Particle-bound reactive oxygen species (PB-ROS) emissions and formation pathways in residential wood smoke under different combustion and aging conditions
Authors: Zhou Jun , Zotter Peter , Bruns Emily A. , Stefenelli Giulia , Bhattu Deepika , Brown Samuel , Bertrand Amelie , Marchand Nicolas , Lamkaddam Houssni , Slowik Jay G. , Prévôt André S. H. , Baltensperger Urs , Nussbaumer Thomas , El-Haddad Imad , Dommen Josef 
Published: May 2018

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.