Dynamics of residential indoor gas- and particle-phase water-soluble organic carbon: measurements during the CASA experiment

Abstract

Previous time-integrated (2 h to 4 h) measurements show that total gas-phase water-soluble organic carbon (WSOC_g) is 10 to 20 times higher inside homes compared to outside. However, concentration dynamics of WSOC_g and total particle phase WSOC (WSOC_p)—are not well understood. During the Chemical Assessment of Surfaces and Air (CASA) experiment, we measured concentration dynamics of WSOC_g and WSOC_p inside a residential test facility in the house background and during scripted activities. A total organic carbon (TOC) analyzer pulled alternately from a particle-into-liquid sampler (PILS) or a mist chamber (MC). WSOC_g concentrations (215 ± 29 μg-C m⁻³) were generally 36× higher than WSOC_p (6 ± 3 μg-C m⁻³) and 20× higher than outdoor levels. A building-specific emission factor (E_f) of 31 mg-C h⁻¹ maintained the relatively high house WSOC_g background, which was dominated by ethanol (46 μg-C m⁻³ to 82 μg-C m⁻³). When we opened the windows, WSOC_g decayed slower (2.8 h⁻¹) than the air change rate (21.2 h⁻¹) and E_f increased (243 mg-C h⁻¹). The response (increased E_f) suggests WSOC_g concentrations are regulated by large near surface reservoirs rather than diffusion through surface materials. Cooking and ozone addition had a small impact on WSOC, whereas surface cleaning, volatile organic compound (VOC) additions, or wood smoke injections had significant impacts on WSOC concentrations. WSOC_g concentration decay rates from these activities (0.4 h⁻¹ to 4.0 h⁻¹) were greater than the normal operating 0.24 h⁻¹ air change rate, which is consistent with an important role for surface removal.