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EVALUATION OF THE ABILITY OF INDICATOR SPECIES TO
DESCRIBE THE OZONE RESPONSE TO PRECURSOR
Mihaela Mircea1, Massimo D'Isidoro1, Alberto
Maurizi1, Francesco Tampieri1, Gabriele Zanini2,
Fabio Monforti2, Lina Vitali2
1Istituto di Scienze dellAtmosfera e del Clima,
Consiglio Nazionale delle Ricerche, 40129
Bologna, Italy 2ENEA PROT-INN Section, Via
Martiri Monte Sole 4, 40129 Bologna, Italy
Introduction The indicator species are widely
used to assess the sensitivity of ozone to the
reduction of emissions of its two main
precursors nitrogen oxides (NOx) and volatile
organic compounds (VOC). These measures are
generally determined by using three-dimensional
photochemical transport models in support to
designation of effective air quality control
strategies. At present, no such research is
available over the whole Italy in spite of the
high number of days with the ozone concentrations
that exceed the threshold value for warning the
public established by European Union regulations.
Therefore, this study evaluates the ozone
response to precursor controls using the regional
air quality model BOLCHEM (Mircea et al., 2007).
The evaluation is performed for three periods
during the summer of the year 1999 1-3 June, 1-4
July, 5-7 August, using the photochemical
mechanisms CB-IV (Gery et al., 1989) and
SAPRC90 (Carter, 1990). In addition, some
indicator species commonly employed in ozone
sensitivity studies are calculated and their
dependency on the size of the analyzed sub-domain
is shown.
Indicator species approach The indicator specie
approach basically relates the variations in
ozone to the variations of the indicator species.
The indicator species can be species or ratio of
species involved in the ozone photochemistry,
thus the relationship ozone sensitivity-indicator
is directly dependent on the photochemical
mechanism used.
Ozone sensitivity to VOC-NOX emissions The
graphs below show the differences in ozone
concentrations between the simulations with VOC
and NOx emissions reduced by 35 (O3 produced
with 65 emissions of VOC - O3 produced with 65
emissions of NOx). These differences are positive
when the NOx reduction is more efficient (NOx
sensitive regime) and negative when the VOC
reduction is more efficient (VOC sensitive
regime).
CB-IV
2 June 1999, 12 UTC
Red crosses O3 references case - O3 (65 NOx)
Green crosses O3 references case - O3 (65VOC)
The graphs above show the changes in ozone
concentration due to the reductions of VOC and
NOx emissions as a function of the indicator
species (O3/NOy and H2O2/NOy) for July. The
results obtained for the other two periods are
similar and in agreement with previous studies
more specifically, the ozone increases under NOx
control and decreases under VOC control..
In order to separate the conditions when
reductions in VOC and/or NOx emissions are
beneficial or detrimental to ozone
concentrations, the indicator species should have
a narrow transition range. As it can be seen from
the graphs below, a narrow transition range can
be obtained only on small domains.
For all the periods investigated here (August not
shown), it can be seen that Italy, including the
big islands Sicily and Sardinia, are mostly
dominated by NOx chemical regimes, independently
of the photochemical mechanism used. However, the
effect of the reduction of NOx predicted with the
CB-IV mechanism is lower than that predicted with
SAPRC90 mechanism. In addition, the urban areas
around cities as Milan, Rome, Naples or
industrialised areas around harbours as Genoa,
Messina, Venice are always in a marked VOC
sensitive regime. It can be also noted that the
differences in the spatial distribution of the
chemical regimes due to the photochemical
mechanism used and due to the meteorological
conditions are comparable.
Milan area 400kmX400km
Milan area 160kmX160km
REFERENCES Buzzi, A., D'Isidoro, M., Diavolio,
S., 2003, Q. J. R. Meteorol. Soc., 129,
1795-1818. Carter, W. P .L., 1990, Atmos.
Environ., 24A, 481-518. Gery, W., Witten, G. Z.,
Killus, J. P., Dodge. M. C., 1989, J. Geophys.
Res., , 94, D10, 12925-12956. Mircea, M.,
D'Isidoro, M., Maurizi, A., Vitali, L., Monforti,
F., Zanini, G., Tampieri, F., 2007, submitted to
Atmos.Environ.
ACKNOWLEDGEMENTS This work was conducted in the
frame of ACCENT and GEMS EC projects, Italian
MIUR project AEROCLOUDS, and was also supported
by the Italian Ministry of Environment through
the Program Italy-USA Cooperation on Science and
Technology of Climate Change.