@article {2432,
	title = {A new broadly tunable (7.4-10.2 eV) laser based VUV light source and its first application to aerosol mass spectrometry},
	journal = {International Journal of Mass Spectrometry},
	volume = {279},
	number = {2-3},
	year = {2009},
	note = {ISI Document Delivery No.: 399TJTimes Cited: 10Cited Reference Count: 78Hanna, S. J. Campuzano-Jost, P. Simpson, E. A. Robb, D. B. Burak, I. Blades, M. W. Hepburn, J. W. Bertram, A. K.},
	month = {Jan},
	pages = {134-146},
	type = {Article},
	abstract = {A laser based vacuum ultraviolet (VUV) light source using resonance enhanced four wave difference mixing in xenon gas was developed for near threshold ionization of organics in atmospheric aerosol particles. The source delivers high intensity pulses of VUV light (in the range of 10(10) to 10(13) photons/pulse depending on wavelength, 5 ns FWHM) with a continuously tunable wavelength from 122 nm (10.2 eV) to 168 nm (7.4 eV). The setup allows for tight (< 1 mm(2)) and precise focusing (mu rad pointing angle adjustability), attributes required for single particle detection. The generated VUV is separated from the pump wavelengths by a custom monochromator which ensures high spectral purity and minimizes absorptive losses. The performance of the source was characterized using organic molecules in the gas phase and optimal working conditions are reported. In the gas phase measurements, photoionization efficiency (PIE) curves were collected for seven different organic species with ionization energies spanning the full wavelength range of the VUV source. The measured appearance energies are very close to the literature values of the ionization energies for all seven species. The effectiveness of the source for single particle studies was demonstrated by analysis of individual caffeine aerosols vaporized by a pulsed CO2 laser in an ion trap mass spectrometer. Mass spectra from single particles down to 300 nm in diameter were collected. Excellent signal to noise characteristics for these small particles give a caffeine detection limit of 8 x 10(5) molecules which is equivalent to a single 75 nm aerosol, or approximately 1.5\% of a 300 nm particle. The appearance energy of caffeine originating from the aerosol was also measured and found to be 7.91 +/- 0.05 eV, in good agreement with literature values. (C) 2008 Elsevier B.V. All rights reserved.},
	keywords = {Aerosol mass spectrometry, analysis, CROSS-SECTIONS, EFFICIENCY, FUEL-RICH FLAMES, GENERATING PARTICLE BEAMS, ION-TRAP, ONLINE, ORGANIC-COMPOUNDS, PARTICULATE MATTER, PHOTOIONIZATION, SINGLE-PHOTON IONIZATION, SURFACE-ANALYSIS, Vacuum ultraviolet light, VACUUM-ULTRAVIOLET PHOTOIONIZATION},
	isbn = {1387-3806},
	url = {<Go to ISI>://000262821900012},
	author = {Hanna, S. J. and Campuzano-Jost, P. and Simpson, E. A. and Robb, D. B. and Burak, I. and Blades, M. W. and Hepburn, J. W. and Bertram, A. K.}
}
@article {2431,
	title = {A study of oleic acid and 2,4-DHB acid aerosols using an IR-VUV-ITMS: insights into the strengths and weaknesses of the technique},
	journal = {Physical Chemistry Chemical Physics},
	volume = {11},
	number = {36},
	year = {2009},
	note = {ISI Document Delivery No.: 491ADTimes Cited: 3Cited Reference Count: 66Hanna, Sarah J. Campuzano-Jost, Pedro Simpson, Emily A. Burak, Itamar Blades, Michael W. Hepburn, John W. Bertram, Allan K.},
	pages = {7963-7975},
	type = {Article},
	abstract = {An investigation of oleic acid and 2,4-dihydroxybenzoic (DHB) acid aerosols was carried out using an aerosol mass spectrometer with pulsed lasers for vaporization and ionization and an ion trap for mass analysis. The extent of ion fragmentation was studied as a function of both vaporization energy and ionization wavelength. Low CO2 laser energies in the vaporization stage and near-threshold single photon ionization resulted in the least fragmented mass spectra. For DHB, only the molecular ion was observed, but for oleic acid fragmentation could not be eliminated. Tandem MS of the main fragment peak from oleic acid was carried out and provided a tool for compound identification. Photoionization efficiency curves were also collected for both DHB and oleic acid and the appearance energies of both parent and fragment ions were measured. Evidence for fragmentation occurring post-ionization is given by the similar appearance energies for both the parent and fragment ions. The results from this study were compared with those from similar experiments undertaken with time-of-flight (TOF) mass analyzers. The degree of fragmentation in the ion trap was considerably higher than that seen with TOF systems, particularly for oleic acid. This was attributed to the long storage interval in the ion trap which allows time for metastable ions to decay. Differences in the degree of fragmentation between the ion trap and TOF studies also provided further evidence for fragmentation occurring post-ionization. For 2,4-dihydroxybenzoic acid, the long delay prior to mass analysis also allowed time for reactions with background gases, in this case water, to occur.},
	keywords = {ATMOSPHERIC PARTICLES, CHEMICAL-ANALYSIS, ENVIRONMENTAL PARTICLES, GENERATING PARTICLE BEAMS, INVERSE FOURIER-TRANSFORM, LASER-DESORPTION/IONIZATION, ORGANIC-COMPOUNDS, QUADRUPOLE ION-TRAP, TRAP MASS-SPECTROMETER, VACUUM-ULTRAVIOLET PHOTOIONIZATION},
	isbn = {1463-9076},
	url = {<Go to ISI>://000269548300022},
	author = {Hanna, S. J. and Campuzano-Jost, P. and Simpson, E. A. and Burak, I. and Blades, M. W. and Hepburn, J. W. and Bertram, A. K.}
}
@article {1516,
	title = {Crystallization of aqueous ammonium sulfate particles internally mixed with soot and kaolinite: Crystallization relative humidities and nucleation rates},
	journal = {Journal of Physical Chemistry A},
	volume = {110},
	number = {28},
	year = {2006},
	note = {ISI Document Delivery No.: 063EXTimes Cited: 12Cited Reference Count: 70Pant, Atul Parsons, Matthew T. Bertram, Allan K.},
	month = {Jul},
	pages = {8701-8709},
	type = {Article},
	abstract = {Using optical microscopy, we investigated the crystallization of aqueous ammonium sulfate droplets containing soot and kaolinite, as well as the crystallization of aqueous ammonium sulfate droplets free of solid material. Our results show that soot did not influence the crystallization RH of aqueous ammonium sulfate particles under our experimental conditions. In contrast, kaolinite increased the crystallization RH of the aqueous ammonium sulfate droplets by approximately 10\%. In addition, our results show that the crystallization RH of aqueous ammonium sulfate droplets free of solid material does not depend strongly on particle size. This is consistent with conclusions made previously in the literature, based on comparisons of results from different laboratories. From the crystallization results we determined the homogeneous nucleation rates of crystalline ammonium sulfate in aqueous ammonium sulfate droplets and the heterogeneous nucleation rates of crystalline ammonium sulfate in aqueous ammonium sulfate particles containing kaolinite. Using classical nucleation theory and our experimental data, we determined that the interfacial tension between an ammonium sulfate critical nucleus and an aqueous ammonium sulfate solution is 0.064 +/- 0.003 J m(-2) (in agreement with our previous measurements), and the contact angle between an ammonium sulfate critical nucleus and a kaolinite surface is 59 +/- 2. On the basis of our results, we argue that soot will not influence the crystallization RH of aqueous ammonium sulfate droplets in the atmosphere, but kaolinite can significantly modify the crystallization RH of atmospheric ammonium sulfate droplets. As an example, the CRH50 ( the relative humidity at which 50\% of the droplets crystallize) ranges from about 41 to 51\% RH when the diameter of the kaolinite inclusion ranges from 0.1 to 5 mu m. For comparison, the CRH50 of aqueous ammonium sulfate droplets (0.5 Am diameter) free of solid material is approximately 34.3\% RH under atmospheric conditions.},
	keywords = {AEROSOL-PARTICLES, ATMOSPHERIC AEROSOL, deliquescence, HETEROGENEOUS NUCLEATION, HYGROSCOPIC GROWTH, MINERAL DUST, ORGANIC-COMPOUNDS, PHASE-TRANSITIONS, TROPOSPHERIC AEROSOLS, WATER-UPTAKE},
	isbn = {1089-5639},
	url = {<Go to ISI>://000239001600013},
	author = {Pant, A. and Parsons, M. T. and Bertram, A. K.}
}
@article {1519,
	title = {Crystallization of aqueous inorganic-malonic acid particles: Nucleation rates, dependence on size, and dependence on the ammonium-to-sulfate},
	journal = {Journal of Physical Chemistry A},
	volume = {110},
	number = {26},
	year = {2006},
	note = {ISI Document Delivery No.: 058DRTimes Cited: 16Cited Reference Count: 63},
	month = {Jul},
	pages = {8108-8115},
	type = {Article},
	abstract = {Using an electrodynamic balance, we determined the relative humidity ( RH) at which aqueous inorganic-malonic acid particles crystallized, with ammonium sulfate ((NH4)(2)SO4), letovicite ((NH4)(3)H(SO4)(2)), or ammonium bisulfate (NH4HSO4) as the inorganic component. The results for (NH4)(2)SO4-malonic acid particles and (NH4)(3)H(SO4)(2)-malonic acid particles show that malonic acid decreases the crystallization RH of the inorganic particles by less than 7\% RH when the dry malonic acid mole fraction is less than 0.25. At a dry malonic acid mole fraction of about 0.5, the presence of malonic acid can decrease the crystallization RH of the inorganic particles by up to 35\% RH. For the NH4HSO4-malonic acid particles, the presence of malonic acid does not significantly modify the crystallization RH of the inorganic particles for the entire range of dry malonic acid mole fractions studied; in all cases, either the particles did not crystallize or the crystallization RH was close to 0\% RH. Size dependent measurements show that the crystallization RH of aqueous (NH4)(2)SO4 particles is not a strong function of particle volume. However, for aqueous (NH4)(2)SO4-malonic acid particles ( with dry malonic acid mole fraction) 0.36), the crystallization RH is a stronger function of particle volume, with the crystallization RH decreasing by 6 +/- 3\% RH when the particle volume decreases by an order of magnitude. To our knowledge, these are the first size dependent measurements of the crystallization RH of atmospherically relevant inorganic-organic particles. These results suggest that for certain organic mole fractions the particle size and observation time need to be considered when extrapolating laboratory crystallization results to atmospheric scenarios. For aqueous (NH4)(2)SO4 particles, the homogeneous nucleation rate data are a strong function of RH, but for aqueous (NH4)(2)SO4-malonic acid particles (with dry organic mole fraction = 0.36), the rates are not as dependent on RH. The homogeneous nucleation rates for aqueous (NH4)(2)SO4 particles were parametrized using classical nucleation theory, and from this analysis we determined that the interfacial surface tension between the crystalline ammonium sulfate critical nucleus and an aqueous ammonium sulfate solution is between 0.053 and 0.070 J m(-2).},
	keywords = {AEROSOL-PARTICLES, ATMOSPHERIC PARTICLES, BALANCE, ELECTRODYNAMIC, HETEROGENEOUS NUCLEATION, HYGROSCOPIC PROPERTIES, MIXTURES, ORGANIC-COMPOUNDS, PHASE-TRANSITIONS, RELATIVE-HUMIDITY, WATER-UPTAKE},
	isbn = {1089-5639},
	url = {<Go to ISI>://000238645600017},
	author = {Parsons, M. T. and Riffell, J. L. and Bertram, A. K.}
}
@article {677,
	title = {The analysis of volatile trace compounds in landfill gases, compost heaps and forest air},
	journal = {Applied Organometallic Chemistry},
	volume = {17},
	number = {3},
	year = {2003},
	note = {ISI Document Delivery No.: 651ZYTimes Cited: 7Cited Reference Count: 28},
	month = {Mar},
	pages = {154-160},
	type = {Article},
	abstract = {Landfill gas, cryotrapped on a loop fashioned from a length of a capillary gas chromatography (GC) column, was examined for volatile organometallic compounds (VOMCs) and for volatile organic compounds (VOCs) by using GC-mass spectrometry (MS). A large number of organic components were present and many were identified, but the only VOMCs present in high enough concentrations to be detected were trimethylstibine and tetramethyltin. The use of inductively coupled plasma (ICP)-MS as an element-specific detector allowed the identification of a number of other organometallic species in the landfill gas, including trimethylarsine and trimethylbismuth, and, for the first time, butyltrimethyltin and dibutyldimethyltin. The presence of molybdenum hexacarbonyl was confirmed. Gas from a large-scale compost heap and from compost incubated in the laboratory contained iodomethane but no common VOMCs (GC-ICP-MS). Only VOCs were present in forest air (GC-MS). Copyright (C) 2003 John Wiley Sons, Ltd.},
	keywords = {(VOCs), BISMUTH, CHROMATOGRAPHY, EMISSIONS, ENVIRONMENT, GC-ICP-MS, GC-MS, METAL-COMPOUNDS, ORGANIC-COMPOUNDS, organotin speciation, phosphine, SITE, volatile organic compounds, volatile organometallic compounds (VONICs), WASTE},
	isbn = {0268-2605},
	url = {<Go to ISI>://000181355200002},
	author = {Maillefer, S. and Lehr, C. R. and Cullen, W. R.}
}
