Abstract. 1 Introduction

Transcription

1 Monitoring traffic related air pollution in the city of Reggio Calabria, Italy S. Calcagno, F.M.M.Cirianni Dipartimento di Ingegneria Elettronica e Matematica Applicata, Universita di Reggio Calabria, Italia Calcagno@ns.ing.unirc.it Abstract A study on air pollution in the city of Reggio Calabria, Italy, took place for a period of three months in 1997, centred on road traffic related pollutants by monitoring the concentration of carbon monoxide on a main street in the city centre. The comparison of the present data with the results of an air pollution monitoring campaign which the authors led in 1993 and part of 1994, aims to determine an experimental model for the forecasting of CO concentrations. The concentration of carbon monoxide was chosen as the most representative air pollutant because of its direct dependence on vehicular emissions, and also the lack of industrial areas in Reggio Calabria results in CO emissions being due almost exclusively to road traffic. The chemical data measured is carbon monoxide, and the meteorological data is wind speed and direction, temperature, cloud cover and atmospheric pressure. Measurements of traffic flows were also taken. The peculiarity of the setting, high traffic flows on an urban road with a low average speed were the premises for particularly high concentration values, but the physical characteristics of the location, and the influence of meteorological factors lowered effects below expected values. On the basis of the results of air pollution monitoring in different times of the year in the same location, a statistical model was obtained, for the purpose of determining concentrations in function of traffic and meteorological data. Application of such a model on a study period gave reliable results. Even if such a model is not reliable in determining concentrations of carbon monoxide in specific locations with different features, it is adaptable to the main traffic arteries of the city, giving a valid indication of the presence of concentrations which exceed the limits set by the current legislation. 1 Introduction The primary source of carbon monoxide emission in the atmosphere is the combustion of hydrocarbons, and the contribution to air pollution by carbon monoxide comes from motor vehicles in the first place and from transport in general. The rate of emission depends on driving conditions, and the most significant emissions are produced by engines running in low gears, which is a

2 968 Air Pollution Modelling, Monitoring and Management usual occurrence in congested or intense traffic, and in the deceleration phase, decreasing in the initial stage of acceleration and at cruising speed, for speeds up to 30 mph. During 1997 a campaign was carried out to measure the carbon monoxide concentrations present in the city centre. The study refers to the maximum legal limits permitted for concentrations of CO in the air and the exposure limits fixed by the air quality standards (limit and guideline values) given in the Premier's Decree (D.P.C.M.) of 28/03/83 and a subsequent Decree of the President of the Republic (D.P.R.) 203 of 24/05/88, which incorporate EEC directives regarding air quality, and to other legislation about atmospheric pollution, with particular reference to the Ministry of Environment and Health Decree of 20/05/91, the Ministry of Environment Decree of 12/11/92 and the D.P.C.M. 8/01/92. The economic reality of the city, which has no industrial areas, and the usually mild climatic conditions throughout the year, which precludes intensive and prolonged use of domestic central heating, are such that one may assume that the CO emissions under examination are caused exclusively by road traffic. The city's geographic location and the influence of weather conditions, especially wind speed and direction become relevant although the limiting values put in place by the D.P.R. 203/88 have almost never been exceeded; in some meteorological and traffic conditions the CO concentration levels have been significantly high for long periods exceeding, not infrequently, the warning levels fixed by the Environment Ministry Decree of 12/11/92 (mean value on the hour equal to 15 mg/mc). The campaign, consisting in continues measurements for three months in the same location has yielded a sufficient volume of data for us to develop an experimental model to forecast CO concentrations. 2 Methods of measurement and instruments The program of measurements consisted in a series of campaigns where readings were taken from a location with a continuous analysis of CO and a terminal for the acquisition of processual data. The principal on which the analyser works is the non dispersive infrared, as required by D.P.C.M. 30/83. Acquisition of the data is operated by a reading of the signal every minute; the analyser provides automatically for the calculation of the average concentration of the pollutant on the hour, recording the data on hardware. Besides values relative to the concentrations of CO, meteorological data is recorded on location, data relative to the speed and direction of the wind and the temperature, recording the maximum, minimum and average value on the hour.

3 Air Pollution Modelling, Monitoring and Management Description of the survey site The city of Reggio Calabria has an urban development which has been highly conditioned by the physical characteristics of the land, limited as it is on one side by the hills and on the other side by the sea. This is the reason why the city developed mainly in length. For this particular urban conformation the local traffic moves along main arteries, which run longitudinally, parallel to the coast. The campaign was done on corso Vittorio Emanuele. This is a level two lane road, about 12 metres wide and with one-way traffic from south to north. For its characteristics, compared to other roads in the city centre, it is relatively free flowing in most hours of the day. Corso Vittorio Emanuele has a place of relevance in the road system, and it's capable of significant traffic flows (up to 2000 veic/h). On one side there are tall buildings, longshore there are two rows of tall trees which give this road a semi-canyon configuration. The sampler was placed at approximately 2 metres from the edge off the road, at a height of 1,8 metres; the meteorological data measuring instruments were placed at a height of 10 metres. In the course of this measurement campaign it turned out that the highest values for CO concentrations corresponded with peak traffic times, frequently exceeding the warning level and with peaks approaching the alarm level (30 mg/mc) r flows (veic/h) hours Figure 1: Traffic flows on an average day 4 Experimental model The average concentration of CO in the air around the observation post depends, during the day, not only on the weather conditions but also on the

4 970 Air Pollution Modelling, Monitoring and Management volume of traffic (it has already been stated that road traffic is practically the only source responsible for the CO emissions in the urban atmosphere of Reggio Calabria). For the chosen site, that is the position in corso Vittorio Emanuele, besides the meteorological measurements, it was necessary to measure the traffic flows. The above figures were recorded at the site and expressed as hourly averages over the 24 hours of each day. The recorded data was used to produce an interpretative, mathematical model which, based on semiempirical statistical relations, could connect the traffic and meteorological data with the values for the concentration of CO and finally to identify the existence of possible connections among these factors. This type of comparison assumes a specifical significance since Reggio Calabria is geographically exposed to winds which keep up throughout the year, with a few windless periods limited mainly to night-time hours or, quite rarely, on one or more consecutive days. Statistically two winds are preponderant, the N/NW wind and the S/SE wind, that alternate in the proportion of three days of one to one day of the other. Any valuation of the CO concentration in the city atmosphere of Reggio Calabria cannot exclude a compete and reliable wind data base, and the site chosen is a road exposed to the winds in all directions. Regarding the meteorological data of wind speed and direction, the data acquired was compared to the meteorological bulletins available from the local airport. The equation required is of the type: Kco= f(vw,dw,q) (1) where: K^o is the concentration of carbon monoxide V\y is the wind velocity expressed in metres per second DW is the wind direction expressed in degrees north Q is the traffic flow expressed in vehicles per hour The determination of the equation refers to the theory of multiple linear regression. Equation (1) assumes the form of: KCQ= mivw + n^dw + mgq (2) The regression was calculated using the recorded data, obtaining the following equation: = Vw Dw Q (3) The obtained value of p% is 0.82 Such value indicates a good correlation between the parameters.

5 Air Pollution Modelling, Monitoring and Management 971 Table 1: Standard deviation and the t statistics relative to wind velocity, direction, and traffic flows. Coeff. stnd error t student V.w D.w Q As a consequence, the three variables which figure in equation (3), are significant to determine the concentrations of CO. 5 Discussion of the results From the analysis of the results it is evident that the daily trend of the CO concentrations varies according to the hour, and therefore to the traffic flow, which presents an extreme regularity in the sequence of heavy and light traffic, and in reference to weekdays or holidays (Sundays). Such a trend is decemible in fig.2, in which the levels of concentration are reported on a typical weekday and on a holiday. Fig. 1 illustrates the movement of the traffic flow on a typical weekday. On days in which the intensity of the wind remains at high values, the average level of concentration is lowered while the trend for CO concentrations remains unchanged. In figs. 3, 4, 5 the trend of the CO concentrations and the speed and direction of the wind are illustrated, the latter expressed in octaves referring to a four week period extracted from the interval in study. It is shown in fig. 3 how the warning level (15 mg/mc) posed by the D.M.A. 12/11/92 was exceeded on several occasions A 8 - CO 6 - (mg/mc) A A [p4 4 - i < '. ' / 4 ' A 2 - ' '/ O C [ 1_ i A A yj ilh,,.. A,. R>p, o Aitf^r i. A A hours Figure 2: Concentrations of CO on a weekday and on a Sunday i A weekday I a Sunday

6 972 Air Pollution Modelling, Monitoring and Management 6 Validation of the model From the comparison of the measured values and the estimated values pertaining to the study period one finds a good reliability in the model, considering above all the distinct variability which characterizes in a special way the meteorological parameters. The model was also verified experimentally by carrying out a campaign of measurements from the 5th to the 11th of may 1997 on the same site and with the same procedure as the previous one. A good likelihood can be seen between the estimated and the measured values, with a possible overestimate which however remains within a 7% margin (cf Tab. 2) 30 y day Figure 3: Carbon monoxide levels in the period from 5/02 to 4/03/1997 wind velocity 6 -- Cmt/sec) Figure 4: Wind velocity in the period from 5/02 to 4/03/1997

7 Air Pollution Modelling, Monitoring and Management 973 wind direction day Figure5: Wind direction in the period from 5/02 to 4/03/1997 Table 2: Comparison between estimated values and measured values on a day of the campaign hour CO(mg/mc) estimated value measured value Conclusions The campaign has underlined that the air quality in the study area, although within the limits set by the Decree of the President of the Republic 203/88, shows partial degradation which not infrequently during the period of observation exceeded the warning level for CO established by the Ministry of Environment Decree of 12/11/92 (mean value on the hour of 15 mg/mc).

8 974 Air Pollution Modelling, Monitoring and Management As this is an area in the heart of the city centre, which attracts a great number of people for, work, shopping and leisure; to safeguard public health it is an essential duty not to neglect air pollution generated by road traffic in the planning of a future road traffic system. References Calcagno S., Cirianni F. (1994), Una Campagna di misura per la determinazione delle concentrazioni di monossido di carbonic nella cittd di Reggio Calabria, Gruppo Scientifico Italiano Studi e Ricerche (MI), in Inquinamento atmosferico, GSISR Finzi G., Brusasca G. (1991), La qualitd dell'aria. Modelli Previsionali e gestionali, Masson G.U.R.I. n 145 del 28/05/1983, n 203 del 16/06/1988, n 126 del 31/05/1991 Horowitz L. (1982), Air quality analysis for urban transportation planning, MIT press Rapporti ISTISAN (1990), Indagine sull'inquinamento atmosferico da traffico autoveicolare nell'area metropolitana di Roma, n. 3 Watkins L. H.(1991), Air pollution from road vehicles, TRRL state of the art review HMSO Mazzali (1989), L'inquinamento atmosferico. Origine, prevenzione, controllo, Pitagora Editrice (BO) Zannetti P. (1990), Air Pollution Modeling, Computational Puublications Mechanics