Impact of human presence on secondary organic aerosols derived from ozone-initiated chemistry in a simulated office environment.

Several studies have documented reductions in indoor ozone levels that occur as a consequence of its reactions with the exposed skin, hair and clothing of human occupants. One would anticipate that consumption of ozone via such reactions would impact co-occurring products derived from ozone's reactions with various indoor pollutants. The present study examines this possibility for secondary organic aerosols (SOA) derived from ozone-initiated chemistry with limonene, a commonly occurring indoor terpene. The experiments were conducted at realistic ozone and limonene concentrations in a 240 m(3) chamber configured to simulate a typical open office environment. During an experiment the chamber was either unoccupied or occupied with 18-20 workers. Ozone and particle levels were continuously monitored using a UV photometric ozone analyzer and a fast mobility particle sizer (FMPS), respectively. Under otherwise identical conditions, when workers were present in the simulated office the ozone concentrations were approximately two-thirds and the SOA mass concentrations were approximately one-half of those measured when the office was unoccupied. This was observed whether new or used filters were present in the air handling system. These results illustrate the importance of accounting for occupancy when estimating human exposure to pollutants in various indoor settings.

Effects of child care center ventilation strategies on volatile organic compounds of indoor and outdoor origins.

Preschool children can be at risk from harmful volatile organic compounds (VOCs) exposures in child care centers (CCCs). However, the effectiveness of ventilation for mitigating indoor VOCs exposures from myriad sources in CCCs is unclear. We investigated relationships between indoor exposures and risks of VOCs from indoor and outdoor sources under differentventilation strategies in 104 tropical CCCs. Factor analyses identified five dominant source groups of which four were associated with indoor sources, and one was associated with both indoor and outdoor sources. Indoor VOCs exposures and risks associated with indoor sources were lower in naturally (NV) and hybrid ventilated (HB) CCCs compared to air-conditioned CCCs (ACMV and AC). This is attributed to enhanced dilution via higher ventilation in NV and HB CCCs compared to ACMV and AC CCCs. Conversely, there were no discernible differences in VOCs exposures and risk associated with both indoorand outdoor sources across differentventilation strategies. The observations made in this study have implications of ventilation strategies used in other settings. To mitigate VOCs exposures and risk, it is important to identify their major indoor and outdoor sources first.