This project involves laboratory studies of heterogeneous processes occurring on dust particles in the atmosphere. Dust represents over one half the tropospheric particle mass burden. It can be transported over trans-continental distances and has a major global impact on pollution, climate, and biogeochemistry. Heterogeneous chemistry occurring on dust significantly impacts both particle and gas phase chemistry in the atmosphere.
The ACE-Asia field campaign in 2001 was the first major study that employed the use of a single particle mass spectrometer to analyze dust chemistry. These observations serve as the inspiration for the planned laboratory kinetics studies, which will also use aerosol time-of-flight mass spectrometry (ATOFMS) for chemical analysis of the particles, along with chemical ionization mass spectrometry (CIMS) to analyze gas phase species. The reactions will occur in an aerosol flow tube with controlled particle size, reactant concentration, humidity, and reaction time. Detailed surface characterization will be performed by U. of Iowa researchers using traditional SEM/EDX (Scanning Electron Microscopy/Energy-Dispersive X-ray analysis), XPS (X-Ray Photoelectron Spectroscopy), and ATR-FTIR (Attenuated Total Reflectance/Fourier-Transform Infra Red Spectroscopy) to probe the same processes. Competitive kinetics experiments will be carried out to characterize the relative reactivity of different types of dust and sea salt with gas phase precursors, and to determine the relative importance of the factors controlling secondary product formation on dust and sea salt. In addition, the project will examine how chemical transformations induced by various acids to form soluble species affect the CCN (cloud-condensation nuclei) potential of the reacted dust particles. A thermal gradient CCN instrument will be interfaced to an ATOFMS using a counterflow virtual impactor to separate and directly measure the chemical differences between those particles that activate versus those that do not.
The kinetic information obtained from the laboratory studies will be used as input to refine regional chemistry models being developed at U. of Iowa and tested by comparing the new outputs to ACE-Asia measurements. The model will be used to develop a mechanistic picture of the heterogeneous processes studied. This information will in turn be used to help design future field campaigns to probe the findings of these lab studies under real world conditions. These studies will contribute to the training of graduate and undergraduate students in atmospheric, analytical, and environmental chemistry. The project will also further develop the quantitative abilities of single-particle mass spectrometry methods.
