1The global peat carbon pool exceeds that of global vegetation and is similar to the current 2 atmospheric carbon pool. Because fire is increasingly appreciated as a threat to peatlands 3 and their carbon stocks, here we review the controls on and effects of peat fires across 4 biomes. Peat fires are dominated by smouldering combustion, which ignites more easily 5 than flaming combustion and persists in wet conditions. In undisturbed peatlands, most of 6 the peat C stock typically is protected from smouldering, and resistance to fire has 7 increased peat carbon storage in boreal and tropical regions over long time scales. 8
As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%-85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
In this work, the kinetic parameters governing the thermal and oxidative degradation of flexible polyurethane foam are determined using thermogravimetric data and a genetic algorithm. These kinetic parameters are needed in the theoretical modeling of the foam's smoldering behavior.Experimental thermogravimetric mass-loss data are used to explore the kinetics of polyurethane foam and to propose a mechanism consisting of five reactions. A lumped model of solid mass-loss based on Arrhenius-type reaction rates and the five-step mechanism is developed to predict the polyurethane thermal degradation. The predictions are compared to the thermogravimetric measurements, and using a genetic algorithm, the method finds the kinetic and stoichiometric parameters that provide the best agreement between the lumped model and the experiments. To date, no study has attempted to describe both forward and opposed smolder-propagation with the same kinetic mechanism. Thus, in order to verify that the polyurethane kinetics determined from thermogravimetric experiments can be used to describe the reactions involved in polyurethane smoldering combustion, the five-step mechanism and its kinetic parameters are incorporated into a simple species model of smoldering combustion. It is shown that the species model agrees with experimental observations and that it captures phenomenologically the spatial distribution of the different species and the reactions in the vicinity of the front, for both forward and opposed propagation. The results indicate that the kinetic scheme proposed here is the first one to describe smoldering combustion of polyurethane in both propagation modes.
Moisture content can be a dominant factor affecting combustion especially in live fuels due to the wide range of moisture content that can be encountered with vegetation. Laboratory experiments are used to study the fire dynamics of Mediterranean Pinus halepensis needles under a range of fuel and flow conditions. A set of 80 experiments with good repeatability were conducted in the Fire Propagation Apparatus (FPA) fire calorimeter. The burning behavior is measured in terms of the evolution of the mass loss rate and the heat release rate from ignition till burn out for different forced flow velocities. Recently collected live and dead needles are compared here for the first time. Additionally, live samples aged for 15 months after collection are presented as an alternative to study changes in live needles. Two different moisture conditions are considered, fresh and oven-dry. The most flammable samples are fresh dead and 15 months aged needles, followed by oven-dry dead, and oven-dry live needles. The least flammable is fresh live needles. Overall, the results show that fire physics and chemistry vary with the fuel and flow conditions, and that moisture content is not the only difference between live and dead fuels, but that the needle bed physicochemical mechanisms matters as well. The loss of volatiles and other changes induced during oven drying is seen to lead to significant differences in the burning behavior.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.