How to model ozone removal process?

Questions?