AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
A Tangled Web: Occupants, Squames, Ozone, SOA and SVOCs in Indoor Environments
CHARLES WESCHLER, UMDNJ-Robert Wood Johnson Medical School
Abstract Number: 217 Working Group: Invited by Conference Chair
Abstract By their very presence and independent of their activities, humans influence the environments they occupy. The outer layer of human skin — the stratum corneum — is covered by lipids including squalene and unsaturated fatty acids. These compounds react readily with ozone, significantly reducing its indoor concentration and generating oxidized byproducts. From first principles, one expects that some byproducts of ozone-lipid chemistry partition between the gas phase and airborne particles, contributing to secondary organic aerosols (SOA) in occupied rooms. Conversely, the lower indoor ozone levels as a consequence of titration by the exposed skin, hair and clothing of occupants means less generation of SOA from ozone-initiated reactions with terpenoids and other unsaturated organic compounds that can serve as SOA precursors indoors. Occupants also inadvertently transfer their skin oils to exposed indoor surfaces and continuously shed their skin as small flakes, known as “squames.” A typical adult sloughs 200,000 - 600,000 squames per minute, equivalent to 30 - 90 mg per hour. Consistent with their origin, these squames contain squalene (~1% by weight) and unsaturated fatty acids. By transferring their oils and depositing their skin flakes onto indoor surfaces, occupants alter indoor environments even when they are no longer present. Evidence for what humans leave behind includes measured levels of squalene in airborne particles and settled dust, as well as human skin microbiota found in airborne particles and on indoor surfaces as determined by rDNA gene-sequence analysis. The squalene and unsaturated fatty acids in settled dust and on indoor surfaces further impact the levels of ozone and, indirectly, SOA. In turn, indoor particles, including squames, their fragments and ozone-derived SOA, can alter the concentrations and fates of co-occurring SVOCs. All else being equal, as particle concentrations increase, gas-phase concentrations of SVOCs decrease, and emission rates of SVOCs from indoor surfaces increase. For any given SVOC, the larger the ratio of its particle- to gas-phase concentration, the larger the influence of particles on its overall dynamics. Additionally, it has been argued recently that airborne particles might enhance the net flux of SVOCs to human surfaces by as much as a factor of five for realistic indoor conditions. In summary, dynamic physical and chemical processes involving people and particles can markedly influence pollutant exposures that humans experience in indoor environments.