Abstract
Abstract. A particle-phase relative rates technique is used to investigate the heterogeneous reaction between OH radicals and tris-2-butoxyethyl phosphate (TBEP) at 298 K by combining aerosol time-of-flight mass spectrometry (C-ToF-MS) data and positive matrix factor (PMF) analysis. The derived second-order rate constants (k2) for the heterogeneous loss of TBEP is (4.44 ± 0.45) × 10−12 cm3 molecule−1 s−1, from which an approximate particle-phase lifetime was estimated to be 2.6 (2.3–2.9) days. However, large differences in the rate constants for TBEP relative to a reference compound were observed when comparing internally and externally mixed TBEP/organic particles, and upon changes in the RH. The heterogeneous degradation of TBEP was found to be depressed or enhanced depending upon the particle mixing state and phase, highlighting the complexity of heterogeneous oxidation in the atmosphere. The effect of gas-particle partitioning on the estimated overall lifetime (gas + particle) for several organophosphate esters (OPEs) was also examined through the explicit modeling of this process. The overall atmospheric lifetimes of TBEP, tris-2-ethylhexyl phosphate (TEHP) and tris-1,3-dichloro-2-propyl phosphate (TDCPP) were estimated to be 1.9, 1.9 and 2.4 days respectively, and are highly dependent upon particle size. These results demonstrate that modeling the atmospheric fate of particle-phase toxic compounds for the purpose of risk assessment must include the gas-particle partitioning process, and in the future include the effect of other particulate components on the evaporation kinetics and/or the heterogeneous loss rates.
Highlights
The effects of fine particles on the atmosphere, climate, and public health are among the central topics in current environmental research (Pöschl, 2005)
We demonstrated that the larger the tracer fragment chosen, the larger the k2 value is derived if the products are highly similar to the reactant and a unit mass resolution (UMR) aerosol mass spectrometer (AMS) is utilized (Liu et al, 2014b)
positive matrix factor (PMF) analysis was performed using the combined AMS data of both tris-2-butoxyethyl phosphate (TBEP)-AN and CA and AN (CA-AN) to provide reference spectra and to assess the ability of PMF to correctly separate the signals of TBEP and CA from their corresponding products
Summary
The effects of fine particles on the atmosphere, climate, and public health are among the central topics in current environmental research (Pöschl, 2005). Oxidant exposure is in turn derived by the measured loss of a gas-phase reference compound, applying known second-order gas-phase rate constants (k2) towards the oxidant Using this method, many studies have reported the uptake coefficients of O3, OH, Cl, and NO3 on various organic aerosols (Hearn and Smith, 2006; George et al, 2007; Lambe et al, 2007; McNeill et al, 2007, 2008; Smith et al, 2009; Kessler et al, 2010, 2012; Renbaum and Smith, 2011; Liu et al, 2012a; Sareen et al, 2013). The derived kinetic parameters are used as inputs into a partitioning model as a means to estimate the overall atmospheric lifetime of OPEs including TBEP, tris-2-ethylhexyl phosphate (TEHP), triphenyl phosphate (TPhP) and tris-1,3-dichloro-2-propyl phosphate (TDCPP)
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