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Kinetics of Heterogeneous Reaction of CaCO3 Particles with Gaseous HNO3 over a...

Liu, Y., E. R. Gibson, J. P. Cain, H. Wang, V. H. Grassian, and A. Laskin (2008), Kinetics of Heterogeneous Reaction of CaCO3 Particles with Gaseous HNO3 over a Wide Range of Humidity, J. Phys. Chem. A, 112, 1561-1571, doi:10.1021/jp076169h.

Heterogeneous reaction kinetics of gaseous nitric acid (HNO3) with calcium carbonate (CaCO3) particles was investigated using a particle-on-substrate stagnation flow reactor (PS-SFR). This technique utilizes the exposure of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO3/H2O/N2, followed by microanalysis of individual reacted particles using computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX). The first series of experiments were conducted at atmospheric pressure, room temperature and constant relative humidity (40%) with a median dry particle diameter of D hp ) 0.85 µm, particle loading densities 2 × 104 e Ns e 6 × 106 cm-2 and free stream HNO3 concentrations of 7, 14, and 25 ppb. The apparent, pseudo first-order rate constant for the reaction was determined from oxygen enrichment in individual particles as a function of particle loading. Quantitative treatment of the data using a diffusion-kinetic model yields a lower limit to the net reaction probability γnet g 0.06 (×3/÷2). In a second series of experiments, HNO3 uptake on CaCO3 particles of the same size was examined over a wide range of relative humidity, from 10 to 80%. The net reaction probability was found to increase with increasing relative humidity, from γnet g 0.003 at RH ) 10% to 0.21 at 80%.

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Research Program: 
Atmospheric Composition Modeling and Analysis Program (ACMAP)
Radiation Science Program (RSP)
Tropospheric Composition Program (TCP)