Kinetics of heterogeneous reaction of CaCO3 particles with gaseous HNO3 over a wide range of humidity.
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 Dp = 0.85 mum, particle loading densities 2 x 104 </= Ns </= 6 x 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 gammanet >/= 0.06 (x3//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 gammanet >/= 0.003 at RH = 10% to 0.21 at 80%.
Liu
Y
Y
William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P. O. Box 999, MSIN K8-88, Richland, Washington 99352, USA.
Gibson
E R
ER
Cain
J P
JP
Wang
H
H
Grassian
V H
VH
Laskin
A
A
D002119:Calcium Carbonate / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D006813:Humidity; D007700:Kinetics; D008855:Microscopy, Electron, Scanning / Q000295:instrumentation / Q000379:methods; D017942:Nitric Acid / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D014961:X-Ray Diffraction
D005740:Gases; D017942:Nitric Acid; D002119:Calcium Carbonate