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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: This paper shows the first occurrence of OPs over theglobal oceans proving that they undergo long-range atmospheric transport over the global oceans toward the Arctic and Antarctica.
Abstract: Organophosphorus compounds (OPs) being applied as flame retardants and plasticizers were investigated in airborne particles over the Pacific, Indian, Arctic, and Southern Ocean. Samples taken during two polar expeditions in 2010/11, one from East Asia to the high Arctic (CHINARE 4) and another from East Asia toward the Indian Ocean to the Antarctic (CHINARE 27), were analyzed for three halogenated OPs (tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCPP) and tris(1,3-dichloro-2-isopropyl) phosphate (TDCP)), four alkylated OPs (tri-n-butyl phosphate (TnBP), tri-iso-butyl phosphate (TiBP), tris(2-butoxyethyl)phosphate (TBEP), and tris(2-ethylhexyl) phosphate (TEHP)), and triphenyl phosphate (TPhP). The sum of the eight investigated OPs ranged from 230 to 2900 pg m(-3) and from 120 to 1700 pg m(-3) during CHINARE 4 and CHINARE 27, respectively. TCEP and TCPP were the predominating compounds, both over the Asian seas as well as in the polar regions, with concentrations from 19 to 2000 pg m(-3) and 22 to 620 pg m(-3), respectively. Elevated concentrations were observed in proximity to the Asian continent enhanced by continental air masses. They decreased sharply toward the open oceans where they remained relatively stable. This paper shows the first occurrence of OPs over the global oceans proving that they undergo long-range atmospheric transport over the global oceans toward the Arctic and Antarctica.

226 citations


Additional excerpts

  • ...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)....

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  • ...In ambient particles, the concentration of TBEP is often lower than other OPEs found in the remote regions (Möller et al., 2012), while it is comparable with that of other OPEs in urban areas (Salamova et al., 2013)....

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  • ...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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  • ...Recent field measurements suggest that OPEs are persistent in air and can undergo medium to long range transport25 (Möller et al., 2012)....

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  • ...In particular, the10 measurements of TPhP in PM in remote regions (Möller et al., 2012), despite its dominant gas-phase loss contribution (based upon our model results) highlights the effect of multi-component particle mixtures on the kinetics of particle degradation....

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Journal ArticleDOI
TL;DR: In this paper, mixed TiO2-SiO2, Saharan dust and Arizona Test Dust were exposed to NO2 in a coated wall flow tube reactor and photoenhanced uptake of NO2 was observed on all samples.
Abstract: [1] Mineral dust contains material such as TiO2 that is well known to have photocatalytic activity. In this laboratory study, mixed TiO2-SiO2, Saharan dust and Arizona Test Dust were exposed to NO2 in a coated wall flow tube reactor. While uptake in the dark was negligible, photoenhanced uptake of NO2 was observed on all samples. For the mixed TiO2-SiO2, the uptake coefficients increased with increasing TiO2 mass fraction, with BET uptake coefficients ranging from 0.12 to 1.9 × 10−6. HONO was observed from all samples, with varying yields, e.g., 80% for Saharan dust. Three-dimensional modeling indicates that photochemistry of dust may reduce the NO2 level up to 37% and ozone up to 5% during a dust event in the free troposphere.

213 citations

Journal ArticleDOI
TL;DR: Levels of 12 organophosphate flame retardants (OPs) were measured in particle phase samples collected at five sites in the North American Great Lakes basin from March 2012 to December 2012 as discussed by the authors.
Abstract: Levels of 12 organophosphate flame retardants (OPs) were measured in particle phase samples collected at five sites in the North American Great Lakes basin from March 2012 to December 2012 (inclusive). The target compounds were three chlorinated OPs [tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP), and tris(1,3-dichloro-2-propyl) phosphate (TDCPP)], three alkyl phosphates [tri-n-butyl phosphate (TnBP), tris(butoxyethyl) phosphate (TBEP), and tris(2-ethylhexyl) phosphate (TEHP)], and six aryl phosphates [triphenyl phosphate (TPP), tri-o-tolyl phosphate (TOTP), tri-p-tolyl phosphate (TPTP), tris(3,5-dimethylphenyl) phosphate (TDMPP), tris(2-isopropylphenyl) phosphate (TIPPP), and tris(4-butylphenyl) phosphate (TBPP)]. Total OP (ΣOP) atmospheric concentrations ranged from 120 ± 18 to 2100 ± 400 pg/m3 at the five sites, with the higher ΣOP levels detected at Cleveland and Chicago. ΣOP concentrations at these urban sites were dominated by the chlorinated OPs (TCEP, TCPP, and TDCP...

213 citations


Additional excerpts

  • ...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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Journal ArticleDOI
TL;DR: In this paper, a detailed gas-phase chemistry mechanism is combined with dust surface uptake processes to explore possible impacts of mineral dust on tropospheric chemistry, including the formation of sulfate and nitrate on dust, along with the dust effects on the photochemical oxidant cycle for the long-range-transported particles with a diameter of 0.1-40 mm.
Abstract: A detailed gas-phase chemistry mechanism is combined with dust surface uptake processes to explore possible impacts of mineral dust on tropospheric chemistry. The formations of sulfate and nitrate on dust are studied along with the dust effects on the photochemical oxidant cycle for the long-range-transported particles with a diameter of 0.1‐40 mm. The results show that mineral dust may influence tropospheric sulfate, nitrate, and O 3 formation by affecting trace gas concentrations and the tropospheric oxidation capacity through surface processes. The postulated heterogeneous mechanism provides a plausible interpretation for the observed high nitrate and sulfate on dust and the anticorrelation between O 3 and dust in East Asia. The presence of dust results in decreases in the concentrations of SO 2 (10%‐53%), (16%‐100%, defined as NO 3 1 N2O5 1 HNO3), HxOy (11%‐59%, p NOy defined as OH1 HO2 1 H2O2), and O3 (11%‐40%) under model conditions representative of spring dust storms in East Asia. The decrease in solar actinic flux and the surface uptake of O 3 and its precursors contribute to the total O 3 decrease for the conditions studied. Nitrate and sulfate, 0.9‐2.1 and 0.3‐10 m gm 23, respectively, are formed on dust particles, mostly in the size range of 1.5‐10 mm. The magnitude of the dust effect strongly depends on the preexisting dust surfaces, the initial conditions, and the selection of model parameters associated with surface uptake processes. The impact of dust reactions on O 3 reduction is highly sensitive to the uptake coefficient and to the possible renoxification from the surface reaction of HNO 3 on dust.

212 citations


Additional excerpts

  • ...…they are used to adequately compute the trace gas and particulate matter content of the5 atmosphere (Kolb et al., 2010), to evaluate the importance of heterogeneous reactions in the atmosphere (Zhang and Carmichael, 1999), and in the assessment of organic aerosol lifetime (Zhou et al., 2012)....

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Book ChapterDOI
01 Jan 2005

211 citations


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

  • ...Using a mass transfer diffusion model (Jacobson, 2005) combined with a partitioning model (Kroll and Seinfeld, 2008; Pankow, 1994)25 (described in detail in the Supplement), evaporation of TBEP is calculated to contribute less than 0.3 % to the particle-phase loss of TBEP within the residence time…...

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  • ...Thus,15 dlncp dt = k2,PcOH +ke − ke M (9) The value of ke was calculated with a mass transfer model for drops (Jacobson, 2005) and a gas-particle partition model (Kroll and Seinfeld, 2008; Pankow, 1994)....

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  • ...Using a mass transfer diffusion model (Jacobson, 2005) combined with a partitioning model (Kroll and Seinfeld, 2008; Pankow, 1994) 25 (described in detail in the Supplement), evaporation of TBEP is calculated to contribute less than 0....

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