UC Irvine

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 °C and 1500 μmol m-2 s-1) ranged from about 50 to 500 μg 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 °C were only about 3 μg m-2 h-1 and consisted primarily of carene and limonene with smaller contributions of α-pinene and β-pinene. A model sensitivity study showed that grass and other herbaceous ground cover can contribute >10% of the total isoprene emission from certain regions, such as Inner Mongolia, but are<4% on a global annual scale. © 2006 Elsevier Ltd. All rights reserved.