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  The MacBeth Project: Passive Samplers Measurements of Benzene Levels in the City of Padua (I)

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Introduction

Air quality surveillance networks regularly monitor concentrations of atmospheric pollutants. However, such measures only evaluate the concentrations of pollutants in the outside air at specific geographic locations. It is crucial to ascertain whether the values recorded actually reflect the exposure which inhabitants are really subjected to, in the course of their daily lives and at work.

The MACBETH project is of particular relevance in this respect.

MACBETH (Monitoring of Atmospheric Concentration of Benzene in European Towns and Homes) is the project LIFE 96 ENV/IT/070 co-financed by the European Commission within the Life program.

The project was comprised among the preparatory actions aimed at helping the application of common policies and laws for environmental protection, with special concern to the safeguard of human beings from atmospheric pollution. The aim was to provide the European law-makers with the correlation between benzene urban pollution level and citizen exposure, in view of the issuing of the Daughter Directive that should regulate benzene urban levels within December the 31st 1999, as foreseen by the 96/62/EC Framework Directive on air Quality.

European Commission's Directorate-General for the Environment (DG XI) asked the European Reference Laboratory for Air Pollution (ERLAP), a body managed by the Joint Research Centre's Environment Institute at Ispra (I), to undertake a major Europe-wide measurement campaign. The project was launched in six test cities across Europe from north to south: Copenhagen (DK), Antwerp (B), Rouen (F), Padua (I), Murcia (E) and Athens (GR). A number of national partners were involved in the various countries.

The project, which monitored atmospheric concentrations of benzene (C6H6 - one of the main causes of urban pollution emitted from car exhausts or as a result of incomplete combustion), was based on a new system of individual measurements. In addition to one hundred external fixed sensors, fifty volunteers carry around mobile sensors throughout the day.

Whereas the average concentration of benzene in the outside air was 4.3 µg/m3 (i.e., much lower than the 10 µg/m3 upper threshold), certain individual cases of exposure in homes or workplaces could be as high as 25 µg/m3.

The Radiello sensors

In order to measure pollution levels in urban environments, the ERLAP developed an innovative and particularly cost-efficient sampling technology. Comprehensive air quality measurements traditionally require quite sophisticated automatic devices whose recordings are automatically transmitted in real time for analysis. The high cost of these devices means that they are placed at only a limited number of locations. This limits the scope for monitoring air quality over large areas.

The Radiello is an ultra-simplified pollution sensor, known as diffusion sensor, which can be used to detect various air pollutants. No bigger than a small test tube (7 cm long, 1 cm in diameter), it contains an absorption material which is able to capture the pollutant by means of molecular diffusion. The cost of the Radiello sensor is minimal, about five euros, which means it can be installed over a very wide area. After being left for a few days, the samples are collected and the absorption levels analysed in a laboratory. Genuine pollution maps can then be drawn up.

In the street, the home and on the person

The Radiello sensors allowed the MACBETH researchers to carry out a triple analysis of benzene pollution in the six European towns. Observable atmospheric concentrations were measured at different locations in the city of Padua (like in other 5 European Cities, see Figure 3), in the home and directly on the person in order to measure the exposure of individuals (see Figures 1 and 2).

Figure 1 - Map of Padua monitoring sites (Radiello location).

Figure 2 –Benzene concentrations resulting from interpolation of measured data.

During the six observation periods, carried out during a five-day period on each occasion, fixed sensors were placed in different urban areas (100 sites per town), in the homes of non-smoking volunteers (50 inhabitants per town) and on the person of these volunteers. Two groups of people have been monitored. One group consisted of a sample of the population that would normally be subject to only average or low direct exposure to automobile traffic, as they spend a large part of their time indoors, notably students and their teachers. The other group were people whose jobs involve a high risk of exposure, such as bus and taxi drivers and highway maintenance workers.

Inequality of risk exposure

The MACBETH results were presented at the International Conference on Air Quality in Europe, held in Venice from 19 to 21 May 1999. They showed the extent to which the people of Europe are far from equal in the face of the benzene threat. Levels range from an average of 3.3 µg/m3 in Copenhagen to 24.9 µg/m3 in Athens. There is a clear increase in benzene pollution as you travel southwards across Europe (see Figure 3). A number of variables must be taken into account to explain this difference, including, no doubt, traffic density and flows, the influence of climate and weather, lifestyles and the structure of the built urban environment.

There was another clear finding: benzene concentration levels are generally, and paradoxically, higher indoors than outdoors. This is a factor which must certainly be taken into account in future. For the rest, the harmful effects of certain high-risk jobs was confirmed.

Figure 3 – Benzene levels in MACBETH cities.

These results have been used also to define the new EU Air Quality Limit Value for benzene.

After the reduction of benzene and PAH content in gasoline (1% and 40% in volume respectively, come into force since 1998 in Italy), C6H6 levels in ambient air have decreased.

Acknowledgments

This text has been kindly revised from the City of Padua. It has been derived from some texts drafted by the Fondazione Salvatore Maugeri (Padua, I) and the Commission (see the websites):

- http://www.europa.eu.int/comm/environment/life/project/Projects/index.cfm?fuseaction=SEARCH.CREATEPAGE&s_ref=LIFE96%20ENV/IT/000070&area=2&yr=1996&n_proj_id=1114&CFID=715359&CFTOKEN=66926972

- http://www.pc4.fsm.it:81/padova/homepage.html

Last Updated

 

13th January 2005
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