including formaldehyde and three monocyclic aromatic compounds (MAC): ..... old data (Recovery = 1/(k x [O3] x t))(1-exp(-k x [O3] x t)), where k is an empirical ...
ATMOSPHERIC VOLATILE ORGANIC COMPOUND MONITORING. OZONE INDUCED ARTEFACT FORMATION. MATTHEW S. BATES 1,2 , NORBERT GONZALEZ-FLESCA 1*, RANJEET SOKHI 2 and VINCENZO COCHEO 3 1 INERIS, Parc Technologique Alata, B.P 2, 60550 Verneuil en Halatte, France 2 University of Hertfordshire, Hatfield, Herts, AL10 9AB, U.K. 3 Fondazione Salvatore Maugeri IRCCS, via Svizzera, 16, I-35127, Italy Abstract. Assessment of population exposure to VOC in ambient atmospheres is receiving heightened interest as the adverse health effects of chronic exposure to certain of these compounds are identified. Active (pumped) and passive samplers are the most commonly used devices for this type of monitoring. It has been shown, however, that these devices, along with all other preconcentration techniques, are susceptible to ozone interference. It is demonstrated that this interference occurs even at low ozone concentrations and that it may result in the under-estimation of population exposure. A convenient and effective ozone scrubbing method is identified and successfully applied and validated for both active and passive samplers for a range of VOC. Key words: Volatile Organic Compounds (VOC), ozone, artefact, passive sampling, active sampling, scrubber, formaldehyde, acetaldehyde, benzene, toluene, styrene.
1. Introduction Volatile Organic Compounds (VOC) are ubiquitous atmospheric species that originate from both natural and anthropogenic sources (Ciccioli). As direct pollutants many cause adverse health effects through acute and/or chronic exposure and they account for a large proportion of the 189 Hazardous Air Pollutants (HAP) listed in the 1990 US EPA Clean Air Act amendments (USEPA, 1990). As secondary pollutants VOC play a polyvalent role in photochemical smog episodes. They not only represent one of the three key ingredients but they can also, as is the case for carbonyl compounds, be produced as intermediates in the complex reactions that produce high concentrations of species such as ozone, hydroxyl radicals, hydrogen peroxide and peroxy acetyl nitrate (PAN) in the troposphere (Megie et al., 1994). Short-term exposure to VOC in the work-place has long been monitored, however it is only more recently that the health effects of chronic exposure to ambient levels of these compounds have been considered. This heightened interest in population exposure assessment was reflected, in 1996, when the World Health Organisation (WHO) published air quality guidelines for Europe (WHO, 1996). Alongside the more classical air pollutants, such as carbon monoxide, nitrogen dioxide and ozone, certain VOC also found their place, including formaldehyde and three monocyclic aromatic compounds (MAC): Environmental Monitoring and Assessment 65: 89–97, 2000. c
2000 Kluwer Academic Publishers. Printed in the Netherlands.
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benzene, toluene and styrene. Unfortunately, few data exist that quantify population exposure to VOC and although urban background concentrations for compounds such as benzene are often continuously monitored, recent work has shown that these levels do not reflect those to which the population is exposed (Gonzalez et al., 1999). This makes comparison to the air quality guidelines a difficult task. To determine the magnitude and source of population exposure, widespread multi-site campaigns are necessary, with parallel monitoring indoors, outdoors and on a personal basis. This type of monitoring may be performed either by active (pumped) or passive sampling. However, from a financial and practical point of view, passive samplers are preferable as they are relatively inexpensive, light-weight, non-invasive and may be left for extended periods during which they require no operator interaction (Brown and Wright 1994). As with all sampling techniques thorough laboratory and field validation to develop a quality assurance protocol are of some guarantee as to the integrity of measurements made in the field (CEN, 1997). However sometimes, unexpected interferences can result in erroneous measurements, one such example is the presence of oxidants like ozone, during VOC sampling. Much evidence exists to show that ozone interferes when actively sampling aldehydes by chemical derivitization with 2,4-dinitrophenylhydrazine (DNPH) (Arnts and Tejada, 1989; Sirju and Shepson, 1995) and in solid adsorbent sampling of monoterpenes (Hoffmann, 1995). Several ozone removal techniques for use in conjunction with active devices have been proposed (Helmig, 1997). The intention of this work is to extend existing knowledge to cover other VOC and to identify the most suitable scrubbing technique for both active and passive sampling. 2. Experimental The experiments carried out for this study were all conducted in a dynamic atmosphere generator that permits reconstitution of VOC-containing atmospheres from the ppm through to the ppb range and the introduction of other co-pollutants such as ozone. The device and its validation are described in detail elsewhere (Jaouen et al. 1995). Expected VOC concentrations were verified by active sampling prior to ozone introduction and good agreement was found (
