On-line determination of polycyclic aromatic hydrocarbons in airborne particulate matter by using pyrolysis/GC–MS

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Abstract

A pyrolysis/GC–MS analytical method for the on-line determination of polycyclic aromatic hydrocarbons (PAHs) in airborne particulate matter collected on cellulose filters has been developed. For the investigation of the thermal behavior of the, loaded with airborne particulate matter, filters thermogravimetric analysis was used. By this method, the 16 standard PAHs were identified and quantified in the atmosphere of Thessaloniki, Greece, for the period from July 1997 to February 1998, where it was found that the concentrations of PAHs range from 0.04 to 5.32 ng m−3 showing comparable concentrations with those found in other large cities in Europe. The recovery found for the individual PAHs ranged from 75 to 117%. The novelty of this investigation is the on-line determination of PAHs in airborne particulates collected on cellulose filters, by pyrolysis GC–MS, where in contrast to other techniques a pretreatment of the sample, like a prior extraction of the PAHs from the filter by an organic solvent, is not necessary. The concentrations of PAHs over a decade in both industrial and urban area of the investigated region are compared.

Introduction

There has been growing concern about the potentially harmful effects on human health of toxic agents known to be in the atmosphere. One threat to our health from airborne organic components are the polycyclic aromatic hydrocarbons (PAHs). PAHs are organic compounds with two or more aromatic rings deriving from incomplete combustion or pyrolytic processes of organic material containing carbon and hydrogen [1]. These processes take place almost everywhere in the ecological system.

The main anthropogenic sources of PAHs are coal-, oil- and gas-burning facilities, so PAHs are found in exhaust, tar, fumes, carbon and petroleum industry, cigarette smoke, forest fires, burning of energy resources, smoked food, water, air and soil [2], [3]. Generally their formation takes place through highly reactive free radicals or by the addition of aromatic rings to an easily available PAH [4]. The addition takes place either by ring closing reactions or Diels–Alder reactions or cycloaddition. The PAHs appear in the atmosphere adsorbed on small particles (d<5 μm) of airborne particulate matter and in this way, they are transported over long distances. The incorporation of PAHs into the particles has been explained by a general condensation and adsorption mechanism; they are initially generated in the gas phase, then adsorbed on particulate matter while undergoing condensation upon cooling of the emission. Due to the large specific surface area of the small particles, a considerable amount of airborne PAHs and especially the less volatile compounds can be expected to be present in the airborne particulate matter [5].

As the PAHs and the particle associated PAHs in ambient air have an important adverse role on human health, many investigations are carried out for the determination of their concentrations and mutagenity in airborne particulate matter [5], [6], [7], [8], [9], [10], [11], [12], [13], [14].

Sixteen PAHs are usually investigated in analytical works, which according to the US Environmental Protection Agency (EPA) are the most widespread and are included in their priority list [15]. A wide number of techniques have been developed for the determination of PAHs in airborne particulate matter. Chromatographic techniques such as GC, GLC or HPLC coupled with fluorescence, UV, FID and MS detectors are the most frequently used [16], [17]. A prior extraction of the filters is always required by these techniques, depending on the sample, with soxhlet and ultrasonic extractions being the most common ones, using a variety of solvents, such as cyclohexane, dichloromethane, benzene, methanol [4], [5], [6], [7], [8], [9], [10], [11]. Some authors reported also direct analysis of PAHs by thermal desorption GC–MS applied mostly to urban dust reference materials [13], [14].

This paper presents the development of an on-line technique, the pyrolysis/GC–MS for the identification and the quantification of PAHs in airborne particulate matter collected on cellulose filters. By this technique a pretreatment of the samples is not necessary, avoiding the time consuming and expensive extraction step. To find out the optimum temperature program for the desorption of the PAHs from the loaded with airborne particulates filters, without reaching the temperature where an interaction of the PAHs with the filter material could take place, several thermal analysis experiments were carried out. As a case study, airborne particulate matter collected from the urban and the industrial large area of Thessaloniki, Greece [18] was used and the results were compared with other data from the same area [10].

Section snippets

Reagents

The following reagents were used: standard of a mixture of 16 PAHs (compounds are given in Table 1), 10 ng μl−1 each in toluene/hexane (1:1, v/v) (J.T. Baker B.V), toluene (Merck, p.a. 99,8%), hexane (Merck, p.a. 97%).

Sample collection

Airborne particulates were collected on 20×25 cm cellulose filters (Whatman No 41), by means of a high-volume sampler (1800 m3/24 h) during the period from July 1997 to February 1998, at three sampling stations of the large area of Thessaloniki, Greece. Two urban areas of the city

Results and discussion

TG was used at first in order to find out the appropriate temperature program, where the desorption of the PAHs from the airborne particulate matters occurs without destroying the cellulose filter. In Fig. 2 the TG curves taken in nitrogen from ambient temperature up to 700 °C with a heating rate of 10 K min−1 for the different samples of filters loaded with airborne particulate matter and for the blank filter, are presented. It results that the loaded with airborne particulate matter filters

Conclusion

Pyrolysis/GC–MS was proven to be a very useful technique for the on-line determination of PAHs on cellulose filters, without using a pretreatment of the sample. Special attention must be given to the temperature programs that are used, in order to avoid a decomposition of the cellulose filter itself, and a new formation of undesirable byproducts. In this matter, additional thermogravimetric investigations are very useful to find out the optimum temperature for the thermal desorption process. In

Acknowledgements

This work was carried out in the framework of the EU's Students Exchange Program ‘Socrates’, between the National Technical University of Athens (NTUA) and the Technical University of Munich (TUM). We would like to thank all those involved in this project.

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