Gabriele Zanini

On the complexity of the boundary layer structure and aerosol vertical distribution in the coastal Mediterranean regions: a case study

The planetary boundary layer structure in the coastal areas, and particularly in complex orography regions such as the Mediterranean, is extremely intricate. In this study, we show the evolution of the planetary boundary layer based on in situ airborne measurements and ground-based remote sensing observations carried out during the MORE (Marine Ozone and Radiation Experiment) campaign in June 2010. The campaign was held in a rural coastal Mediterranean region in Southern Italy. The study focuses on the observations made on 17 June. Vertical profiles of meteorological parameters and aerosol size distribution were measured during two flights: in the morning and in the afternoon. Airborne observations were combined with ground-based LIDAR, SODAR, microwave and visible radiometer measurements, allowing a detailed description of the atmospheric vertical structure. The analysis was complemented with data from a regional atmospheric model run with horizontal resolutions of 12, 4 and 1 km, respectively; back-trajectories were calculated at these spatial resolutions. The observations show the simultaneous occurrence of dust transport, descent of mid-tropospheric air and sea breeze circulation on 17 June. Local pollution effects on the aerosol distribution, and a possible event of new particles formation were also observed. A large variability in the thermodynamical structure and aerosol distribution in the flight region, extending by approximately 30 km along the coast, was found. Within this complex, environment-relevant differences in the back-trajectories calculated at different spatial resolutions are found, suggesting that the description of several dynamical processes, and in particular the sea breeze circulation, requires high-resolution meteorological analyses. The study also shows that the integration of different observational techniques is needed to describe these complex conditions; in particular, the availability of flights and their timing with respect to the occurring phenomena are crucial.

Modeling Air Quality over Italy with MINNI Atmospheric Modeling System: From Regional to Local Scale

This study shows part of the results obtained during the operational evaluation of MINNI atmospheric modeling system over Italy. MINNI is the Italian Integrated Assessment Modelling System for supporting the International Negotiation Process on Air Pollution and assessing Air Quality Policies at national/local level sponsored by the Italian Ministry of the Environment. The evaluation was carried out for both meteorology and air quality for the years 1999 and 2005. Changes of meteorological variables and of ozone concentrations in relation to the change of horizontal grid resolution were also investigated. The results show the capability of the modelling system to reconstruct the meteorological and ozone fields over Italy.

Study of the Impact of Low vs. High Resolution Meteorology on Air Quality Simulations Using the MINNI Model Over Italy

Modelling air quality requires the description of a large number of processes interacting each other. In order to properly model concentrations of atmospheric pollutants it is crucial to have a realistic reproduction of meteorological parameters, which can be critical in areas presenting a complex orography like the Italian peninsula. This work shows an analysis of the results obtained with the national model MINNI at two different horizontal resolutions (20 and 4 km), for a whole year over Italy. Comparisons between modelled and observed temperature and pollutants concentrations are carried out. The prediction of temperature is improved with the increase of model spatial resolution, as it is for pollutants like NO2 and CO, while the improvement is not always evident for O3 concentrations. Results are discussed providing an interpretation of the observed features.

Ozone Modeling over Italy: A Sensitivity Analysis to Precursors Using BOLCHEM Air Quality Model

The sensitivity of ozone to the reduction of NOx and VOC over Italy has been investigated with the air quality model BOLCHEM, which includes two photochemical mechanisms: SAPRC-90 and CB-IV. The study has been carried out for some case studies during the years 1999 and 2003. The results show the relative importance of precursors in reducing the ozone levels and allow identifying regions of Italy where local emissions reduction strategies are less effective. This study also shows the effect of the errors in isoprene inventories on ozone concentrations.

BOLCHEM Air Quality Model: Performance Evaluation over Italy

The modeling system BOLCHEM for air quality simulations has been run to study the evolution of tropospheric ozone over the Italian peninsula during 1999. The comparison of measured and modeled ozone time series shows that BOLCHEM predicts well the ozone concentrations. The summer cases are better simulated than the winter ones. The model configuration using SAPRC90 meets always the US-EPA criteria for the statistical indexes UPA, MNBE and MANGE. The Italian peninsula has a very complex topography, therefore the separation of meteorology and chemistry in offline simulations can lead to a loss of potentially important information about atmospheric processes, which often have a much smaller time scale than the meteorological output frequency. Here, we show the ability of a new developed air quality model, BOLCHEM, to reproduce the observed ozone concentrations for four clear sky periods (one from winter, the others from summer season) selected based on Meteosat images of Europe. The calculated O3 concentrations were compared with measurements made at rural or semi-rural stations. The statistical measures recommended by the U.S. Environmental Protection Agency (US-EPA, 2005) for air quality model validations were also computed for hourly values of ozone concentration. BOLCHEM couples the meteorological model BOLAM (Buzzi et al., 2003) to SAPRC90 (Carter, 1990), and CB-IV (Gery et al., 1989) as alternative photochemi- cal mechanisms. The mechanisms were chosen since they adopt different criteria for grouping the organic gases: CB-IV groups the organics according to bond type, while SAPRC90 groups them according to molecule type. Figure 1 shows that the agreement between simulated and measured ozone concentrations is good for both summer and winter. Generally, the model has diffi- culties in reproducing low ozone concentrations observed during the winter and during the night. A more extensive discussion of the results can be found in Mircea et al. (2007). Table 1 shows the statistical indexes recommended by US-EPA (US- EPA, 2005). It can be seen that generally, UPA is lower than 35%, MNBE is lower than 15%, MANGE is lower than 30-35%.

Impact of Saharan Dust on PM10 Concentrations in the FARM model

This study aims to improve the performance of the Flexible Air quality Regional Model FARM by including dust concentrations from a dust transport model (SKIRON) into Lateral Boundary Conditions (LBCs). A sensitivity test has been performed in order to assess the impact of SKIRON Saharan dust on PM10 modelled concentrations. A dust episode (25th–30th July 2005) has been simulated running FARM on a 20 × 20 km2 resolution domain over Italy. Preliminary results from three simulations: NDC (“no dust” case), DC (“dust” case) and DC1.3 (“dust multiplied by a factor 1.3” case) have been compared to PM10 ground measurements from the Italian Air Quality Network.

Impact of Saharan Dust on PM10 Daily Exceedances over Italy During 2003–2005

The assessment of the anthropogenic and natural contributions to PM10 concentrations is a key issue for the development of air quality policies in Europe. In areas such as the Mediterranean basin, a consistent fraction of the natural contribution to PM10 concentration is given by dust particles transported from Sahara. This study presents an estimate of the dust contribution to PM10 concentrations in years 2003–2005 at six Italian locations. The reduction (%) in the number of daily exceedances of the PM10 limit value (50μgm−3) after subtraction of the African dust contribution is also presented.The reduction varies with station between 20% and 50% in 2005 and between 5% and 25% in 2003 and 2004.

PLPM: A NEW PHOTOCHEMICAL LAGRANGIAN PARTICLE MODEL. BASIC IDEAS AND PRELIMINARY RESULTS.

In mesoscale applications EMs integrate equations over a numerical grid having cells as large as some kilometres, for efficiency. This causes the resolution of meteorological fields and orography to be limited. Also, emissions are uniformly distributed within the cell containing the source, which prevents detailing the concentration field close to strong sources as industrial plant chimneys. This problem is faced either reducing the grid size, or using the Lagrangian plume in grid technique in the initial phase, until the plume size can be compared to the grid extension. Transport and diffusion in LPMs are instead independent from any grid and all the available meteorological information can be used. Also, nestings of higher resolution in regions with complex atmospheric circulation are possible. Diffusion coefficients are proportional to the concentration gradient (K-theory) in some EMs. Under convective meteorological conditions this is questionable since the null vertical concentration gradient produces a null turbulent vertical flux of mass. In reality, the average vertical well-mixing is due to a counterbalance between strong local upwards or downwards motions. The use of a higher-order closure scheme solves this problem but adds additional partial differential equations to an already complex non-linear system. On the other hand, LPMs can describe convective local updrafts and downdrafts appropriately (e.g. Luhar and Britter, 1989) and thus correctly reproduce high stack emission descent and ground-level emission rise in the initial diffusion phase.

Performance Evaluation Of The QUADRICSMachine In Solving Chemical Rate Equations Of AState-of-the-art Photochemical Module

The integration of stiff, very coupled, ordinary differential equations which describe pollutant chemical reactions is the most intensive computational task of photochemical models, since it requires at least 70% of the total CPU time. As a consequence of the local nature of these equations, the integration can be performed very efficiently by a SIMD architecture. In this work we present the porting of QSSA (Quasi Steady State Approximation) chemical solver of CALGRID photochemical model on the SIMD massively parallel platform Quadrics/APElOO which offers, in QH4 configuration, a peak performance of 25 Gflops.