Emission characteristics and airesurface exchange of gaseous mercury at the largest active landﬁll in Asia Wei Zhu a, e , Zhonggen Li a, * , Xiaoli Chai b, * , Yongxia Hao b , Che-Jen Lin a, c, d , Jonas Sommar a , Xinbin Feng a a State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China b State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China c Department of Civil Engineering, Lamar University, Beaumont, TX 77710, USA d College of Environment and Energy, South China University of Technology, Guangzhou 510006, China e University of Chinese Academy of Sciences, Beijing 100049, China highlights  The emission of gaseous elemental mercury from the largest active landﬁll in Asia is characterized.  The interstitial gas mercury concentration in the landﬁll exhibits signiﬁcant spatial variability.  Gaseous elemental mercury concentration in landﬁll gas declines with the age of landﬁll cells.  Strong mercury emission from MSW surface can be effectively contained by application of a thin layer clay cover. article info Article history: Received 7 March 2013 Received in revised form 20 May 2013 Accepted 28 May 2013 Keywords: Landﬁll GEM ﬂux Landﬁll gas Interstitial gas GEM Shanghai abstract The emission characteristics and air-surface exchange of gaseous elemental mercury (GEM) at Laogang landﬁll in Shanghai, China, the largest active landﬁll in Asia, has been investigated during two intensive ﬁeld campaigns in 2011 and 2012. The mercury (Hg) content in municipal solid waste (MSW) varied widely from 0.19 to 1.68 mg kg 1 . Over the closed cell in the landﬁll, the mean ambient air GEM concentration was virtually indistinguishable from the hemispherical background level (1.5e2.0 ng m 3 ) while the con- centration downwind of ongoing landﬁll operation (e.g. dumping, burying and compacting of MSW) was clearly elevated. GEM emission through landﬁll gas (LFG) was identiﬁed as a signiﬁcant source. GEM concentrations in LFGs collected from venting pipes installed in different landﬁll cells varied widely from 3.0 to 1127.8 ng m 3 . The GEM concentrations were found negatively correlated to the age of LFG cells, suggesting GEM released through LFG declined readily with time. The GEM emission from this source alone was estimated to be 1.23e1.73 mg h 1 . GEM emission from cover soil surfaces was considerably lower and at a scale comparable to that of background soil surfaces. This is in contrast to earlier reports showing enhanced GEM emissions from landﬁll surfaces in Southern China, probably due to the difference in soil Hg content and gas permeability characteristics of soils at different sites. Vertical concentration proﬁles of GEM in the interstitial gas of buried MSW were sampled, perhaps for the ﬁrst time, which exhibited a wide spatial variability (4.9e713.1 ng m 3 ) in the 3-year-old landﬁll cell investigated. GEM emission from landﬁll operation was estimated to be 290e525 mg h 1 using a box model. This suggests that GEM degassing from Laogang landﬁll is quantitatively largely dominated by emissions from daily landﬁlling operations with a much smaller contribution from LFG venting and insigniﬁcant (bi-directional ﬂuxes near zero) contribution from surfaces capped with a soil layer. This study reveals divergent GEM emission patterns among landﬁll cells of different ages, and provides essential emission estimates for formulating Hg emission reduction strategies for a large landﬁll. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Mercury (Hg) is a ubiquitous persistent pollutant being subject to long-range transport and environmental cycling (Durnford et al., 2010). Concern of Hg pollution is mainly from its potent bio-accumulative * Corresponding authors. Tel.: þ86 851 5890 446; fax: þ86 851 5891 609. E-mail addresses: lizhonggen@vip.skleg.cn (Z. Li), xlchai@tongji.edu.cn (X. Chai), fengxinbin@vip.skleg.cn (X. Feng). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atmosenv.2013.05.083 Atmospheric Environment 79 (2013) 188e197