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Air Quality

Description of the Problem

In many metropolitan areas, the large concentration of various human activities causes significant amounts of pollutants to be emitted. The city of Milan suffers from the typical serious pollution problems that can be encountered in metropolitan areas. Vehicular traffic and emissions from building-heating systems have been identified as the main sources of pollutants in the city. When considering the whole provincial area, other pollution sources from industrial processes to combustion become relevant.

An extensive air quality monitoring network has been operating in the province of Milan for about thirty years. The collected data show that, to this day, legal air quality standards for all pollutants are not being met. Effective emission-reduction measures, relative to the use of low-sulphur fuels for building-heating plants, have been in effect since 1973, and a net reduction of SO₂ sulphur dioxide concentrations have been observed over the last ten years. Even if high peak values continue to be measured in the presence of intense traffic conditions, a general decrease of carbon monoxide over the period of the last eight years has also been identified. There are three main factors responsible: the weather conditions in the last winters have been favourable to atmospheric dispersion and led to an improvement typically of winter pollutant air quality during the last years of measurements; the increase in the average Italian vehicular fleet of catalysed vehicles and the so-called "bollino blu" ("blue stamp") measure; a smog check programme of maintenance and inspection of the vehicles, initially promoted by the Lombardy Region and now carried on by the provincial administrations.

At present, the main air quality problems are represented by secondary pollutants, such as nitro-oxides and especially ozone, whose trend does not show a tendency to decrease. Moreover, attention is also called to other classes of dangerous pollutants, such as "PM10," particles with diameter < 10 µm, and hydrocarbons, such as benzene.

The regulations and instruments for the management and protection of air quality are based on national and regional laws. The standards establishing the air quality limit values and guidelines are outlined in the Premier’s Decree of 28/3/83 and the Decree by the President of the Republic of 24/5/88 (DPR 203), which incorporate EEC directives on air quality regulations. The DPR 203 decree also establishes emission limits for many stationary sources. Italian law requires that when critical pollution episodes occur emergency measures be taken in order to limit the harmful effects of high pollutant concentrations on human health and the environment. As for long-term measures adoption, the Ministerial Decree of 20th May 1991 required the regional administrations to draw up the Air Quality Management Plan to ensure that air quality standards are complied with.

Data Sources

For air quality monitoring in the metropolitan area and as a basis for problem analysis and the elaboration of improvement programmes, a number of continuous quality measuring activities are carried out by the provincial administration, which is responsible for air quality control and prevention according to Italian law. To guarantee homogeneous measuring and calibration methods, the provincial networks are involved in the air quality assurance programme carried on at the regional level. Data are automatically transmitted from local microprocessors interfaced with measuring equipment monitoring sites to the operative provincial centres. Then, after being checked and validated, data are transmitted to the Department of the Environment of the Lombardy Region to be archived on the EIS (Environment Information System). AURORA, a series of modular and integrated tools including databases on environment, regional technical mapping, and support tools for the management, presentation, and elaboration of the acquired data was developed by the Department of the Environment. Moreover, the Lombardy Region and the Emilia-Romagna Regione have reached an agreement on a common project, called "NEBULA," that aims to promote and realise the network services necessary to the public authorities involved in the management of the environment. The introduction into this modelling system is also underway.

The air quality in the metropolitan area of Milan is controlled by the surveying network of the Province of Milan, managed in collaboration with the IV Unità Operativa - PMIP of Milan. The network has been working since the late 1960s, with the initial purpose of controlling the city-centre area, which is more exposed to high concentrations of polluting substances. Afterwards, the network was subsequently extended and now covers most of the province’s territory, with thirty-five stations for surveying chemical compounds (SO₂, NO, NO_x, CO, PTS total suspended particulates, O₃) and meteorological parameters, as described in the chapter on climate in Milan. The monitoring sites outside Milan are located in very different areas which are of particular interest due to the density of the residential population, or in those where there is a significant number of large industrial plants, or in suburban regions, where it is possible to survey ozone far from sources of intense precursors. Every month measuring campaigns are made by mobile laboratory all over the provincial territory to supplement information provided by the permanent network. Besides the conventional pollutants mentioned above, some VOC (Volatile Organic Compounds) measuring campaigns have been carried out by using the DOAS (Differential Optical Absorption Spectrometry) technique, while PM10 has been measured and analysed by the laboratory of Electronic Microscopy since last year. Next year, two measuring campaigns by means of nitro-oxides passive analysers are going to be carried out in wintertime and in summertime.

The emissions inventory for the city of Milan contains estimates from domestic heating plants and traffic according to a 1 km²-grid system. The updating of this data and the extension to a greater area and to other emission sources are underway, in the frame of the Province of Milan emissions inventory. Moreover, following a "top-down" approach, yearly emissions data, from CORINAIR inventory, have been used to compute hourly data over the metropolitan area. Specific spatial and temporal profiles and methods are also being applied by CISE for the Lombardy Region to disaggregate CORINAIR emissions data all over the regional territory emissions at the municipal level.

Methods

Air quality data relative to the Milan metropolitan area are processed and elaborated at different levels. The basic level analysis is carried out by a specific software package that allows one to compute simple statistical analysis, to compare for the same station different monitors, to compare the pollution wind increases, to visualise alarm conditions, and to select data at different temporal levels (average daily, yearly, percentile, etc.). This information is very useful for the daily activity of data control and validation and for periodical monthly and yearly summaries. To represent spatial distribution of air quality values, data are evaluated using geo-statistical methods, such as interpolation or gridding or symbols, depending on the degree to which data for that pollutant can be considered representative for more extensive areas. Generally, maps refer to the number of air quality standard excesses or to the value of specific statistical parameters, such as the percentile or median for a 1-year concentration, etc.

More complex studies are carried out using statistical and modelling tools. For example, Cluster Analysis has been applied to detect similar behavioural patterns between surveying stations at different locations and altitudes in relation to hourly ozone trends or to investigate the spatial distribution of nitrogen-oxides throughout the provincial area or to describe the relation between meteorological conditions and carbon monoxide concentrations with the ultimate aim of being able to predict them.

To reproduce and investigate the dispersion of air pollutants, different kinds of models are used and the choice of the most suitable model depends on many factors, such as the spatial scale of the phenomena to simulate types of pollutants and emissions sources and data availability for the study case. At PMIP, US Environmental Protection Agency (EPA) gaussian models are generally applied for regulatory purposes, for example to evaluate the behaviour of primary air pollutants emitted from point or line source such as an industrial plant or a street. They provide the spatial distribution of the concentration on the basis of the characteristics of the emission source (stack height and diameter, emission rate, etc.) and meteorological data input, such as wind direction and intensity, Pasquill stability, and mixing height. Photochemical numerical models are also applied to describe ozone and reactive chemical compounds and to provide for a required simulation period the evolution of concentrations specified on 3-D domain. For example, to investigate ozone over the mesoscale basin, including the metropolitan area of Milan, the photochemical dispersion model CALGRID has been applied. This model, developed for California Air Resources Board (CARB) by a group of researchers (Yamartino, et al), allows for the calculation of the temporal evolution of three-dimensional concentration fields of both inert and chemically reactive pollutants treated by the chemical mechanism SAPRC ’90, which takes into account fifty-four species (most of them lumped) and 129 reactions.

Results

For divulgative purposes regarding data and information about air quality in Milan and its province, daily activities are carried out by PMIP of Milan. Daily bulletins about air quality are sent by fax to health and administrative authorities and to the press. Bulletins include a description of the air quality situation for the current day, information about "attention" and "alarm" excesses, and the tendency forecasted for the next day; a summary is also broadcast on television.

Roughly every year, "Studies for the Air Quality Evaluation in the Province of Milan" is printed and distributed by the Department of Environment of the Province of Milan, including historical series trends, excess summary, and maps with commentariess about every pollutant. Data for specific periods and sites of the monitoring network are provided on magnetic media. Recently a CD-ROM, including historical series’ of data, was made available.

Air quality bulletins concerning all the monitoring sites over the territory of the Lombardy Region and data statistical analysis are included in the previously mentioned AURORA and are distributed by the Department of Environmental Protection of the Lombardy Region.

The results from the application of dispersion models have been finalised for two different purposes: to define the potential impact area from point source and thereby optimise the choice of measuring site locations and also to quantify the effects on the air quality levels in Milan due to the adoption of a single measure or due to the implementation of a group of strategies included in the plans’ programme (Traffic Urban Plan, Mobility Plan, etc.). Moreover, specific studies have been carried out to investigate the behaviour of pollutants and the influence of meteorological conditions and emissions levels on the resulting measured air pollution concentrations. Monographs have been published by the Province of Milan in regards to specific studies, such as those in modelling applications or in statistical data analysis.

Finally, in the frame of environmental plans involving the metropolitan area of Milan, the Air Quality Management Plan of the Lombardy Region, currently underway, and the Energy Plan of the metropolitan area of Milan by Servizio Energia-Province of Milan have to be mentioned.

Uses

For the purpose of supplying the public with air quality information in real time, an air quality bulletin is broadcast on television every day and sent to the main newspapers. Specific evaluations are generally carried out for local health offices, municipal, provincial, and regional environmental authorities, etc.