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Introduction

This work is part of the 1998 Environmental Budget worked out by the Veneto Region Environmental Protection Agency (ARPAV) for the industrial area of Porto Marghera, Venice (I). Using the PSR scheme (OECD, 1994), pressure (energy and raw materials consumption, air and water emissions, garbage production, etc.) and State indicators (air, water and soil monitoring, dispersion models, etc.) have been characterized:

- to better know how the amount of pollution and the consumption of resources are balanced in this industrial site;

- to enable decision-makers, public administrations and industries to set priorities in environmental policies;

- to present the state of the environment in a way that it is understandable for the public;

- to compare the current state of the local environment with quality targets.

Porto Marghera industrial site is located 5 km NW of the historical centre of Venice, between the urban inland (Mestre, Marghera and Malcontenta) and the coastal lagoon. It spans an area of 2000 hectares: 1400 ha for industries, 340 ha of water channels; 120 ha for the commercial harbour; 80 ha for roads and railway; and 40 ha are State land. The main activities are: coke-derived production, petrochemical production, refining, aluminium and semi-finished material production, shipyards work, chemistry, fertilizer production, waste and wastewater treatment, coastal oil storage, and energy production. The area counts 295 firms, with 13,740 employees.

In order to achieve a better sustainability in the Porto Marghera industrial site, in 1998 national and regional public authorities, in accordance with local industries, signed an Agreement Program to decrease pollutant emissions. At first, the Regional Environmental Agency (ARPAV) evaluated mass and energy balances by collecting production and environmental data which was supplied by local industrial plants. Using this data, air toxic emissions from point and area sources were characterized. To define new air emission targets for the various industrial activities a modelling approach has been followed.

Looking at the Energy production sector, six power plants for energy and vapour production are located in Porto Marghera. Two of them are natural gas-powered, two more are mainly carbon-powered, the one serving the refinery is gas-powered, while the last one which serves the most important petrochemical plant is powered with oil, methane and gas recovered from various plants located in this industrial settlement. This study wasn’t focussed only on Power plants impact to air quality, but they can be considered the major SO₂ emitters in the area (see Table 4).

Meteorological characterization

The selection of meteorological critical events by listing acute SO₂ concentration episodes in the residential area nearby was used for the Short term worst-case simulation as the Mestre and Marghera urban agglomerations are on the leeward side of the industrial area.

Predominant critical conditions for their exposition are:

- neutral conditions (“D” stability class);

- mixing height: 50/350 m (winter time); 50/250 (summer time);

- wind direction: from South to North;

- wind speed: 3-4,5 m/s (winter time);. 2-4 m/s (summer time).

For Long term simulation, a Joint Frequency Function was built, based on one year’s (1998) meteorological data . RASS (Radio Acoustic Sounding System) data allowed for the computation of the mixing height and stability classes, while ground meteorological measures allowed for the collection of the other model input parameters.

Tracers and their emissions

Each production cycle was identified through one or more emitted substances, the “tracers”. A “rough” preliminary health risk assessment, based on emission amount and toxic/carcinogenic effects, allowed for the selection of “tracers” from a list of about thirty pollutants investigated. The choice was made on the basis of an Impact Index, computed for each pollutant:

- as a product of its total annual emission and its Unit Risk (1);

- as a ratio between its total annual emission (chronic effects) or hourly emission (acute effects) and its Reference Exposure Level (μg/m³) (2).

The following Tables (1, 2, 3) show the hierarchy, in terms of carcinogenic and toxic (acute and chronic) potential health risk for all the substances emitted in the industrial area. Selected tracers are highlighted in yellow. The Unit Risk factor is defined as the estimated probability of a person contracting cancer as a result of constant exposure to an ambient concentration of 1 µg/m³ over a lifetime period equal to 70 years. The concentration level at or below which no adverse health effects are anticipated for a specified exposure duration is termed the Reference Exposure Level (REL).

Table 1 – Impact index due to potential carcinogenic effects.

Table 2 – Impact index due to acute toxic effects.

Table 3 – Impact index due to chronic toxic effects.

Sulphur Dioxide, Chlorine, Acrylonitrile and Vinyl Chloride are the “tracers” identified. They area emitted respectively by 43, 6, 28 and 6 stacks or point sources with the following total annual emission: Sulphur Dioxide: 19375 ton/y; Chlorine: 1,17 ton/y; Acrylonitrile: 4,26 ton/y; Vinyl Chloride: 6,60 ton/y.

Table 4 - SO₂ emissions from 43 point sources in Porto Marghera.

The modelling approach objective was to assess short and long term impact on environment and health due to air emissions (Pressure), and to evaluate the sustainability of emission reduction policies in the industrial area of Porto Marghera.

Short and long term scenarios have been modeled to evaluate acute and chronic health impact. According to EPA Risk Assessment Guidelines (CAPCOA, 1993), the ISC3 (Industrial Source Complex) model was used to compute air pollutant concentrations.

Figure 1 - Computational domain.

This Gaussian model, developed by the EPA and AMS, is based on a stability classes approach. Since a single wind speed and direction is used in the whole domain, the referenced domain which is a rectangle 20x15 km² wide (100x75 cells) and is centred on the industrial area of Porto Marghera (see Figure 1), partially satisfies this supposition..

In Figures 2a, 2b, 2c and in Table 5, SO₂ short term results are reported, for winter and summer simulations, and a mixing height of 275 m in which all the emissions should be combined is used. In Table 6, 1998 SO₂ long term simulation is reported.

Figure 2a – SO2 summer short term run

Figure 2b – SO2 winter short term run

Figure 2c – SO2 summer short term run (Hmix = 275 m)

Table 5 - Short term simulation for Sulphur Dioxide (winter and summer time).

Table 6 - Long term simulation for Sulphur Dioxide (1998).

SO₂ long term simulation results have been compared to monitoring data collected by 14 stations of the local air-quality network (see Figure 4). Correlation is good, as shown by the following parameters:

- correlation coefficient: 0,78;

- bias: 8,9 µg/m³;

- root mean square error: 6,7 µg/m³.

Figure 4 - Comparison between SO₂ measures (µg/m³, annual mean) and dispersion model estimates (µg/m³, annual mean).

Conclusions

The application of the ISC3 Gaussian model to Sulphur Dioxide has shown that there are no acute nor chronic health risks referable to this substance, in fact SO₂ short term maximum value (466 µg/m³) and long term maximum value (72 µg/m³) are both lower then its acute and chronic REL (660 µg/m³).

More results are available for the other “tracers” (Chlorine, Acrylonitrile and Vinyl Chloride) and some improvements to the present assessment have been foreseen: the evaluation of carcinogenic risk referred to Acrylonitrile and Vinyl Chloride concentrations computed with the model; the implementation of emission databases (increasing the number of firms and pollutants to be considered); the analysis of incidental scenarios; and the performance of more advanced air quality dispersion models (e.g. the Eulerian CALPUFF and SPRAY).

References

- ARPAV, (2000), ‘Rapporto Ambientale d’Area della Zona Industriale di Porto Marghera’, prima edizione, Edizioni Hyper.

- California Air Pollution Control Officers Association (CAPCOA), (1993), ‘Air toxic “Hot Spots” Program’.

- OECD, (1994), ‘Environmental Indicators’, Paris.

- U.S. EPA, (1995), ‘User’s Guide for the Industrial Source Complex (ISC3) Dispersion Models’.

Acknowledgements

This text is part of a poster presented at the 7th conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes held on May 28-31, 2001 in Belgirate, Italy.

We thank the authors: A. Benassi¹, F. Liguori¹, G. Maffeis² and the contributors: ARPAV - Servizio Rischi Industriali, ARPAV - Servizio ACCAVIA, Ente della Zona Industriale di Porto Marghera, dr. Paolo Bidoli.

¹Veneto Region Environmental Protection Agency – Department of Venice, Mestre (VE), Italy

Last Updated

13th January 2005