Abstract
Abstract. Wood combustion emissions can induce oxidative stress in the human respiratory tract by reactive oxygen species (ROS) in the aerosol particles, which are emitted either directly or formed through oxidation in the atmosphere. To improve our understanding of the particle-bound ROS (PB-ROS) generation potential of wood combustion emissions, a suite of smog chamber (SC) and potential aerosol mass (PAM) chamber experiments were conducted under well-determined conditions for different combustion devices and technologies, different fuel types, operation methods, combustion regimes, combustion phases, and aging conditions. The PB-ROS content and the chemical properties of the aerosols were quantified by a novel ROS analyzer using the DCFH (2′,7′-dichlorofluorescin) assay and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). For all eight combustion devices tested, primary PB-ROS concentrations substantially increased upon aging. The level of primary and aged PB-ROS emission factors (EFROS) were dominated by the combustion device (within different combustion technologies) and to a greater extent by the combustion regimes: the variability within one device was much higher than the variability of EFROS from different devices. Aged EFROS under bad combustion conditions were ∼ 2–80 times higher than under optimum combustion conditions. EFROS from automatically operated combustion devices were on average 1 order of magnitude lower than those from manually operated devices, which indicates that automatic combustion devices operated at optimum conditions to achieve near-complete combustion should be employed to minimize PB-ROS emissions. The use of an electrostatic precipitator decreased the primary and aged ROS emissions by a factor of ∼ 1.5 which is however still within the burn-to-burn variability. The parameters controlling the PB-ROS formation in secondary organic aerosol were investigated by employing a regression model, including the fractions of the mass-to-charge ratios m∕z 44 and 43 in secondary organic aerosol (SOA; f44−SOA and f43−SOA), the OH exposure, and the total organic aerosol mass. The regression model results of the SC and PAM chamber aging experiments indicate that the PB-ROS content in SOA seems to increase with the SOA oxidation state, which initially increases with OH exposure and decreases with the additional partitioning of semi-volatile components with lower PB-ROS content at higher OA concentrations, while further aging seems to result in a decay of PB-ROS. The results and the special data analysis methods deployed in this study could provide a model for PB-ROS analysis of further wood or other combustion studies investigating different combustion conditions and aging methods.
Highlights
Numerous studies worldwide have shown a link between exposure to airborne particulate matter (PM) and morbidity and mortality (Beelen et al, 2013; Dockery et al, 1993; He et al, 2016), and a strong correlation of airborne PM with lung function (Lee et al, 2011; Pope et al, 2002; Adam et al, 2015; Hwang et al, 2015)
The pellet boiler (PB)-reactive oxygen species (ROS) and organic aerosol (OA) emission factors are presented in Table 2 for all combustion conditions, together with the number of tests, the combustion efficiency (MCE), the air-to-fuel ratio (λ), and the aerosol bulk properties determined with the AMS (OM : organic carbon (OC), O : C and H : C ratios)
We only considered the smog chamber (SC) data and will discuss whether the potential aerosol mass (PAM) chamber data could be satisfactorily explained by the same parameterization or whether the amount of particlebound ROS (PB-ROS) formed under different conditions, with high OH concentrations in the PAM chamber, is different
Summary
Numerous studies worldwide have shown a link between exposure to airborne particulate matter (PM) and morbidity and mortality (Beelen et al, 2013; Dockery et al, 1993; He et al, 2016), and a strong correlation of airborne PM with lung function (Lee et al, 2011; Pope et al, 2002; Adam et al, 2015; Hwang et al, 2015). Exposure to wood combustion particles may cause moderate inflammatory activity, cell death and DNA damage, and adverse effects to airway epithelia (Krapf et al, 2017; Tapanainen et al, 2012; Muala et al, 2015; Marabini et al, 2017). These adverse effects may be related to oxidative stress caused by free radicals induced by inhaled PM, which overwhelms the antioxidants in the body (Lobo et al, 2010)
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