Kinetics and mechanisms of heterogeneous reaction of NO2 on CaCO3 surfaces under dry and wet conditions State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China
Received: 07 Jan 2009 – Published in Atmos. Chem. Phys. Discuss.: 17 Mar 2009Abstract. With increasing NO2 concentration in the troposphere, the importance of
NO2 reaction with mineral dust in the atmosphere needs to be evaluated.
Until now, little is known about the reaction of NO2 with CaCO3.
In this study, the heterogeneous reaction of NO2 on the surface of
CaCO3 particles was investigated at 296 K and NO2 concentrations
between 4.58×1015 molecules cm−3 to 1.68×1016 molecules cm−3,
using diffuse reflectance infrared Fourier transform
spectroscopy (DRIFTS) combined with X-ray photoelectron spectroscopy (XPS)
and scanning electron microscopy (SEM), under wet and dry conditions.
Nitrate formation was observed under both conditions, while nitrite was
observed under wet conditions, indicating the reaction of NO2 on the
CaCO3 surface produced nitrate and probably nitrous acid (HONO).
Relative humidity (RH) influences both the initial uptake coefficient and
the reaction mechanism. At low RH, surface −OH is formed through
dissociation of the surface adsorbed water via oxygen vacancy, thus
determining the reaction order. As RH increases, water starts to condense on
the surface and the gas-liquid reaction of NO2 with the condensed water
begins. With high enough RH (>52% in our experiment), the gas-liquid
reaction of NO2 with condensed water becomes dominant, forming
HNO3 and HONO. The initial uptake coefficient γ0 was
determined to be (4.25±1.18)×10−9 under dry conditions
and up to (6.56±0.34)×10−8 under wet conditions. These
results suggest that the reaction of NO2 on CaCO3 particle is
unable to compete with that of HNO3 in the atmosphere. Further studies
at lower NO2 concentrations and with a more accurate assessment of the
surface area for calculating the uptake coefficient of the reaction of
NO2 on CaCO3 particle and to examine its importance as a source of
HONO in the atmosphere are needed.
Revised: 15 Dec 2009 – Accepted: 16 Dec 2009 – Published: 20 Jan 2010
Citation: Li, H. J., Zhu, T., Zhao, D. F., Zhang, Z. F., and Chen, Z. M.: Kinetics and mechanisms of heterogeneous reaction of NO2 on CaCO3 surfaces under dry and wet conditions, Atmos. Chem. Phys., 10, 463-474, doi:10.5194/acp-10-463-2010, 2010.