Research publications

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Open Access
Seasonal variability and trends of volatile organic compounds in the lower polar troposphere
(American Geophysical Union, 2003-01-01) Rudolph, J.; Stein, O.; Rohrer, F.; Koppmann, R.; Brauers, T.; Gautrois, M.
Open Access
The Use of Photoionization, Flameionization and Electron Capture Detectors in Series for the Determination of Low Molecular Weight Trace Components in the Non Urban Atmosphere
(Taylor & Francis, 1983) Jebsen, C.; Rudolph, J.
Open Access
Hydrocarbons in the Non-Urban Atmosphere: Analysis, Ambient Concentrations and Impact on the Chemistry of the Atmosphere
(Taylor & Francis, 1985) Khedim, A.; Rudolph, J.
Open Access
Determination of Peroxyacetylnitrate (PAN) in Unpolluted Areas
(Taylor & Francis, 1985) Diederich, S.; Rudolph, J.; Vierkorn-Rudolph, B.
Open Access
The Use of Automated "On Line" Gaschromatrography for the Monitoring of Organic Trace Gases in the Atmosphere at Low Levels
(Taylor & Francis, 1990) Pilwat, G.; Khedim, A.; Johnen, F.J.; Rudolph, J.
Open Access
Laboratory studies of bromide oxidation in the presence of ozone: Evidence for glass-surface mediated reaction
(Springer Verlag, 2002) Anastasio, C.; Mozurkewich, M.
The reaction of sodium bromide particles in the presence of ozone was studied in a flow system both under dark conditions and with 254 nm radiation. We found that there was significant formation of gaseous bromine (probably Br2) in the presence of ozone in the dark, and that bromide deposited to the walls of the Pyrex reaction flask was its source. The observed rate of gaseous bromine formation in these experiments was approximately 100–1000 times faster than expected based on the knownrate constant for aqueous reaction of bromide with ozone. While the mechanism responsible for this enhanced reactivity was not identified, based on previous reports we suggest that the glass surface converted ozone to more reactive species, such as hydroxyl radical, which in turn oxidized bromide. In the presence of 254 nm radiation, rates of gaseous bromine collection were further enhanced, likely as a result of increased radical production in the system, and wall-deposited bromide was also the source of the gaseous bromine. In these `light' experiments, there was a significant decline in ozone mixing ratios, consistent with bromine radical chemistry. These results suggest the possibility that ozone reacting with internally mixed silicate/sea-salt particles might be a significant mechanism for the oxidation of particulate halides, and subsequent release of photoactive halogen species, in the marine boundary layer.
Open Access
Measurement of the coagulation rate constant for sulphuric acid particles as a function of particle size
(Elsevier, 2001) Chan, T.W.; Mozurkewich, M.
A new method for the determination of coagulation rate constants for monodisperse, neutral particles is described. In this method, a differential mobility analyzer (DMA) is used to prepare a monodisperse aerosol and a second DMA is used to separate the coagulation products from the original monodisperse particles. The experiments are carried out under initial rate conditions so that typically 5–9% of the monomer particles undergo coagulation. Experimental results at 298±1 K for H2SO4/H2O particles with diameters of 49–127 nm and a composition of 72–73% H2SO4 by mass gave enhancement factors, relative to rate constants calculated for hard spheres, that vary from about 1.2 for the largest particles to 2.8 for the smallest particles. Fitting these results to a theoretical expression accounting for van der Waals forces gives a Hamaker constant of (6.4±2.6)×10−13 erg. We also give convenient formulas for computing coagulation enhancement factors from the Hamaker constant.
Open Access
A novel injector for low temperature flow kinetic studies
(American Institute of Physics, 1994) Henry, B.E.; Fried, A.; Fox, J.; Mozurkewich, M.; Calvert, J.G.
A new enclosed injector system for low temperature kinetic studies is described. This system offers a number of advantages over more conventional designs of moveable inlet injectors. The enclosed injector prevents the introduction of contaminants into the flow reactor. In conventional designs, ambient contaminants adsorbed onto the outside of the injector could be transported into the flow reactor. The enclosed injector exposes the reactant gas to the same length of inlet tubing at a uniform temperature regardless of the injector position. In addition, the enclosed injector minimizes temperature gradients in the flow reactor caused by heat transfer along the injector. This is a particular problem when the flow reactor is operated near atmospheric pressure at reduced temperatures. Finally, this design is significantly more compact than conventional injector designs. This system has been successfully employed in studies of the heterogeneous reaction of N2O5 with sulfuric acid aerosols over the temperature range 225–293 K.
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
Optimization of a heat engine based on dissipative system
(American Institute of Physics, 1983) Mozurkewich, M.; Berry, R.S.
A new class of heat engine is analyzed in which the working fluid operates in a dissipative process, never in equilibrium. The conditions are found for stability and for the generation of work. Then the optimal path is found for operating the general dissipative engine by means of optimal control theory. The optimal cycle consists of arcs of constant power and of approximately instantaneous adiabats. If the heat flow is a function of temperature only, then the constant power arcs become isotherms. An upper bound is found to the power output.Two examples are worked out in detail: a light‐driven dissipative engine whose absorption is a step function of temperature, and a light‐driven dissipative engine whose working fluid undergoes a chemical reaction (isomerization), absorbing light in the isomeric form favored at high temperatures.
Open Access
Optimal paths for thermodynamic system: the ideal Otto cycle
(American Institute of Physics, 1982) Mozurkewich, M.; Berry, R.S.
We apply the method of optimal control theory to determine the optimal piston trajectory for successively less idealized models of the Otto cycle. The optimal path has significantly smaller losses from friction and heat leaks than the path with conventional piston motion and the same loss parameters. The resulting increases in efficiency are of the order of 10%.
Open Access
Maximum work from a finite reservoir by sequential Carnot cycles
(American Association of Physics Teachers, 1981) Ondrechen, M.J.; Anderson, B.; Mozurkewich, M.; Berry, R.S.
The production of work from a heat source with finite heat capacity is discussed. We examine the conversion of heat from such a source first by a single Carnot engine and then by a sequence of Carnot engines. The optimum values of the operating temperatures of these engines are calculated. The work production and efficiency of a sequence with an arbitrary number of engines is derived, and it is shown that the maximum available work can be extracted only when the number of cycles in the sequence becomes infinite. The results illustrate the importance of recovery or bottoming processes in the optimization of work-producing systems. In addition, the present model illuminates one practical limitation of the Carnot cycle: The Carnot efficiency is only obtainable from a heat source with infinite heat capacity. However, another cycle, somewhat reminiscent of the Otto and Brayton cycles, is derived which will provide the maximum efficiency for a heat source with a finite heat capacity.
Open Access
Finite-time thermodynamics: engine performance Improved by optimized piston motion
(National Academy of Science, 1981) Mozurkewich, M.; Berry, R.S.
The methods of finite-time thermodynamics are used to find the optimal time path of an Otto cycle with friction and heat leakage. Optimality is defined by maximization of the work per cycle; the system is constrained to operate at a fixed frequency, so the maximum power is obtained. The result is an improvement of about 10% in the effectiveness (second-law efficiency) of a conventional near-sinusoidal engine.
Open Access
Determination of the nucleation rate from observation of a SO2 induced atmospheric nucleation event
(AGU, 2002) Verheggen, B.; Mozurkewich, M.
A method to determine the particle nucleation rate directly from atmospheric measurements is presented. During the Southern Ontario Oxidant Study (SONTOS) field campaign in rural Ontario, Canada, particle size distributions and concentrations of a range of photochemical species were measured. On 25 August 1993, the size distribution showed a pronounced peak in the concentration of nucleation mode particles. This correlated with, but lagged behind, a peak in the SO2 concentration. The data imply that nucleation occurred aloft as an SO2 plume was entrained into the growing boundary layer. The particle growth rates were determined from the evolution of the measured particle size distributions, while accounting for coagulation and dilution. In principle, measurements of precursor species are not needed. However, in this case study, the ground-based measurements did not reflect the aerosol concentrations in the plume aloft; as a result, extrapolation of the growth rate was necessary. This was accomplished by using a one-dimensional model to calculate the gas phase sulfuric acid concentration. The particle growth rate due to condensation of H2SO4 was calculated and used to extrapolate the observed growth backward to obtain the time of formation. From the particle number in a certain size interval, suitably corrected for losses by coagulation and dilution, and the time interval in which they formed, the nucleation rate can be determined. We obtained nucleation rates of 5–40 cm−3 s−1 for sulfuric acid mixing ratios of 3–10 pptv. These nucleation rates are higher than predicted by classical binary nucleation theory for H2SO4 and H2O.
Open Access
The hydrolysis of CINO3 on sub micron liquid sulphuric acid aerosols
(AGU, 1998) Ball, S.; Fried, A.; Mozurkewich, M.
The reactive uptake of ClONO2 on liquid sulfuric acid has been measured for size‐selected, sub‐micron aerosol in the composition range 36–54% H2SO4 by weight at ≈ 250 K. A comparison with results from studies employing bulk surfaces at similar temperatures and compositions shows no evidence for a dependence of the reaction probability, γ, on size. We use this observation to estimate an upper limit to the diffuso‐reactive length of 26 nm for the ClONO2 + H2O reaction on 43 weight % aerosol at 248 K. But, the present values of γ are consistently lower than bulk values observed at lower temperatures and similar composition, suggesting that γ is temperature dependent.
Open Access
The reaction probability of N2O5 with sulphuric acid aerosols at stratospheric temperatures and compositions
(AGU, 1994) Fried, A.; Henry, B.E.; Calvert, J.G.; Mozurkewich, M.
We have measured the rate of reaction of N2O5 with H2O on monodisperse, submicrometer H2SO4 particles in a low‐temperature flow reactor. Measurements were carried out at temperatures between 225 K and 293 K on aerosol particles with sizes and compositions comparable to those found in the stratosphere. At 273 K, the reaction probability was found to be 0.103 ± 0.006, independent of H2SO4 composition from 64 to 81 wt %. At 230 K, the reaction probability increased from 0.077 for compositions near 60% H2S04 to 0.146 for compositions near 70% H2SO4. Intermediate conditions gave intermediate results except for low reaction probabilities of about 0.045 at 260 K on aerosols with about 78% H2SO4. The reaction probability did not depend on particle size. These results imply that the reaction occurs essentially at the surface of the particle. A simple model for this type of reaction that reproduces the general trends observed is presented. The presence of formaldehyde did not affect the reaction rate.
Open Access
Reaction possibility of N2O5 on aqueous aerosols
(AGU, 1988) Mozurkewich, M.; Calvert, J.G.
The reaction probability, γ, of N2O5 (to form HNO3) with monodisperse NH3/H2SO4/H2O aerosols has been measured in a flow tube reactor at atmospheric pressure. Experiments were performed at temperatures of 274 and 293 K and at relative humidities of 1–76%. It appears that the presence of a liquid phase is necessary for reaction. With NH4HSO4 aerosol, γ values are nonzero, even below the deliquescence point of the pure salt, and show a gradual increase with increasing relative humidity up to constant values of 0.05 and 0.09 for 293 and 274 K, respectively. Experiments with aerosols of varied NH3/H2SO4 ratios suggest that evaporation of NH3 from the NH4HSO4 aerosols creates excess H2SO4 on the surface. This can take up water vapor to provide the reactant for N2O5 below the deliquescence point of NH4HSO4. The present observations are consistent with the reaction of N2O5 with moist aerosols being a major removal mechanism for odd nitrogen and a major source of HNO3 in the nighttime troposphere. The same reaction on H2SO4 aerosols may be of significance in the stratosphere.
Open Access
Mass accommodation coefficient for HO2 radicals on aqueous particles
(AGU, 1987) Mozurkewich, M.; McMurray, P.H.; Guppta, A.; Calvert, J.G.
The rate of reaction of gas phase HO2 radicals with a monodisperse, submicrometer aerosol was measured in a flow tube reactor at atmospheric pressure. At the relative humidity of the experiments (75%), the aerosol consisted of concentrated solution droplets of either LiNO3 or NH4HSO4. When the aerosol contained a sufficient amount of Cu(II) ions, reaction of HO2 with the aerosol was observed. The mass accommodation coefficient for HO2 on aqueous particles was determined to be greater than 0.2. This implies that in clouds HO2 mass transport will be limited by gas-phase diffusion and HO2 will be in equilibrium at the gas-liquid interface. Reactions of HO2 with Cu(I) and Cu(II) ions in submicrometer aerosols may have a significant role in converting atmospheric odd hydrogen radicals into H2O2.
Open Access
NO3 radical measurements in a polluted marine environment: links to ozone formation
(Copernicus Publications, 2009) McLaren, R.; Wojtal, P.; Majonis, D.; McCourt, J.; Halla, J.D.
Nighttime chemistry in polluted regions is dominated by the nitrate radical (NO3) including its direct reaction with natural and anthropogenic hydrocarbons, its reaction with NO2 to form N2O5, and subsequent reactions of N2O5 to form HNO3 and chlorine containing photolabile species. We report nighttime measurements of NO3, NO2, and O3, in the polluted marine boundary layer southwest of Vancouver, BC during a three week study in the summer of 2005. The concentration of N2O5 was calculated using the well known equilibrium, NO3+NO2↔N2O5. Median overnight mixing ratios of NO3, N2O5 and NO2 were 10.3 ppt, 122 ppt and 8.3 ppb with median N2O5/NO3 molar ratios of 13.1 and median nocturnal partitioning of 4.9%. Due to the high levels of NO2 that can inhibit approach to steady-state, we use a method for calculating NO3 lifetimes that does not assume the steady-state approximation. Median and average lifetimes of NO3 in the NO3-N2O5 nighttime reservoir were 1.1–2.3 min. We have determined nocturnal profiles of the pseudo first order loss coefficient of NO3 and the first order loss coefficients of N2O5 by regression of the NO3 inverse lifetimes with the [N2O5]/[NO3] ratio. Direct losses of NO3 are highest early in the night, tapering off as the night proceeds. The magnitude of the first order loss coefficient of N2O5 is consistent with, but not verification of, recommended homogeneous rate coefficients for reaction of N2O5 with water vapor early in the night, but increases significantly in the latter part of the night when relative humidity increases beyond 75%, consistent with heterogeneous reactions of N2O5 with aerosols with a rate constant khet=(1.2±0.4)×10−3 s−1−(1.6±0.4)×10−3 s−1. Analysis indicates that a correlation exists between overnight integrated N2O5 concentrations in the marine boundary layer, a surrogate for the accumulation of chlorine containing photolabile species, and maximum 1-h average O3 at stations in the Lower Fraser Valley the next day when there is clear evidence of a sea breeze transporting marine air into the valley. The range of maximum 1-h average O3 increase attributable to the correlation is ΔO3=+1.1 to +8.3 ppb throughout the study for the average of 20 stations, although higher increases are seen for stations far downwind of the coastal urban area. The correlation is still statistically significant on the second day after a nighttime accumulation, but with a different spatial pattern favouring increased O3 at the coastal urban stations, consistent with transport of polluted air back to the coast.
Open Access
Photochemistry of Formic Acid Monomer at 222 nm
(Wiley-Blackwell, 1994) Irwin, R.S.; Singleton, D.L.; Paraskevopoulos, G.; McLaren, R.
The yields of CO2 and CO formed from the gas-phase photolysis at 222 nm of very low pressures of formic acid where the monomer predominates have been determined using FTIR spectroscopy. The observed ratio of CO2/CO approaches unity as the formic acid pressure approaches zero. Previous studies have shown that the quantum yield for HCOOH + hv OH + HCO (or H + CO) is 0.70 at 298 K. The present experimental results indicate that the ratio of the quantum yields of the possible molecular photolysis channels forming H2 + CO2 (1b) and H2O + CO (1c) is ca. 1. Including this result in an analysis of previously reported quantum yields of CO and CO2 determined at higher pressures of formic acid, where both monomer and dimer contribute significantly to the products, indicates that 1b = 1c = 0.