Emissions during grilling with wood pellets and chips

Abstract

The quality check of grilling wood pellets should be of a critical importance as smoke from their combustion has a direct contact with food, impacts human safety, and pollutes the atmosphere. Therefore, the main purpose of this study is to investigate the purity of grilling wood pellets and chips available on the market, analyze the properties of their combustion gases, and determine if a relationship between the fuel composition and emissions during grilling can be established. In this study, we investigated 45 types of BBQ wood pellets and wood chips available for purchase in the USA and Europe. Based on reflected light microscopy analysis, the samples are composed dominantly of biomass, ranging from 87.5 to 99.8 vol % for wood pellets and 96.5 to 99.1 vol % for wood chips, with the average impurities content of 1.7 vol % for wood pellets and 2.2 vol % for wood chips. The undesired components included bark, mineral matter, charcoal, coke, metal, rust, slag, and petroleum products. Our data show that grilling with wood pellets and chips leads to elevated emissions of particulate matter (PM), NO 2 , SO 2 , CO, CO 2 , and formaldehyde in comparison with recommended exposure limits. The average emissions of PM are higher from wood chips than from pellets by approximately 85 μg/m 3 , and they come mainly from PM 2.5 ; the contribution from PM of 2.5–10 μm in size is rather insignificant. CO 2 emissions, on average 2.67% from pellets and 2.27% from wood chips, were elevated comparing with a typical outdoor air level of 0.03–0.05% (300–500 ppm). The level of emissions of individual components also changes during the grilling cycle, and depends on the type of combusted wood, grilling conditions and fuel moisture content. • Reflected light microscopy is valuable tool to identify impurities in pellet fuels. • Some wood pellets contain a wide range of impurities. • Contaminants include mineral matter, charcoal, metals, rust and petroleum products. • Contamination ranges between 0.2 and 12.5 vol %. • Source material and combustion conditions influence the emissions during grilling.