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

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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)