Helen Langley DeWitt

Learn More
Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn's moon, Titan. One of Titan's most captivating features is the thick organic haze layer surrounding the moon, believed to be formed from photochemistry high in the CH(4)/N(2) atmosphere. It has been suggested that a similar haze layer may have formed on the(More)
Recent attempts to resolve the faint young Sun paradox have focused on an early Earth atmosphere with elevated levels of the greenhouse gases methane (CH(4)) and carbon dioxide (CO(2)) that could have provided adequate warming to Earth's surface. On Titan, the photolysis of CH(4) has been shown to create a thick haze layer that cools its surface. Unlike(More)
The impact of cloud events on isoprene secondary organic aerosol (SOA) formation has been studied from an isoprene /NOx / light system in an atmospheric simulation chamber. It was shown that the presence of a liquid water cloud leads to a faster and higher SOA formation than under dry conditions. When a cloud is generated early in the photooxidation(More)
While water insoluble organics are prevalent in the atmosphere, it is not clear how the presence of such species alters the chemical and physical properties of atmospheric aerosols. Here we use a combination of FTIR spectroscopy, Transmission Electron Microscopy (TEM) and Aerosol Mass Spectrometry (AMS) to characterize ammonium sulfate particles coated with(More)
The presence of sulfur mass-independent fractionation (S-MIF) in sediments more than 2.45 × 10(9) years old is thought to be evidence for an early anoxic atmosphere. Photolysis of sulfur dioxide (SO(2)) by UV light with λ < 220 nm has been shown in models and some initial laboratory studies to create a S-MIF; however, sulfur must leave the atmosphere in at(More)
Aerosol-cloud interaction contributes to the largest uncertainties in the estimation and interpretation of the Earth's changing energy budget. The present study explores experimentally the impacts of water condensation-evaporation events, mimicking processes occurring in atmospheric clouds, on the molecular composition of secondary organic aerosol (SOA)(More)
Impact of palmitic acid coating on the water uptake and loss of ammonium sulfate particles R. M. Garland, M. E. Wise, M. R. Beaver, H. L. DeWitt, A. C. Aiken, J. L. Jimenez, and M. A. Tolbert Department of Chemistry and Biochemistry and CIRES, University of Colorado, Boulder, Colorado, USA now at: Department of Geological Sciences and Department of(More)
  • 1