Global and regional impacts of land cover changes on isoprene emissions derived from spaceborne data and the MEGAN model

Abstract. Among the biogenic volatile organic compounds (BVOCs) emitted by plant foliage, isoprene is by far the most important in terms of both global emission and atmospheric impact. It is highly reactive in the air, and its degradation favours the generation of ozone (in the presence of NOx) and secondary organic aerosols. A critical aspect of BVOC emission modelling is the representation of land use and land cover (LULC). The current emission inventories are usually based on land cover maps that are either modelled and dynamic or satellite-based and static. In this study, we use the state-of-the-art Model of Emissions of Gases and Aerosols from Nature (MEGAN) model coupled with the canopy model MOHYCAN (Model for Hydrocarbon emissions by the CANopy) to generate and evaluate emission inventories relying on satellite-based LULC maps at annual time steps. To this purpose, we first intercompare the distribution and evolution (2001–2016) of tree coverage from three global satellite-based datasets, MODerate resolution Imaging Spectroradiometer (MODIS), ESA Climate Change Initiative Land Cover (ESA CCI-LC), and the Global Forest Watch (GFW), and from national inventories. Substantial differences are found between the datasets; e.g. the global areal coverage of trees ranges from 30 to 50×106 km2, with trends spanning from −0.26 to +0.03 % yr−1 between 2001 and 2016. At the national level, the increasing trends in forest cover reported by some national inventories (in particular for the US) are contradicted by all remotely sensed datasets. To a great extent, these discrepancies stem from the plurality of definitions of forest used. According to some local censuses, clear cut areas and seedling or young trees are classified as forest, while satellite-based mappings of trees rely on a minimum height. Three inventories of isoprene emissions are generated, differing only in their LULC datasets used as input: (i) the static distribution of the stand-alone version of MEGAN, (ii) the time-dependent MODIS land cover dataset, and (iii) the MODIS dataset modified to match the tree cover distribution from the GFW database. The mean annual isoprene emissions (350–520 Tg yr−1) span a wide range due to differences in tree distributions, especially in isoprene-rich regions. The impact of LULC changes is a mitigating effect ranging from 0.04 to 0.33 % yr−1 on the positive trends (0.94 % yr−1) mainly driven by temperature and solar radiation. This study highlights the uncertainty in spatial distributions of and temporal variability in isoprene associated with remotely sensed LULC datasets. The interannual variability in the emissions is evaluated against spaceborne observations of formaldehyde (HCHO), a major isoprene oxidation product, through simulations using the global chemistry transport model (CTM) IMAGESv2. A high correlation (R > 0.8) is found between the observed and simulated interannual variability in HCHO columns in most forested regions. The implementation of LULC change has little impact on this correlation due to the dominance of meteorology as a driver of short-term interannual variability. Nevertheless, the simulation accounting for the large tree cover declines of the GFW database over several regions, notably Indonesia and Mato Grosso in Brazil, provides the best agreement with the HCHO column trends observed by the Ozone Monitoring Instrument (OMI). Overall, our study indicates that the continuous tree cover fields at fine resolution provided by the GFW database are our preferred choice for constraining LULC (in combination with discrete LULC maps such as those of MODIS) in biogenic isoprene emission models.

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Global and regional impacts of land cover changes on isoprene emissions derived from spaceborne data and the MEGAN model

10.5194/acp-2021-95 ◽

2021 ◽

Author(s):

Beata Opacka ◽

Jean-François Müller ◽

Trissevgeni Stavrakou ◽

Maite Bauwens ◽

Katerina Sindelarova ◽

...

Keyword(s):

Land Cover ◽

Interannual Variability ◽

Transport Model ◽

National Level ◽

Remotely Sensed ◽

Tree Cover ◽

Emission Inventories ◽

Mato Grosso ◽

Wide Range ◽

The Impact

Abstract. Among the biogenic volatile organic compounds (BVOCs) emitted by plant foliage, isoprene is by far the most important in terms of both global emission and atmospheric impact. It is highly reactive in the air, and its degradation favours the generation of ozone (in presence of NOx) and secondary organic aerosols. A critical aspect of BVOC emission modelling is the representation of land use and land cover (LULC). The current emission inventories are usually based on land cover maps that are either modelled and dynamic or satellite-based and static. In this study, we use the state-of-the-art MEGAN model coupled with the canopy model MOHYCAN to generate and evaluate emission inventories relying on satellite-based LULC maps at annual time steps. To this purpose, we first intercompare the distribution and evolution (2001–2016) of tree coverage from three global satellite-based datasets, MODIS, ESA CCI-Land Cover (ESA CCI-LC) and the Global Forest Watch (GFW), and from national inventories. Substantial differences are found between the datasets, e.g. the global areal coverage of trees ranges from 30 to 50 Mkm2, with trends spanning from −0.26 % yr−1 to +0.03 % yr−1 between 2001 and 2016. At national level, the increasing trends in forest cover reported by some national inventories (in particular for the US) are contradicted by all remotely-sensed datasets. Three inventories of isoprene emissions are generated, differing only in their LULC datasets used as input: (i) the static distribution of the stand-alone version of MEGAN, (ii) the time-dependent MODIS land cover dataset, and (iii) the MODIS dataset modified to match the tree cover distribution from the GFW database. The mean annual isoprene emissions (350–520 Tg yr−1) span a wide range due to differences in tree distributions, especially in isoprene-rich regions. The impact of LULC changes is a mitigating effect ranging from 0.04 to 0.33 % yr−1 on the positive trends (0.94 % yr−1) mainly driven by temperature and solar radiation. This study highlights the uncertainty in spatial distributions and temporal variability of isoprene associated to remotely-sensed LULC datasets. The interannual variability of the emissions is evaluated against spaceborne observations of formaldehyde (HCHO), a major isoprene oxidation product, through simulations using the global chemistry-transport model (CTM) IMAGESv2. A high correlation (R > 0.8) is found between the observed and simulated interannual variability of HCHO columns in most forested regions. The implementation of LULC change has little impact on this correlation, due to the dominance of meteorology as driver of short-term interannual variability. Nevertheless, the simulation accounting for the large tree cover declines of the GFW database over several regions, notably Indonesia and Mato Grosso in Brazil, provides the best agreement with the HCHO column trends observed by OMI. Overall, our study indicates that the continuous tree cover fields at fine resolution provided by the GFW database are our preferred choice for constraining LULC (in combination with discrete LULC maps such as those of MODIS) in biogenic isoprene emission models.

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Comparison of Regional Simulation of Biospheric CO2 Flux from the Updated Version of CarbonTracker Asia with FLUXCOM and Other Inversions over Asia

Remote Sensing ◽

10.3390/rs12010145 ◽

2020 ◽

Vol 12 (1) ◽

pp. 145 ◽

Cited By ~ 3

Author(s):

Samuel Takele Kenea ◽

Lev D. Labzovskii ◽

Tae-Young Goo ◽

Shanlan Li ◽

Young-Suk Oh ◽

...

Keyword(s):

Land Cover ◽

Interannual Variability ◽

Tropical Forests ◽

Transport Model ◽

Southern Oscillation ◽

Carbon Sink ◽

Mixed Forest ◽

Atmospheric Composition ◽

Carbon Uptake ◽

The Impact

There are still large uncertainties in the estimates of net ecosystem exchange of CO2 (NEE) with atmosphere in Asia, particularly in the boreal and eastern part of temperate Asia. To understand these uncertainties, we assessed the CarbonTracker Asia (CTA2017) estimates of the spatial and temporal distributions of NEE through a comparison with FLUXCOM and the global inversion models from the Copernicus Atmospheric Monitoring Service (CAMS), Monitoring Atmospheric Composition and Climate (MACC), and Jena CarboScope in Asia, as well as examining the impact of the nesting approach on the optimized NEE flux during the 2001–2013 period. The long-term mean carbon uptake is reduced in Asia, which is −0.32 ± 0.22 PgC yr−1, whereas −0.58 ± 0.26 PgC yr−1 is shown from CT2017 (CarbonTracker global). The domain aggregated mean carbon uptake from CTA2017 is found to be lower by 23.8%, 44.8%, and 60.5% than CAMS, MACC, and Jena CarboScope, respectively. For example, both CTA2017 and CT2017 models captured the interannual variability (IAV) of the NEE flux with a different magnitude and this leads to divergent annual aggregated results. Differences in the estimated interannual variability of NEE in response to El Niño–Southern Oscillation (ENSO) may result from differences in the transport model resolutions. These inverse models’ results have a substantial difference compared to FLUXCOM, which was found to be −5.54 PgC yr−1. On the one hand, we showed that the large NEE discrepancies between both inversion models and FLUXCOM stem mostly from the tropical forests. On the other hand, CTA2017 exhibits a slightly better correlation with FLUXCOM over grass/shrub, fields/woods/savanna, and mixed forest than CT2017. The land cover inconsistency between CTA2017 and FLUXCOM is therefore one driver of the discrepancy in the NEE estimates. The diurnal averaged NEE flux between CTA2017 and FLUXCOM exhibits better agreement during the carbon uptake period than the carbon release period. Both CTA2017 and CT2017 revealed that the overall spatial patterns of the carbon sink and source are similar, but the magnitude varied with seasons and ecosystem types, which is mainly attributed to differences in the transport model resolutions. Our findings indicate that substantial inconsistencies in the inversions and FLUXCOM mainly emerge during the carbon uptake period and over tropical forests. The main problems are underrepresentation of FLUXCOM NEE estimates by limited eddy covariance flux measurements, the role of CO2 emissions from land use change not accounted for by FLUXCOM, sparseness of surface observations of CO2 concentrations used by the assimilation systems, and land cover inconsistency. This suggested that further scrutiny on the FLUXCOM and inverse estimates is most likely required. Such efforts will reduce inconsistencies across various NEE estimates over Asia, thus mitigating ecosystem-driven errors that propagate the global carbon budget. Moreover, this work also recommends further investigation on how the changes/updates made in CarbonTracker affect the interannual variability of the aggregate and spatial pattern of NEE flux in response to the ENSO effect over the region of interest.

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Evaluating the impact of different spaceborne land cover distributions on isoprene emissions and their trends using the MEGAN model.

10.5194/egusphere-egu2020-15832 ◽

2020 ◽

Author(s):

Beata Opacka ◽

Jean-François Müller ◽

Jenny Stavrakou ◽

Maite Bauwens ◽

Alex B. Guenther

Keyword(s):

Land Cover ◽

Degradation Products ◽

Input Parameter ◽

Remotely Sensed ◽

Atmospheric Composition ◽

Tree Cover ◽

Biogenic Emissions ◽

Large Variability ◽

Community Land Model ◽

The Impact

The biogenic volatile organic compounds (BVOCs) are emitted globally at about 1100 Tg per year of which almost half of the share is entailed by isoprene. Isoprene is highly reactive in the atmosphere, and its degradation products impact the atmospheric composition through the generation of ozone (in presence of NOx typical of polluted areas) and secondary organic aerosols, and may pose a risk to human health. Isoprene is mainly emitted by plant foliage, with trees being the major contributors due to their relatively high emission factors.In the modelling framework of biosphere-atmosphere interactions, the representation of land cover and vegetation distributions is a key aspect. We use the state-of-the-art biogenic emission model MEGAN (Guenther et al. 2012) coupled with a multi-layer canopy model MOHYCAN (M&#252;ller et al. 2008) to estimate isoprene emissions on the global scale. In its current standard version, the model uses a static plant functional type (PFT) distribution obtained from the Community Land Model (CLM4) for 2000. Our objective is to replace the static map by time-dependent PFT distributions based on satellite global land cover maps, and estimate the resulting biogenic emissions over 2001-2018. To this purpose, we use either the MODIS land cover dataset (Friedl and Sulla-Menashe, 2019), or the MODIS dataset modified to account for tree cover changes from Hansen et al. (2013). Comparisons with the ESA-CCI dataset (Poulter et al. 2015) and the FAOSTAT (www.fao.org) database are performed and the trends over large forested regions are discussed. The comparisons show a large variability in the representation of the tree cover by the available remotely-sensed datasets, leading to different spatial distributions and temporal variability in the estimated isoprene emissions. This gives a measure of the uncertainty associated to this input parameter. This work is conducted in the frame of the ALBERI project that aims at assessing links between biogenic emissions and remotely-sensed photosynthesis indicators, funded by BELSPO through the STEREO III programme.&#160;&#160;

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Analysis of Land Use Land Cover in Annapurna Conservation Area in Gandaki Province, Nepal using Vegetation Index and Land Use Land Cover Datasets

10.21523/gcj5.18020204 ◽

2019 ◽

Vol 2 (2) ◽

pp. 87-99

Author(s):

Shiva Pokhrel ◽

Chungla Sherpa

Keyword(s):

Land Use ◽

Land Cover ◽

Vegetation Index ◽

National Level ◽

Climate Mitigation ◽

Land Use Land Cover ◽

Conservation Area ◽

Barren Land ◽

Wide Range ◽

Annapurna Conservation Area

Conservation areas are originally well-known for protecting landscape features and wildlife. They are playing key role in conserving and providing a wide range of ecosystem services, social, economic and cultural benefits as well as vital places for climate mitigation and adaptation. We have analyzed decadal changes in land cover and status of vegetation cover in the conservation area using both national level available data on land use land cover (LULC) changes (1990-2010) and normalized difference vegetation index (NDVI) (2010-2018) in Annapurna conservation area. LULC showed the barren land as the most dominant land cover types in all three different time series 1990, 2000 and 2010 with followed by snow cover, grassland, forest, agriculture and water body. The highest NDVI values were observed at Southern, Southwestern and Southeastern part of conservation area consisting of forest area, shrub land and grassland while toward low to negative in the upper middle to the Northern part of the conservation area.

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The EU as an “enforcement patchwork”: the impact of national enforcement for compliance with EU water law in Spain and Britain

Journal of Public Policy ◽

10.1017/s0143814x13000238 ◽

2013 ◽

Vol 34 (2) ◽

pp. 331-353 ◽

Cited By ~ 3

Author(s):

Mónica García Quesada

Keyword(s):

Waste Water Treatment ◽

National Level ◽

State Level ◽

Detailed Examination ◽

Deterrent Effect ◽

Eu Law ◽

Wide Range ◽

The Uk ◽

The Impact ◽

The Eu

AbstractFailures of compliance with European Union (EU) directives have revealed the EU as a political system capable of enacting laws in a wide range of different policy areas, but facing difficulties to ensure their actual implementation. Although the EU relies on national enforcement agencies to ensure compliance with the EU legislation, there is scarce analysis of the differential deterrent effect of national enforcement in EU law compliance. This article examines the enforcement of an EU water directive, the Urban Waste Water Treatment Directive, in Spain and the UK. It focuses on the existing national sanctions for disciplining actors in charge of complying with EU requirements, and on the actual use of punitive sanctions. The analysis shows that a more comprehensive and active disciplinary regime at the national level contributes to explain a higher degree of compliance with EU law. The article calls for a detailed examination of the national administrative and criminal sanction system for a more comprehensive understanding of the incentives and disincentives to comply with EU law at the national state level.

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The Impact of Land Cover Change on Surface Energy and Water Balance in Mato Grosso, Brazil

Earth Interactions ◽

10.1175/ei176.1 ◽

2006 ◽

Vol 10 (19) ◽

pp. 1-17 ◽

Cited By ~ 40

Author(s):

Julia Pongratz ◽

Lahouari Bounoua ◽

Ruth S. DeFries ◽

Douglas C. Morton ◽

Liana O. Anderson ◽

...

Keyword(s):

Land Use ◽

Surface Energy ◽

Land Cover ◽

Morphological Changes ◽

Canopy Temperature ◽

Surface Fluxes ◽

Evergreen Forest ◽

Wet Season ◽

Mato Grosso ◽

The Impact

Abstract The sensitivity of surface energy and water fluxes to recent land cover changes is simulated for a small region in northern Mato Grosso, Brazil. The Simple Biosphere Model (SiB2) is used, driven by biophysical parameters derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) at 250-m resolution, to compare the effects of different land conversion types. The mechanisms through which changes in vegetation alter surface fluxes of energy, momentum, water, and carbon are analyzed for both wet and dry seasons. It is found that morphological changes contribute to warming and drying of the atmosphere while physiological changes, particularly those associated with a plant’s photosynthetic pathway, counterbalance or exacerbate the warming depending on the type of conversion and the season. Furthermore, this study’s results indicate that initial clearing of evergreen and transition forest to bare ground increases canopy temperature by up to 1.7°C. For subsequent land use such as pasture or cropland, the largest effect is seen for the conversion of evergreen forest to C3 cropland during the wet season, with a 21% decrease of the latent heat flux and 0.4°C increase in canopy temperature. The secondary conversion of pasture to cropland resulted in slight warming and drying during the wet season driven mostly by the change in carbon pathway from C4 to C3. For all conversions types, the daily temperature range is amplified, suggesting that plants replacing forest clearing require more temperature tolerance than the trees they replace. The results illustrate that the effect of deforestation on climate depends not only on the overall extent of clearing but also on the subsequent land use type.

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Detecting the impact of land cover change on observed rainfall

PeerJ ◽

10.7717/peerj.7523 ◽

2019 ◽

Vol 7 ◽

pp. e7523 ◽

Cited By ~ 1

Author(s):

Chun Xia Liang ◽

Floris F. van Ogtrop ◽

R. Willem Vervoort

Keyword(s):

Land Cover ◽

Land Cover Change ◽

Large Scale ◽

Southern Oscillation ◽

Rainfall Variability ◽

Tree Cover ◽

Trend Test ◽

South Central ◽

The Impact ◽

Step Trend

Analysis of observational data to pinpoint impact of land cover change on local rainfall is difficult due to multiple environmental factors that cannot be strictly controlled. In this study we use a statistical approach to identify the relationship between removal of tree cover and rainfall with data from best available sources for two large areas in Australia. Gridded rainfall data between 1979 and 2015 was used for the areas, while large scale (exogenous) effects were represented by mean rainfall across a much larger area and climatic indicators, such as Southern Oscillation Index and Indian Ocean Dipole. Both generalised additive modelling and step trend tests were used for the analysis. For a region in south central Queensland, the reported change in tree clearing between 2002–2005 did not result in strong statistically significant precipitation changes. On the other hand, results from a bushfire affected region on the border of New South Wales and Victoria suggest significant changes in the rainfall due to changes in tree cover. This indicates the method works better when an abrupt change in the data can be clearly identified. The results from the step trend test also mainly identified a positive relationship between the tree cover and the rainfall at p < 0.1 at the NSW/Victoria region. High rainfall variability and possible regrowth could have impacted the results in the Queensland region.

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Family structure and affluence in adolescent eating behaviour: a cross-national study in forty-one countries

Public Health Nutrition ◽

10.1017/s1368980020003584 ◽

2020 ◽

pp. 1-12

Author(s):

Apolinaras Zaborskis ◽

Monika Grincaitė ◽

Aistė Kavaliauskienė ◽

Riki Tesler

Keyword(s):

Family Structure ◽

National Level ◽

Eating Behaviour ◽

Soft Drinks ◽

National Study ◽

Family Affluence ◽

Intact Family ◽

Wide Range ◽

The Impact ◽

Cross National

Abstract Objective: To investigate the family structure and affluence-related inequality in adolescent eating behaviour. Design: Multivariate binary logistic regression and path analyses were employed to evaluate the impact of family structure and affluence on the consumption of fruits, vegetables, sweets and soft drinks among adolescents. Setting: The cross-national Health Behaviour in School-aged Children study in 2013/2014 across forty-one countries. Participants: Adolescents aged 11–15 years old (n 192 755). Results: Adolescents from a non-intact family were less likely to eat daily fruits (OR 0·82; 95 % CI 0·80, 0·84), vegetables (OR 0·91; 95 % CI 0·89, 0·93) and sweets (OR 0·96; 95 % CI 0·94, 0·99), but were more likely to consume soft drinks (OR 1·14; 95 % CI 1·11, 1·17), compared with their counterparts from an intact family. Adolescents who had the lowest family affluence scores (FAS) were less likely to eat daily fruits (OR 0·51; 95 % CI 0·49, 0·53), vegetables (OR 0·58; 95 % CI 0·56, 0·60) and sweets (OR 0·94; 95 % CI 0·90, 0·97), but were more likely to consume soft drinks (OR 1·25; 95 % CI 1·20, 1·30), compared with their counterparts who had the highest FAS. Across countries, a wide range of social inequality in daily consumption of foods was observed. Conclusions: Among adolescents in Europe, Canada and Israel, there was a high level of family structure and family affluence inequalities in daily food consumption. Different aspects of family socio-economic circumstances should be considered at the national level designing effective interventions to promote healthy eating among adolescents.

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The European Court of Human Rights Interptetation of Migrants Cases: Basic Doctrinal Approaches

Право України ◽

10.33498/louu-2019-06-132 ◽

2019 ◽

pp. 132

Author(s):

SVITLANA KARVATSKA

Keyword(s):

Human Rights ◽

Comparative Method ◽

National Level ◽

Migration Policy ◽

Practical Consideration ◽

European Court ◽

Wide Range ◽

Migrants Rights ◽

The Right ◽

The Impact

The doctrinal substantiation of the practical consideration of precedents in relation to ensuring and violating the migrants’ rights is in sight of the representatives of various field of science. It is also a subject of complex international legal, political, historical, economic, demographic, anthropological and social studies. However, a rapid dynamic development, caused by various factors in migration processes, and its institutionalization requires picky and thorough scientific analysis of some important issues such as the migration problem, the impact of the right to migrate, political and rational incentives for migration, consideration of the interpretation of such cases by the European Court of Human Rights (ECtHR) for a further and comprehensive settlement of migration policy on both European and national level. Although particular steps are being taken to create a sustainable regulatory framework for the recognition and assurance of human rights in response to current challenges and to systemic drawbacks of the national human rights mechanism – the problems of migration and asylum are very urgent and thorny. The purpose of the article is to analyse doctrinal approaches and legal positions of the ECtHR in the process of interpretation in the field of migration. The use of the research methodology was caused by the specifics of the study subject. The comprehensive approach to analysis, which combines a wide range of philosophical, general scientific, special scientific and legal methods, served as a research basis. Thus, the dialectical method has allowed substantiating a regular nature of the formation of an evolutionary approach to the interpretation of ECtHR judgments. The anthropological approach emphasized on the place and role of man in the process of legal interpretation. With the help of the hermeneutic method, the concept of the categories “migrant”, “migrants’ rights”, “asylum”, as well as the content of the doctrinal approaches and legal positions of the Court were disclosed, while a systematic method reflected the interrelationship between them. The statistical method made it possible to quantitatively synthesize the case law of the ECtHR in the field of migration and asylum. The use of the comparative method allowed to carry out a comparative analysis of doctrinal approaches employed by the Court in considering various categories of migration issues in different periods of its activities. It is proved that the ECtHR uses many doctrinal approaches, the Court emphasizes on the need to adhere to the principle of wide margin of appreciation. In cases of deportation of foreigners convicted of a criminal offense, the Court is guided by the principle of proportionality. Most of the cases examined by the ECtHR concerning migrants are related to the provision of asylum. The interpretation activities of the Court are focused on identifying barriers to asylum and formulating the principle of prohibition of dismissal, if the asylum seeker was forced to leave his country caused by various circumstances such as humanitarian crisis, non-selective violence, real threat / danger, denial of justice, or unlawful detention or conviction by a manifestly unfair trial in country of residence, or procedural violations against migrants and etc. The ECtHR has also focused on assessing the risks of not granting asylum, in particular, harsh treatment and has formulated the predominance principle of the child’s extraordinary vulnerability, which prevails over the status of the illegal stay presence as a foreigner on the territory of the state

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Simulation of SOA formation in the Landes pine forest in south-western France, relative weight of initial ozone, NO3 and OH attack ?

10.5194/egusphere-egu2020-19763 ◽

2020 ◽

Author(s):

Arineh Cholakian ◽

Matthias Beekmann ◽

Isabelle Coll ◽

Pierre-Marie Flaud ◽

Emilie Perraudin ◽

...

Keyword(s):

High Resolution ◽

Land Cover ◽

Forest Canopy ◽

Transport Model ◽

Relative Weight ◽

Organic Aerosol ◽

Canopy Effect ◽

Concentration Changes ◽

Set Up ◽

The Impact

Organic aerosol (OA) still remains one of the most difficult components of the aerosol to simulate, given the multitude of its formation precursors, the uncertainty of its formation pathways and the lack of measurements of its detailed composition. The LANDEX project (The LANDes Experiment), during its intensive field campaign in summer 2017, gives us the opportunity to compare a detailed list of measurements (VOC, NOx, radicals including NO3, aerosol components, &#8230;) obtained within and above the Landes forest canopy, to simulations performed with CHIMERE, a regional Chemistry-Transport Model. The Landes forest is situated in the south-western part of France, and is one of the largest anthropized forest in Europe (1 million ha), composed by a majority of maritime pine trees, strong terpene emitters, providing a large potential for biogenic SOA formation.In order to simulate organic aerosol build-up in this area, the set-up of a specific model configuration, adapted to local peculiarities, was necessary. As the forest is inhomogeneous, with interstitial agricultural fields, high-resolution 1 km simulations over the forest area were performed, imbedded into a 5 km resolved French and a 25 km resolved European domains. BVOC emissions were predicted by MEGAN, but specific land cover needed to be used, chosen from the comparison of several high-resolution land-cover databases. Also, the tree species distribution needed updated for the specific conditions of the Landes forest. In order to understand the canopy effect in the forest, sensitivity tests were also performed and the diffusivity between the first two layers were changed. The impact of each of these refinements with respect to the standard model set-up on the concentration changes of biogenic VOCs and organic aerosol was calculated and compared to observations. In addition, the sensitivity of SOA build-up with respect to the organic aerosol scheme (standard scheme within CHIMERE, VBS schemes with updated yields for OA formation from BVOCs, &#8230;) was assessed.The ensemble of simulations allowed tracing back the origin of BSOA build-up within and above the Landes forest canopy. Above the canopy, the major simulated pathway of SOA formation is monoterpene oxidation by NO3, while within the canopy, for sufficiently low mixing during nighttime, the NO3 radical is suppressed and only little contributes to SOA build-up. This is in accordance to observations and reactivity considerations which show that within the canopy, ozone attack on sesquiterpenes is the major nighttime SOA source. &#160;

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