Sources and fluxes of Pt, Ir and REE in the Seoul metropolitan area through wet scavenging processes Tseren-Ochir Soyol-Erdene a , Yeongcheol Han a , Borom Lee a , Youngsook Huh a, b, * a School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Republic of Korea b Research Institute of Oceanography, Seoul National University, Seoul 151-747, Republic of Korea article info Article history: Received 7 September 2010 Received in revised form 7 January 2011 Accepted 7 January 2011 Keywords: Rainwater Platinum group elements Wet-deposition flux Enrichment factor abstract Platinum group elements (PGEs: Pt and Ir) and rare earth elements (REEs) were analyzed in rainwater samples collected in Seoul during the summer of 2008 to identify their sources and quantify their wet- deposition fluxes to the Earth’s surface environment. Major (Na, K, Mg, Ca, NH 4 þ , SO 4 2 , NO 3  , Cl  and F  ) and minor (Fe, Ba, Y and Hf) elements were also measured to facilitate interpretation. Evaluation of elemental correlations, crustal enrichment factors, Ir/Pt ratios and REE patterns indicated meteoric/ volcanic sources for Pt and Ir and additional anthropogenic sources for Pt. REEs were predominantly of crustal origin. The relationship between concentrations and rainfall indicated that below-cloud scav- enging (wash-out) was the main scavenging mechanism for most elements. The wet-deposition fluxes in Seoul were higher than those recorded in polar ice cores for Pt and Ir and were comparable to those from other rainwater studies of REEs in East Asia. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Atmospheric wet deposition is an important pathway in the geo-chemical cycles of elements. It transports chemical species accumulated in the atmosphere to the Earth’s surface and ecosys- tems. Most previous studies of precipitation chemistry have focused on major and minor elements. However, in face of their steadily increasing environmental concentrations due to human activities, there is an increasing need to evaluate ultra-trace (as low as fmol kg 1 ¼ 10 15 mol kg 1 ) elements such as the platinum group elements (PGEs: Ru, Rh, Pd, Os, Ir, Pt) and the rare earth elements (REEs: La to Lu). PGE abundances are extremely low in the continental crustdin the range of 0.02e0.5 ppb (Peucker-Ehrenbrink and Jahn, 2001). Worldwide industrial application of PGEs is steadily increasing in many sectors due to their excellent catalytic characteristics; in particular, the use of Pt, Rh and Pd for production of automobile catalytic converters has increased since the 1970s. Natural abun- dances of REEs in the continental crust are higher than those of PGEsdin the range of 0.3e64 ppm (Taylor and McLennan, 1995). Global production of REEs has increased over the past few decades owing to applications such as petroleum cracking, manufacture of magnets, pigments, batteries and magnetic refrigeration that are used in industrial fields (Haxel et al., 2002). In addition to direct industrial emissions, increased erosion due to agricultural activities or deforestation may also contribute to the rise in PGEs and REEs in the global atmosphere (Rauch and Morrison, 2008). Many studies have reported significant increases in PGE and REE levels in urban environments (soils, airborne particles and water and watershed sediments) in recent years due to increases in anthropogenic emissions (Wiseman and Zereini, 2009). However, low concentrations and associated analytical difficulties, especially for PGEs, have prevented elucidation of their distribution in and transport through the atmosphere and hydrosphere. In this paper, we report the contents of PGEs (Pt and Ir) and YREEs (yttrium and rare earth elements) in rainwater in Seoul, Korea to investigate their sources and wet-deposition fluxes. Major and minor elements are also reported to aid interpretation. 2. Methods 2.1. Site description Seoul is the capital city of Korea and is located in the west- central part of the Korean Peninsula in East Asia (Fig. 1). It has a population of 10.5 million within an area of 605.4 km 2 and it ranks as the 48th most populated city in the world (Brinkhoff, 2010). In the winter, air masses coming from inland Siberia are polluted and * Corresponding author. School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Republic of Korea. E-mail address: yhuh@snu.ac.kr (Y. Huh). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.01.023 Atmospheric Environment 45 (2011) 1970e1978