Polycyclic aromatic hydrocarbons in air on small spatial and temporal scales e I. Levels and variabilities Gerhard Lammel a, b, * , Jana Klánová a , Predrag Ili  c c , Ji  rí Kohoutek a , Bojan Gasi  c d , Igor Kovaci  c e , Nata  sa Laki  c c , Ranka Radi  c e a Masaryk University, Research Centre for Toxic Compounds in the Environment, Kamenice 3, 62500 Brno, Czech Republic b Max Planck Institute for Chemistry, J.-J.-Becher-Weg 27, 55128 Mainz, Germany c Institute for Protection, Ecology and Informatics, Vidovdanská 43, 78000 Banja Luka, Republic of Srpska, Bosnia and Hercegovina d Institute for Chemical and Bioengineering, ETH Zürich, Hönggerberg, 8093 Zürich, Switzerland e Republic Hydrometeorological Institute, Put Banjalu ckog odreda b.b., 78000 Banja Luka, Republic of Srpska, Bosnia and Hercegovina article info Article history: Received 19 January 2010 Received in revised form 15 July 2010 Accepted 17 July 2010 Keywords: Polycyclic aromatic hydrocarbons Urban aerosol Air pollution Spatial variability abstract Polycyclic aromatic hydrocarbons (PAHs) were measured together with inorganic air pollutants at two urban sites and one rural background site in the Banja Luka area, Bosnia and Hercegovina, during 72 h in July 2008 using a high time resolution (5 samples per day) with the aim to study the spatial and temporal variabilities and to explore the significance of averaging effects inherent to 24 h-sampling. Measurement uncertainty was quantified on basis of three independent side-by-side samplers, deployed at one of the sites. PAH abundances in the urban and rural environments differed largely. Levels at the urban sites exceeded the levels at the rural site by >100%. The discrepancy was largely dominated by emission of 3e4 ring PAHs in the city, while 5e6 ring PAHs were more evenly distributed between city sites and the hill site. During the night a higher fraction of the semivolatile PAHs might have been stored in the soil or sorbed to surfaces. PAH patterns were undistinguishable across the three sites. However, concentrations of more particle-associated substances differed significantly between the urban sites than between one of the urban sites and the rural site (3s uncertainty). Time-averaging (on a 24 h-basis) would have masked the significant inter-site differences of half of the substances which were found at different levels (on a 4 h-basis). Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are an unavoidable by- product of any kind of combustion, in particular incomplete combustion processes. Therefore, these substances are ubiquitous in the polluted atmospheric environment in the ng m 3 concen- tration range. The gaseous state is predominant for the lighter molecular weight PAHs, while the substances with more than 4 rings are preferentially associated with the aerosol particles (Finlayson-Pitts and Pitts, 2000; ECPACWG, 2001). The significance of PAH abundance is caused by the health hazard they pose upon inhalation: Among atmospheric trace chemical substances, PAHs are considered to pose the highest human health risk (WHO, 2003). The distribution and fate of PAHs in the atmosphere has been the subject of numerous studies covering a wide range of spatio- temporal scales and relevant sources (references in Finlayson-Pitts and Pitts, 2000; Prevedouros et al., 2005; Tsapakis and Stephanou, 2005; Lammel et al., 2009; Balasubramanian and He, in press). Most studies focused on occurrence of the parent PAHs, while nitro-PAHs gained interest in the chemistry of nitrogen oxides rich atmo- spheres (Finlayson-Pitts and Pitts, 2000) and alkylated and partly oxygenated PAHs had significantly less been addressed so far. Due to analytical limitations most studies so far relied on 12 h- or 24 h-samples of the gaseous and particulate fractions. In urban and rural environments winter levels are significantly higher than summer levels, because of higher emissions (residential heating), less mixing and less photochemical sinks (e.g. Schauer et al., 2003; Holoubek et al., 2007). The gradient between urban and rural environments is not necessarily large (Herrmann et al., 2006; Lammel et al., in press). Resistance to photochemical degradation is not well understood: In the gas-phase the reaction with the hydroxyl radical limits the parent PAHs’ atmospheric residence times to hours or days at most (Finlayson-Pitts and Pitts, 2000; ECPACWG, 2001). When associated with particles, however, PAHs may undergo long-range transport * Corresponding author. Masaryk University, Research Centre for Environmental Chemistry and Ecotoxicology, Kamenice 3, Brno 62500, Czech Republic. Tel.: þ420 54949 2860; fax: þ420 54949 2840. E-mail address: lammel@recetox.muni.cz (G. Lammel). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2010.07.034 Atmospheric Environment 44 (2010) 5015e5021