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Journal ArticleDOI

OH-initiated heterogeneous oxidation of tris-2-butoxyethyl phosphate: implications for its fate in the atmosphere

19 Nov 2014-Atmospheric Chemistry and Physics (Copernicus GmbH)-Vol. 14, Iss: 22, pp 12195-12207
TL;DR: In this paper, 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.
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.

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Citations
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01 Dec 2010
TL;DR: It is found that even when gas phase organics are removed, it takes ∼24 h for pure α-pinene SOA particles to evaporate 75% of their mass, which is in sharp contrast to the ∼10 min time scale predicted by current kinetic models.
Abstract: Field measurements of secondary organic aerosol (SOA) find significantly higher mass loads than predicted by models, sparking intense effort focused on finding additional SOA sources but leaving the fundamental assumptions used by models unchallenged. Current air-quality models use absorptive partitioning theory assuming SOA particles are liquid droplets, forming instantaneous reversible equilibrium with gas phase. Further, they ignore the effects of adsorption of spectator organic species during SOA formation on SOA properties and fate. Using accurate and highly sensitive experimental approach for studying evaporation kinetics of size-selected single SOA particles, we characterized room-temperature evaporation kinetics of laboratory-generated α-pinene SOA and ambient atmospheric SOA. We found that even when gas phase organics are removed, it takes ∼24 h for pure α-pinene SOA particles to evaporate 75% of their mass, which is in sharp contrast to the ∼10 min time scale predicted by current kinetic models. Adsorption of “spectator” organic vapors during SOA formation, and aging of these coated SOA particles, dramatically reduced the evaporation rate, and in some cases nearly stopped it. Ambient SOA was found to exhibit evaporation behavior very similar to that of laboratory-generated coated and aged SOA. For all cases studied in this work, SOA evaporation behavior is nearly size-independent and does not follow the evaporation kinetics of liquid droplets, in sharp contrast with model assumptions. The findings about SOA phase, evaporation rates, and the importance of spectator gases and aging all indicate that there is need to reformulate the way SOA formation and evaporation are treated by models.

299 citations

Journal ArticleDOI
TL;DR: Experimental and computational studies have begun to reveal the detailed reaction mechanisms and kinetics for gas-phase O3, NO3, and OH when they impinge on organic surfaces, which will help others more accurately predict the properties of aerosols, the environmental impact of interfacial oxidation, and the concentrations of tropospheric gases.
Abstract: Heterogeneous chemistry of the most important atmospheric oxidants, O3, NO3, and OH, plays a central role in regulating atmospheric gas concentrations, processing aerosols, and aging materials. Recent experimental and computational studies have begun to reveal the detailed reaction mechanisms and kinetics for gas-phase O3, NO3, and OH when they impinge on organic surfaces. Through new research approaches that merge the fields of traditional surface science with atmospheric chemistry, researchers are developing an understanding for how surface structure and functionality affect interfacial chemistry with this class of highly oxidizing pollutants. Together with future research initiatives, these studies will provide a more complete description of atmospheric chemistry and help others more accurately predict the properties of aerosols, the environmental impact of interfacial oxidation, and the concentrations of tropospheric gases.

86 citations

Journal ArticleDOI
TL;DR: It is revealed for the first time that water has a negative role in the ·OH-initiated degradation of TCPP by modifying the stabilities of prereactive complexes and transition states via forming hydrogen bonds, which unveils one underlying mechanism for the observed persistence ofTCP in the atmosphere.
Abstract: Tris(2-chloroisopropyl) phosphate (TCPP), a widely used organophosphate flame retardant, has been recognized as an important atmospheric pollutant. It is notable that TCPP has potential for long-range atmospheric transport. However, its atmospheric fate is unknown, restricting its environmental risk assessment. Herein we performed quantum chemical calculations to investigate the atmospheric transformation mechanisms and kinetics of TCPP initiated by ·OH in the presence of O2/NO/NO2, and the effects of ubiquitous water on these reactions. Results show the H-abstraction pathways are the most favorable for the titled reaction. The calculated gaseous rate constant and lifetime at 298 K are 1.7 × 10–10 cm3molecule–1 s–1 and 1.7 h, respectively. However, when considering atmospheric water, the corresponding lifetime is about 0.5–20.2 days. This study reveals for the first time that water has a negative role in the ·OH-initiated degradation of TCPP by modifying the stabilities of prereactive complexes and transi...

72 citations

Journal ArticleDOI
TL;DR: It is recommended that long-term monitoring programs targeting flame retardants (FRs) include urban sites, which provide an early indicator of effectiveness of control measures of targeted FRs, while at the same time providing information on emission sources and trends of replacement FR chemicals.

42 citations

01 Dec 2012
TL;DR: Using optical and fluorescence microscopy, images are presented that show the coexistence of two noncrystalline phases for real-world samples collected on multiple days in Atlanta, GA as well as for laboratory-generated samples under simulated atmospheric conditions that reveal that atmospheric particles can undergo liquid–liquid phase separations.
Abstract: A large fraction of submicron atmospheric aerosol particles contains both organic material and inorganic salts. As the relative humidity cycles in the atmosphere and the water content of the particles correspondingly changes, these mixed particles can undergo a range of phase transitions, possibly including liquid–liquid phase separation. If liquid–liquid phase separation occurs, the gas-particle partitioning of atmospheric semivolatile organic compounds, the scattering and absorption of solar radiation, and the reactive uptake of gas species on atmospheric particles may be affected, with important implications for climate predictions. The actual occurrence of liquid–liquid phase separation within individual atmospheric particles has been considered uncertain, in large part because of the absence of observations for real-world samples. Here, using optical and fluorescence microscopy, we present images that show the coexistence of two noncrystalline phases for real-world samples collected on multiple days in Atlanta, GA as well as for laboratory-generated samples under simulated atmospheric conditions. These results reveal that atmospheric particles can undergo liquid–liquid phase separations. To explore the implications of these findings, we carried out simulations of the Atlanta urban environment and found that liquid–liquid phase separation can result in increased concentrations of gas-phase NO3 and N2O5 due to decreased particle uptake of N2O5.

29 citations

References
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Journal ArticleDOI
TL;DR: The main findings were that frequent vacuum cleaning resulted in lower FR concentrations in dust and that dermal contact with dust was as important for the intake of organophosphate FRs as dust ingestion.
Abstract: This study investigates the occurrence of 37 organohalogen and organophosphate flame retardants (FRs) from Norwegian households (n = 48) and classrooms from two primary schools (n = 6). Around 80% of the targeted FRs were detected in air and dust from the sampling sites. The comparison of settled dust with floor dust revealed no statistical differences between median concentrations of the FRs (n = 12). Decabromodiphenyl ether and tris(2-butoxyethyl) phosphate showed the highest median floor dust concentrations in both environments. In the air samples, the highest concentrations were observed for 2,2',4,4'-tetrabromodiphenyl ether and tris(1-chloro-2-propyl) phosphate. Remarkably, the emerging FR, 4-(1,2-dibromoethyl)-1,2-dibromocyclohexane, abbreviated as TBECH or DBE-DBCH, showed the highest indoor air concentrations reported in the literature (households, 77.9 pg/m(3) and schools, 46.6 pg/m(3)). Good Spearman correlations between the FR concentrations in dust and air (0.36 < R < 0.76) showed that is possible to estimate the concentrations in air from analyzed dust, or vice versa. Sources and pathways of exposure to FRs were assessed for the households. The main findings were that frequent vacuum cleaning resulted in lower FR concentrations in dust and that dermal contact with dust, for both children and mothers, was as important for the intake of organophosphate FRs as dust ingestion.

312 citations


"OH-initiated heterogeneous oxidatio..." refers background in this paper

  • ...However, TBEP has been measured in both house 10 dust (Dodson et al., 2012; Ali et al., 2012; Cequier et al., 2014) and ambient particles (Möller et al....

    [...]

  • ...However, TBEP has been measured in both house10 dust (Dodson et al., 2012; Ali et al., 2012; Cequier et al., 2014) and ambient particles (Möller et al., 2012; Salamova et al., 2013)....

    [...]

Journal ArticleDOI
TL;DR: Although the estimated exposure is well below the corresponding reference doses (RfDs), caution is needed given the likely future increase in use of these FRs and the currently unknown contribution to human exposure by other pathways such as inhalation and diet.

309 citations

Journal ArticleDOI
TL;DR: In this article, the effects of adsorption of spectator organic species during SOA formation on SOA properties and fate were investigated. And the results showed that SOA evaporation behavior is nearly size-independent and does not follow the evapuration kinetics of liquid droplets, in contrast with model assumptions.
Abstract: Field measurements of secondary organic aerosol (SOA) find significantly higher mass loads than predicted by models, sparking intense effort focused on finding additional SOA sources but leaving the fundamental assumptions used by models unchallenged. Current air-quality models use absorptive partitioning theory assuming SOA particles are liquid droplets, forming instantaneous reversible equilibrium with gas phase. Further, they ignore the effects of adsorption of spectator organic species during SOA formation on SOA properties and fate. Using accurate and highly sensitive experimental approach for studying evaporation kinetics of size-selected single SOA particles, we characterized room-temperature evaporation kinetics of laboratory-generated α-pinene SOA and ambient atmospheric SOA. We found that even when gas phase organics are removed, it takes ∼24 h for pure α-pinene SOA particles to evaporate 75% of their mass, which is in sharp contrast to the ∼10 min time scale predicted by current kinetic models. Adsorption of “spectator” organic vapors during SOA formation, and aging of these coated SOA particles, dramatically reduced the evaporation rate, and in some cases nearly stopped it. Ambient SOA was found to exhibit evaporation behavior very similar to that of laboratory-generated coated and aged SOA. For all cases studied in this work, SOA evaporation behavior is nearly size-independent and does not follow the evaporation kinetics of liquid droplets, in sharp contrast with model assumptions. The findings about SOA phase, evaporation rates, and the importance of spectator gases and aging all indicate that there is need to reformulate the way SOA formation and evaporation are treated by models.

307 citations

01 Dec 2010
TL;DR: It is found that even when gas phase organics are removed, it takes ∼24 h for pure α-pinene SOA particles to evaporate 75% of their mass, which is in sharp contrast to the ∼10 min time scale predicted by current kinetic models.
Abstract: Field measurements of secondary organic aerosol (SOA) find significantly higher mass loads than predicted by models, sparking intense effort focused on finding additional SOA sources but leaving the fundamental assumptions used by models unchallenged. Current air-quality models use absorptive partitioning theory assuming SOA particles are liquid droplets, forming instantaneous reversible equilibrium with gas phase. Further, they ignore the effects of adsorption of spectator organic species during SOA formation on SOA properties and fate. Using accurate and highly sensitive experimental approach for studying evaporation kinetics of size-selected single SOA particles, we characterized room-temperature evaporation kinetics of laboratory-generated α-pinene SOA and ambient atmospheric SOA. We found that even when gas phase organics are removed, it takes ∼24 h for pure α-pinene SOA particles to evaporate 75% of their mass, which is in sharp contrast to the ∼10 min time scale predicted by current kinetic models. Adsorption of “spectator” organic vapors during SOA formation, and aging of these coated SOA particles, dramatically reduced the evaporation rate, and in some cases nearly stopped it. Ambient SOA was found to exhibit evaporation behavior very similar to that of laboratory-generated coated and aged SOA. For all cases studied in this work, SOA evaporation behavior is nearly size-independent and does not follow the evaporation kinetics of liquid droplets, in sharp contrast with model assumptions. The findings about SOA phase, evaporation rates, and the importance of spectator gases and aging all indicate that there is need to reformulate the way SOA formation and evaporation are treated by models.

299 citations


"OH-initiated heterogeneous oxidatio..." refers background in this paper

  • ...Furthermore, recent studies have found that SOA is a semisolid phase with high viscosity (Abramson et al., 2013; Vaden et al., 2011) and that aged SOA demonstrated a slower evaporation rate than fresh5 or uncoated SOA (Vaden et al., 2011)....

    [...]

  • ...…Liu et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion D iscussion P aper | D iscussion P aper | D iscussion P aper | D iscussion P aper | (Vaden et al., 2011)....

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Journal ArticleDOI
TL;DR: Levels of 13 organophosphate esters (OPEs) and 45 brominated and chlorinated flame retardants (BFRs) were measured in particle phase atmospheric samples collected at Longyearbyen on Svalbard in the European Arctic from September 2012 to May 2013, and ΣOPE concentrations were 1-2 orders of magnitude higher than the ΣBFR concentrations.
Abstract: Levels of 13 organophosphate esters (OPEs) and 45 brominated and chlorinated flame retardants (BFRs) were measured in particle phase atmospheric samples collected at Longyearbyen on Svalbard in the European Arctic from September 2012 to May 2013. Total OPE (ΣOPEs) concentrations ranged from 33 to 1450 pg/m3, with the mean ΣOPE concentration of 430 ± 57 pg/m3. The nonchlorinated tri-n-butyl phosphate (TnBP) and 2-ethylhexyl-diphenyl phosphate (EHDPP) were the most abundant OPE congeners measured, and the sum of all nonchlorinated OPE concentrations comprised ∼75% of the ΣOPE concentrations. The most abundant chlorinated OPE was tris(1-chloro-2-propyl) phosphate (TCPP). Total BFR concentrations (ΣBFRs) were in the range of 3–77 pg/m3, with a mean concentration of 15 ± 3 pg/m3. 2-Ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB) and bis(2-ethylhexyl)tetrabromophthalate (TBPH) were among the relatively abundant BFRs measured in these samples and comprised ∼46% and 17% of ΣBFR concentrations, respectively. Total PBD...

240 citations


"OH-initiated heterogeneous oxidatio..." refers background in this paper

  • ...It has also been detected in remote regions, although its concentration is lower than other OPEs (Möller et al., 2011, 2012; Salamova et al., 2014)....

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