Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
1680-7367
1680-7375
4
6
2004
10.5194/acpd-4-7881-2004
http://www.atmos-chem-phys-discuss.net/4/7881/2004/
http://www.atmos-chem-phys-discuss.net/4/7881/2004/acpd-4-7881-2004.html
http://www.atmos-chem-phys-discuss.net/4/7881/2004/acpd-4-7881-2004.pdf
7881
7915
2004-12-03
Characterisation of the photolytic HONO-source in the atmosphere simulation chamber SAPHIR
F. Rohrer
B. Bohn
T. Brauers
D. Brüning
F.-J. Johnen
A. Wahner
J. Kleffmann
kleffman@uni-wuppertal.de
Institut für Chemie und Dynamik der Geosphäre II: Troposphäre, Forschungszentrum Jülich, Jülich, Germany
Physikalische Chemie/FB C, Bergische Universität Wuppertal, Wuppertal, Germany
HONO formation has been proposed as an important OH radical source in
simulation chambers for more than two decades. Besides the heterogeneous
HONO formation by the dark reaction of NO<sub>2</sub> and adsorbed water, a
photolytic source has been proposed to explain the elevated reactivity in
simulation chamber experiments. However, the mechanism of the photolytic
process is not well understood so far.
<br><br>
As expected, production of HONO and NO<sub>x</sub> was also observed inside the
new atmosphere simulation chamber SAPHIR under solar irradiation. This
photolytic HONO and NO<sub>x</sub> formation was studied with a sensitive HONO
instrument under reproducible controlled conditions at atmospheric
concentrations of other trace gases. It is shown that the photolytic HONO
source in the SAPHIR chamber is not caused by NO<sub>2</sub> reactions and that it
is the only direct NO<sub>y</sub> source under illuminated conditions. In
addition, the photolysis of nitrate which was recently postulated for the
observed photolytic HONO formation on snow, ground, and glass surfaces, can
be excluded in the chamber. A photolytic HONO source at the surface of the
chamber is proposed which is strongly dependent on humidity, on light
intensity, and on temperature. An empirical function of the form
S(HONO)=a<sub>1,2</sub>×J(NO<sub>2</sub>)×(1+(RH/RH<sub>0</sub>)<sup>2</sup>)×exp(−T<sub>0</sub>/T)
describes these dependencies and reproduces the
observed HONO formation rates to within 10%. It is shown that the
photolysis of HONO represents the dominant radical source in the SAPHIR
chamber for typical tropospheric O<sub>3</sub>/H<sub>2</sub>O concentrations. For these
conditions, the HONO concentrations inside SAPHIR are similar to recent
observations in ambient air.