Corrigendum to “Seasonal variations of Quercus pubescens isoprene emissions from an in natura forest under drought stress and sensitivity to futureclimate change in the Mediterranean area”

International audienc

ECLAIRE third periodic report

The ÉCLAIRE project (Effects of Climate Change on Air Pollution Impacts and Response Strategies for European Ecosystems) is a four year (2011-2015) project funded by the EU's Seventh Framework Programme for Research and Technological Development (FP7)

ECLAIRE: Effects of Climate Change on Air Pollution Impacts and Response Strategies for European Ecosystems. Project final report

The central goal of ECLAIRE is to assess how climate change will alter the extent to which air pollutants threaten terrestrial ecosystems. Particular attention has been given to nitrogen compounds, especially nitrogen oxides (NOx) and ammonia (NH3), as well as Biogenic Volatile Organic Compounds (BVOCs) in relation to tropospheric ozone (O3) formation, including their interactions with aerosol components. ECLAIRE has combined a broad program of field and laboratory experimentation and modelling of pollution fluxes and ecosystem impacts, advancing both mechanistic understanding and providing support to European policy makers. The central finding of ECLAIRE is that future climate change is expected to worsen the threat of air pollutants on Europe’s ecosystems. Firstly, climate warming is expected to increase the emissions of many trace gases, such as agricultural NH3, the soil component of NOx emissions and key BVOCs. Experimental data and numerical models show how these effects will tend to increase atmospheric N deposition in future. By contrast, the net effect on tropospheric O3 is less clear. This is because parallel increases in atmospheric CO2 concentrations will offset the temperature-driven increase for some BVOCs, such as isoprene. By contrast, there is currently insufficient evidence to be confident that CO2 will offset anticipated climate increases in monoterpene emissions. Secondly, climate warming is found to be likely to increase the vulnerability of ecosystems towards air pollutant exposure or atmospheric deposition. Such effects may occur as a consequence of combined perturbation, as well as through specific interactions, such as between drought, O3, N and aerosol exposure. These combined effects of climate change are expected to offset part of the benefit of current emissions control policies. Unless decisive mitigation actions are taken, it is anticipated that ongoing climate warming will increase agricultural and other biogenic emissions, posing a challenge for national emissions ceilings and air quality objectives related to nitrogen and ozone pollution. The O3 effects will be further worsened if progress is not made to curb increases in methane (CH4) emissions in the northern hemisphere. Other key findings of ECLAIRE are that: 1) N deposition and O3 have adverse synergistic effects. Exposure to ambient O3 concentrations was shown to reduce the Nitrogen Use Efficiency of plants, both decreasing agricultural production and posing an increased risk of other forms of nitrogen pollution, such as nitrate leaching (NO3-) and the greenhouse gas nitrous oxide (N2O); 2) within-canopy dynamics for volatile aerosol can increase dry deposition and shorten atmospheric lifetimes; 3) ambient aerosol levels reduce the ability of plants to conserve water under drought conditions; 4) low-resolution mapping studies tend to underestimate the extent of local critical loads exceedance; 5) new dose-response functions can be used to improve the assessment of costs, including estimation of the value of damage due to air pollution effects on ecosystems, 6) scenarios can be constructed that combine technical mitigation measures with dietary change options (reducing livestock products in food down to recommended levels for health criteria), with the balance between the two strategies being a matter for future societal discussion. ECLAIRE has supported the revision process for the National Emissions Ceilings Directive and will continue to deliver scientific underpinning into the future for the UNECE Convention on Long-range Transboundary Air Pollution

Sensitivity of isoprene emissions from the terrestrial biosphere to 20th century changes in atmospheric CO2 concentration, climate, and land use

We describe the development and analysis of a global model based on Model of Emissions of Gases and Aerosols from Nature (MEGAN) (Guenther et al., 2006) for estimating isoprene emissions from terrestrial vegetation. The sensitivity of calculated isoprene emissions to descriptors including leaf age, soil moisture, atmospheric CO2 concentration, and regional variability of emission factors is analyzed. The validity of the results is evaluated by comparison with compilations of published field-based canopy-scale observations. Calculated isoprene emissions reproduce above-canopy flux measurements and the site-to-site variability across a wide range of latitudes, with the model explaining 60% of the variance. Although the model underestimates isoprene emissions, especially in northern latitude localities, this disagreement is significantly corrected when regional variability of emission factors for particular plant functional types is considered (r(2) = 0.78). At the global scale, we estimate a terrestrial biosphere isoprene flux of 413 TgC yr(-1) using the present-day climate, atmospheric CO2 concentration, and vegetation distribution, and this compares with other published estimates from global modeling studies of 402 to 660 TgC yr(-1). The validated model was used to calculate changes in isoprene emissions in response to atmospheric CO2 increase, climate change, and land use change during the 20th century (1901-2002). Changes in all of these factors are found to impact significantly on isoprene emissions over the course of the 20th century. Between 1901 and 2002, we estimate that at the global scale, climate change was responsible for a 7% increase in isoprene emissions, and rising atmospheric CO2 caused a 21% reduction. However, by the end of the 20th century (2002), anthropogenic cropland expansion has the largest impact reducing isoprene emissions by 15%. Overall, these factors combined to cause a 24% decrease in global isoprene emissions during the 20th century. It remains to be determined whether predicted 21st century warming and increased use of isoprene-emitting crops for biofuels ( e. g., oil palm) will more than offset any future CO2 suppression of isoprene emission rates

Global modelling of volatile organic compound emissions

The majority of volatile organic compounds emitted from the terrestrial biosphere (BVOCs) are highly reactive hydrocarbons that have been shown to affect atmospheric composition across the full range of temporal scales from fractions of seconds to centuries and spatial scales from μm to global. Furthermore, biogenic emissions are thought to account for around 90 % of the total quantity of non-methane hydrocarbons released into the atmosphere each year. As a result, BVOCs have substantial air quality and climate impacts, and there is an urgent need to quantify and map their emissions as precisely as possible. In this chapter we outline the use of computer models to estimate annual global emissions of BVOCs and the on-going efforts to validate and constrain the output from such models. The current generation of BVOC emission models generally includes only the constitutive emissions of a handful of compounds: chiefly isoprene, monoterpenes and methanol, which are thought to account for about 80 % of the total flux from the biosphere. At present, it is estimated by global models that total annual emission of isoprene amounts to around 500 Tg of carbon, with the emissions dominated by tropical ecosystems and by tree species. The emissions of monoterpenes are similarly distributed, although high levels of monoterpene emissions are also seen from the boreal forests. There is currently no consensus on the annual estimate of monoterpene emission, with estimates ranging from 30 to 150 Tg of carbon. Apart from these main compounds, the biosphere emits many hundreds of different compounds, some of which are produced as a short-lived, transient response to stress rather than as constitutive emissions. We discuss the role that biogenic emissions of reactive trace gases play in the Earth system as a whole, and consider the potential feedbacks that exist between BVOC emissions, atmospheric composition, air quality and climate, and the terrestrial biosphere, and how these can be studied with Earth system models. We finally suggest ways of improving and further developing the global models

Biogenic isoprene emissions, dry deposition velocity, and surface ozone concentration during summer droughts, heatwaves, and normal conditions in southwestern Europe

International audienceAt high concentration, tropospheric O3 deteriorates air quality, inducing adverse effects on human and ecosystem health. Meteorological conditions are key to understand the variability of O3 concentration, especially during extreme weather events. They modify the photochemistry activity and the vegetation state. An important source of uncertainties and inaccuracy in simulating surface O3 during droughts and heatwaves is the lack of interactions between the biosphere and the troposphere. Based on the biogenic emission model MEGANv2.1 and the chemistry-transport model CHIMERE v2020r1, the first objective of this study is to assess the sensitivity of biogenic emissions, O3 dry deposition and surface O3 to biomass decrease and soil dryness effect (using several configurations) during the extremely dry summer 2012. Secondly, this research aims at quantifying the variation of observed (EEA's air quality database, 2000-2016) and simulated (CHIMERE, 2012-2014) surface O3 during summer heatwaves and agricultural droughts that have been identified using the Percentile Limit Anomalies (PLA) method. Our sensitivity analysis shows that soil dryness is a key factor during drought events, decreasing considerably the C5H8 emissions and O3 dry deposition velocity. This effect has a larger impact than the biomass decrease. However, the resulting effect on surface O3 remains limited. Based on a cluster approach using the PLA indicator, we show that observed O3 concentration is on average significantly higher during heatwaves (+18µg/m3 in daily maximum) and droughts (+9µg/m 3) compared to normal conditions. Despite a difference of several µg/m3 , CHIMERE correctly simulates the variations of O3 concentration between the clusters of extreme events. The overall increase of surface O3 during both heatwaves and droughts would be explained by O3 precursor emission enhancement (in agreement with HCHO satellite observations), O3 dry deposition decrease and favourable weather conditions. However, we simulated a decrease of C5H8 emissions (in agreement with HCHO observations) during droughts not accompanied by a heatwave, resulting in a non-significant difference of surface O3 compared to normal conditions (from both observations and simulations)