Worldwide heavy oil and bitumen deposits amount to 9 trillion barrels of oil distributed in over 280 basins around the world, with Canada home to oil sands deposits of 1.7 trillion barrels. The ...global development of this resource and the increase in oil production from oil sands has caused environmental concerns over the presence of toxic compounds in nearby ecosystems and acid deposition. The contribution of oil sands exploration to secondary organic aerosol formation, an important component of atmospheric particulate matter that affects air quality and climate, remains poorly understood. Here we use data from airborne measurements over the Canadian oil sands, laboratory experiments and a box-model study to provide a quantitative assessment of the magnitude of secondary organic aerosol production from oil sands emissions. We find that the evaporation and atmospheric oxidation of low-volatility organic vapours from the mined oil sands material is directly responsible for the majority of the observed secondary organic aerosol mass. The resultant production rates of 45-84 tonnes per day make the oil sands one of the largest sources of anthropogenic secondary organic aerosols in North America. Heavy oil and bitumen account for over ten per cent of global oil production today, and this figure continues to grow. Our findings suggest that the production of the more viscous crude oils could be a large source of secondary organic aerosols in many production and refining regions worldwide, and that such production should be considered when assessing the environmental impacts of current and planned bitumen and heavy oil extraction projects globally.
Ethyl nitrate (EN; C
H
ONO
) is an important component of atmospheric "odd nitrogen" (NO
) whose main source is marine emissions. To correctly describe its air-water transfer and model its global ...distribution, accurate values for its temperature- and salinity-dependent Henry's law solubility constants are needed. Here, we report Henry's law (H
) constants for EN in deionized (DI) water, synthetic sea salt solutions (SSS), and n-octanol at temperatures between 278.2 K and 303.2 K. For DI water, H
constants of (2.03 ± 0.06) M atm
at 293.2 K and (4.88 ± 0.13) M atm
at 278.2 K were observed (all stated uncertainties are at the 1σ level). The data are best described by ln(H
(aq)/Matm
) = -(16.2 ± 0.4)+(4.94 ± 0.11) × 10
/T and ln(H
(octanol)/Matm
) = -(11.1 ± 1.9)+(4.15 ± 0.33) × 10
/T, from which the octanol-water partition coefficient (K
) was calculated. A temperature-independent salting-out factor of 1.25 ± 0.03 and Setschenow constant of K
= (0.33 ± 0.04) mol kg
were determined for SSS. Liquid-phase losses of EN were negligible in all solvents (k
< 1 × 10
s
). The H
(aq) values agree with results by Kames (1993) but are between 2% (at 303.2 K) and 19% (at 278.2 K) lower than the widely used parameterization by Kames and Schurath (1992), indicating a systemic bias in the EN literature and modelling of the Earth's nitrogen cycle.
We describe the results from online measurements of nitrated phenols using a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) with acetate as reagent ion in an oil and gas production ...region in January and February of 2014. Strong diurnal profiles were observed for nitrated phenols, with concentration maxima at night. Based on known markers (CH4, NOx, CO2), primary emissions of nitrated phenols were not important in this study. A box model was used to simulate secondary formation of phenol, nitrophenol (NP), and dinitrophenols (DNP). The box model results indicate that oxidation of aromatics in the gas phase can explain the observed concentrations of NP and DNP in this study. Photolysis was the most efficient loss pathway for NP in the gas phase. We show that aqueous-phase reactions and heterogeneous reactions were minor sources of nitrated phenols in our study. This study demonstrates that the emergence of new ToF-CIMS (including PTR-TOF) techniques allows for the measurement of intermediate oxygenates at low levels and these measurements improve our understanding on the evolution of primary VOCs in the atmosphere.
A well-characterized source of nitrous acid vapour (HONO) is essential for
accurate ambient air measurements by instruments requiring external
calibration. In this work, a compact HONO source is ...described in which gas
streams containing dilute concentrations of HONO are generated by flowing
hydrochloric acid (HCl) vapour emanating from a permeation tube over
continuously agitated dry sodium nitrite (NaNO2) heated to 50 ∘C. Mixing ratios of HONO and potential by-products
including NO, NO2, and nitrosyl chloride (ClNO) were quantified by Fourier transform infrared (FTIR) and thermal-dissociation cavity ring-down spectroscopy (TD-CRDS). A key parameter is the concentration of HCl, which
needs to be kept small (<4 ppmv) to avoid ClNO formation. The
source produces gas streams containing HONO in air in >95 %
purity relative to other nitrogen oxides. The source output is rapidly
tuneable and stabilizes within 90 min. Combined with its small size and portability, this source is highly suitable for calibration of HONO
instruments in the field.
This work describes an incoherent broadband cavity-enhanced absorption
spectroscopy (IBBCEAS) instrument for quantification of HONO and NO2 mixing ratios in ambient air. The instrument is operated in ...the
near-ultraviolet spectral region between 361 and 388 nm. The mirror
reflectivity and optical cavity transmission function were determined from
the optical extinction observed when sampling air and helium. To verify the
accuracy of this approach, Rayleigh scattering cross sections of nitrogen
and argon were measured and found to be in quantitative agreement with literature
values. The mirror reflectivity exceeded 99.98 %, at its maximum near 373 nm, resulting in an absorption path length of 6 km from a 1 m long optical cavity. The instrument precision was assessed through Allan variance analyses and showed minimum deviations of ±58 and ±210 pptv (1σ) for HONO and NO2, respectively, at an optimum acquisition time of 5 min. Measurements of HONO and NO2 mixing ratios in laboratory-generated mixtures by IBBCEAS were compared to thermal dissociation cavity ring-down spectroscopy (TD-CRDS) data and agreed within combined experimental uncertainties. Sample ambient air data collected in Calgary are presented.
The mechanistic details of the Ce(IV)-driven oxidation of water mediated by a series of structurally related catalysts formulated as Ru(tpy)(L)(OH(2))(2+) L = 2,2'-bipyridine (bpy), 1; ...4,4'-dimethoxy-2,2'-bipyridine (bpy-OMe), 2; 4,4'-dicarboxy-2,2'-bipyridine (bpy-CO(2)H), 3; tpy = 2,2';6'',2''-terpyridine is reported. Cyclic voltammetry shows that each of these complexes undergo three successive (proton-coupled) electron-transfer reactions to generate the Ru(V)(tpy)(L)O(3+) (Ru(V)=O(3+)) motif; the relative positions of each of these redox couples reflects the nature of the electron-donating or withdrawing character of the substituents on the bpy ligands. The first two (proton-coupled) electron-transfer reaction steps (k(1) and k(2)) were determined by stopped-flow spectroscopic techniques to be faster for 3 than 1 and 2. The addition of one (or more) equivalents of the terminal electron-acceptor, (NH(4))(2)Ce(NO(3))(6) (CAN), to the Ru(IV)(tpy)(L)O(2+) (Ru(IV)=O(2+)) forms of each of the catalysts, however, leads to divergent reaction pathways. The addition of 1 eq of CAN to the Ru(IV)=O(2+) form of 2 generates Ru(V)=O(3+) (k(3) = 3.7 M(-1) s(-1)), which, in turn, undergoes slow O-O bond formation with the substrate (k(O-O) = 3 × 10(-5) s(-1)). The minimal (or negligible) thermodynamic driving force for the reaction between the Ru(IV)=O(2+) form of 1 or 3 and 1 eq of CAN results in slow reactivity, but the rate-determining step is assigned as the liberation of dioxygen from the Ru(IV)-OO(2+) level under catalytic conditions for each complex. Complex 2, however, passes through the Ru(V)-OO(3+) level prior to the rapid loss of dioxygen. Evidence for a competing reaction pathway is provided for 3, where the Ru(V)=O(3+) and Ru(III)-OH(2+) redox levels can be generated by disproportionation of the Ru(IV)=O(2+) form of the catalyst (k(d) = 1.2 M(-1) s(-1)). An auxiliary reaction pathway involving the abstraction of an O-atom from CAN is also implicated during catalysis. The variability of reactivity for 1-3, including the position of the RDS and potential for O-atom transfer from the terminal oxidant, is confirmed to be intimately sensitive to electron density at the metal site through extensive kinetic and isotopic labeling experiments. This study outlines the need to strike a balance between the reactivity of the Ru═O(z) unit and the accessibility of higher redox levels in pursuit of robust and reactive water oxidation catalysts.
Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO
) represents one of the important interactions between anthropogenic emissions related to combustion and natural ...emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO
-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO
-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO
radical, the difficulty of characterizing the spatial distributions of BVOC and NO
within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry-climate models. This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO
-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO
-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.
The Henry's law solubility (HS) and liquid-phase loss rate constants (kl) of the tropospheric trace gas constituents
peroxyacetic nitric anhydride (PAN; CH3C(O)O2NO2, commonly known as peroxyacetyl ...nitrate) and peroxypropionic nitric
anhydride (PPN; C2H5C(O)O2NO2, also known as peroxypropionyl nitrate) in deionized (DI) water and of PPN in n-octanol
were measured using a flow bubble apparatus at temperatures between 5.0 and 25.0 ∘C. For PAN in DI water, the observed values
for HS,aq are consistent with the literature, whereas the solubility of PPN in DI water is slightly lower than literature
values, ranging from HScp(PPN)aq = (1.49 ± 0.05) M atm−1 at 25.0 ∘C to
HScp(PPN)aq = (7.01 ± 0.25) M atm−1 at 5.0 ∘C (stated uncertainties are
at the 1σ level). The data are best described by
ln(HScp(PAN)aq/Matm-1) = -(17.8±0.3) + (5620±85)/T and
ln(HScp(PPN)aq/Matm-1) = -(19.5±1.7) + (5955±480)/T, where T is in
kelvin. For n-octanol, the PPN solubility ranges from
HScp(PPN)oct = (88±5)Matm-1 at 25.0 ∘C to
HScpoct = (204±16)Matm-1 at 5.0 ∘C and is best described by
ln(HScp(PPN)oct/Matm-1) = -(6.92±0.75) + (3390±320)/T. n-Octanol–water
partition coefficients (KOW) for PPN were determined for the first time, ranging from 59 ± 4 at 25.0 ∘C to
29 ± 3 at 5.0 ∘C. Observed loss rate constants in DI water are consistent with recent literature and larger than the thermal
dissociation rates for both PAN and PPN, consistent with a hydrolysis mechanism, whereas kl values in n-octanol are
significantly smaller than gas-phase dissociation rate constants, likely owing to a “cage effect” in the organic liquid. The results imply that
uptake of either PAN or PPN on cloud water and organic aerosol is negligible but that uptake of PPN may constitute an
overlooked source of peroxy radicals in organic aerosol.
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