Robert McLaren

Reactive uptake of glyoxal by particulate matter

from 1.05 � 10 � 11 to 23.1 � 10 � 11 mg particle � 1 min � 1 in the presence of � 5 ppb glyoxal. Uptake coefficients (g) of glyoxal varied from 8.0 � 10 � 4 to 7.3 � 10 � 3 with a median g =2 .9� 10 � 3 , observed for (NH4)2SO4 seed aerosols at 55% relative humidity. Increased g values were related to increased particle acidity, indicating that acid catalysis played a role in the heterogeneous mechanism. Experiments conducted at very low relative humidity, with the potential to be highly acidic, resulted in very low reactive uptake. These uptake coefficients indicated that the heterogeneous loss of glyoxal in the atmosphere is at least as important as gas phase loss mechanisms, including photolysis and reaction with hydroxyl radicals. Glyoxal lifetime due to heterogeneous reactions under typical ambient conditions was estimated to be thet = 5–287 min. In rural and remote areas the glyoxal uptake can lead to 5–257 ng m � 3 of secondary organic aerosols in 8 hours, consistent with recent ambient measurements.

Analysis of Motor Vehicle Sources and Their Contribution to Ambient Hydrocarbon Distributions at Urban Sites In Toronto During the Southern Ontario Oxidants Study

Hydrocarbon distributions measured in the urban area of Toronto during the Southern Ontario Oxidants Study of 1992 are presented. Comparison is made to hydrocarbon distributions measured in other urban areas. Relative concentrations of olefins were found to be depleted aloft compared to the surface level measurements. Chemical mass balance modelling was used to apportion the measured hydrocarbon distributions at York University and other roadside sites to gasoline based sources. The most dominant contributing source was vehicle exhaust. The relative amount of unburned gasoline at York University was found to be significant in the summer, and higher than that observed there during the winter or at other roadside sites. The relative amount of evaporative emissions (gasoline vapour) apportioned by the CMB model at roadside sites was compared to evaporative emissions predicted by a mobile emission factor model, MOBILE5C. The percentage of gasoline based non-methane hydrocarbons (NMHC) apportioned to gasoline vapour by the CMB model was equivalent within error to the relative amount of evaporative NMHC predicted by the MOBILE5C model for summer temperatures. For winter temperatures, the MOBILE5C model predicted significantly less evaporative emissions than that apportioned by the CMB model. An anthropogenic source of isoprene in the urban area has been proposed and tested. The inclusion of an isoprene flux in the exhaust source profile, consistent with that measured in the Auto/Oil Air Quality Improvement Research Program, results in calculated isoprene concentrations that are in agreement with observed concentrations at roadside sites and at York University in the winter. During summer, the combustion related isoprene can only account for a small fraction of the observed isoprene at downtown sites and at York University, at most 20%.

Fluorination effects on the inner-shell spectra of unsaturated molecules

The applicability of the perfluoro effect to the X-ray spectra (300–800 eV) of unsaturated organic molecules is explored. The C1s and F1s (and Ols where appropriate) oscillator strength spectra of five fluoroethylenes, octafluorocyclopentene, formyi fluoride, carbonyl fluoride, hexa-fluorobutadiene, trifluoroacetic acid, hexafluorobutyne-2, hexafluoroacetone, and octafluorona-phthalene were derived from electron impact energy loss spectra recorded under electric-dipole scattering conditions. These spectra are analyzed and compared with those of their perhydro analogs, several of which (naphthalene, acetic acid, butyne-2) are reported for the first time. In unsaturated systems in which all the atoms lie in the molecular plane, such as ethylene, formaldehyde, benzene, etc., perfluorination results in approximately 10 eV shifts of the inner-shell energy loss spectra to higher energies, yet the term values for the C1s→1π∗ excitations are shifted by only 1 eV and often less. In direct contrast, the term values for the equivalent C1s→1π∗ excitations in unsaturated systems having atoms out of the molecular plane, such as butene-2 and acetone, are shifted upward by up to 3 eV upon perfluorination. These different spectral behaviors of planar and nonplanar systems on fluorination quantitatively parallel those which were observed earlier for valence-level ionization potentials (10–20 eV) and attributed to the perfluoro effect. It is observed for the first time that the C1s→1π∗ excitation energies in planar hydrocarbons are only very weakly dependent on the spatial extent of the π-electron system. An explanation involving a localized C1s hole is proposed to rationalize this behavior. The perfluoro effect also predicts that excitations to σ∗ MOs will become relatively low-lying in highly fluorinated planar systems. Such low-lying inner-shell excitations induced by fluorination are observed in the fluoroethylene series and in the fluorocarbonyls. When the negative-ion spectra of the fluoroethylenes are assigned in a self-consistent manner, a σ∗ MO is found to drop into the vicinity of 1π∗ upon fluorination. A similar intrusion of the lowest σ★ MO among the π∗ MOs is also observed upon fluorinating benzene, while evidence for this in the case of naphthalene is less clear, on account of the complex pattern of multiple C1s→nπ∗ transitions in this molecule. Inner-shell oscillator strength distributions are reported for all the spectra considered herein. In general, perfluorination increases the oscillator strengths of C1s→1π∗ transitions by up to a factor of two. Variation of the C1s→1π∗ and O1s→17π∗ oscillator strengths in the series H2CO, HFCO, F2CO shows clearly how the 17π∗ MO becomes more polarized toward C as fluorination proceeds. In some cases, C1s→σ∗ (C-F) oscillator strengths exceed those for C1s→1π∗ transitions.

Impact of Fuel Quality Regulation and Speed Reductions on Shipping Emissions: Implications for Climate and Air Quality

Atmospheric emissions of gas and particulate matter from a large ocean-going container vessel were sampled as it slowed and switched from high-sulfur to low-sulfur fuel as it transited into regulated coastal waters of California. Reduction in emission factors (EFs) of sulfur dioxide (SO₂), particulate matter, particulate sulfate and cloud condensation nuclei were substantial (≥ 90%). EFs for particulate organic matter decreased by 70%. Black carbon (BC) EFs were reduced by 41%. When the measured emission reductions, brought about by compliance with the California fuel quality regulation and participation in the vessel speed reduction (VSR) program, are placed in a broader context, warming from reductions in the indirect effect of SO₄ would dominate any radiative changes due to the emissions changes. Within regulated waters absolute emission reductions exceed 88% for almost all measured gas and particle phase species. The analysis presented provides direct estimations of the emissions reductions that can be realized by California fuel quality regulation and VSR program, in addition to providing new information relevant to potential health and climate impact of reduced fuel sulfur content, fuel quality and vessel speed reductions.

Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol

Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) 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. NO3-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 NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 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 NO3-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 NO3-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.

Sensitivity of ozone concentrations to VOC and NOx emissions in the Canadian Lower Fraser Valley

Abstract The SAPRC90 chemical mechanism module implemented in CALGRID is updated for the specific emissions and applications of the Lower Fraser Valley (LFV) of British Columbia, Canada. The kinetic and mechanistic parameters of lumped VOC reactions recalculated using the LFV emissions profiles are noticeably different from those based on default emissions profiles, indicating the importance of tailoring the parameters to specific regions. The sensitivities of ozone concentrations to total and speciated VOC and NOx emissions as well as to the NO 2 NO x ratios are determined. Significant VOC model species are identified based on the impact of their emissions on ozone formation in the LFV. Of note is the importance of the emissions of a lumped class of aromatics, ARO2, which contains mostly isomers of xylene and trimethylbenzene and is derived chiefly from the use and distribution of gasoline fuels. The ARO2 emissions make the largest contribution of all model VOC species to the ozone levels in the urban plume. The results indicate that reduction of AR02 emissions alone could achieve significant reduction of ozone levels in the LFV. Base case emissions of NOx(NO or NO2) in the LFV contribute negatively to the ozone formation. Any overestimation of NOx or underestimation of VOC in the emissions inventory could cause underestimations of ozone levels by photochemical models.

Inner‐shell excitations in weak‐bond molecules

It is proposed that Rydberg and valence σ* conjugate orbitals have separate existences and can be seen in the same spectrum if the σ* MO can be disentangled from the Rydberg manifold. Because the energy of the σ* MO is a consequence of the σ–σ* split resulting from bond formation, the spectra of molecules having weak bonds should show low‐lying transitions to σ* in addition to the conjugate Rydberg bands. Inelastic electron scattering spectra in the x‐ray region (270–730 eV) of molecules having bond strengths in the 20–50 kcal/mol regime clearly show well‐isolated transitions to low‐lying σ* MOs, and in some cases the simultaneous presence of virtual σ* and Rydberg conjugate orbitals. The general characteristics of excitations from C 1s, O 1s, and F 1s inner orbitals to σ* MOs are listed and illustrated by the x‐ray spectra of several compounds in which the weak bond involves the O–O or O–F linkage. Quantitative inner‐shell optical oscillator strengths derived from the energy loss spectra are reported for...

An optimized method for the determination of volatile and semi-volatile aldehydes and ketones in ambient particulate matter

A method has been developed to measure aldehydes and ketones associated with atmospheric particles. Carbonyl compounds from particulate material collected on Teflon-coated glass-fiber filters were simultaneously extracted and derivatized with an appropriate 2,4-dinitrophenylhydrazine (2,4-DNPH) solution. The efficiency of this procedure utilizing various 2,4-DNPH concentrations and solvent compositions was studied for 13 carbonyl compounds of atmospheric importance. These include formaldehyde, acetaldehyde, acetone, dicarbonyls such as glyoxal and methylglyoxal, and biogenic carbonyls such as pinonaldehyde and nopinone. An extraction solution containing 3 × 10−2 M 2,4-DNPH, in 60% acetonitrile/40% water, and pH 3 was most efficient in extracting and derivatizing these aldehydes and ketones (83-100% recovery). Improved sample enrichment and 2,4-DNPH purification methods were developed that afforded detection limits of 0.009-5.6 ng m−3. The relative standard deviation for replicate analyses were 1.9-10.1%. Carbonyl compounds in ambient particulate samples were quantified during a recent field study. Median values for nine carbonyl species ranged from 0.01-33.9 ng m−3 during the study.

Characterization of Vehicle Emissions in Vancouver BC During the 1993 Lower Fraser Valley Oxidants Study

Abstract As part of the 1993 Lower Fraser Valley Oxidants Study, measurements of mobile source emission factors were performed in the Cassiar Tunnel on the Trans-Canada Highway to measure the on-road contribution to the ozone-forming precursors (NOx and speciated hydrocarbons) along with CO. Observed emission factors were compared to the Canadian versions of the U.S. Environmental Protection Agencys MOBILE models, MOBILE4.1C and MOBILE5C, to assess uncertainty in the predicted mobile source contributions to the Vancouver emissions inventory. A total of 16 1-h runs were made. The timing of the individual runs was designed to encompass different traffic volumes, driving conditions, and times of day. A total of 24,513 vehicles traversed the tunnel during the study, with approximately 91% light-duty vehicles, 4% heavy-duty spark ignition vehicles, and 5% heavy-duty diesel vehicles. MOBILE5C overpredicted the observed value of CO by ∼2%, NMHC by 24%, and NOx by 13%, while MOBILE4.1C underpredicted the observed values by 36, 29, and 23% for CO, NMHC, and NOx respectively.

Differences between measured and reported volatile organic compound emissions from oil sands facilities in Alberta, Canada.

Significance Validation of volatile organic compound (VOC) emission reports, especially from large industrial facilities, is rarely attempted. Given uncertainties in emission reports, their evaluation and validation will build confidence in emission inventories. It is shown that a top-down approach can provide measurement-based emission rates for such emission validation. Comparisons with emission reports from Alberta oil sands surface mining facilities revealed significant differences in VOC emissions between top-down emissions rates and reports. Comparison with VOC species emission reports using currently accepted estimation methods indicates that emissions were underestimated in the reports for most species. This exercise shows that improvements in the accuracy and completeness of emissions estimates from complex facilities would enhance their application to assessing the impacts of such emissions. Large-scale oil production from oil sands deposits in Alberta, Canada has raised concerns about environmental impacts, such as the magnitude of air pollution emissions. This paper reports compound emission rates (E) for 69–89 nonbiogenic volatile organic compounds (VOCs) for each of four surface mining facilities, determined with a top-down approach using aircraft measurements in the summer of 2013. The aggregate emission rate (aE) of the nonbiogenic VOCs ranged from 50 ± 14 to 70 ± 22 t/d depending on the facility. In comparison, equivalent VOC emission rates reported to the Canadian National Pollutant Release Inventory (NPRI) using accepted estimation methods were lower than the aE values by factors of 2.0 ± 0.6, 3.1 ± 1.1, 4.5 ± 1.5, and 4.1 ± 1.6 for the four facilities, indicating underestimation in the reported VOC emissions. For 11 of the combined 93 VOC species reported by all four facilities, the reported emission rate and E were similar; but for the other 82 species, the reported emission rate was lower than E. The median ratio of E to that reported for all species by a facility ranged from 4.5 to 375 depending on the facility. Moreover, between 9 and 53 VOCs, for which there are existing reporting requirements to the NPRI, were not included in the facility emission reports. The comparisons between the emission reports and measurement-based emission rates indicate that improvements to VOC emission estimation methods would enhance the accuracy and completeness of emission estimates and their applicability to environmental impact assessments of oil sands developments.