Reactivity of Semivolatile Organic Compounds with Hydroxyl Radicals, Nitrate Radicals, and Ozone in Indoor Air

Abstract

Indoor semivolatile organic compounds (SVOCs) originate from indoor and outdoor sources. These SVOCs partition among different phases and available surfaces, which increases their residence time indoors to several years. SVOCs may also react with indoor oxidants, such as hydroxyl radicals (OH), nitrate radicals (NO3), and ozone. In the present study, the second‐order reaction rate constants of 72 SVOCs in indoor air (gas and particle phases) at room temperature and ambient air pressure were retrieved from the literature. The pseudo–first‐order reaction rate constants of these SVOCs were calculated for the indoor concentration ranges of OH, NO3, and ozone. Then, the extent to which the chemical reaction had a meaningful impact on the removal of SVOCs from the indoor environment was quantitatively analyzed. The orders of magnitude of the second‐order rate constant ranged between 10−15 and 10−10 cm3/(molecule·s) for OH/SVOC reactions, 10−17 and 10−12 cm3/(molecule·s) for NO3/SVOC reactions, and 10−20 and 10−16 cm3/(molecule·s) for ozone/SVOC reactions in indoor air. Assuming that the highest indoor reactant concentrations were 1.8 × 106 molecules/cm3 (7.3 × 10−5 ppb) for OH, 2.5 × 108 molecules/cm3 (10−2 ppb) for NO3, and 1.4 × 1012 molecules/cm3 (58 ppb) for ozone, the highest pseudo–first‐order rate constants in the gas phase for the studied reactions of OH/SVOCs (n = 72), NO3/SVOCs (n = 3), and ozone/SVOCs (n = 14) reached 1.5 h−1 (OH/benzo[a]pyrene), 0.41 h−1 (NO3/acenaphthene), and 1.0 h−1 (ozone/aldrin and ozone/heptachlor), respectively. The pseudo–first‐order rate constants in the particle phase for the studied reactions of OH/SVOCs (n = 13), NO3/SVOCs (n = 6), and ozone/SVOCs (n = 14) at the high indoor reactant concentrations reached 0.09 h−1 (OH/DEHP), 5.8 h−1 (NO3/pyrene), and 11 h−1 (ozone/benzo[a]pyrene), respectively. These results indicate that the chemical reactions of some SVOCs in indoor air have a meaningful impact compared to the air exchange rate, which should be considered in future studies on indoor air quality modeling.

A long-term dynamic model for predicting the concentration of semivolatile organic compounds in indoor environments: Application to phthalates

“…3). BBzP are much lower than the AER (25 h -1 in the environmental chamber, and between 0.5 and 0.71 h -1 in the test house), e.g., for the reaction with the hydroxyl radical in the gas phase, the k1g is between 5.1×10 -3 and 1.4×10 -1 h -1 for DEHP and between 2.6×10 -3 and 7.2×10 -2 h -1 for BBzP) [16]. Therefore, the reactivity of the two phthalates does not have significant influence on their are significantly different (Fig.…”

“…Information on SVOC emissions from other indoor sources is not available in the literature. The mass transfer coefficients [26,27], partition coefficients [6,28] and reaction rate constants [16] can be calculated using methods developed in previous studies. Table S1 in the SI.…”

“…The SVOC concentrations in the gas phase, airborne particles, settled dust, and on each sink surface were predicted. Later, the model was improved by considering the deposition of airborne particles, the resuspension of settled dust [14,15], and the reactivity of SVOCs with hydroxyl radicals, nitrate radicals, and ozone [16]. For the prediction of SVOC concentrations for a large dataset of buildings, a probabilistic approach based on Monte Carlo simulation was developed to predict the distribution of the SVOC concentrations under equilibrium conditions [17].…”

Assessing Human Exposure to SVOCs in Materials, Products, and Articles: A Modular Mechanistic Framework

“…86-88, 92, 93 The reactivity of SVOCs with oxidizing agents varies greatly and thus indoor chemistry may not be relevant for all applications. 94 For chemical reactions in the gas phase to affect indoor environments, their reaction rate has to be shorter than or close to the air exchange rate. 75 This time constraint does not apply to reactions on indoor surfaces, making them particularly important.…”

Semi-volatile organic compounds in French dwellings: An estimation of concentrations in the gas phase and particulate phase from settled dust

“…SVOC mass transfer mechanisms have been investigated in depth in a number of studies (Liu et al, 2012;Rauert and Harrad, 2015;Takigami et al, 2008;Webster et al, 2009;Weschler and Nazaroff, 2017;Wu et al, 2018;Xu et al, 2012). Mechanistic models that do not rely on the equilibrium partitioning assumption have been developed to address the dynamic SVOC mass transfer processes (Wei et al, 2017b;Xu et al, 2010). The present study did not choose an indepth mechanistic model for the prediction because these models usually require detailed information on indoor environments and a number of mass transfer parameters as inputs.…”