5th iLEAPS Science Conference Abstracts - D2

Abstracts – Session D2

Measuring and modelling biogenic volatile organic compounds (BVOCs)

D201 ORAL-0217: MEGAN3 Emission Factor Processor: A transparent approach for estimating biogenic emission factors

Alex Guenther

Biogenic emissions research has focused on the identification and quantification of processes controlling variations in emission activity. This is probably because these activities tend to be more interesting and easier to publish that studies of emission factors. However, uncertainties in emission factors make an important contribution and may even dominate the total uncertainty in biogenic emission rate estimates. The task of assigning emission factors is challenging due to the diverse measurement approaches and the immense biological and chemical diversity of biogenic VOC and has generally been accomplished through a relatively opaque process.  More systematic approaches can lead to unsatisfactory results, due to the limited data availability and because of unrepresentative measurements, but there is a need for a more integrative, transparent and informative approach for estimating biogenic emission factors that will engage the measurement community to provide more suitable emissions data. The Model of Emissions of Gases and Aerosols from Nature - Emission Factor Processor (MEGAN-EFP) has been developed in response to this need and used to reconcile emission factors for well-studied compounds, such as isoprene, and to develop strategies for improving emission factor estimates of other biogenic compounds. The MEGAN-EFP approach enables users to determine the basis of each emission factor and facilitates improvements to existing emission factors and assessments of uncertainties. The MEGAN-EFP consists of open source Python code that will be freely available to the regulatory and scientific communities. In this presentation, the MEGAN-EFP and other novel features of the MEGAN3 next generation model will be described and the application of the MEGAN-EFP to reconciling emission model (e.g., BEIS vs MEGAN) and measurements discrepancies will be demonstrated. Strategies and potential roadblocks for future improvements of biogenic emission factors will also be discussed. 

D202 - ORAL-0129: The impact of LULCC on the emission of BVOCs during the 21st century

Almut Arneth, Stijn Hantson, Sebastian Szogs, Peter Anthoni, Jonathan Doelman, Florian Humpenöder, Alex Popp, Tom Pugh, Elke Stehfest

Land-use and land-cover change (LULCC) is one of the key drivers of anthropogenic climate change. In addition to greenhouse gases such as CO2 or CH4, LULCC affects also the emission of  biogenic volatile organic compounds (BVOCs). We investigate the impact of changing LULCC on the emission of isoprene and monoterpenes during the 21st century using a range of different land-use projections, applying the dynamic vegetation modelling framework LPJ-GUESS. Climate change, and atmospheric CO2-concentration are based on the RCP2.6 scenario. The different LULCC-scenarios explore the impact of different land-based climate change mitigation strategies (such as afforestation and avoided deforestation, or bioenergy). We show that the increase of land area under crops or grassland would lead to a significant decrease of BVOC emissions, with a strong negative correlation between the fraction of managed global land area and the emission of isoprene and monoterpenes. The choice of crops is important, especially for the bioenergy scenarios in which increasing fractional cover leads to decreasing BVOC emissions in our simulations; use of woody bioenergy crops could reverse this decrease. The strong impact of LULCC on the global and regional emission of BVOCs implies the need to include the impact of these changes in projections of atmospheric composition and air quality.

D203 - ORAL-0264: Regional scale modelling of SOA formation using COSMO-MUSCAT

Ralf Wolke1, Marie Luttkus1, Kathrin Gatzsche1, Andreas Tilgner1, Hartmut Herrmann1

1Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany

Secondary organic aerosol (SOA) is the major burden of the atmospheric organic particulate matter. SOA particles are formed via the oxidation of volatile organic carbons (VOCs), where the volatility of the VOCs is lowered. Accordingly, gaseous compounds can either nucleate to form new particles or condense on existing particles. The framework of SOA formation under natural conditions is very complex, because there are a multitude of gas-phase precursors, atmospheric degradation processes and products after oxidation.  Up to now, simulations predominantly underestimate measured SOA mass. Thus, the present study has the aim to improve the understanding of SOA processes.
 
The model system COSMO-MUSCAT (Wolke et al., 2012) is used for studying the formation of SOA and its influence on total PM concentrations. The established model system is enhanced by the biogenic emission scheme of Steinbrecher et al. (2009) and an advanced SOA approach. The applied biogenic emission model takes into account over 100 different tree species, temperature, humidity and solar radiation. The SOA formation was described by the updated SORGAM module of Li et al. (2013) and an extension for sesquiterpenes. Furthermore, extremely low volatility organic compounds (ELVOCs) were incorporated in the formation mechanism. ELVOCs are suggested to promote aerosol particle formation (Jokinen et al., 2015). The new approach was applied for process studies and the simulation of field campaigns. The influence of different sources and formation pathways is analyzed. The results are compared with the former scheme and available detailed measurements (especially for the TROPOS field site Melpitz).

References:

Jokinen et al.(2015) PNAS, 112 (23), 7123-7128; Li et al. (2013) Atmos. Chem. Phys., 13, 6289–6304; Steinbrecher et al. (2009) Atmos. Environ., 43, 1380–1391; Wolke et al. (2012) Atmos. Environ., 53, 110–130.

D204 - ORAL-0197: Evaluation of UK Biogenic VOC emissions from the JULES land surface model

Garry Hayman1, Edward Comyn-Platt1, Massimo Vieno2, Ben Langford2

1Centre for Ecology & Hydrology, Wallingford, United Kingdom 2Centre for Ecology & Hydrology, Edinburgh, United Kingdom

Emissions of biogenic non-methane volatile organic compounds (NMVOCs) are important for air quality and atmospheric composition. Through their contribution to the production of tropospheric ozone and secondary organic aerosol (SOA), biogenic VOCs indirectly contribute to climate forcing and climate feedbacks. Biogenic VOCs encompass a wide range of compounds and are produced by plants for growth, development, reproduction, defence and communication. There are both biological and physico-chemical controls on emissions. Only a few of the many biogenic VOCs are of wider interest and only two or three (isoprene and the monoterpenes, α- and β -pinene) are represented in chemical transport models.
 
We use the Joint UK Land Environment Simulator (JULES), the UK community land surface model, to estimate biogenic VOC emission fluxes. JULES is a process-based model that describes the water, energy and carbon balances and includes temperature, moisture and carbon stores. JULES currently provides emission fluxes of the 4 largest groups of biogenic VOCs: isoprene, terpenes, methanol and acetone. The isoprene emission scheme in JULES, which depends on the electron requirement for isoprene synthesis, was implemented by Pacifico et al.. A semi-empirical approach is used for the other species.
 
In this study, we compare JULES biogenic VOC emission estimates of isoprene and terpenes with (a) flux measurements made at selected sites in the UK and Europe and (b) gridded estimates for the UK from the EMEP/EMEP4UK atmospheric chemical transport model, using site-specific or EMEP4UK driving meteorological data, respectively. We compare the UK-scale emission estimates with literature estimates. We generally find good agreement in the comparisons but the estimates are sensitive to the choice of the base or reference emission potentials.

D205 - ORAL-0082: A Sustainable Way to Mitigate Ozone Pollution by Reducing Biogenic VOCs through Landscape Management Programme

Pallavi Saxena1

1School of Environmental Sciences, Jawaharlal Nehru University, Delhi, India

Trees can affect air quality in several ways. Ideally, all tree effects on air quality especially ozone pollution would be included in tree selection to maximize net benefits. This control measure claims reductions for BVOC emissions only. BVOCs were included as an initial step in air quality planning because they were most readily quantified. The Tree BVOC Index (TBI) is an alternative prescriptive approach that provides an estimate of projected and actual emission reductions. A TBI less than or equal to 1.0 informs the user that their tree planting program is on track to meet its goal. In the present study, four tree species were selected viz. Dalbergia sissoo, Butea monosperma, Mangifera indica and Azadirachta indica at two sites namely Site I, traffic intersection and Site II, industrial for determination of Tree BVOC index by calculating ratio of future emissions from a proposed or current planting of trees at particular sites annually in a capital city of India, Delhi. The results indicated that Dalbergia sissoo and Butea monosperma calculated Tree BVOC index was found to be 3.22 and 2.11 at Site I and 3.79 and 2.43 at Site II respectively while 0.66 and 0.22 at Site I and 0.69 and 0.22 at Site II in case of Mangifera indica and Azadirachta indica respectively. Hence, the study concludes that among four selected trees, Mangifera indica and Azadirachta indica which have calculated TBI values less than 1 were found to suitable for planting and can be used as in greenbelt development programmes while Dalbergia sissoo and Mangifera indica which have values more than 1 were not recommended for planting especially for mitigating ozone pollution. Hence, Tree BVOC index can be used as a sustainable way to mitigate ozone pollution and can be used for landscape development programmes.

D206 ORAL-0193: Biogenic volatile organic compounds at a grazed savannah-grassland in South Africa

Pieter van Zyl1, Kermeels Jaars1, Johan Paul Beukes1, Heidi Hellén2, Ville Vakkari2, Miroslav Josipovic1, Andrew Venter1, Matti Räsänen3, Leandra Knoetze1, Dirk Cilliers1, Stefan Siebert1, Markku Kulmala3, Janne Rinne4, Alex Guenther5, Lauri Laakso2, Hannele Hakola2

1North-West University, Potchefstroom, South Africa 2Finnish Meteorological Institute, Helsinki, Finland 3Department of Physics, University of Helsinki, Helsinki, Finland 4Lund University, Lund, Sweden 5Department of Earth System Science, University of California, Irvine, The United States of America

BVOC measurements were conducted through two long-term sampling campaigns at Welgegund (South Africa), which is considered to be a regionally representative background site situated in savannah grassland. Very few BVOC measurements exist for grassland savannah and results presented in this study are the most extensive for this type of landscape.  The annual median concentrations of isoprene, 2-methyl-3-butene-2-ol (MBO), monoterpenes and sesquiterpenes (SQT) during the first campaign were 14, 7, 120 and 8 pptv, respectively, and 14, 4, 83 and 4 pptv, respectively, during the second campaign.  The sum of the concentrations of the monoterpenes were at least an order of magnitude higher than the concentrations of other BVOC species, with a-pinene being the most abundant species.  The highest BVOC concentrations were observed during the wet season and elevated soil moisture was associated with increased BVOC concentrations.  Comparisons with measurements conducted at other landscapes in southern Africa and the rest of the world indicated significantly lower BVOC concentrations for the grassland savannah.  Furthermore, BVOC concentrations were an order of magnitude lower compared to total aromatic concentrations measured at Welgegund.  An analysis of concentrations by wind direction indicated that isoprene concentrations were higher from the western sector that is considered to be a relatively clean regional background region with no large anthropogenic point sources. Statistical analysis indicated that soil moisture had the most significant impact on atmospheric levels of MBO, monoterpenes and SQT concentrations, while temperature had the greatest influence on isoprene levels. The combined O3 formation potentials of all the BVOCs measured calculated with MIR coefficients during the first and second campaign were 1162 and 1022 pptv, respectively.  a-Pinene and limonene had the highest reaction rates with O3, while isoprene exhibited relatively small contributions to O3 depletion.  Limonene, a-pinene and terpinolene had the largest contributions to the OH-reactivity of BVOCs.

D207 - ORAL-0385: Isoprene emission from moorland: using Scottish field flux measurements to improve European model predictions

Ben Langford1, James Cash1, 2, Massimo Vieno1, Julia Drewer1, Mathew Heal2, Eiko Nemitz1

1NERC Centre for Ecology and Hydrology (CEH), Penicuik, United Kingdom 2School of Chemistry, The University of Edinburgh, Edinburgh, United Kingdom

Isoprene is a trace gas emitted from the biosphere in huge quantities in response to changes in light and temperature. Once in the atmosphere the isoprene molecule reacts quickly with OH, and in the presence of sunlight and oxides of nitrogen (NOx) can lead to the formation of ground level ozone, a powerful oxidant that causes damage to plants, crops and buildings and is harmful to human health. Significant efforts have been undertaken to understand better the processes that control the emission rates of isoprene from plants and to develop predictive emission algorithms, which underpin air quality and climate models. Here, we present eddy covariance flux measurements of isoprene made above a Scottish moorland, Auchencorth Moss, over a period of several weeks between June and July, 2015. In parallel, individual plants at the site were screened using leaf cuvette measurements in order to identify those species responsible for the observed emission rates. This analysis indicated that the isoprene fluxes at this site can be attributed almost entirely to bryophytes, with the largest emission rates associated with the mosses Sphagnum fallax and Polytrichum strictum. Using the ecosystem-scale flux measurements made we challenge the performance of the commonly used isoprene emission algorithms of Guenther et al. (1993; 2012), which were developed specifically for use with vascular plants, to replicate fluxes from an ecosystem where emissions are dominated by bryophytes. Optimisation of the light response curve used in these algorithms resulted in a much improved reproduction of the observed fluxes. By integrating the optimised emission algorithm into the EMEP model we assess the contribution of isoprene emitted from moorland to episodes of ground level ozone pollution in Europe under both current and future climate scenarios.

D208 - ORAL-0222:  Two-way ecosystem-atmosphere fluxes of volatile organic compounds detected across the mass spectrum: But how many matter?

Dylan Millet1, Hariprasad Alwe1

1University of Minnesota, Saint Paul, The United States of America

Volatile organic compounds (VOCs) play a major role in the atmosphere by reacting with oxidants and as precursors to key secondary chemicals. Terrestrial ecosystems are simultaneously a major source and a major sink of atmospheric VOCs; however, these two-way fluxes are poorly constrained and an important source of uncertainty in current models. Here we present new measurements by high-resolution time-of-flight mass spectrometry (PTR-QiTOF) over a mixed deciduous forest during the 2016 PROPHET-AMOS campaign in Michigan, USA. Sampling combined flux measurements by eddy covariance at the canopy top with hourly vertical profiling from the forest floor to above-canopy. The measurements provide constraints on fluxes across the entire mass spectrum of detected VOCs, and reveal patterns indicating emission or deposition for some compounds, but a combination of both for others. Of the 650 ions detected by PTR-QiTOF during the study, 421 had detectable upward, downward, or bidirectional flux. While 10 ions alone accounted for 90% of the total nominal upward flux (molar basis), 91 were required to account for 99% of the upward flux, and 234 ions were required to account for 99% of the total nominal downward flux. Here we explore these results with the aim of better understanding i) how well our models capture this 2-way land-atmosphere carbon exchange, and ii) to what degree the fluxes for the large number of ions outside of the traditionally-measured subset actually matter for tropospheric composition.

D209 - ORAL-0139: Diterpene and other isoprenoid emissions by the Mediterranean shrub Halimnium halimifolium L. determined by the PTR-TOF-IRIS system

Ana Maria Yáñez-Serrano1, Lukas Fasbender1, Jürgen Kreuzwieser2, Christiane Werner

1Chair of Ecosystem Physiology, University of Freiburg, Freiburg, Germany 2Chair of Tree Physiology, University Freiburg, Freiburg, Germany

Mediterranean plant species emit a wide range of BVOC into the atmosphere. Such emissions often occur in a light and temperature dependent manner. In the present study, we investigated the BVOC emission from leaves of the Mediterranean shrub Halimnium halimifolium L. under controlled conditions in climate chambers. For the first time, we demonstrate online emissions of the diterpene kaurene using a PTR-TOF-MS coupled to an Isotope Ratio Spectrometer (PTR-TOF-IRIS system). Additional GC-MS analysis and calibration with an authentic standard verified the emission of this diterpene. Daily patterns of kaurene emission indicated a strong light-dependency. 13C-labelling experiments with positionally labelled pyruvate, a central molecule in the carbon metabolism, corroborated the emission of kaurene through plant biosynthesis as the isotope m/z 274.26 of kaurene increased when labelling took place. Nevertheless, this 13C incorporation seemed to be dependent on emission strength and suggested that emission of kaurene mainly occurs from stored pools and only to a minor extent from recently fixed carbon. Interestingly, kaurene emission in darkness differed from monoterpene and sesquiterpenes emissions. Emission of the latter compounds decreased with darkening; however, kaurene emissions only transiently decreased and increased thereafter to the same levels observed during the light period.  We assume that stomatal closure limits kaurene release directly after darkening, while a subsequent increase in leaf internal concentrations could be driving emissions due to strong gradients between leaf and atmosphere. The atmospheric implications of this study result from the high reactivity of kaurene, especially towards ozone, as well as the unknown role on aerosol formation potential, which to our knowledge has not been studied. Furthermore, there is no consideration of this type of compound in any atmospheric chemistry model, therefore, more measurements and model constrains are needed to understand the role and fate of diterpenes in plants and in the atmosphere.

D210 - POSTER-0093: The iDirac: Isoprene Measurements from Tropical Forests

Conor Bolas1, Valerio Ferracci2, Neil Harris2, Shahrul Nadzir3, Iq Mead2, Andrew Robinson1, Rod Jones1, Alex Archibald1

1University of Cambridge, Cambridge, United Kingdom 2University of Cranfield, Cranfield, United Kingdom 3Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia

Isoprene is a highly important biogenic VOC emitted by certain species of plants into the atmosphere. Rapidly oxidised in the air, its subsequent chemistry plays a significant part in determining atmospheric composition, aerosol formation and the oxidising capacity of the troposphere. Development of a novel portable gas chromatography instrument, the iDirac, in our lab has allowed the possibility of long term measurements from various remote and challenging sites. Currently, we investigate an improved quantification of isoprene emissions from tropical forests from the poorly sampled region of Southeast Asia.
 
Emission from trees is the greatest source of isoprene and particularly in the tropics, where temperatures are higher. Quantifying this emission is a challenge has been poorly represented in global models to date. Measurements in Malaysian Borneo hope to examine isoprene from individual trees of certain species and relate this to observed environmental factors and ambient isoprene levels. Based on previous field data and an up-coming campaign, the eventual aim is to be able to scale up individual leaf measurements to individual trees and eventually to forest-scale.

D211 - POSTER-0094: How biogenic isoprene emission responses to  vegetation variations globally?

Weihua Chen1, Alex Guenther2, Xuemei Wang3, Ming Chang3

1Sun Yat-Sen University, Guangzhou, China 2University of California, Irvine, Irvine, The United States of America 3Jinan University, Guangzhou, China

Isoprene, as the predominant BVOCs component, is mainly emitted by forest and plays a vital role in atmospheric environment. This paper presents a study of the change in biogenic isoprene emissions that would result from vegetation variations between 2000 and 2015 based on the satellite vegetation data coupled with modeling isoprene data. The result showed that 48% pixels is observed to level off with the difference of tree cover rate ranged between -1 ~ 1% during 2000 and 2015. 13% pixels showed a high positive difference (>5%), mainly found in the eastern regions of USA, Russia and Canada, the central parts of China, where the country has focused its main reforestation efforts. While 4.9% pixels showed a high negative difference (< -5%), which were mainly distributed in the northwestern regions of South America (e.g. Columbia, Amazon rainforest), western parts of Africa (e.g. Cameroon, Equatorial Guinea, Congo), southern Asia (e.g. Indonesia, Cambodia), eastern areas of Australia, which was related to wildfires, logging, grazing and alternations in land use. 

D212- POSTER-0096: The characteristic of BVOCs emission and its effect on secondary formation in Pearl River Delta, China

Xuemei Wang1, Shuping Situ2, Weihua Chen3, Ming Chang1, Alex Guenther4

1Jinan University, Guangzhou, China 2Foshan Environmental Monitoring Center, Foshan, China 3Sun Yat-Sen University, Guangzhou, China 4University of California, Irvine, Irvine, The United States of America

BVOCs, as mainly emitted from natural terrestrial, interacts with anthropogenic emissions and affect atmospheric chemistry, and subsequently affect ozone and SOA formation, and ultimately air quality and climate change. This work uses MEGAN model coupled with WRF/Chem to investigate the spatial and temporal variation of BVOCs emission, and further to study its effect on ozone and SOA formation in Peal River Delta (PRD) region, one of the most developed regions in China. PRD is dominated by broadleaf trees (BT) with the cover rate of 25.1%, following by needleleaf trees (NT) with the value of 17.4%. In general, BVOCs mainly distributes in rural PRD with the total amount of 155.61×106 kg in Jan., Apr., Jul., and Oct., 2008, of which, isoprene and monoterpene are the major components with the proportion of 47.6% and 40.4% on average. BT is the dominant emitter for isoprene, and NT is the primary emitter for monoterpene, while BT and NT contribute comparably to sesquiterpene. Compared with anthropogenic VOCs (AVOCs), the total amount of BVOCs emission is relative lower but the BVOCs emission rate (ER) is much higher than AVOCs during daytime. Currently, MEGAN model could better estimate monoterpene emission flux but still overestimate isoprene flux derived from Relaxed Eddy Accumulation (REA) measurement, which is conducted in Dinghushan (DHS), PRD. Sensitivity analysis and Monte Carlo method are applied to study isoprene emission uncertainties deduced by input data, including meteorological parameters (MET), Leaf Area Index (LAI), Plant Functional Type (PFT) and Emission Factor (EF). Of which, EF for BT showed highest uncertainties, following by the total dependence on temperature and radiation and photosynthetically active radiation (PAR). BVOCs mainly impact ozone peak in downwind areas with the concentration as high as 25 ppb over PRD region, while BVOCs primarily influence BSOA in western and eastern rural PRD region.

D213 - POSTER-0352: Volatile organic compounds and ozone fluxes over an oilseed rape crop near Paris

Benjamin Loubet, Florence Lafouge, Pauline Buysse, Lais Gonzaga, Raluca Ciuraru, Céline Decuq, Olivier ZURFLUH , Alain Fortineau, Olivier Fanucci, Jean-Christophe Gueudet, François Truong, Christophe Boissard, Sabina Assan, Valérie Gros

Volatile organic compounds (VOC) play an essential role in atmospheric chemistry. VOCs are mainly emitted by plants and crops, which represent more than 50% of the surface in France, may contribute significantly to national emissions. From another point of view, ozone (O3) deposition to crops is deleterious and modifies the plant metabolism.  In this study, we analyze eddy covariance fluxes of VOCs and ozone over an oilseed rape field at the ICOS FR-GRI site near Paris, from April to July 2017. Concentration profiles and branch chambers measurements provide additional information on the locations of sources and sinks of VOCs. VOCs were measured using a PTR-TOF-Qi-MS (where Qi stands for Quadrupole Ion guide), while ozone was measured with a chemiluminescence analyser. We report fluxes for a large number VOCs masses. The sources and sinks of VOC in the canopy are interpreted in terms crop phenology and the potential for reaction with ozone and NOx is evaluated. This study takes place in the ADEME CORTEA COV3ER French project (http://www6.inra.fr/cov3er).