A Study of the Chemical Degradation of ClONO2 in the ...

8 Ravishankara et al.: Chemical Degradation
3OO i
I00
00(p) + CIONO,
i I I
0 5 I0 15
rntorr of ClONO 2
FIGURE 1
A plot of the pseudo-first order rate constant for
the decay of OH [O], or O(3p) [O] as a function of
ClONO
!
ments of the rate constant kl, and finding
steadily increasing k 1 values with an increase
in the residence time. However, at 245 K there
was no evidence for the decomposition of ClONO 2.
For this reason, both reactions were studied at
the reduced temperature of 245 K.
Ozone was prepared by passing 02 through an
ozonator. Before use, 03 was purified by
continuously pumping while at 195 K; its purity
was checked by UV absorption spectroscopy. UHP
grade Matheson H 2 and 02, and UHP gold label Ar
were used without further purification.
RESULTS AND DISCUSSION
The rate constants for both Reactions (1) and
(2) were measured at 245 K simulating stratospheric
temperatures. The pseudo-first order
rate constants, k' 1 and k2, ' for the disappearance
of O(3p) and OH are shown as a function of the
ClON02 pressure in Figure 1. Linear least square
analyses of the data were carried out to obtain
the bimolecular rate constants, kbi. At 245 K,
the kbi values are
2 pressure at 245 K. The error bars in these -13
plots show the total uncertainty observed in three kl = (2.0 +.2) x 10
to four independent measurements of the first order and
-1 -1
cc molecule sec
rate constant at a given ClONO 2 pressure. k2 = (3.7 +.2) x 10 -13 cc molecule-lsec -1.
UV spectrum. On the basis of these analyses,
together with calculations of the O(3P) loss due For Reactions (1) and (2), the quoted errors are
to the reaction, O(3P) + NO 2 --+ NO + 02 (Davis two standard deviations.
et al., 1973), the NO 2 impurity level was placed
at less than .5%. It should be noted, however,
In the investigations of Reactions (1) and (2)
the concentration of ClONO 2 (>1014 molecule cm -3)
that at 298 K there was evidence indicating that was typically a thousand times greater than that
ClONO 2 decomposed in the glass reaction cell when of either O(3P) (