Development of chemical transformation mechanisms to be
used in
models of urban areas and urban plumes
Yvonne Andersson-Sköld
Melica, Fjällgatan 3E, s 413 17 Göteborg, Sweden
Summary
It is well known that deposition and heterogenous processes influence the
oxidation processes in the atmosphere and vice versa. The overall goal
of this subproject is to implement experiemental kinetical and mechanistical
data and information about gaseous and heterogenous processes into atmospheric
models. The updated chemical schemes will be tested and devloped /simplified
for urban areas and urban plumes.
Hera are presented results of tests in which empirical data have been
used to simulate the urban heterogenous formation of HONO and HNO3. The
conclusions are that, among the heterogenous reaction studied, only the
formtion of HNO3 from water and N2O5 has any significant influence
on the ozone concentration. Also the influence of deposition rates
have been tested and it was found that the deposition of ozone has a significant
influence on the calculated concentrations of ozone whereas the deposition
of other species deposited has a very limited effect.
Aim of the reserach
The aim of the research is to implement, develope and updating chemical
schemes for gaseous and heterogenous processes . The schemes will be developed
to focus on NOx, aerosols/particulates and oxidants.
Activities during the year
The IVL photochemical trajectory model has been used for a preliminary
investigation of deposition and some heterogenous reactions. Simulations
have been conducted for the London plume and the concentrations of ozone
and NOy species have been calculated. Empirical data have been used to
simulate the heterogenous formation of HONO and HNO3.
The chemical scheme of the IVL photochemical trajecotory model is being
updated regarding aromatic volatile organic compounds and biogenic volatile
and semi volvatile organic compounds.
Principal results
In Figure 1 the simulated ozone concentrations are shown for a base case
of the London plume (eg. Derwent, 1990) and for a scenario where the deposition
rate of ozone has been increased with 50 %. In figure 2 is also shown
the effect on ozone when several or all deposition rates (including ozone)
are increased with 50 %. According to these Figures and regarding ozone
the depostion rate of ozone it self is the most important deposition rate.
Figure 1 Simulated ozone concentration (ppb) in the London plume
for a case with standard deposition, and a case when the deposition rate
of ozone has been increased with 50 % (Ozone depostion x 1.5)
Figure 2. The effect on ozone when the deposition rate of only ozone
(Ozone depostion x 1.5), the deposition rates of some species including
ozone and when all depsotion rates are increased with 50 % (All deposition
x 1.5)
Figure 3 Simulated ozone concentrations (ppb) in the London plume for
one scenario the rate constants of the heterogenous formation of
HONO and HNO3 from water and NO2 varies from zero to 0.02 % per hour.
Figure 4 The influence on ozone due to varios heterogenous reactions
producing HONO and /or HNO3.
and investigated in this study is shown in relation to the case
without any heterogenous reactions occuring in the system. As can be seen
the major influence on ozone and HNO3 is found for the the formation of
HNO3 from water and N2O5
According to Figures 3 and 4 the heterogenous formation of HONO and
HNO3 has an influence on the simulated ozone levels. The major influence
on ozone, according to this study, is found for the formation of HNO3 from
water and N2O5.
Main conclusions
The conclusions of this study therefore are that among the heterogenous
reaction studied here only the formtion of HNO3 from water and N2O5.. has
any significant influence on the ozone concentration. The deposition of
ozone has a significant influence on the calculated concentrations of ozone
whereas the deposition of other species deposited has a very limited effect.
Aim of the coming year
The aim of the coming year is to continue the work on interactions between
different phases.
Acknowledgement
This work has been funded by the Swedish Environmental Protection Board
(NV) which is gratefully acknowledged.
References.
Altenstedt, J. and Andersson-Sköld, Y., "Sensitivity Studies of the
Chemical Scheme of the IVL Photochemical Trajectory Model", IVL Report
B 1217, 1996
Andersson-Sköld, Y, "Updating the chemical scheme for the IVL photochemical
trajectory model", ", IVL Report B 1151, 1995
Andersson-Sköld, Y and Altenstedt, J., "Tests of heterogenous processes
in the London ", A Contribution to Subproject – SATURN, Proceeding EUROTRACII,
1998/9
Andersson-Sköld, Y and Simpson D., "Comparison of the chemical
schemes of the EMEP
MSC-W and IVL photochemical trajectory models", EMEP/MSC-W Note
1/97, 1997
Becker, K.H., Cox, R.A., Le Bras, G. Lesclaux, R., Moortgat, G.K, Sidebottom,
H.W., Zellner, R. Wirtz, K., Roehl, C., and Hayman, G.D., "Chemical mechanisms
used in the EMEP ozone model re-evalueted by the LACTOZ steering committe",
Wuppertal, 1993
Derwent, R.G., Atmos. Environ., 24 A (10), (1990),pp 2615-2624