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Title: Airborne observations reveal elevational gradient in tropical forest isoprene emissions

Abstract

Terrestrial vegetation emits vast quantities of volatile organic compounds (VOCs) to he atmosphere1-3, which influence oxidants and aerosols leading to complex feedbacks on air quality and climate4-6. Isoprene dominates global non-methane VOC emissions with tropical regions contributing ~80% of global isoprene emissions2. Isoprene emission rates vary over several orders of magnitude for different plant species, and characterizing this immense biological chemodiversity is a challenge for estimating isoprene emission from tropical forests. Here we present the isoprene emission estimates from aircraft direct eddy covariance measurements over the pristine Amazon forest. We report isoprene emission rates that are 3 times higher than satellite top-down estimates and 35% higher than model predictions based on satellite land cover and vegetation specific emission factors (EFs). The results reveal strong correlations between observed isoprene emission rates and terrain elevations which are confirmed by similar correlations between satellite-derived isoprene emissions and terrain elevations. We propose that the elevational gradient in the Amazonian forest isoprene emission capacity is determined by plant species distributions and can explain a substantial degree of isoprene emission variability in tropical forests. Finally, we apply this approach over the central Amazon and use a model to demonstrate the impacts on regional air quality.

Authors:
ORCiD logo [1];  [1];  [2];  [2]; ORCiD logo [2]; ORCiD logo [3];  [2];  [4];  [5];  [6]; ORCiD logo [6];  [7];  [8];  [9];  [10];  [11];  [2]; ORCiD logo [2];  [12];  [8] more »;  [2];  [2] « less
  1. Univ. of California, Irvine, CA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Univ. of Science and Technology of China, Anhui (China)
  4. Harvard Univ., Cambridge, MA (United States)
  5. Univ. de Sao Paulo, Sao Paulo (Brazil)
  6. Univ. of California, Irvine, CA (United States)
  7. Royal Belgian Institute for Space Aeronomy, Brussels (Belgium)
  8. National Institute for Space Research, Sao Paulo (Brazil)
  9. Univ. Federal do Oeste do Para, Para (Brazil)
  10. Univ. do Estado do Amazonas, Amazonas (Brazil)
  11. Instituto de Pesquisas Energeticas e Nucleares, Sao Paulo (Brazil)
  12. National Institute for Amazonian Research, Amazonas (Brazil)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1361963
Report Number(s):
PNNL-SA-125338; PNNL-SA-128460
Journal ID: ISSN 2041-1723; KP1701000
Grant/Contract Number:
AC05-76RL01830
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 8; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; atmospheric chemistry; biogeochemistry

Citation Formats

Gu, Dasa, Guenther, Alex B., Shilling, John E., Yu, Haofei, Huang, Maoyi, Zhao, Chun, Yang, Qing, Martin, Scot T., Artaxo, Paulo, Kim, Saewung, Seco, Roger, Stavrakou, Trissevgeni, Longo, Karla M., Tota, Julio, de Souza, Rodrigo Augusto Ferreira, Vega, Oscar, Liu, Ying, Shrivastava, Manish, Alves, Eliane G., Santos, Fernando C., Leng, Guoyong, and Hu, Zhiyuan. Airborne observations reveal elevational gradient in tropical forest isoprene emissions. United States: N. p., 2017. Web. doi:10.1038/ncomms15541.
Gu, Dasa, Guenther, Alex B., Shilling, John E., Yu, Haofei, Huang, Maoyi, Zhao, Chun, Yang, Qing, Martin, Scot T., Artaxo, Paulo, Kim, Saewung, Seco, Roger, Stavrakou, Trissevgeni, Longo, Karla M., Tota, Julio, de Souza, Rodrigo Augusto Ferreira, Vega, Oscar, Liu, Ying, Shrivastava, Manish, Alves, Eliane G., Santos, Fernando C., Leng, Guoyong, & Hu, Zhiyuan. Airborne observations reveal elevational gradient in tropical forest isoprene emissions. United States. doi:10.1038/ncomms15541.
Gu, Dasa, Guenther, Alex B., Shilling, John E., Yu, Haofei, Huang, Maoyi, Zhao, Chun, Yang, Qing, Martin, Scot T., Artaxo, Paulo, Kim, Saewung, Seco, Roger, Stavrakou, Trissevgeni, Longo, Karla M., Tota, Julio, de Souza, Rodrigo Augusto Ferreira, Vega, Oscar, Liu, Ying, Shrivastava, Manish, Alves, Eliane G., Santos, Fernando C., Leng, Guoyong, and Hu, Zhiyuan. Tue . "Airborne observations reveal elevational gradient in tropical forest isoprene emissions". United States. doi:10.1038/ncomms15541. https://www.osti.gov/servlets/purl/1361963.
@article{osti_1361963,
title = {Airborne observations reveal elevational gradient in tropical forest isoprene emissions},
author = {Gu, Dasa and Guenther, Alex B. and Shilling, John E. and Yu, Haofei and Huang, Maoyi and Zhao, Chun and Yang, Qing and Martin, Scot T. and Artaxo, Paulo and Kim, Saewung and Seco, Roger and Stavrakou, Trissevgeni and Longo, Karla M. and Tota, Julio and de Souza, Rodrigo Augusto Ferreira and Vega, Oscar and Liu, Ying and Shrivastava, Manish and Alves, Eliane G. and Santos, Fernando C. and Leng, Guoyong and Hu, Zhiyuan},
abstractNote = {Terrestrial vegetation emits vast quantities of volatile organic compounds (VOCs) to he atmosphere1-3, which influence oxidants and aerosols leading to complex feedbacks on air quality and climate4-6. Isoprene dominates global non-methane VOC emissions with tropical regions contributing ~80% of global isoprene emissions2. Isoprene emission rates vary over several orders of magnitude for different plant species, and characterizing this immense biological chemodiversity is a challenge for estimating isoprene emission from tropical forests. Here we present the isoprene emission estimates from aircraft direct eddy covariance measurements over the pristine Amazon forest. We report isoprene emission rates that are 3 times higher than satellite top-down estimates and 35% higher than model predictions based on satellite land cover and vegetation specific emission factors (EFs). The results reveal strong correlations between observed isoprene emission rates and terrain elevations which are confirmed by similar correlations between satellite-derived isoprene emissions and terrain elevations. We propose that the elevational gradient in the Amazonian forest isoprene emission capacity is determined by plant species distributions and can explain a substantial degree of isoprene emission variability in tropical forests. Finally, we apply this approach over the central Amazon and use a model to demonstrate the impacts on regional air quality.},
doi = {10.1038/ncomms15541},
journal = {Nature Communications},
number = ,
volume = 8,
place = {United States},
year = {Tue May 23 00:00:00 EDT 2017},
month = {Tue May 23 00:00:00 EDT 2017}
}

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  • Isoprene (Is) emissions by plants represent a loss of carbon and energy resources leading to the initial hypothesis that fast growing pioneer species in secondary tropical forests allocate carbon primarily to growth at the expense of isoprenoid defenses. In this study, we quantified leaf isoprene and methanol emissions from the abundant pantropical pioneer tree species Vismia guianensis and ambient isoprene concentrations above a diverse secondary forest in the central Amazon. As photosynthetically active radiation (PAR) was varied (0 to 3000 µmol m -2 s -1) under standard leaf temperature (30 °C), isoprene emissions from V. guianensis increased without saturation upmore » to 80 nmol m -2 s -1. A nonlinear increase in isoprene emissions with respect to net photosynthesis (Pn) resulted in the fraction of Pn dedicated to isoprene emissions increasing with light intensity (up to 2 % of Pn). Emission responses to temperature under standard light conditions (PAR of 1000 µmol m -2 s -1) resulted in the classic uncoupling of isoprene emissions ( T opt, iso > 40 °C) from net photosynthesis ( T opt, Pn = 30.0–32.5 °C) with up to 7 % of Pn emitted as isoprene at 40 °C. Under standard environmental conditions of PAR and leaf temperature, young V. guianensis leaves showed high methanol emissions, low Pn, and low isoprene emissions. In contrast, mature leaves showed high Pn, high isoprene emissions, and low methanol emissions, highlighting the differential control of leaf phenology over methanol and isoprene emissions. High daytime ambient isoprene concentrations (11 ppbv) were observed above a secondary Amazon rainforest, suggesting that isoprene emissions are common among neotropical pioneer species. The results are not consistent with the initial hypothesis and support a functional role of methanol during leaf expansion and the establishment of photosynthetic machinery and a protective role of isoprene for photosynthesis during high temperature extremes regularly experienced in secondary rainforest ecosystems.« less
    Cited by 3
  • Isoprene (Is) emissions by plants represent a loss of carbon and energy resources leading to the initial hypothesis that fast growing pioneer species in secondary tropical forests allocate carbon primarily to growth at the expense of isoprenoid defenses. In this study, we quantified leaf isoprene and methanol emissions from the abundant pantropical pioneer tree species Vismia guianensis and ambient isoprene concentrations above a diverse secondary forest in the central Amazon. As photosynthetically active radiation (PAR) was varied (0 to 3000 µmol m -2 s -1) under standard leaf temperature (30 °C), isoprene emissions from V. guianensis increased without saturation upmore » to 80 nmol m -2 s -1. A nonlinear increase in isoprene emissions with respect to net photosynthesis (Pn) resulted in the fraction of Pn dedicated to isoprene emissions increasing with light intensity (up to 2 % of Pn). Emission responses to temperature under standard light conditions (PAR of 1000 µmol m -2 s -1) resulted in the classic uncoupling of isoprene emissions ( T opt, iso > 40 °C) from net photosynthesis ( T opt, Pn = 30.0–32.5 °C) with up to 7 % of Pn emitted as isoprene at 40 °C. Under standard environmental conditions of PAR and leaf temperature, young V. guianensis leaves showed high methanol emissions, low Pn, and low isoprene emissions. In contrast, mature leaves showed high Pn, high isoprene emissions, and low methanol emissions, highlighting the differential control of leaf phenology over methanol and isoprene emissions. High daytime ambient isoprene concentrations (11 ppbv) were observed above a secondary Amazon rainforest, suggesting that isoprene emissions are common among neotropical pioneer species. The results are not consistent with the initial hypothesis and support a functional role of methanol during leaf expansion and the establishment of photosynthetic machinery and a protective role of isoprene for photosynthesis during high temperature extremes regularly experienced in secondary rainforest ecosystems.« less
  • Isoprene and monoterpene emission rates are essential inputs for atmospheric chemistry models that simulate atmospheric oxidant and particle distributions. Process studies of the biochemical and physiological mechanisms controlling these emissions are advancing our understanding and the accuracy of model predictions but efforts to quantify regional emissions have been limited by a lack of constraints on regional distributions of ecosystem emission capacities. We used an airborne wavelet-based eddy covariance measurement technique to characterize isoprene and monoterpene fluxes with high spatial resolution during the 2013 SAS (Southeast Atmosphere Study) in the southeastern United States. The fluxes measured by direct eddy covariance weremore » comparable to emissions independently estimated using an indirect inverse modeling approach. Isoprene emission factors based on the aircraft wavelet flux estimates for high isoprene chemotypes (e.g., oaks) were similar to the MEGAN2.1 biogenic emission model estimates for landscapes dominated by oaks. Aircraft flux measurement estimates for landscapes with fewer isoprene emitting trees (e.g., pine plantations), were about a factor of two lower than MEGAN2.1 model estimates. The tendency for high isoprene emitters in these landscapes to occur in the shaded understory, where light dependent isoprene emissions are diminished, may explain the lower than expected emissions. This result demonstrates the importance of accurately representing the vertical profile of isoprene emitting biomass in biogenic emission models. Airborne measurement-based emission factors for high monoterpene chemotypes agreed with MEGAN2.1 in landscapes dominated by pine (high monoterpene chemotype) trees but were more than a factor of three higher than model estimates for landscapes dominated by oak (relatively low monoterpene emitting) trees. This results suggests that unaccounted processes, such as floral emissions or light dependent monoterpene emissions, or vegetation other than high monoterpene emitting trees may be an important source of monoterpene emissions in those landscapes and should be identified and included in biogenic emission models.« less
  • Using local observed emission factor, meteorological data, vegetation 5 information and dynamic MODIS LAI, MEGANv2.1 was constrained to predict the isoprene emission from Dinghushan forest in the Pearl River Delta region during a field campaign in November 2008, and the uncertainties in isoprene emission estimates were quantified by the Monte Carlo approach. The results indicate that MEGAN can predict the isoprene emission reasonably during the campaign, and the mean value of isoprene emission is 2.35 mg m-2 h-1 in daytime. There are high uncertainties associated with the MEGAN inputs and calculated parameters, and the relative error can be as highmore » as -89 to 111% for a 95% confidence interval. The emission factor of broadleaf trees and the activity factor accounting for light and temperature dependence are the most important contributors to the uncertainties in isoprene emission estimated for the Dinghushan forest during the campaign. The results also emphasize the importance of accurate observed PAR and temperature to reduce the uncertainties in isoprene emission estimated by model, because the MEGAN model activity factor accounting for light and temperature dependence is highly sensitive to PAR and temperature.« less
  • A biogenic emissions model for isoprene, monoterpenes, and nitric oxide has been developed with algorithms that rely on normalized difference vegetative index values derived from satellite remote sensing data to infer leaf area index. The model obtains emission factors from the Biogenic Emission Inventory System (BEIS). This biogenic emissions model, combined with a dry deposition model, was applied with environmental variable values supplied by MM5 (the fifth-generation Mesoscale Model). The modeled temporal variations and spatial distributions of the surface emissions rates of isoprene, monoterpenes, and nitric oxide the eastern US agreed well with reported simulations, measurements, and inferences. Use ofmore » the satellite data generates considerable detail in the spatial patterns, high temporal resolution, and a smooth seasonal variation in the emission rates. The new biogenic emissions model was used with a photochemistry modeling system to infer ozone (O{sub 3}) concentrations in the lower troposphere above the eastern United States for a two-day case in July 1995, which had O{sub 3} episodes studied previously by the Ozone Transport Assessment Group. Compared to the results from the OTAG application of BEIS2, the satellite-data-derived isoprene emissions were slightly lower in the northeastern United States, which resulted in smaller values of O{sub 3} concentration and were 3-4 times higher in southeastern mixed forests, which had little impact on O{sub 3} except near strong NO{sub x} emission sources.« less