Influence of Ventilation Rate and Indoor Air Mixing on Ozone-Human Skin Chemistry.

Abstract

Human exposure to indoor air pollutants can be impacted both by the rate of outdoor air ventilation and by indoor air mixing driven by fans. To elucidate these effects, we monitored human chemical emissions in an occupied climate chamber, under three air change rates (ACRs: 0.5, 2.5, and 3 h^-1), and, for the highest ACR, with and without mixing fans. Experiments were conducted with ozone present at all ACRs (0.5, 1.5, and 3 h^-1), with additional no-ozone conditions at the two higher ACRs. Volatile organic compounds (VOC) were measured with chemical ionization mass spectrometry (CIMS) using two different reagents (H₃O⁺ and NO⁺). Increasing the ACR reduced the steady-state mixing ratios of all measured compounds. When mixing fans were switched off, ozone volume mixing ratios (VMRs) increased from 25 to 35 ppb, while 6-MHO levels decreased ∼20% from 1.4 to 1.1 ppb. Changes in 6-MHO (6-methyl-5-hepten-2-one) and O₃ resulted in a relatively unchanged 4-OPA (4-oxopentanal) production rate, resulting in a VMR of 1.8 ppb. Future modeling of this mechanism is needed. These results emphasize the importance of both ventilation (ACR) and air mixing (fans) in determining indoor chemical concentrations.