Summary

• Forest residues are non-merchantable woody biomass found in forests and wood waste from logging practices and industrial operations, such as sawmills. Forest residues are a convenient fuel for open-burning and conventional biomass burning systems (e.g., fireplaces and wood stoves), but more recently have been considered as a fuel for advanced wood combustion (AWC) integrated energy systems, used for electricity production in addition to heating. • AWC systems are defined as wood-fired high-efficiency automated energy systems with air pollution controls. Favored for use in Europe, they supply heating at economically achievable conditions, use wood resources efficiently, and can be an integral part of district energy systems. • Emissions from open-burning and conventional biomass burning systems may contain such air contaminants as carbon dioxide (CO2), elemental carbon, polycyclic aromatic hydrocarbons (PAHs), benzene, aldehydes, polychlorinated dibenzo-P-dioxins (PCDDs), and free radicals, as well as particulate matter (PM). In comparison, emissions of PM, carbon monoxide (CO) and volatile organic compounds (VOCs) from advanced wood combustion (AWC) systems, such as gasification, are considered to be an order of magnitude lower than conventional combustion systems. • The quantity and chemical composition of airborne pollutants emitted from biomass burning depends on combustion characteristics and operating conditions, such as complete combustion, more likely with AWC systems, which leads to lower levels of pollutants and likely lower toxicity. Hygroscopicity (ease of absorbing water) is an important characteristic of PM originating from complete combustion, which reduces the probability of PM deposition in lungs, and therefore PM induced toxicity