Article pubs.acs.org/EF
Analysis of Gas-Phase Carbonyl Compounds in Emissions from Modern Wood Combustion Appliances: Influence of Wood Type and Combustion Appliance Ahmed A. Reda,†,‡,∇ H. Czech,† J. Schnelle-Kreis,*,‡ O. Sippula,§,∇ J. Orasche,†,‡,∇ B. Weggler,†,‡,∇ G. Abbaszade,‡,∇ J. M. Arteaga-Salas,‡,∇ M. Kortelainen,§ J. Tissari,§ J. Jokiniemi,§,∇ T. Streibel,†,‡,∇ and R. Zimmermann†,‡,∇ †
Institute of Chemistry, University of Rostock, Rostock, Germany Joint Mass Spectrometry Center, “Comprehensive Molecular Analytics”, Helmholtz Zentrum München, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany § Department of Environmental Science, University of Eastern Finland, Kuopio, Finland ∇ HICE−Helmholtz Virtual Institute of Complex Molecular Systems in Environmental HealthAerosols and Health (www.hice-vi.eu) ‡
S Supporting Information *
ABSTRACT: Gas-phase emission samples of carbonyl compounds (CCs) were collected from two modern wood combustion appliances. Multiple repetitions were conducted on masonry heater operated with three logwood species (birch, beech, and spruce) and for a pellet boiler operated by softwood pellet with normal combustion and unoptimized combustion (in which the secondary combustion air flow rate was decreased). The sampling of CCs was performed from diluted exhaust using 2,4dinitrophenylhydrazine (DNPH) cartridges. The CCs-hydrazone derivatives were analyzed by a gas chromatography−selective ion monitoring−mass spectrometry (GC-SIM-MS) method. Twelve (12) CCs were quantified in the masonry heater emissions and 8 in the pellet boiler emissions. The total carbonyl emission factors (EFs) for logwood were determined to be as follows: birch, 113 ± 18 mg kg−1; beech, 178 ± 31 mg kg−1; spruce, 171 ± 19 mg kg−1; and, for softwood pellet with normal combustion, 6 ± 0.9 mg kg−1 and for softwood pellet with unoptimized combustion, 6.5 ± 1 mg kg−1. In masonry heater operation, birch exhibits the lowest emission factors, compared to other wood types. No significant differences were noticed between the emission of normal and unoptimized combustion for the pellet boiler operation. The emission profile examination showed that formaldehyde and acetaldehyde were the predominated carbonyls in the emission, regardless of the wood type. Time-resolved results obtained via single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) depict that, in masonry heater emissions, most carbonyls are produced as a new batch of wood is introduced.
1. INTRODUCTION Biomass and wood combustion represent one of the major air pollution sources during the last decade.1,2 Residential wood combustion (RWC) has been claimed to be a significant source of fine particle mass emissions, particulate polycyclic aromatic hydrocarbons (PAHs), and volatile organic compounds (VOCs).3 The relative contribution of (open and domestic) biomass burning emissions to the global annual emission is ∼25% for CO, ∼18% for NOx, and ∼6% for non-methane volatile organic compounds (NMVOC) and CH4.4 The European Committee for Standardization (CEN), under Committee TC335, has published 27 technical specifications (pre-standards) for solid biofuels during 2003−2006. Now these technical specifications are upgraded to full European standards (EN). When EN standards are enforced, the national standards must be withdrawn or adapted to these EN standards.5 RWC has been shown to be a major contributor to local indoor and outdoor air pollution during the winter months in residential areas of Europe, thus seriously affecting air quality and public health.6 One of the main concerns associated with wood-burning devices, particularly small-scale © 2015 American Chemical Society
appliances such as woodstoves, is their high level of emission from incomplete fuel combustion. The emissions from these appliances are highly variable and dependent on factors such as appliance type and wood consumed (properties) as well as combustion conditions, such as temperature and air mixing in the combustion chamber.7 Carbonyl compounds (CCs) are a group of important emission products from wood combustion1 that result from the wood-burning process. Depending on the combustion conditions of wood, the reaction will not completely go to full oxidation (i.e., CO2 and H2O) but will instead produce organics (such as carbonyls) among other partial combustion products and unburnt products such as char, or aromatized PAHs/soot. The mechanism of ignition and combustion of wood is mainly based on the pyrolysis (thermal decomposition) of the main components of the wood, cellulose, hemicellulose, and lignin.8 The pyrolysis of wood and especially cellulose has been Received: December 23, 2014 Revised: May 13, 2015 Published: May 14, 2015 3897
DOI: 10.1021/ef502877c Energy Fuels 2015, 29, 3897−3907
Article
Energy & Fuels
Figure 1. Schematic diagram of the experimental setup showing the dilution channels, position of the gas phase sampling (DNPH cartridges), and the online SPI-MS system marked by the highlighted box.
investigated intensively since the 1970s.9 According to Shafizadeh et al.,10 thermal degradation products of woods arising at 300−500 °C via the depolymerization of cellulose to anhydroglucose units, followed by conformation changes such as transglycosylation to yield levoglucosan as the major product. Above 500 °C, the ring-opening reaction of levoglucosan occurs, along with dehydration and decarboxylation. Primary products of levoglucosan pyrolysis are formaldehyde, furfural, acetaldehyde, higher aldehydes, diacetyls, water, CO2, and CO. Later, different mechanisms discussed the pyrolysis of cellulose and the formation of volatiles.11 More recent reviews on the pyrolysis of biomass were published by Collard and Blin,12 which discussed the recent mechanisms and composition products from the conversion of cellulose, hemicelluloses, and lignin. Recently, there has been a growing interest in carbonyls in the atmosphere, for two important reasons. Firstly, some carbonyls, such as formaldehyde, acrolein, or acetaldehyde, are known or suspected to be toxic and possibly carcinogenic. Consequently, exposure to high concentrations of these chemicals may have adverse effects on human health and well-being.13 Secondly, CCs are critically important for tropospheric chemistry, because they are a significant source of free radicals and act as precursors of photochemical oxidants such as ozone and peroxyacyl nitrates.9c The primary emission sources of CCs include motor vehicles,14 ship engines,15 incomplete combustion of hydrocarbon fuels in industrial processes,16 cigarette smoke,17 and residential wood combustion.18 CCs can also be produced as secondary airborne pollutants via the photochemical oxidation of atmospheric hydrocarbons.19 Previous studies related to the emissions of gaseous compounds from residential biomass burning activities showed
high emission rates of CCs to the atmosphere. Formaldehyde and acetaldehyde were found to prevail with the highest concentrations among all emitted pollutants.1,20 These studies also showed a different emission pattern for carbonyls, depending upon the appliance or wood types used. In recent years, a significant amount of information was collected regarding the emissions of carbonyls during wood combustion processes from fireplaces and woodstoves. A study by Cerqueira et al.21 investigated the emissions of formaldehyde and acetaldehyde from a residential woodstove fueled with common wood species growing in Portugal: maritime pine, eucalyptus, cork oak, holm oak, and pyrenean oak. Another study by Evtyugina et al.6 investigated the VOCs emission, which includes some carbonyls from domestic woodstove and fireplace combustion appliances that are common in middle and southern Europe with three different wood types: European beech, Pyrenean oak, and black poplar. For pellet boilers, different studies have discussed the emissions from these appliances.22−24 Most of these studies investigated the particle and/or the gaseous emissions from pellet boilers or discussed differences in the emissions from burning different pellet types. Only one study showed information concerning some heavy carbonyls (starting from pentanal) in pellet boiler emission,25 which have been sampled by (Tenax GR) adsorbent and analyzed by thermal desorption cold-trap injector−gas chromatography−mass spectrometry (TCT-GCMS). The sampling of carbonyls in this study was done using 2,4-dinitrophenylhydrazine (DNPH) cartridges. DNPH derivatization was used earlier to collect carbonyls in ambient26 and emission aerosols.15 To our knowledge, to date, there are no data available for carbonyl compounds in pellet boiler emissions that apply DNPH derivatization. 3898
DOI: 10.1021/ef502877c Energy Fuels 2015, 29, 3897−3907
Article
Energy & Fuels Table 1. Wood Chemical and Physical Properties Used in the Combustion Experiments parameter
limit of quantification, LOQ
analysis method
softwood pellets
birch log
beech log
spruce log
moisture (%) ash content @ 550 °C (% (w/w, dry)) carbon (% (w/w, dry)) hydrogen (% (w/w, dry)) nitrogen (% (w/w, dry)) oxygen (% (w/w, dry)) sulfur (% (w/w, dry)) chlorine (% (w/w, dry)) lower heat value (kJ per kg fuel)
0.1 0.1 0.2 0.1 0.05
DIN EN 14774-2 DIN EN 14775 DIN EN 15104 DIN EN 15104 DIN EN 15104 calculated DIN EN 15289 DIN EN 15289 DIN EN 14918
7.3 0.36 51.7 6.0 0.29 41.6 0.006 0.006 18380
7.2 0.69 51.0 6.0 0.40 41.9 0.006
