Transactions on Ecology and the Environment vol 28, © 1999 WIT Press, www.witpress.com, ISSN 1743-3541
Absorption Cross Sections of HOCH%OOH Vapour
between 205 and 360 nm at 298 K
A contribution to subproject CMD
Stefan Bauerle and Geert K. Moorgat
Max-Planck-Institut fur Chemie, Division ofAtmospheric Chemistry,
P.O. Box 3060, D-55020Mainz, Germany
Introduction
Recent studies (Gab et al, 1985; Hellpointer and Gab, 1989; Lee et al, 1993;
Sauer et al, 1996; Neeb et al, 1997; Sauer, 1997) have shown that the gas
phase reaction of ozone with a variety of biogenic and anthropogenic alkenes
contributes to the formation of hydrophilic organic peroxides, which can cause
severe damage to plants. Hydroxymethylhydroperoxide (HMHP; HOC^OOH)
for example, which results from addition of water to the ozonolysis
intermediate CtbOO, has various toxic effects on plant cells and enzymes and
is suggested to be the most responsible species for leaf necrosis. All these
peroxides may be removed from the atmosphere predominantly by reaction
with OH radicals, by photolysis, and/or by rainout and washout. This study
reports the determination of the absorption spectrum of HMHP, and the
evaluation of its photolysis rate.
Experimental
The apparatus and experimental techniques employed in this work have been
described previously (Moortgat et al, 1989). A 44.2 L quartz cell equipped
with two sets of White optics was employed. One set was used for the infrared
region (1 = 43.3 m), from which the concentrations of the compounds were
determined; the other set was aimed for the measurement of the peroxide
absorption in the UV region (1 = 9.82). Infrared spectra in the range from
450-4000 cnf* at a resolution of 0.5 cm"* were measured with a Bomem
DA8.2 FTIR spectrometer coupled to a liquid nitrogen cooled MCT detector.
UV absorption was monitored with a monochromator/diode array camera
arrangement.
Proceedings ofEUROTRAC Symposium '98
Editors: P.M. Borrell and P. Borrell
© 1999: WITPRESS, Southampton
Transactions on Ecology and the Environment vol 28, © 1999 WIT Press, www.witpress.com, ISSN 1743-3541
S. Bauerle and G.K. Moorgat
70
HMHP was synthesised by bubbling HCHO vapour through a 30 % t^Oi
solution at around 60 °C. Ten microliters of the reaction mixture were
transferred into the reactor via a glass syringe. The amount of HMHP in the
cell was determined using a peak infrared absorption coefficient at 1049 cm"*
of 81049 = log(Io/I)/cl = 3.18 x 10 cm molecule . This absorption coefficient
was obtained by assuming that the observed degradation products of HMHP in
the gas phase result from its decomposition reactions, presumably at the walls
of the reactor:
HOOHbOOH
-95 %
-» HCOOH +
-» HCHO + H
The total of HCOOH and HCHO formed was then assumed to be equal to the
observed decrease of HMHP. The slow decomposition of HMHP into HCOOH
is displayed in Fig. 1.
1000
1050
1100
1200
wave number (cm~^)
Fig. 1: FUR spectra at different times which show the simultaneous decay of HMHP
and the formation of HCOOH.
Results
The absorption spectrum of HMHP is shown in Fig. 2 together with literature
spectra of %O2 and CHsOOH (Chemical Kinetics and Photochemical Data,
1994)
Transactions on Ecology and the Environment vol 28, © 1999 WIT Press, www.witpress.com, ISSN 1743-3541
Absorption Cross Sections
71
Js
o 1e-18
this work HOCHjOOH
JPL values for HgO?
JPL values for CHjOOH
1e-20
1e-22
200
240
280
320
wavelength [nm]
Fig. 2: Plot of absorption cross sections for HMHP, MHP
Kinetics and Photochemical Data, 1994).
O'zen ith angle
JO" zen ith angle
«30" zen ith angle
ro° zen ith angle
// /
/'
1
/ //
// /
/rf 7
360
and
(Chemical
f
/
>
>
^
/i
'I
1e-7
J-value (s'b
Fig. 3:
Calculated vertical distribution of the J values for different zenith-angles.
The photodissociation rate J* of a species X is the product of the actinic flux I
with the absorption cross section a and the quantum yield $ integrated over all
wavelengths X: J% = I I(X) a(X) c|>x(X) dX. These J values are needed in models
to simulate photochemical loss processes. To estimate the photodissociation
rates the program LUTHER (Moebus, 1984), developed at the MPI, was used.
The calculations employed our absorption cross sections a(X) and the solar
spectrum I^,(X) according to Shettle et al. (1989) (290-800 nm) corrected for
the absorptions of ozone, oxygen and NOi and using an albedo of 0.3. The
Transactions on Ecology and the Environment vol 28, © 1999 WIT Press, www.witpress.com, ISSN 1743-3541
72
S. Bauerle and G.K. Moorgat
calculated J values for HMHP are shown in Fig. 3 for zenith angles of 0, 30°,
50° and 70° in the altitude range 0 to 55 km.
Atmospheric fate of HOCHiOOH
1
Photolysis
HOCHzOOH + h v
->
HOC%O + OH
HOCH2O + O2
->
HCOOH + HOz
The calculated atmospheric photodissociation rate for 30° zenith angle at
ground level is 2.7 x 10~^ s~* (see Fig. 3). The corresponding lifetime Tphot = 4.3
days.
2
Reaction with OH
a)
b)
Abstraction of the peroxidic H atom
HOCHzOOH + OH
->
HOCH2OO + HzO
HOCH2OO + NO
->
HOCHzO + NOz
HOCHzO + 02
->
HCOOH+ HO2
Abstraction of the H atom in a-position
HOCH2OOH + OH
->
HOCHOOH + %O
HOCHOOH
-»
HCOOH + OH
TQH was then estimated to be 2.1 days by using the OH rate coefficient for
CHsOOH (Chemical Kinetics, 1994) ^98= 5.5 x 10"^ cm^ molecule'^ s"^ and
[OH] = 1 x 1 0 * molecule cm ^.
3
Thermal decomposition
It can be expected that HMHP has a longer lifetime when formed in the
atmosphere than in the laboratory, since the observed decay of HMHP into
HCOOH and %O is heterogeneous decomposition on the reactor walls.
4
Rainout/washout
Could be an important sink for HMHP since its solubility in water is high. Up
to 0.8 |imol L~^ were found in rain water investigations (Hellpointer and Gab,
1989; Lee etai, 1993; Sauerefa/., 1996).
Transactions on Ecology and the Environment vol 28, © 1999 WIT Press, www.witpress.com, ISSN 1743-3541
Absorption Cross Sections
73
Conclusions
The measured UV
absorption cross sections and the calculated
photodissociation rates lead to the assumption that photolysis is probably a
minor loss process for HOCIfeOOH. The major atmospheric degradation
pathways are expected to be reaction with OH radicals and/or rainout and
washout. This has to be confirmed by further experiments.
Photolysis and reaction with OH lead to the same products. Both would provide
an atmospheric source for HCOOH.
References
Chemical Kinetics and Photochemical Data for Use in Stratospheric Modelling,
Evaluation Number 11, JPL Publication 94-26 (1994).
S. Gab, E. Hellpointer, W.V. Turner and F. Korte, Nature 316 (1985) 535.
E. Hellpointer and S. Gab, Nature 337 (1989) 631.
J.H. Lee, D.F. Leahy, I.N. Tang and L. Newman, J. ofGeophys. Res. 98 (1993) 2911.
K.H. Moebus, Documentation for the LUTHER-Program, MPI Mainz (1984).
G.K. Moortgat, R.A. Cox, G. Schuster, J.P. Burrows and G.S. Tyndall, J. Chem. Soc.
Faraday Trans. II85 (1989) 809.
P. Neeb, F. Sauer, O. Horie and G.K. Moortgat, Atmos. Environ. 31 (1997) 1417.
F. Sauer, G. Schuster, C. Schafer and G.K. Moortgat, Geophys. Res. Lett. 23 (1996)
2605.
F. Sauer, Dissertation, Universitat Mainz, January 1997.
E.P. Shettle, G.P. Anderson and L.A. Hall, Extraterrestrial Solar Spectrum for Use
with LOWTRAN, AFGL/OPA, Hanscan AFB.MA 01731, update (1989).