Gentle photoionization of organic constituents using vacuum ultraviolet aerosol mass spectrometry

Aerosol particles have long been a primary focus of the atmospheric community due to their influence on human health, radiative forcing, and participation in atmospheric chemistry. Conventionally, aerosols have been collected on filters and analyzed off-line by GC-MS, LC-MS, and FTIR. These techniques made valuable inroads to particle speciation, however, the inherent physical and chemical artifacts during sampling initiated the development of a succession of on-line aerosol mass spectrometers. Currently, a variety of real-time aerosol mass spectrometers, many with single particle analysis capabilities, have been developed and installed in laboratories as well as in the field. Atmospheric aerosols are complex mixtures of inorganic and organic species, and whereas analysis of inorganics is rather straightforward due to their robust nature, organics are fragile and analysis is challenging. Several researchers have moved specifically towards analysis of organic aerosol particles, attempting to simplify peak assignment by reducing the fragmentation of these delicate molecules. The initial portion of this project involved design and development of an aerosol mass spectrometer, ideal for analyzing a wide size range of organic aerosol particles. The novel mass spectrometer uses both continuous vaporization with a cartridge heater and quasiiv continuous photoionization by tunable vacuum ultraviolet light produced by synchrotron radiation. Coupling continuous vaporization and ionization techniques with a high brightness photon source allows analysis of ultrafine aerosol particles, which have high toxicity and high number concentration in ambient air. Several atmospherically relevant organic molecules are examined, along with a more complex yet more realistic secondary organic aerosols formed from terpene ozonolysis. Finally, a timing circuit used to analyze single particles (diameter > 200nm) was designed and developed. The versatile electronic circuit can be used to couple multi-laser systems having pre-triggering requirements to single particle arrival in the ionization region of the mass spectrometer. It can also be applied to continuous vaporization and ionization schemes where one wants to pulse ions into a time of flight analyzer as particles arrive in the interaction region

Water adsorption on alpha-Fe2O3(0001) at near ambient conditions

We have investigated hydroxylation and water adsorption on {alpha}-Fe{sub 2}O{sub 3}(0001) at water vapor pressures up to 2 Torr and temperatures ranging from 277 to 647 K (relative humidity (RH) {<=} 34%) using ambient-pressure x-ray photoelectron spectroscopy (XPS). Hydroxylation occurs at the very low RH of 1 x 10{sup -7}% and precedes the adsorption of molecular water. With increasing RH, the OH coverage increases up to one monolayer (ML) without any distinct threshold pressure. Depth profiling measurements showed that hydroxylation occurs only at the topmost surface under our experimental conditions. The onset of molecular water adsorption varies from {approx}2 x 10{sup -5} to {approx}4 x 10{sup -2}% RH depending on sample temperature and water vapor pressure. The coverage of water reaches I ML at {approx} 15% RH and increases to 1.5 ML at 34% RH

Carbon oxidation state as a metric for describing the chemistry of atmospheric organic aerosol

A detailed understanding of the sources, transformations and fates of organic species in the environment is crucial because of the central roles that they play in human health, biogeochemical cycles and the Earth's climate. However, such an understanding is hindered by the immense chemical complexity of environmental mixtures of organics; for example, atmospheric organic aerosol consists of at least thousands of individual compounds, all of which likely evolve chemically over their atmospheric lifetimes. Here, we demonstrate the utility of describing organic aerosol (and other complex organic mixtures) in terms of average carbon oxidation state, a quantity that always increases with oxidation, and is readily measured using state-of-the-art analytical techniques. Field and laboratory measurements of the average carbon oxidation state, using several such techniques, constrain the chemical properties of the organics and demonstrate that the formation and evolution of organic aerosol involves simultaneous changes to both carbon oxidation state and carbon number.United States. Environmental Protection Agency (Science To Achieve Results (STAR) program (grant R833746))United States. Dept. of Energy (DOE: grant DE-FG02-05ER63995)United States. Dept. of Energy (DOE: grant ATM-0449815)United States. Dept. of Energy (DOE: grant ATM-0919189)United States. National Oceanic and Atmospheric Administration (NOAA: grant NA08OAR4310565)United States. Dept. of Energy (Director, Office of Energy Research, Office of Basic Energy Sciences, and Chemical Sciences Division of the US DOE (contract no. DE-AC02-05CH11231))Lawrence Berkeley National Laboratory (Laboratory Directed Research and Development Program)Henry & Camille Dreyfus Foundatio

Subliming Surfaces: volatile binding media in heritage conservation

This book brings together 22 papers and posters that were presented at the conference ‘Subliming Surfaces: Volatile Binding Media in Heritage Conservation’ in Cambridge, April 2015