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Modelling Arctic Biogenic Volatile Organic Compounds emissions (MABVOC)

Periodic Reporting for period 1 - MABVOC (Modelling Arctic Biogenic Volatile Organic Compounds emissions (MABVOC))

Reporting period: 2016-12-01 to 2018-11-30

Biogenic volatile organic compounds (BVOCs), emitted from living organisms (mainly plants), are reactive and have significant effects on the air quality, climate and ecosystem processes. BVOCs influence the climate system through lengthening the lifetime of methane (a potent greenhouse gas), changing atmospheric ozone concentration (air pollutant and also greenhouse gas), and increasing secondary organic aerosol (SOA, influencing the solar radiation received by the Earth). The Arctic is warming at twice the global rate, and the warming-included drastic changes in plants and permafrost can result in substantial impacts on the BVOC emissions. Recent field and lab observations from the Arctic indicate that BVOC emissions from arctic plants are particularly sensitive to climate warming. In addition, warming-induced permafrost thaw can also release large amounts of BVOCs. All these observed features related to arctic BVOC emissions from plants and soils have not been considered in the state-of-the-art model estimates. This project added these plant-related emission features into a process-based ecosystem model, LPJ-GUESS, and addressed the importance of these features in terms of estimating pan-Arctic plant BVOC emissions. To estimate BVOC emissions from soils (further focus on permafrost soil), this project summarized the current process understanding about soil BVOCs and proposed a framework for adding soil BVOC processes in large-scale models.

The recent report Global Warming of 1.5 ºC, issued by the Intergovernmental Panel on Climate Change (IPCC), stated the goal of limiting global warming of 1.5 ºC above pre-industrial levels and stressed the global response to the threat of climate change. The society emphasis on climate change focuses on how the climate will change in the next few decades and also on how we can adapt to these changes. This project seeks to solve one of the key puzzles in understanding the role of the Arctic in regional and global climate systems, which can contribute to improve the predictions of the extent of climate warming and associated changes. The climate models suggest a continuous warming in the Arctic. The amplified warming in the Arctic will result in large losses of ice and snow, which not only pose threats to local people’s livelihoods, customs and infrastructure, but also contribute to the sea-level rise around the world. Fundamental studies devoted to process understanding of arctic ecosystems and their feedbacks to the climate system in the context of climate warming are of utmost societal important at the local and global levels. This project tackles poorly-understood issues about BVOC emissions from the arctic plants and soils; therefore, it can provide missing but essential data to quantify BVOC feedbacks to atmospheric chemistry and also reduce models’ uncertainties in predicting regional climate change.

The overall objective of this project is to first explicitly incorporate arctic BVOC dynamics based on field observations into a large-scale ecosystem model, LPJ-GUESS, and thereafter apply the developed model to estimate and predict of BVOC emissions over the pan-Arctic region.
This project included three working packages (WPs) and at the end it totally ran for 13 months (of the original 24). In total, this project delivered one submitted manuscript and one extended publication, and two more publications will be delivered afterwards.
In WP1, I did a thorough literature review about current process understanding of soil BVOCs, and proposed a framework for modelling soil BVOCs in large-scale ecosystem models. Through the literature review, I summarized the often-reported chemical compounds released from soil, collected published data about measured soil BVOC fluxes, reviewed the mathematical approaches used for modelling ecosystem gas fluxes in a general term, and came up a framework which can be used for soil BVOC modelling. All this information has been described in the submitted review article.
In WP2, I compiled a new list of arctic plant function types (PFTs) based on plant BVOC emission diversity, and assigned leaf-level emission capacity values for the new list of PFTs following the measurement data. A new temperature response curve for arctic plants’ emissions was extracted from the field data, which can better capture the observed high temperature sensitivity. Meanwhile, I also implemented a leaf-level energy balance module in LPJ-GUESS to account for the decoupling of leaf temperature from air temperature. All implementation/coding work of these abovementioned features in the WP2 has been conducted. In the WP2, I also analyzed unpublished data about plant emissions in response to 3 and 13 years of warming in subarctic tundra ecosystems, which led to an additional publication.
In WP3, the plan is to quantify net BVOC emission over the pan-Arctic, assess differences across different large-scale models and predict future changes in response to climate change. So far, I finished the historical and future simulations of plant BVOC emission from this region and some of the simulations about pan-Arctic plant BVOC emissions have been included in a cross-site data-model integration manuscript led by Prof. Rinnan.
The current regional/global estimations of terrestrial ecosystem emissions assume that vegetation is the main BVOC emitter, and there are no considerations of soil uptake and emission of BVOCs. However, many field and lab studies have reported potentially high emissions from soils (including litter, root and soil organic matter) as well as uptake of atmospheric BVOCs by soil microbes. Moreover, soil emissions of BVOC could be especially important to consider in the Arctic where the highly organic soils harbor massive amounts of carbon. In WP1, we summarized the current knowledge about soil BVOCs, and concluded with a list of compounds and processes that could be of interest to consider in models. The modelling framework we proposed is an important step for initiating modelling exercises on soil BVOC fluxes, which are currently not accounted for in large-scale ecosystem models.
Recent observations found that several arctic plants can have high BVOC emission potentials possibly due to the important role of emitted compounds in stress resistance and adaption to extreme conditions. Moreover, BVOC emissions from arctic plants are found to be highly temperature sensitive. In addition, the field observations found that the canopy/leaf temperature that arctic plants experience can be much higher than the often-measured air temperature at 2 m height under sunny conditions. Until this project, the existing regional/global estimations of terrestrial ecosystem emissions assume that BVOC emissions from the Arctic are ignorable; however, these estimations were limited to include the observed emission features, e.g. high emission potentials and temperature sensitivity, decoupling of leaf-air temperature. In WP2, we highlighted the importance of including these observed features about arctic plant emissions into the LPJ-GUESS and updated the regional emission numbers.
The final results from this project will improve the current estimations of net ecosystem BVOC fluxes over the pan-Arctic region and thus the feedbacks to the climate system. This level of information is important not only for researchers, but also for the society to better understand how the arctic climate will change in future.
Summary about this project