No abstract

Certain alkenes known to have significant indoor concentrations react with O 3 at rates that are comparable to or faster than typical air exchange rates in commercial and residential buildings; these reactions produce the hydroxyl radical (OH) in meaningful yields. The present study uses a onecompartment mass balance model to investigate the indoor production of OH as a consequence of such chemistry. Important sources for indoor OH include the reactions of O 3 with d-limonene, R-terpinene, 2-methyl-2-butene, and R-pinene, while important sinks include the reaction of indoor OH with d-limonene, nitrogen dioxide, ethanol, formaldehyde, carbon monoxide, and isoprene. The modeling indicates that the OH sources and sinks equilibrate in tens of milliseconds, an interval much shorter than the residence time for a parcel of indoor air. Indoor O 3 drives the production of OH, which scales nonlinearly with the concentration of O 3 . At 20 ppb indoor O 3 , using average indoor concentrations for key reactants, the model predicts a steady-state indoor OH concentration of 6.7 × 10 -6 ppb (1.7 × 10 5 molecules/cm 3 ). This is smaller than a typical midday outdoor OH concentration of 2 × 10 -4 ppb (5 × 10 6 molecules/ cm 3 ) but larger than measured nighttime outdoor levels.The OH radical at 6.7 × 10 -6 ppb will oxidize saturated organics 2-5 orders of magnitude faster than O 3 at 20 ppb. In many cases, the expected oxidation products are more irritating and corrosive than their precursors.

No abstract

Indoor and outdoor ozone concentrations were measured from late May through October at three office buildings with very different ventilation rates. The indoor values closely tracked the outdoor values, and, depending on the ventilation rate, were 20 to 80 percent of those outdoors. The indoor/outdoor data are adequately described with a mass balance model. The model can also be coupled with reported air exchange rates to estimate indoor/outdoor ratios for other structures. The results from this and previous studies indicate that indoor concentrations are frequently a significant fraction of outdoor values. These observations, and the fact that most people spend greater than 90 percent of their time indoors, indicate that indoor ozone exposure (concentration X time) is greater than outdoor exposure for many people. Relatively inexpensive strategies exist to reduce indoor ozone levels, and these could be implemented to reduce the public's total ozone exposure.