scholarly journals Technical note: Pyrolysis principles explain time-resolved organic aerosol release from biomass burning

2021 ◽  
Vol 21 (20) ◽  
pp. 15605-15618
Author(s):  
Mariam Fawaz ◽  
Anita Avery ◽  
Timothy B. Onasch ◽  
Leah R. Williams ◽  
Tami C. Bond
Keyword(s):  
Moisture Content ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Organic Aerosol ◽  
Product Formation ◽  
Technical Note ◽  
Wood Combustion ◽  
Single Experiment ◽  
Transfer Resistance

Abstract. Emission of organic aerosol (OA) from wood combustion is not well constrained; understanding the governing factors of OA emissions would aid in explaining the reported variability. Pyrolysis of the wood during combustion is the process that produces and releases OA precursors. We performed controlled pyrolysis experiments at representative combustion conditions. The conditions changed were the temperature, wood length, wood moisture content, and wood type. The mass loss of the wood, the particle concentrations, and light-gas concentrations were measured continuously. The experiments were repeatable as shown by a single experiment, performed nine times, in which the real-time particle concentration varied by a maximum of 20 %. Higher temperatures increased the mass loss rate and the released concentration of gases and particles. Large wood size had a lower yield of particles than the small size because of higher mass transfer resistance. Reactions outside the wood became important between 500 and 600 ∘C. Elevated moisture content reduced product formation because heat received was shared between pyrolysis reactions and moisture evaporation. The thermophysical properties, especially the thermal diffusivity, of wood controlled the difference in the mass loss rate and emission among seven wood types. This work demonstrates that OA emission from wood pyrolysis is a deterministic process that depends on transport phenomena.

scholarly journals Technical Note: Pyrolysis principles explain time-resolved organic aerosol release from biomass burning

2021 ◽  
Author(s):  
Mariam Fawaz ◽  
Anita Avery ◽  
Timothy B. Onasch ◽  
Leah R. Williams ◽  
Tami C. Bond
Keyword(s):  
Moisture Content ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Organic Aerosol ◽  
Product Formation ◽  
Technical Note ◽  
Wood Combustion ◽  
Single Experiment ◽  
Transfer Resistance

Abstract. Emission of organic aerosol (OA) from wood combustion is not well constrained; understanding the governing factors of OA emissions would aid in explaining the reported variability. Pyrolysis of the wood during combustion is the process that produces and releases OA precursors. We performed controlled pyrolysis experiments at representative combustion conditions. The conditions changed were the temperature, wood length, wood moisture content, and wood type. The mass loss of the wood, the particle concentrations, and light gas concentrations were measured continuously. The experiments were repeatable as shown by a single experiment, performed nine times, in which the real-time particle concentration varied by a maximum of 20 %. Higher temperatures increased the mass loss rate and the released concentration of gases and particles. Large wood size had a lower yield of particles than the small size because of higher mass transfer resistance. Reactions outside the wood became important between 500 and 600 °C. Elevated moisture content reduced product formation because heat received was shared between pyrolysis reactions and moisture evaporation. The thermophysical properties, especially the thermal diffusivity, of wood controlled the difference in the mass loss rate and emission among seven wood types. This work demonstrates that OA emission from wood pyrolysis is a deterministic process that depends on transport phenomena.

scholarly journals Photochemical degradation of iron(III) citrate/citric acid aerosol quantified with the combination of three complementary experimental techniques and a kinetic process model

2021 ◽  
Vol 21 (1) ◽  
pp. 315-338
Author(s):  
Jing Dou ◽  
Peter A. Alpert ◽  
Pablo Corral Arroyo ◽  
Beiping Luo ◽  
Frederic Schneider ◽  
...  
Keyword(s):  
Citric Acid ◽  
Mass Loss ◽  
Gas Phase ◽  
Organic Compounds ◽  
Chemical Reactions ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Organic Aerosol ◽  
Photochemical Degradation ◽  
Aerosol Aging

Abstract. Iron(III) carboxylate photochemistry plays an important role in aerosol aging, especially in the lower troposphere. These complexes can absorb light over a broad wavelength range, inducing the reduction of iron(III) and the oxidation of carboxylate ligands. In the presence of O2, the ensuing radical chemistry leads to further decarboxylation, and the production of .OH, HO2., peroxides, and oxygenated volatile organic compounds, contributing to particle mass loss. The .OH, HO2., and peroxides in turn reoxidize iron(II) back to iron(III), closing a photocatalytic cycle. This cycle is repeated, resulting in continual mass loss due to the release of CO2 and other volatile compounds. In a cold and/or dry atmosphere, organic aerosol particles tend to attain highly viscous states. While the impact of reduced mobility of aerosol constituents on dark chemical reactions has received substantial attention, studies on the effect of high viscosity on photochemical processes are scarce. Here, we choose iron(III) citrate (FeIII(Cit)) as a model light-absorbing iron carboxylate complex that induces citric acid (CA) degradation to investigate how transport limitations influence photochemical processes. Three complementary experimental approaches were used to investigate kinetic transport limitations. The mass loss of single, levitated particles was measured with an electrodynamic balance, the oxidation state of deposited particles was measured with X-ray spectromicroscopy, and HO2. radical production and release into the gas phase was observed in coated-wall flow-tube experiments. We observed significant photochemical degradation with up to 80 % mass loss within 24 h of light exposure. Interestingly, we also observed that mass loss always accelerated during irradiation, resulting in an increase of the mass loss rate by about a factor of 10. When we increased relative humidity (RH), the observed particle mass loss rate also increased. This is consistent with strong kinetic transport limitations for highly viscous particles. To quantitatively compare these experiments and determine important physical and chemical parameters, a numerical multilayered photochemical reaction and diffusion (PRAD) model was developed that treats chemical reactions and the transport of various species. The PRAD model was tuned to simultaneously reproduce all experimental results as closely as possible and captured the essential chemistry and transport during irradiation. In particular, the photolysis rate of FeIII, the reoxidation rate of FeII, HO2. production, and the diffusivity of O2 in aqueous FeIII(Cit) ∕ CA system as function of RH and FeIII(Cit) ∕ CA molar ratio could be constrained. This led to satisfactory agreement within model uncertainty for most but not all experiments performed. Photochemical degradation under atmospheric conditions predicted by the PRAD model shows that release of CO2 and repartitioning of organic compounds to the gas phase may be very important when attempting to accurately predict organic aerosol aging processes.

scholarly journals Photochemical degradation of iron(III)-citrate/citric acid aerosol quantified with the combination of three complementary experimental techniques and a kinetic process model

2020 ◽  
Author(s):  
Jing Dou ◽  
Peter A. Alpert ◽  
Pablo Corral Arroyo ◽  
Beiping Luo ◽  
Frederic Schneider ◽  
...  
Keyword(s):  
Citric Acid ◽  
Relative Humidity ◽  
Mass Loss ◽  
Gas Phase ◽  
Organic Compounds ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Organic Aerosol ◽  
Photochemical Degradation ◽  
Aerosol Aging

Abstract. Iron(III) carboxylate photochemistry plays an important role in aerosol aging, especially in the lower troposphere. These complexes can absorb light over a broad wavelength range, inducing the reduction of iron(III) and the oxidation of carboxylate ligands. In the presence of O2, ensuing radical chemistry leads to further decarboxylation, and the production of ·OH, HO2·, peroxides, and oxygenated volatile organic compounds, contributing to particle mass loss. The ·OH, HO2·, and peroxides in turn re-oxidize iron(II) back to iron(III), closing a photocatalytic cycle. This cycle is repeated resulting in continual mass loss due to the release of CO2 and other volatile compounds. In a cold and/or dry atmosphere, organic aerosol particles tend to attain highly viscous states. While the impact of reduced mobility of aerosol constituents on dark chemical reactions has received substantial attention, studies on the effect of high viscosity on photochemical processes are scarce. Here, we choose iron(III)-citrate (FeIII(Cit)) as a model light absorbing iron carboxylate complex that induces citric acid (CA) degradation to investigate how transport limitations influence photochemical processes. Three complementary experimental approaches were used to investigate kinetic transport limitations. The mass loss of single, levitated particles was measured with an electrodynamic balance, the oxidation state of deposited particles was measured with X-ray spectromicroscopy, and HO2· radical production and release into the gas phase was observed in coated wall flow tube experiments. To quantitatively compare these experiments and determine important physical and chemical parameters, a numerical multi-layered photochemical reaction and diffusion (PRAD) model that treats chemical reactions and transport of various species was developed. We observed significant photochemical degradation, with up to 80 % mass loss within 24 hours of light exposure. Interestingly, we also observed that mass loss always accelerated during irradiation, resulting in an increase of the mass loss rate by about a factor of 10. When we increased relative humidity, the observed particle mass loss rate also increased. This is consistent with strong kinetic transport limitations for highly viscous particles. The PRAD model was tuned to reproduce all experimental results and captured the essential chemistry and transport during irradiation. In particular, the photolysis rate of FeIII, the re-oxidation rate of FeII, HO2· production, and the diffusivity of O2 in aqueous FeIII(Cit)/CA system as function of relative humidity and FeIII(Cit) / CA molar ratio could be constrained. Photochemical degradation under atmospheric conditions predicted by the PRAD model shows that release of CO2 and re-partitioning of organic compounds to the gas phase may be very significant to accurately predict organic aerosol aging processes.

scholarly journals SN 2009ip: CONSTRAINTS ON THE PROGENITOR MASS-LOSS RATE

2013 ◽  
Vol 768 (1) ◽  
pp. 47 ◽  
Author(s):  
E. O. Ofek ◽  
L. Lin ◽  
C. Kouveliotou ◽  
G. Younes ◽  
E. Göğüş ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate

Effect of Sample Width on Downward Flame Spread over Typical Energy Conservation Material at a High Elevation Area

2014 ◽  
Vol 664 ◽  
pp. 199-203 ◽  
Author(s):  
Wei Guang An ◽  
Lin Jiang ◽  
Jin Hua Sun ◽  
K.M. Liew
Keyword(s):  
Mass Loss ◽  
Flame Spread ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
High Elevation ◽  
Flame Height ◽  
Spread Rate ◽  
Flame Spread Rate ◽  
Sample Width ◽  
Downward Flame Spread

An experimental study on downward flame spread over extruded polystyrene (XPS) foam at a high elevation is presented. The flame shape, flame height, mass loss rate and flame spread rate were measured. The influences of width and high altitude were investigated. The flame fronts are approximately horizontal. Both the intensity of flame pulsation and the average flame height increase with the rise of sample width. The flame spread rate first drops and then rises with an increase in width. The average flame height, mass loss rate and flame spread rate at the higher elevation is smaller than that at a low elevation, which demonstrates that the XPS fire risk at the higher elevation area is lower. The experimental results agree well with the theoretical analysis. This work is vital to the fire safety design of building energy conservation system.

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