h i g h l i g h t sLocal constrained MEGAN tends to estimate isoprene emission reasonably well. Considerably high uncertainties were found for isoprene emission using Monte Carlo approach. Key uncertainty sources in isoprene emission estimated were identified. a r t i c l e i n f o a b s t r a c tWith local observed emission factor and meteorological data, this study constrained the Model of Emissions of Gases and Aerosols from Nature (MEGAN) v2.1 to estimate isoprene emission from the Dinghushan forest during fall 2008 and quantify the uncertainties associated with MEGAN parameters using Monte Carlo approach. Compared with observation-based isoprene emission data originated from a campaign during this period at this site, the local constrained MEGAN tends to reproduce the diurnal variations and magnitude of isoprene emission reasonably well, with correlation coefficient of 0.7 and mean bias of 47.5%. The results also indicate high uncertainties in isoprene emission estimated, with the relative error varied from À89.0e111.0% at the 95% confidence interval. The key uncertainty sources include emission factors, g TLD , photosynthetically active radiation (PAR) and temperature. This implies that accurate input of emission factor, PAR and temperature is a key approach to reduce uncertainties in isoprene emission estimation.

Whole-system fluxes of isoprene from a moist acidic tundra ecosystem and leaf-level emission rates of isoprene from a common species (<i>Salix pulchra</i>) in that same ecosystem were measured during three separate field campaigns. The field campaigns were conducted during the summers of 2005, 2010 and 2011 and took place at the Toolik Field Station (68.6&deg; N, 149.6&deg; W) on the north slope of the Brooks Range in Alaska, USA. The maximum rate of whole-system isoprene flux measured was over 1.2 mg C m⁻² h⁻¹ with an air temperature of 22 °C and a PAR level over 1500 μmol m⁻² s⁻¹. Leaf-level isoprene emission rates for <i>S. pulchra</i> averaged 12.4 nmol m⁻² s⁻¹ (27.4 μg C gdw⁻¹ h^&minus;1) extrapolated to standard conditions (PAR = 1000 μmol m⁻² s⁻¹ and leaf temperature = 30 &deg;C). Leaf-level isoprene emission rates were well characterized by the Guenther algorithm for temperature with published coefficients, but less so for light. Chamber measurements from a nearby moist acidic tundra ecosystem with little <i>S. pulchra</i> emitted significant amounts of isoprene, but at lower rates (0.45 mg C m⁻² h^&minus;1) suggesting other significant isoprene emitters. Comparison of our results to predictions from a global model found broad agreement, but a detailed analysis revealed some significant discrepancies. An atmospheric chemistry box model predicts that the observed isoprene emissions have a significant impact on Arctic atmospheric chemistry, including a reduction of hydroxyl radical (OH) concentrations. Our results support the prediction that isoprene emissions from Arctic ecosystems will increase with global climate change

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Whole-system fluxes of isoprene from a~moist acidic tundra ecosystem and leaf-level emission rates of isoprene from a common species (<i>Salix pulchra</i>) in that same ecosystem were measured during three separate field campaigns. The field campaigns were conducted during the summers of 2005, 2010 and 2011 and took place at the Toolik Field Station (68.6&deg; N, 149.6&deg; W) on the north slope of the Brooks Range in Alaska, USA. The maximum rate of whole-system isoprene flux measured was over 1.2 mg C m^&minus;2 h^&minus;1 with an air temperature of 22 &deg; C and a PAR level over 1500 &mu;mol m^&minus;2 s^&minus;1. Leaf-level isoprene emission rates for <i>S. pulchra</i> averaged 12.4 nmol m^&minus;2 s^&minus;1 (27.4 &mu;g C gdw^&minus;1 h^&minus;1) extrapolated to standard conditions (PAR = 1000 &mu;mol m^&minus;2 s^&minus;1 and leaf temperature = 30&deg; C). Leaf-level isoprene emission rates were well characterized by the Guenther algorithm for temperature, but less so for light. Chamber measurements from a nearby moist acidic tundra ecosystem with less <i>S. pulchra</i> emitted significant amounts of isoprene, but at lower rates (0.45 mg C m^&minus;2 h^&minus;1). Comparison of our results to predictions from a global model found broad agreement, but a detailed analysis revealed some significant discrepancies. An atmospheric chemistry box model predicts that the observed isoprene emissions have a significant impact on Arctic atmospheric chemistry, including the hydroxyl radical (OH). Our results support the prediction that isoprene emissions from Arctic ecosystems will increase with global climate change