HR: 1340h
AN: A53C-1359    [Abstracts]
TI: Chemical Transformation of CaCO₃ Particles by Heterogeneous Reaction with HNO₃: Kinetic Measurements over a Wide Range of Humidity
AU: Gibson, E R
EM: egibson@asl-analytical.com
AF: Departments of Chemistry and Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA 52242, United States
AU: * Liu, Y
EM: yong.liu@pnl.gov
AF: W.R. Wiley Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, P.O.Box 999 MSIN K8-88, Richland, WA 99352, United States
AU: Cain, J P
EM: jcain@usc.edu
AF: Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, United States
AU: Wang, H
EM: haiw@usc.edu
AF: Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, United States
AU: Grassian, V H
EM: vicki-grassian@uiowa.edu
AF: Departments of Chemistry and Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA 52242, United States
AU: Laskin, A
EM: Alexander.Laskin@pnl.gov
AF: W.R. Wiley Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, P.O.Box 999 MSIN K8-88, Richland, WA 99352, United States
AB: Mineral dust aerosol comprises one of the largest mass fractions of the total global aerosol loading. As mineral dust aerosol is entrained and transported through the atmosphere, it can undergo heterogeneous reactions with trace atmospheric gases, which alter the chemical balance of the atmosphere. Meanwhile, changes the particle chemical composition and surface properties also occur, and in this way affect the impact of the particle on climate through direct and indirect radiative forcing. The importance of heterogeneous interactions between mineral dust and reactive trace gases on a global scale has been demonstrated by several modeling studies. A number of field studies have shown that particles containing solid calcium carbonate (CaCO₃) undergo complete, irreversible processing by heterogeneous reaction with gaseous nitric acid (HNO₃) to form highly hygroscopic Ca(NO₃)₂. Such conversion of insoluble material to soluble material strongly affects the hygroscopic properties of mineral dust particles, as well as their ability to serve as cloud condensation nuclei. Uptake of HNO3 on mineral dust is one of the most important, but least certain parameters in the analysis of the impact of dust on tropospheric ozone concentrations. To assess this impact, accurate measurements of the heterogeneous uptake coefficient (γ) under conditions representative of the atmosphere are critical. In the present work, we investigate the heterogeneous reaction of gaseous HNO₃ with CaCO₃ particles using a novel technique that utilizes exposure of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO₃/H₂O/N₂, followed by microanalysis of individual particles. Chemical transformation of micron size CaCO₃ particles by heterogeneous interaction with HNO3 concentrations of 7- 25 ppb, similar to those found in a polluted atmosphere, and reactive uptake over a wide relative humidity range are reported. The net reaction probability (γ_net) was found to increase with an increase in the relative humidity, from 0.003 at RH = 10% to 0.21 at 80%.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting