# BOLCHEM: model applications

## Simulation of an ozone episode over Italy

In this study ( download the extended abstract here), we focused on an ozone episode that occurred over Italy during the first week of July 1999, when a west moving wave coming from northern Africa crossed the Italian peninsula with temperatures reaching values up to 20°C at 850 hPa level, creating ideal meteorological conditions for the developing of photochemical pollution at lower atmospheric levels, especially over the highly industrialized and urbanized region of Po valley.

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The BOLCHEM was run with an horizontal resolution of 20 km. The lower level was approximately at 20m above the surface. Two different simulations were accomplished for the period 1-7 July 1999. using the chemical mechanism SAPRC90 and CB-IV, respectively.

The simulated ozone concentrations (units in $LaTeX code: \mu g/m^3$) using the two chemical schemes at the lowest model level oare shown in the figures at the left side (left SAPRC90, right CB-IV). Figures refer to 2$LaTeX code: ^{nd}$ July at 15 UTC (40 hour simulation). The ozone fields show a very similar spatial distribution. Differences in the maximum concentrations can be appreciated: in general SAPRC-90 simulation shows higher values than CB-IV one.

The time series (figures below) of ozone concentration at three rural and one sub-urban (Torino Lingotto) stations are showed at figures below. The diurnal cycle is generally well reproduced by the two chemical mechanisms and the concentrations computed with the two schemes are similar.

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## Model simulations of the ozone concentrations over Europe during the summer 2003 heat wave

This work ( Villani et al., 2005) presents the effect of different meteorological drivers and chemical mechanisms on the resulting chemical concentrations computed with BOLCHEMand CHIMERE(Vautard et al. ,2001). In particular, ozone concentrations were simulated with the two models for some days of the heat wave event of the summer 2003 over Europe, from 30$LaTeX code: ^{th}$ July to 3$LaTeX code: ^{rd}$ August. These five days are representative of the beginning of a particularly intense episode of photochemical pollution over Northern Europe.

The simulations were performed using the same emissions, initial and boundary conditions for the chemical species. The comparison aimed at investigating the O3 concentrations reproduced with:

• CHIMERE driven by different meteorological fields, which are modelled by meteorological models MM5 and BOLAM;
• CHIMERE and BOLCHEM, characterised by two different chemical mechanisms (MELCHIOR2 in CHIMERE, and SAPRC90 in BOLCHEM), but driven by the same meteorological fields (BOLAM).

Figures show the ozone concentration simulated using the different modelling sistems on 3$LaTeX code: ^{rd}$ August 2003 at 15UTC.
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$LaTeX code: O_3 (\mu g/m^3)$ simulated with BOLCHEM
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$LaTeX code: O_3 (\mu g/m^3)$ simulated with CHIMERE-BOLAM
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$LaTeX code: O_3 (\mu g/m^3)$ simulated with CHIMERE-MM5

References

R. Vautard, M. Beekmann, J. Roux, and D. Gomber. 2001. "Validation of a hybrid forecasting system for the ozone concentrations over the Paris area". Atmos. Environ., 35(14), 2449-2461.

M. G. Villani, P. D'Aulerio, M. D'Isidoro, A. Buzzi, F. Fierli, A. Maurizi, M. Mircea and F. Tampieri. "Model Simulations of the Ozone Concentrations over Europe During the Summer 2003 Heat Wave".First ACCENT Symposium, Urbino, Sept. 12th-16th 2005. Download extended abstract

## Saharan dust

In order to simulate the transport of Saharan dust over Italy, a dust emission scheme has been coupled to BOLCHEM. The dust forecast is a mandatory request for the air quality models since the mineral dust particles i) affect the ozone formation by uptaking gases as HNO3, H2O2, HO2, etc.; ii) alter the atmospheric radiation budget and consequently affect the convective activity and the latent heat fluxes in the areas where water evaporates from surface and iii) contribute substantially to the total aerosol mass usually employed in developing the EU regulations. The dust emission scheme presently implemented in BOLCHEM considers the distribution of preferential dust source areas, soil types and surface conditions like vegetation cover and soil moisture. The flux of dust at surface is calculated as a function of friction velocity that, in turn, depends on winds. Figures show the simulated dust field, integrated over all levels, and the MODIS image (right) at 16 july 2003, 12.35 UTC, respectively.

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Simulated Saharan dust transport.
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MODIS image (Source: NASA.)

## Point source release tests

work in progress... ...