Single Particle Laboratory Studies of Heterogeneous Reactions of Trace Atmospheric Gases with Particles Present in the Troposphere
EMSL Project ID
2539
Abstract
It is becoming increasingly clear that heterogeneous processes involving particulate matter in the atmosphere can greatly perturb the chemical composition of both the troposphere and the stratosphere. Mineral dust and sea salt represent major and ubiquitous tropospheric aerosol components. While there are a growing number of modeling studies which suggest that reactions on the surface of mineral and sea salt aerosol may play an important role in the tropospheric NOy, SOy and O3 budgets, there is very little detailed understanding of the chemistry which occurs on the surface of aerosol particles. In order to incorporate heterogeneous chemistry into atmospheric chemistry models, the rates and mechanisms of these reactions must be understood. Kinetic studies of heterogeneous chemistry is complicated by the fact that these studies are typically done using bulk samples which contain many particles. Diffusion into the sample and how to take the diffusion into account has caused disagreement between scientists in the literature. Studies of single particles will circumvent this problem. In the proposed studies, we plan to investigate the heterogeneous chemistry of mineral dust and sea salt using single particle analysis. This summer we plan to continue and expand our collaboration with Dr. Alexander Laskin, EMSL Research Scientist and Dr. James Cowin, EMSL Chief Scientist. The objective is to follow up upon preliminary experiments performed at PNNL in January 2002 before the installation of the New Environmental Scanning Electron Microscope. In our previous experiments tropospheric particles including NaCl, Sea Salt, CaCO3, and SiO2 were imaged and analyzed using the scanning electron microscope (SEM) and the energy dispersive x-ray (EDX) analyzer at EMSL. These particles were imaged prior to and after reaction with nitric acid, a trace atmospheric gas in the troposphere that is thought to react with tropospheric particles. Since these reactions must be done under relative humidity conditions appropriate to the troposphere, reactions were carried out ex situ and samples were then carried over to the microscope. There was little control of the environment of the particles during this transfer period. Thus with the new setup relative humidity studies can be monitored in situ, an important improvement over the last set of experiments. In addition, automated EDX analysis was completed on the particles prior to reaction but not on the reacted particles. In the experiments to be done in June 2002, particles will be monitored with EDX analysis before, during and after reaction so as to learn more about changes in chemical composition. 1. Tropospheric particles (e.g. NaCl, CaCO3, Sea Salt and SiO2) will be imaged and their reaction will be monitored with trace gases, such as HNO3, and as a function of relative humidity. 2. The deliquescence and efflorescence of these particles after reaction with nitric acid will be monitored as a function of relative humidity as these properties are important in climate models and need to be understood more. 3. If time allows, heterogeneous reactions of acetic acid will be investigated as organic acids are important components of the earth?s atmosphere.
Project Details
Project type
Exploratory Research
Start Date
2002-06-01
End Date
2002-06-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members