FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

demonstrating that BrO and ClO with GEM are endothermic (27) and thus reaction 2 and 3 are most
probably not important for the removal of Hg o in the atmosphere.
Instead of BrO and ClO, GEM may react with Cl and/or Br. Therefore the data were analysed
assuming relative rate conditions between ozone and GEM. The method is widely used under
laboratory conditions, where the reaction of interest is proceeding in competition with another
reaction with a well-known reaction rate constant. So the system here is:
and
O + X → product
3 (4)
Hg + X → product
(5),
where X is either Br or Cl and assuming that all other reactions are of negligible importance for the
removal of ozone and GEM.
The kinetic equations for reaction 4 and 5 are:
and
[ GEM ]
∫
[ GEM ]
[ O ]
3
∫
[ O ]
t
t
d ln [ O ] = −k
[ X ]dt
(6)
3 0
3
t
∫
4
0
t
d ln [ GEM ] = −k
[ X ]dt
(7),
0
respectively.
∫
5
0
Integrating equation and dividing equation 6 with 7 the relative rate expression is obtained.
[ GEM ]
[ GEM ]
[ ]
[ ] ⎟⎟
O ⎞ 3 0
O
⎛
⎛
0 ⎞ k5
ln ⎜ ⎟ = • ln⎜
⎜
(8).
⎝
t ⎠ k4
⎝ 3 t ⎠
A plot of ln([GEM]0/[GEM]t against ln([O3]0/[O3]t should give a straight line with intercept 0 and a
slope equal to k5/k4. Fig. 4 shows such a plot using the data from Station Nord. Data were selected
for periods where the initial concentration of GEM was above 0.4 ng/m 3 in order to ensure good
signal to noise ratio and where three consecutive measurements of both ozone and GEM are
decreasing. All measurement included were in periods with 24 hour daylight. There is a strong
linear correlation (