Centre for Atmospheric Chemistry

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Open Access
12C/13C kinetic isotope effects of the gas-phase reactions of isoprene, methacrolein, and methyl vinyl ketone with OH radicals
(Elsevier, 09-Mar) Iannone, Richard; Koppmann, Ralf; Rudolph, Jochen
The stable-carbon kinetic isotope effects (KIEs) for the gas-phase reactions of isoprene, methacrolein (MACR), and methyl vinyl ketone (MVK) with OH radicals were studied in a 25 L reaction chamber at (298 ± 2) K and ambient pressure. The time dependence of both the stable-carbon isotope ratios and the concentrations was determined using a gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) system. The volatile organic compounds (VOCs) used in the KIE experiments had natural-abundance isotopic composition thus KIE data obtained from these experiments can be directly applied to atmospheric studies of isoprene chemistry. All 13C/12C KIE values are reported as ε values, where ε = (KIE – 1) × 1000‰, and KIE = k12/k13. The following average stable-carbon KIEs were obtained: (6.56±0.12)‰ (isoprene), (6.47±0.27)‰ (MACR), and (7.58±0.47)‰ (MVK). The measured KIEs all agree within uncertainty to an inverse molecular mass (MM) dependence of OHε(‰) = (487±18)MM–1,which was derived from two previous studies [J. Geophys. Res. 2000, 105, 29329–29346; J. Phys. Chem. A 2004, 108, 11537–11544]. Upon adding the isoprene, MACR, and MVK OHε values from this study, the inverse MM dependence changes only marginally to OHε(‰) = (485±14)MM–1. The addition of these isoprene OHε values to a recently measured set of O3ε values in an analogous study [Atmos. Environ. 2008, 42, 8728–8737] allows for estimates of the average change in the 12C/13C ratio due to processing in the troposphere.
Open Access
12C/13C kinetic isotope effects of the gas-phase reactions of isoprene, methacrolein, and methyl vinyl ketone with OH radicals
(Elsevier, 2009) Iannone, R.; Koppmann, R.; Rudolph, J.
Open Access
Absolute Oscillator Strengths From the K-Shell Spectra of Fluoroethenes and 1,3-perfluorobutadiene
(American Physical Society, 1987) McLaren, R.; Clark, S.A.C.; Ishii, I.; Hitchcock, A.P.
Absolute oscillator strengths in the region of carbon and fluorine K-shell excitation have been derived for CH2CH2, CH2CHF, cis-CHFCHF, CH2CF2, CHFCF2, CF2CF2, 1,3-C4H6, and 1,3-C4F6 from electron-energy-loss spectra recorded under dipole-dominated conditions. The methods used to derive absolute oscillator strengths from relative energy-loss intensities are discussed in detail. The accuracy of the procedures is tested through comparisons with literature results for N2, CO, and CO2. The total C 1s→π* and C 1s→σ*(C—F) intensities increase systematically as the degree of fluorination increases. The spectra are discussed in terms of bond-length correlation and potential barrier concepts.
Open Access
Aerosol growth and the condensation coefficient for water: a review
(Taylor & Francis, 1986) Mozurkewich, M.
The transfer of gas phase species to aerosols depends critically on the condensation (or sticking) coefficient. Reported values for water on water vary from 0.03 to 1. Theoretical arguments indicate that the condensation coefficient should be near unity for polar species on an aqueous surface. As long as heat transfer is properly accounted for, measurements on bulk water support this conclusion. The theory of aerosol growth is reviewed and a somewhat modified form is presented. Experimental measurements of aerosol growth are consistent with a condensation coefficient of unity but indicate that the thermal accommodation coefficient may be somewhat smaller. Aerosols grown on natural condensation nuclei may have smaller condensation coefficients owing to the presence of organic films.
Open Access
Aerosol particle size distributions in the lower Fraser Valley: evidence for particle nucleation and growth.
(Copernicus Publications, 2004) Mozurkewich, M.; Chan, T.W.; Aklilu, Y.; Verheggen, B.
Particle size distributions from 9 to 640nm diameter were measured at Eagle Ridge in the lower Fraser Valley from 13 August to 1 September 2001 as part of the Pacific 2001 Air Quality Study. The site was on top of a ridge, about 300m above the valley floor, in a predominantly agricultural area about 70km ESE of Vancouver. To further characterize the particles, their hygroscopic properties (affinity for water) were measured. The maximum of the number distributions was generally between 40 and 100nm diameter, but the number distribution was sometimes dominated by ultrafine particles with diameters below 40nm. These ultrafine particles, which appeared to some extent on all days, were frequently associated with elevated levels of CO and NOx, as expected for fresh vehicular emissions. The appearance of these fresh emissions was most pronounced when the growing mixed layer reached the altitude of the site. In contrast, pronounced nucleation events occurred on the five cleanest days; these resulted in particle number concentrations as high as 5x104 particles cm-3 and growth rates of 5 to 10nmhr-1. Nucleation appears to have been triggered when the UV flux reached about 25Wm-2. The growth of these newly formed particles was probably driven by the photochemical oxidation of biogenic organic compounds. Dramatic growth events were also observed on the afternoons of the more polluted days; these produced an extremely narrow mode σ<0.3) at a diameter of about 40nm. Rainy days showed low number concentrations with the size distributions shifted to small sizes. On one of these days there was evidence of nucleation not far from the site; this may have been occurring in the vicinity of the clouds.
Open Access
Aerosol speciation and mass prediction from toluene oxidation under high NOx conditions
(Elsevier, 2010) Kelly, J.L.; Michelangeli, D.V.; Makar, P.A.; Hastie, D.R.; Mozurkewich, M.; Auld, J.
A kinetically based gas-particle partitioning box model is used to highlight the importance of parameter representation in the prediction of secondary organic aerosol (SOA) formation following the photo-oxidation of toluene. The model is initialized using experimental data from York University's indoor smog chamber and provides a prediction of the total aerosol yield and speciation. A series of model sensitivity experiments were performed to study the aerosol speciation and mass prediction under high NOx conditions (VOC/NOx = 0.2). Sensitivity experiments indicate vapour pressure estimation to be a large area of weakness in predicting aerosol mass, creating an average total error range of 70 μg m−3 (range of 5–145 μg m−3), using two different estimation methods. Aerosol speciation proved relatively insensitive to changes in vapour pressure. One species, 3-methyl-6-nitro-catechol, dominated the aerosol phase regardless of the vapour pressure parameterization used and comprised 73–88% of the aerosol by mass. The dominance is associated with the large concentration of 3-methyl-6-nitro-catechol in the gas-phase. The high NOx initial conditions of this study suggests that the predominance of 3-methyl-6-nitro-catechol likely results from the cresol-forming branch in the Master Chemical Mechanism taking a significant role in secondary organic aerosol formation under high NOx conditions. Further research into the yields and speciation leading to this reaction product is recommended.
Open Access
Airborne Observations of Strong Biogenic NOx Emissions from the Namibian Savanna at the End of the Dry Season
(AGU, 1996) Harris, G.W.; Wienhold, F.G.; Zenker, T.
We report the observation of substantial emissions of NO x from a several-hundred-square-kilometer region of savanna in northern Namibia in September 1992. The estimated emission rates lie near the high end of the range of values reported from flux chamber studies on various tropical savanna soils and appear to be associated with a light rainfall event which occurred 4 days prior to the observations. If our measurements are typical for this situation, then biogenic emission of NO x following sporadic rainfall events during and at the end of the dry season may be an important regional source rivaling that arising from savanna burning and may have important consequences for regional scale ozone formation.
Open Access
Airborne studies of emissions from savanna fires in southern Africa. 1. Aerosol emissions measured with a laser optical particle counter
(AGU, 1996) LeCanut, P.; Andreae, M.O.; Harris, G.W.; Wienhold, F.G.; Zenker, T.
During the SAFARI-92 experiment (Southern Africa Fire Atmosphere Research Initiative, September–October 1992), we flew an instrumented DC-3 aircraft through plumes from fires in various southern African savanna ecosystems. Some fires had been managed purposely for scientific study (e.g., those in Kruger National Park, South Africa), while the others were “fires of opportunity” which are abundant during the burning season in southern Africa. We obtained the aerosol (0.1–3.0 μm diameter) number and mass emission ratios relative to carbon monoxide and carbon dioxide from 21 individual fires. The average particle number emission ratio ΔN/ΔCO (Δ: concentrations in plume minus background concentrations) varied between 14±2 cm−3 ppb−1 for grasslands and 23±7 cm−3 ppb−1 for savannas. An exceptionally high value of 43±4 cm−3 ppb−1 was measured for a sugarcane fire. Similarly, the mass emission ratio ΔM/ΔCO varied from 36±6 ng m−3 ppb−1 to 83±45 ng m−3 ppb−1, respectively, with again an exceptionally high value of 124±14 ng m−3 ppb−1 for the sugarcane fire. The number and mass emission ratios relative to CO depended strongly upon the fire intensity. Whereas the emission ratios varied greatly from one fire to the other, the aerosol number and volume distributions as a function of particle size were very consistent. The average background aerosol size distribution was characterized by three mass modes (0.2–0.4 μm, ≈1.0 μm, and ≈2.0 μm diameter). On the other hand, the aerosol size distribution in the smoke plumes showed only two mass modes, one centered in the interval 0.2–0.3 μm and the other above 2 μm diameter. From our mean emission factor (4±1 g kg−1 dm) we estimate that savanna fires release some 11–18 Tg aerosol particles in the size range 0.1–3.0 μm annually, a somewhat lower amount than emitted from tropical forest fires. Worldwide, savanna fires emit some 3–8 × 1027 particles (in the same size range) annually, which is expected to make a substantial contribution to the cloud condensation nuclei population in the tropics.
Open Access
Airborne studies of emissions from savanna fires in southern Africa. 2. Aerosol chemical composition
(AGU, 1998) Andreae, M.O.; Andreae, T.W.; Annegarn, H.; Beer, F.; Cachier, H.; Elbert, W.; Harris, G.W.; Maenhaut, W.; Salma, I.; Swap, R.; Wienhold, F.G.; Zenker, T.
We investigated smoke emissions from fires in savanna, forest, and agricultural ecosystems by airborne sampling of plumes close to prescribed burns and incidental fires in southern Africa. Aerosol samples were collected on glass fiber filters and on stacked filter units, consisting of a Nuclepore prefilter for particles larger than ∼1–2 μm and a Teflon second filter stage for the submicron fraction. The samples were analyzed for soluble ionic components, organic carbon, and black carbon. Onboard the research aircraft, particle number and volume distributions as a function of size were determined with a laser‐optical particle counter and the black carbon content of the aerosol with an aethalometer. We determined the emission ratios (relative to CO2 and CO) and emission factors (relative to the amount of biomass burnt) for the various aerosol constituents. The smoke aerosols were rich in organic and black carbon, the latter representing 10–30% of the aerosol mass. K+ and NH4+ were the dominant cationic species in the smoke of most fires, while Cl− and SO42- were the most important anions. The aerosols were unusually rich in Cl−, probably due to the high Cl content of the semiarid vegetation. Comparison of the element budget of the fuel before and after the fires shows that the fraction of the elements released during combustion is highly variable between elements. In the case of the halogen elements, almost the entire amount released during the fire is present in the aerosol phase, while in the case of C, N, and S, only a small proportion ends up as particulate matter. This suggests that the latter elements are present predominantly as gaseous species in the fresh fire plumes studied here.
Open Access
Aircraft Measurements of NOx Over the Eastern Pacific and Continental United States and Implications for Ozone Production
(AGU, 1990) Carroll, M.A.; Hastie, D.R.; Ridley, B.A.; Rodgers, M.O.; Torres, A.L.; Davis, D.D.; Bradshaw, J.D.; Sandholm, S.T.; Schiff, H.I.; Karecki, D.R.; Harris, G.W.; Mackay, G.I.; Gregory, G.L.; Condon, E.P.; Trainer, M.; Hubler, G.; Montzka, D.D.; Madronich, S.; Albritton, D.L.; Singh, H.B.; Beck, S.M.; Shipham, M.C.; Bachmeier, A.S.
Measurements of NO, NO2, O3, and CO are presented from 13 aircraft flights made over the eastern Pacific Ocean and the continental United States in August and September 1986 during the NASA GTE/CITE 2 program. Measurements of NO by three different groups (two different techniques) and of NO2 by three different groups (three different techniques) are presented and examined along with calculated NO x (NO + NO2) for correlations with O3, CO, and dew-point temperature (DPT) primarily as a function of air mass category. Median values of NO and NO2 in the marine boundary layer were 4.0 and 10.4 pptv, respectively, and 12.4 and 18.0 pptv in the marine free troposphere. In the continental boundary layer, median values of NO and NO2 were 34.5 and 75.0 pptv, respectively, and 13.0 and 36.0 pptv at altitudes above 3 km in air masses having continental influence. In the maritime NO x data set a negative correlation is often observed between NO x and DPT, while positive correlations were typically observed between NO x and O3 and between NO x and CO. As expected, then, negative correlations were often observed between O3 and DPT and between CO and DPT, along with positive correlations between CO and O3. In the continental data set, positive correlations were typically observed between NO x and DPT, O3, and CO. Additionally, the various air masses were examined with respect to regions of net ozone production or net ozone destruction. In all but one case in the marine boundary layer, model calculations indicate that there is significant ozone destruction. In the continental boundary layer, however, calculations indicate significant ozone production. In the middle free troposphere at 5 ± 1 km, the in situ ozone formation was most often nearly in balance with ozone destruction.
Open Access
Aircraft measurements of O3, HNO3 and N2O in the winter arctic lower stratosphere during STREAM I
(AGU, 1995) Bergman, A.; van Velthoven, P.; Wienhold, F.G.; Waibel, A.; Zenker, T.; Frenzel, A.; Bolder, M.; Lielieveld, J.; Harris, G.W.; Arnold, F.
Simultaneous in situ measurements of O3, HNO3, and N2O were performed in the Arctic (68°–74°N) lower stratosphere during February 1993 on board a Cessna Citation aircraft up to 12.5 km altitude, during the first Stratosphere-Troposphere Experiment by Aircraft Measurements (STREAM) campaign. Strong variations in the concentrations, distributions, and ratios of these trace gases were found from the maximum altitude down to the tropopause. Close to the tropopause, vortex air was present with relatively low N2O concentrations. The observed N2O-HNO3 relation agrees with earlier measurements of total nitrogen and N2O inside the vortex, suggesting subsidence of vortex air across the bottom of the vortex. This air also contained low O3 concentrations relative to N2O, indicating enhanced O3 loss by chemical reactions involving stratospheric particles. Based on trajectory calculations and assuming a potential temperature cooling rate of 0.6 K d−1, we estimate an O3 loss of 4–7 ppbv d−1 (0.9–1.2% d−1), in the Arctic lower stratosphere for the period January–February 1993. Air parcels originating from middle latitudes, containing relatively low O3 and N2O concentrations, may have originated from the vortex earlier in the winter. In addition, the results also show high HNO3 concentrations relative to O3 and N2O. Air parcels originating from high latitudes may have been enriched in HNO3 by sedimentation and evaporation of nitric acid containing particles, which would explain the relatively high HNO3 concentrations and HNO3/O3 ratios measured. Heterogeneous chemistry on sulfuric acid particles, probably enhanced in concentration by gravitational settling of the Pinatubo aerosol, is the most plausible explanation for the observed high HNO3 concentrations relative to N2O in air parcels originating from midlatitudes.
Open Access
Analysis of Motor Vehicle Sources and Their Contribution to Ambient Hydrocarbon Distributions at Urban Sites In Toronto During the Southern Ontario Oxidants Study
(Elsevier, 1996) Lai, J.Y.K.; Singleton, D.L.; McLaren, R.; Singer, E.; Khouw, B.; Niki, H.; Wu, Z.
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%.
Open Access
Application of absolute principal component analysis to size distribution data: identification of particle origins
(Copernicus Publications, 2007) Chan, T.W.; Mozurkewich, M.
Absolute principal component analysis can be applied, with suitable modifications, to atmospheric aerosol size distribution measurements. This method quickly and conveniently reduces the dimensionality of a data set. The resulting representation of the data is much simpler, but preserves virtually all the information present in the original measurements. Here we demonstrate how to combine the simplified size distribution data with trace gas measurements and meteorological data to determine the origins of the measured particulate matter using absolute principal component analysis. We have applied the analysis to four different sets of field measurements that were conducted at three sites in southern Ontario. Several common factors were observed at all the sites; these were identified as photochemically produced secondary aerosol particles, regional pollutants (including accumulation mode aerosol particles), and trace gas variations associated with boundary layer dynamics. Each site also exhibited a factor associated specifically with that site: local industrial emissions in Hamilton (urban site), processed nucleation mode particles at Simcoe (polluted rural site), and transported fine particles at Egbert (downwind from Toronto).
Open Access
Application of an improved method for measurements of gaseous nitric acid in the nonurban atmosphere
(Springer Verlag, 1991) Müller, K.P.; Rudolph, J.
A modified filter technique to separate particles and gaseous HNO3 is described, which is based on the use of filters of the Millipore FPLG type in combination with a virtual impactor. It enables routine measurements of gaseous HNO3 in the atmosphere at background levels. Some results of measurements both in the marine background and over rural and semi-rural continental regions are presented.
Open Access
Applications of quantum cascade lasers for sensitive trace gas measurements of CO, CH4 and HHO
(Springer Verlag, 2008) Schiller, C.L.; Bozem, H.; Gurk, C.; Parchatka, U.; Königstedt, R.; Harris, G.W.; Fischer, H.
We describe here a sensitive quantum cascade laser absorption spectrometer (QCLAS) employed for aircraft based measurements during the GABRIEL 2005 and HOOVER 2006 and 2007 campaigns. This 3-channel instrument measures CO, HCHO, CH4 and N2O using a 64-m path double corner cube White cell. Performance of the instrument was examined for the four species and precisions for CO, N2O and CH4 were measured in the field to be 0.5, 0.5 and 0.7% respectively (2σ). The 1σ detection limit for HCHO was ∼500 pptv for a 2 s average, while signal averaging of the HCHO over a 2 min time interval resulted in a 150 pptv detection limit with a duty cycle of 60%.
Open Access
Applications of Time-Resolved Step-Scan and Rapid-Scan FTIR Spectroscopy: Dynamics from 10 Seconds to 10 Nanoseconds
(Society for Applied Spectroscopy, 1993) Johnson, T.J.; Simon, A.; Weil, J.M.; Harris, G.W.
The step-scan technique in Fourier transform infrared (FT-IR) spectroscopy is employed in new applications of time resolved spectroscopy (TRS). Results are demonstrated on time-resolved laser emissions and photolytically generated chemical reactions using both emission and absorption modes. New achievements in FT-IR temporal resolution are demonstrated, as well as the complementary nature of step-scan and rapid-scan time-resolved spectroscopy.
Open Access
Assessment of emissions data for the Toronto region using aircraft-based measurements and an air quality model
(Elsevier, 2001) Plummer, D.A.; McConnell, J.C.; Neary, L.; Kaminski, J.; Drummond, J.; Narayan, J.; Young, V.; Hastie, D.R.
An aircraft-based measurement campaign was conducted during the summer of 1996 in the vicinity of Toronto, Canada. The objective of the campaign was to assess the errors in a particular emission inventory used by three-dimensional air quality models. Measurements of NO2 and hydrocarbons were made both upwind and downwind of Toronto, on days with strong synoptic-scale flow from a west to northerly direction. The chemical composition of the background airmass on these days was typical of unpolluted continental air. Measurements have been compared with the output from an on-line air quality model (MC2-AQ) run at 5 km resolution and suggest that emissions of NOx from Toronto are well described in the emission database, though evidence that NOx emissions are underestimated for suburban regions surrounding Toronto was found. In general, no significant underestimation of hydrocarbon emissions was found, though emissions of the model propane species, which includes acetylene and benzene, was underestimated by at least a factor of two.
Open Access
Atmospheric Concentrations and Temporal Variations of C1-C3 Carbonyl Compounds at Two Rural Sites in Central Ontario
(Elsevier, 1991) Shepson, P.B.; Hastie, D.R.; Schiff, H.I.; Polizzi, M.; Bottenheim, J.W.; Anlauf, K.; Mackay, G.I.; Karecki, D.R.
Measurements of formaldehyde, acetaldehyde, acetone and propionaldehyde concentrations were made at two rural sites in central Ontario. One site (at Egbert, Ont.) is located ≈60 km northwest of Toronto, while the other site (at Dorset, Ont.) is ≈150 km northeast of the Egbert site. Measurements were made using a modified version of a derivatization technique in which sample air is pumped through Teflon tubes packed with silica gel that is coated with 2,4-dinitrophenylhydrazine (DNPH). The product hydrazones were separated and quantified using HPLC. Quantitative determinations of formaldehyde, acetaldehyde and acetone were made for 49 and 47 samples at the Dorset and Egbert sites, respectively, between 25 July and 30 August 1988. The average concentrations determined at the Dorset site for formaldehyde, acetaldehyde, and acetone were 1.6, 0.46 and 1.8 ppb, respectively, and for the Egbert site the corresponding averages were 1.8, 0.57 and 1.6 ppb. A set of 10 samples from the Egbert site were analysed for propionaldehyde yielding an average concentration of 0.03 ppb. The formaldehyde measurements were compared with measurements made at the same time using Tunable Diode Laser Absorption Spectroscopy. The observed concentrations reported here are compared with previously reported measurements of these species and interpreted in terms of atmospheric variables (e.g. meteorology, concentrations of precursor hydrocarbons) influencing their concentrations.
Open Access
Atmospheric measurements during Polarstern cruise ANT VII/1, 54° N to 32° S: An overview
(Springer Netherlands, 1992) Platt, U.; Rudolph, J.; Brauers, T.; Harris, G.
A comprehensive set of trace gas concentrations and meteorological parameters were measured simultaneously during a cruise of the research vessel Polarstern from Bremerhaven (54° N, 8° E) to Rio Grande (32° S, 52° W) during the period from 15 September to 9 October 1988. This paper describes the general features of the cruise and summarizes the measurements made, the techniques employed, and the placement of the instruments on board the ship. The synoptic data base is used to characterize the nature and possible origins of the air masses encountered during the cruise and to draw some general conclusions from the measurements.
Open Access
Atmospheric measurements of HONO by tunable diode laser absorption spectroscopy
(Springer Verlag, 2001) Schiller, C.L.; Locquiao, S.; Johnson, T.J.; Harris, G.W.
Ambient gas phase nitrous acid (HONO) has been measured by Tunable Diode Laser Absorption Spectroscopy with sub-ppbv detection limits. An R-branch line in the 1263.4 cm–1 3 band was found tobe free of interference and suitable for ambient HONO measurements. Nitrous acid was measured during the night and early morning at an urban site in Toronto, Canada, during the summer of 1998. Average mixing ratios, integrated over 30 minutes, ranged from below the minimum detection limit of 300 pptv to 1.9 ppbv, with the highest concentrations observed during the early morning hours. During the night of 19 June 1998, the concentration of HONO increased by as much as 0.5 ppbv/hr. The usual decrease in HONO after sunrise was delayed by a few hours, possibly due to a combination of an increase in the production rate of HONO with rush hour, and attenuation of the early morning light by high NO2 within the aerosol fog/haze.