Title of Example

Example

Introduction

PAH are persistent compounds, characterized by low water-solubility and high capacity to adhere to organic matter; they are mainly caused by incomplete combustion processes of fossil fuels, and are therefore present in car combustion and heating systems emissions. The PAH concentration in the urban atmosphere can reach few ng/m³, while the specific components concentration has a variable relationship according to the specific emission source.

In Italy the DM 25.11.1994 (“Technical legislation updating on concentration limits and attention and warning levels for atmospheric pollutants in urban areas and dispositions on some pollutants according to the DM 15.04.1994”) has made it obligatory for PM_10, C₆H₆ and PAH data collection in the PM₁₀ fraction in the urban areas with a population > 150,000 inhabitants, such as the City of Venice-Mestre.

The national decree has given indications on reference methods for measuring and sampling and relative air quality standards defined as “air quality objectives”. Specifically, these are meant as annual mobile average value to be reached and to be complied with, starting from a determined date (according to 01.01.1996 and 01.01.1999 reference, see table 1). The PAH is a hydrocarbon class whose composition include two or more condensed benzene rings. The PAH class is therefore formed by a rather heterogeneous number of substances, characterized by different toxicological properties.

The US EPA has drafted a major toxicity PAH list comprising benzo(a)pyrene, characterized by the highest carcinogenic power (= 1). This is the reason why the annual air quality objectives on PAH concentrations refer to benzo(a)pyrene concentration.

The environmental importance of PAH derives from the ascertained carcinogenic action of some of them, particularly of those condensed in the atmospheric particulate matter.

To bring back the PAH environment concentration to health reference values (National Institute of Public Health - ISTISAN 91/27 Report) the concept of equivalent benzo(a)pyrene, that allows the determination of the overall risk deriving from PAH exposure, from the risk amount caused by benzo(a)pyrene (cancerogenic power = 1), plus those of the other active IPA:

- benzo(a)anthracene (carcinogenic power = 0,006);

- dibenzo(a,h)anthracene (carcinogenic power = 0,6);

- indeno(1,2,3-c,d)pyrene (carcinogenic power = 0,08);

- benzo(b)fluorantene (carcinogenic power = 0,11);

- benzo(j)fluorantene (carcinogenic power = 0,03);

- benzo(k)fluorantene (carcinogenic power = 0,03).

The annual value, with the aim of the comparison of quality objectives, is given by the mobile average of registered daily values.

Table 1 - Benzo(a)pyrene air quality objectives (national decree 25.11.1994)

While for PM₁₀ and benzene the Daughter Directives implementation has meant the annulment of relative quality objectives, replaced by daily and annual limit values, in the case of benzo(a)pyrene, the 1.0 ng/m³ air quality objective is still effective. This value will be substituted by the 4th Daughter Directive implementation on Heavy metals and PAH.

Monitoring modalities in Venice-Mestre urban area

Following the decrees operative suggestions, to locate emissions sources and the exposure evaluation, the PAH atmospheric level is given by the concentration value measured in PM₁₀ on a 24h basis. To evaluate the annual average value of PAH concentration, the measurement should be carried out for at least 15 days per month. The reference method for PAH measurement is the capillary column gas-chromatography and flame ionization detector.

The systematic measurements should be carried out in at least one of the A, B, C type stations, in order to identify the area average value, representative of the urban area various exposure situations. The stations’ classification have been drafted in the D.M. 20.05.1991 (now annulled following the EU Air Quality Directives implementation) identifying:

- A type station, reference or basic station, where all primary and secondary pollutants and basic weather inputs are measured, as well as PM₁₀, benzene and benzo(a)pyrene pollutants to be evaluated by means of manual analytical method. Such stations should be preferably located in areas which are not directly affected by urban emission sources (parks, pedestrian areas, etc.);

- B type station situated in high density residential areas where some primary and secondary pollutants are measured, with particular reference to NO₂, HC, SO₂, PM with Pb content and mass characterization;

- C type station, placed on high traffic areas with reference to car vehicle pollutants (CO, VOC), on high exposure risk areas like high traffic and low ventilated roads. In this case, the concentration values are characterized by a representativity limited to the immediate surrounding areas close to the sampling point.

In the A type stations meteorological data should also be collected. The Venice-Mestre urban network stations where PAH monitoring is carried out are: Parco Bissuola (A); via Antonio Da Mestre (B); via Circonvallazione (C).

Figure 1 - City of Venice air quality monitoring stations (PAH monitoring stations: Parco Bissuola, Via Circonvallazione, Via A. Da Mestre)

At the mentioned continuous air quality monitoring stations sampling is also carried out, for PM₁₀ and PAH via HPLC analysis, with reference to benzo(a)anthracene, benzo(b)fluorantene, benzo(k)fluorantene and benzo(a)pyrene.

The PM₁₀ sampling (using Tecora instruments, that are in compliance with the Directives reference method) is carried out using a sampling line located inside the monitoring station with 24h sampling cycles by means of glass fibre filters. The PM₁₀ and PAH analytic determinations are carried out in the laboratory, after the end of the filters sampling cycle, respectively by means of gravimetric analysis and HPLC.

The PM₁₀ gravimetric determination is carried out on each sampled filter, while the benzo(a)pyrene determinations are alternatively carried out every two sampled filters. In this way, generally, for each monitoring campaign lasting about 1 month, at least 15 PM₁₀ and 7 PAH measures are assured.

PAH levels in Venice-Mestre urban area

The annual mobile average, provided for by the D.M. 25.11.1994 as the benzo(a)pyrene evaluation tool, gives satisfying results only when data are homogenously distributed within the span of the months considered. In the benzo(a)pyrene concentration annual average estimation has therefore been considered preferable to using the average of the monthly averages, that is less sensitive to the effects of the varaibility of data distribution throughout the different periods and therefore allows sensibly weighing up each seasonal period.

The updated mobile averages up to December 2002 of benzo(a)pyrene concentration, calculated as an average of monthly averages, give 1,5 ng/m³ value for the Parco Bissuola station, 1,2 ng/m³ for the Via A. Da Mestre station and 1,5 ng/m³ for the Via Circonvallazione station, therefore exceeding the 1 ng/m³ air quality objective prescribed by Italian legislation. This objective corresponds also to the annual mean target value in the EU Proposal for a directive of the European Parliament and of the Council relating to arsenic, cadmium, mercury, nickel and polycyclic aromatic hydrocarbons in ambient air.

Such values show a benzo(a)pyrene “area” pollution, which presents an almost homogeneous diffusion in the urban centre. The 2002 area average, as average of annual averages of the three different stations, is 1,4 ng/m³. The overall downward trend of the benzo(a)pyrene annual average in the urban area surveyed during 2001 (1,5 ng/m³), in comparison to 2000 (1,8 ng/m³), does not seem to be confirmed for 2002.

In the urban area, the benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluorantene and benzo(k)fluorantene monthly average trend shows a concentration peak during fall and winter months, and, as already pointed out, a strong trend to quality objective exceedance for benzo(a)pyrene of 1 ng/m³, defined by DM 25.11.1994 as annual mobile average.

Last Updated

13th January 2005