PEER-REVIEWED ARTICLE bioresources.com González et al. (2017). “Oat hull biochar,” BioResources 12(1), 2040-2057. 2040 Effects of Pyrolysis Conditions on Physicochemical Properties of Oat Hull Derived Biochar María Eugenia González, a, * Luis Romero-Hermoso, b Aixa González, a Pamela Hidalgo, b Sebastian Meier, b,c Rodrigo Navia, b,d,e and Mara Cea b,d The effects of the pyrolysis conditions in terms of temperature (400 to 600 °C), residence time (0.5 to 3.5 h), nitrogen flux (0 to 1 L/min), and temperature increase rate (1.5 to 3 °C/min) on the physicochemical properties of biochar were studied. The physicochemical properties evaluated in the biochar were specific surface area, pore volume, average pore size, total carbon content, pH, total acidity, elemental composition, and polycyclic aromatic hydrocarbons (PAHs) content. A higher specific surface area of 108.28 m 2 /g and a mean pore size diameter of about 2.24 nm were found when the pyrolysis was conducted at 600 °C. In general, the pH and total acidity increased with the increased pyrolysis temperature. The total PAH concentration in all of the combinations studied varied from 0.16 to 8.73 μg/kg, and only phenanthrene, pyrene, and chrysene were detected. The increased temperature seemed to decrease the PAH concentration in the biochar. Nevertheless, there was no correlation found between the PAH content and the combined evaluated parameters. Keywords: Pyrolysis conditions; Biochar; Physicochemical properties; Polycyclic aromatic hydrocarbons Contact information: a: Núcleo de Investigación en Bioproductos y Materiales Avanzados (BioMA), Dirección de Investigación, Universidad Católica de Temuco, Temuco, Chile; b: Scientific and Technological Bio Resources Nucleus-BIOREN, University of La Frontera, Av. Francisco Salazar 01145, Temuco, Chile; c: Instituto Nacional de Investigaciones Agropecuarias. INIA Carillanca, Casilla Postal 58-D Temuco, Chile; d: Department of Chemical Engineering, University of La Frontera, Av. Francisco Salazar 01145, Temuco, Chile; e: Centre for Biotechnology & Bioengineering (CeBiB), University of La Frontera, Av. Francisco Salazar 01145, Temuco, Chile; * Corresponding author: mgonzalez@uct.cl INTRODUCTION In recent years, the number of biochar publications has increased rapidly, with a number of studies evaluating the physical and chemical characteristics of biochar used as a soil amendment (Novak et al. 2009; Biederman and Harpole 2013), soil remediator (Qin et al. 2013; Waqas et al. 2014), raw material for catalyst development (Dehkhoda and Ellis 2013), modifier agent in the controlled release formulations of nutrients (González et al. 2015), and immobilization support (González et al. 2013). The physicochemical properties of biochar, such as pore diameter, size distribution, total surface area, and nutrient content, are closely related to the pyrolysis conditions and the original biomass feedstock (Chen et al. 2014; Manyà et al. 2014). The pyrolysis temperature causes chemical and physical changes to the feedstock, such as decreasing the H/C, O/C, and (N+O)/C ratios. For example, high temperatures increase the specific surface area (Devi and Saroha 2015) but decrease the amount of biochar produced, and they cause demethylation and decarboxylation reactions that result in high amounts of carbonized and aromatic structures (Chen et al. 2014; Devi and Saroha 2015).