Single Particle Laboratory Studies of Heterogeneous Reactions of Trace Atmospheric Gases with Particles Present in the Troposphere
EMSL Project ID
2410a
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 authentic mineral dusts using single particle analysis.
This summer we plan to continue and expand our collaboration with Dr. Alexander Laskin, EMSL Senior Research Scientist and Dr. James Cowin, EMSL Chief Scientist. The objective is to follow up upon experiments performed at PNNL in June 2002. 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. 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. In addition, automated EDX analysis was completed on the particles prior to and after reaction. In the experiments to be done in June 2003;
1. Authentic dust particles will be imaged, analyzed with EDX, and their reaction will be monitored with trace gases such as HNO3 and CH3COOH.
2. Tropospheric particles (e.g. NaCl, CaCO3, Sea Salt and SiO2) will be imaged and their reaction will be monitored with trace gases, such as CH3COOH, and as a function of relative humidity.
3. The deliquescence and efflorescence of these particles after reaction with nitric acid and acetic acid will be monitored as a function of relative humidity as these properties are important in climate models and must be fully understood.
Project Details
Project type
Exploratory Research
Start Date
2003-06-01
End Date
2005-06-20
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members