AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Buildup Rate of Organic Film on Household Surfaces Estimated from Particle Production from the Heated Surfaces
LANCE WALLACE, Wayne Ott, Charles Weschler, Alvin Lai, EPA - retired
Abstract Number: 22 Working Group: Indoor Aerosols
Abstract Ultrafine particles are produced in very large quantities by heating electric stovetops and cooking pans. These particles may be ultimately due to an organic film (possibly SVOCs) coating the heated surfaces. When heated, molecules escape from the surface, but as they enter cooler air, supersaturation and condensation occur and particles are created. As time goes on, a surface that has been heated, losing its surface film, will build up a new film after it cools. Assuming a relatively unchanging indoor environment, the buildup would be expected to approach an equilibrium thickness. The time to equilibrium has been estimated by several investigators, varying from a few months to a few years. We report on initial results from an extended experiment to measure whether indeed an equilibrium can be reached in an inhabited house, and if so what the time to equilibrium might be. We also consider the relation between particle production and surface temperature. The approach is to heat surfaces (e.g. borosilicate glass Petri dishes) until no particles are created and then to reheat them after known intervals during which they are exposed to indoor air in an inhabited home. Size-resolved particles in the range of 3-160 nm are counted. Presently 70 experiments have been carried out over exposure periods from 3 to 98 days. Initial indications are that the characteristic time tau may be on the order of 120 days. Observed production rates range from about 10 billion to 1 trillion particles per square cm, with an associated mass of about 0.03 to 3 micrograms per square cm. Few particles are produced below temperatures of 200 degrees C, or above temperatures of 350 degrees C. These values may change as further experiments accumulate (to more than 200 days) over the period between now and the AAAR conference.