Balancing Reductions in Exposure to VOCs and their Secondary Products Indoors vs. the Infiltration of Outdoor Pollutants

Ventilation and source control (e.g. using low volatile organic compound (VOC) emitting materials) are two recommended approaches to control indoor air pollution and VOC’s in particular. Decisions on how to minimize exposure can be supported by indoor air chemistry modeling, since the relationships between VOC’s, their precursors, and building ventilation is so complex. For example, modeling could be used to examine the impact of altering building ventilation. Increasing ventilation could remove some VOC’s while bringing in more oxidants such as hydroxyl radicals, ozone and nitrogen oxides, that could react indoors. In this analysis, we used the Simplified Indoor Air Chemistry Simulator (SIACS), currently under development at EPA, to investigate the relative benefits of reducing all indoor VOC emissions (by using source control) vs. reducing infiltration of ambient oxidants (by making buildings tighter), focusing on a few selected gas-phase compounds with known adverse human health impacts. The modeled scenario used CMAQ ambient air and weather data for Atlanta, Phoenix, New York City and Minneapolis during July, and indoor VOC emissions from the literature. Infiltration was the only source of ventilation. The results for this scenario showed that while secondary species such as PAN-like compounds, acrolein, and glyoxal were reduced by both strategies, the reduction was greater (2-25 times, 1.5 times and 3 times greater, respectively) by decreasing infiltration than by reducing all indoor emissions. Conversely, the reduction of formaldehyde and acetaldehyde, which have important indoor sources, was greater (20 times and 4 times greater, respectively) when indoor emissions were reduced for all VOCs than by increasing infiltration. Indoor ozone and nitric acid concentrations rose somewhat in response to lower indoor VOC emissions, but could be controlled by reducing infiltration. These preliminary results show that, in the modeled scenario, different and sometimes conflicting strategies are needed to control various indoor pollutants, which could be balanced by considering relative risks.