Atmospheric Chemistry Laboratory

Group Members
Lead: Laura Iraci (650-604-0129)
Annalise Van Wyngarden (650-604-2793)
Bruce Phebus

Group Home Page Under Construction

Research Objectives
To understand how interactions between gases and particles occur in the Earth's highly complex atmosphere, our research group studies aerosol processes in a controlled laboratory setting. To do this, we use a variety of spectrometric and high vacuum techniques in applications such as a traditional Knudsen Cell flow system and a multiphase aqueous reactor with infrared detection. We are especially interested in the interactions of organic gases with sulfate aerosols and possible anthropogenic changes in the effectiveness of these aerosols to serve as cloud condensation nuclei. The long-term goals of our research program are to understand the organic trace composition of upper tropospheric and lower stratospheric (UT/LS) particles and ultimately explore how the chemistry of sulfate/organic aerosols can influence the climate system and global chemical processes.

Research Activities
Our current research examines the solubility and reactivity of oxygenated organics in mixed sulfate/organic systems. Recent studies have explored the liquid-phase reactions of small aldehydes, of aldehydes and ketones with ethanol, and of methanol with nitric acid. We have also observed that acetic acid may be the dominant dissolved oxygenated organic compound in UT/LS aerosols, and we hypothesize that the presence of acetic acid may affect the uptake of other compounds.

Active projects focus on the heterogeneous chemistry of UT/LS organics and the effect of cloud cycling on aerosol properties. Aerosol particles in the upper troposphere and lower stratosphere (UT/LS) are composed predominantly of sulfuric acid and water, and they are known to contain trace amounts of organic material. When activated into cloud drops, the volume of these particles increases by five orders of magnitude, suggesting that significant amounts of additional organic material may be incorporated at that time. Although it is commonly believed that this additional material is re-volatilized once a cloud evaporates, the solubility of oxygenated organics can be significantly higher in strongly acidic solutions, and liquid-phase reactions can serve to further sequester material. Furthermore, as aerosol particles activate into cloud droplets, they experience radical changes in composition, viscosity, and pH. These cloud conditions will favor different chemical behavior than did the starting conditions, but this evolution is not considered in chemical models of the particles in our atmosphere. As non-precipitating cloud droplets dry out and return to the aerosol state, they will be changed relative to their original state. While the community is starting to acknowledge probable changes to the physical form of aerosol particles during process such as this, the potential chemical changes have not been explored. A parallel topic of interest is the formation of resilient surface films of organic material from these acidic systems. We are studying the formation conditions and rates for these organic films, as well as exploring the possible impact of these films on mass transfer across the interface.

A related study of the effects of boreal fires on the aerosol composition of the lower stratosphere is underway. Those studies currently do not involve a laboratory component, but rather rely on data collected by several satellite instruments.

Our newest apparatus is being constructed to examine the growth of water ice clouds on present and past Mars to assist in the interpretation and modeling of results from the Mars Global Surveyor and Mars Odyssey missions. We will determine the supersaturation conditions needed to initiate ice growth on martian dust particles. This parameter is crucial for modeling the cloud formation on Mars and understanding the heat balance of the atmosphere, yet values used currently have no experimental foundation. The importance of the chemical composition of the dust will be explored, as will the phase of ice formed and the effect of cooling rate on the ice properties.