Isoprene and monoterpene emissions from an Inner Mongolia grassland

ARTICLE IN PRESS Atmospheric Environment 40 (2006) 5753–5758 www.elsevier.com/locate/atmosenv Isoprene and monoterpene emissions from an Inner Mongolia grassland Jianhui Bai a , Bradly Baker b , Baosheng Liang c , James Greenberg d , Alex Guenther d, a LAGEO, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China California State University at Sacramento, Department of Chemistry, 6000 J Street, Sacramento, CA 95819, USA c Environmental College of Peking University, Beijing 100871, China d 1850 Table Mesa Drive, National Center for Atmospheric Research, Boulder, Colorado 80305, USA b Received 7 February 2005; received in revised form 6 April 2006; accepted 6 May 2006 Abstract Terpenoid emissions were measured at a grassland site in Inner Mongolia, China during four campaigns over a 2-year period. Emissions were strongly correlated with light and temperature and the variations could be simulated using a canopy emission model. Substantial seasonal and interannual variations in isoprene emissions were also observed. Area averaged isoprene emissions normalized to standard above-canopy temperature and light conditions (30 1C and 1500 mmol m 2 s 1 ) ranged from about 50 to 500 mg m 2 h 1 . These rates are more than an order of magnitude higher than those previously reported for temperate grasslands but are lower than emission rates observed from ground cover vegetation at higher latitudes. Isoprene emissions from this Inner Mongolia grassland may be dominated by emissions from sedges, e.g. Carex appendiculata. Total monoterpene emissions normalized to a standard temperature of 30 1C were only about 3 mg m 2 h 1 and consisted primarily of carene and limonene with smaller contributions of a-pinene and b-pinene. A model sensitivity study showed that grass and other herbaceous ground cover can contribute 410% of the total isoprene emission from certain regions, such as Inner Mongolia, but areo4% on a global annual scale. r 2006 Elsevier Ltd. All rights reserved. Keywords: Biogenic emissions inventory; Carex; China; Volatile organic compounds (VOCs) 1. Introduction The chemical composition of the atmosphere is an important component of the global environment and observed trends in trace gas concentrations demonstrate that it is changing rapidly (Brasseur et al., 1999). Vegetation produces over 90% of the global annual nonmethane volatile organic com- Corresponding author. Tel.: +1 303 497 1447; fax: +1 303 497 1477. E-mail address: guenther@ucar.edu (A. Guenther). 1352-2310/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2006.05.019 pound (VOC) emissions which are dominated by the terpenoid compound, isoprene (Guenther et al., 1995). Isoprene oxidation influences OH and ozone concentrations and has a significant role in CO production, the formation of organic acids, and the photochemical conversion of NO y species (Guenther et al., 1999). Studies of biogenic VOC (BVOC) have focused on forests which are thought to be the dominant global source of BVOC. Although grasslands and pastures cover one quarter of the Earth’s land surface (Guenther et al., 1995), relatively few studies