scholarly journals Supplementary material to "Dynamic changes of optical and chemical properties of tar ball aerosols by atmospheric photochemical aging"

2018 ◽  
Author(s):  
Chunlin Li ◽  
Quanfu He ◽  
Julian Schade ◽  
Johannes Passig ◽  
Ralf Zimmermann ◽  
...  
Keyword(s):  
Chemical Properties ◽  
Dynamic Changes ◽  
Supplementary Material ◽  
Photochemical Aging ◽  
And Chemical Properties

scholarly journals Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging

2019 ◽  
Vol 19 (1) ◽  
pp. 139-163 ◽  
Author(s):  
Chunlin Li ◽  
Quanfu He ◽  
Julian Schade ◽  
Johannes Passig ◽  
Ralf Zimmermann ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Light Absorption ◽  
Chemical Properties ◽  
Oh Radical ◽  
Dynamic Changes ◽  
Photochemical Process ◽  
Tar Balls ◽  
Photochemical Aging ◽  
And Chemical Properties

Abstract. Following wood pyrolysis, tar ball aerosols were laboratory generated from wood tar separated into polar and nonpolar phases. Chemical information of fresh tar balls was obtained from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and single-particle laser desorption/resonance enhanced multiphoton ionization mass spectrometry (SP-LD-REMPI-MS). Their continuous refractive index (RI) between 365 and 425 nm was retrieved using a broadband cavity enhanced spectroscopy (BBCES). Dynamic changes in the optical and chemical properties for the nonpolar tar ball aerosols in NOx-dependent photochemical process were investigated in an oxidation flow reactor (OFR). Distinct differences in the chemical composition of the fresh polar and nonpolar tar aerosols were identified. Nonpolar tar aerosols contain predominantly high-molecular weight unsubstituted and alkyl-substituted polycylic aromatic hydrocarbons (PAHs), while polar tar aerosols consist of a high number of oxidized aromatic substances (e.g., methoxy-phenols, benzenediol) with higher O : C ratios and carbon oxidation states. Fresh tar balls have light absorption characteristics similar to atmospheric brown carbon (BrC) aerosol with higher absorption efficiency towards the UV wavelengths. The average retrieved RI is 1.661+0.020i and 1.635+0.003i for the nonpolar and polar tar aerosols, respectively, with an absorption Ångström exponent (AAE) between 5.7 and 7.8 in the detected wavelength range. The RI fits a volume mixing rule for internally mixed nonpolar/polar tar balls. The RI of the tar ball aerosols decreased with increasing wavelength under photochemical oxidation. Photolysis by UV light (254 nm), without strong oxidants in the system, slightly decreased the RI and increased the oxidation state of the tar balls. Oxidation under varying OH exposure levels and in the absence of NOx diminished the absorption (bleaching) and increased the O : C ratio of the tar balls. The photobleaching via OH radical initiated oxidation is mainly attributed to decomposition of chromophoric aromatics, nitrogen-containing organics, and high-molecular weight components in the aged particles. Photolysis of nitrous oxide (N2O) was used to simulate NOx-dependent photochemical aging of tar balls in the OFR. Under high-NOx conditions with similar OH exposure, photochemical aging led to the formation of organic nitrates, and increased both oxidation degree and light absorption for the aged tar ball aerosols. These observations suggest that secondary organic nitrate formation counteracts the bleaching by OH radical photooxidation to eventually regain some absorption of the aged tar ball aerosols. The atmospheric implication and climate effects from tar balls upon various oxidation processes are briefly discussed.

scholarly journals Dynamic changes of optical and chemical properties of tar ball aerosols by atmospheric photochemical aging

2018 ◽  
Author(s):  
Chunlin Li ◽  
Quanfu He ◽  
Julian Schade ◽  
Johannes Passig ◽  
Ralf Zimmermann ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Refractive Index ◽  
High Molecular Weight ◽  
Oxidation State ◽  
Chemical Properties ◽  
Dynamic Changes ◽  
Photochemical Process ◽  
Tar Balls ◽  
Photochemical Aging ◽  
And Chemical Properties

Abstract. Following wood pyrolysis, tar ball aerosols were generated from wood tar separated into polar and nonpolar phases. Chemical information of fresh tar balls was obtained from the high-resolution time-of-flight aerosol mass spectrometer (HiRes-ToF-AMS) and laser desorption/resonance enhanced multiphoton ionization mass spectrometry (LD-REMPI-MS), and their refractive index between 365 and 425 nm were retrieved using a broadband cavity enhanced spectroscopy. Dynamic changes of the optical and chemical properties for the nonpolar tar ball aerosols in NOx-dependent photochemical process were investigated in an oxidation flow reactor (OFR). Distinct differences in the chemical composition of the polar and nonpolar tar aerosols were identified. Nonpolar tar aerosols contain predominantly high-molecular weight unsubstituted and alkyl-substituted polycylic aromatic hydrocarbons (PAHs), while polar tar aerosols consist of a high number of oxidized aromatic substances (e.g., methoxy-phenols, benzenediol) with higher O : C ratio and carbon oxidation state. Fresh tar aerosols have light absorption characteristics similar to atmospheric BrC with higher absorption efficiency towards the UV wavelengths. The average retrieved refractive index (RI) are 1.661 + 0.020i and 1.635 + 0.003i for the nonpolar and polar tar aerosols, respectively, with absorption Ångström exponent (AAE) between 5.7 and 7.8 in the wavelength region 365–425 nm. The RI fits a volume mixing rule for internally mixed nonpolar/polar tar aerosols. The RI of the tar aerosols decreased with increasing wavelength under photochemical oxidation. Photolysis by UV light (254 nm), without strong oxidants in the system, slightly decreased the RI and increased the oxidation state of the tar balls. Oxidation under varying OH exposure levels and in the absence of NOx diminished the absorption (bleaching), and increased the O : C ratio. The photobleaching of tar ball aerosols via photochemically induced OH-oxidation is mainly attributed to decomposition of chromophoric aromatics, nitrogen-containing organics, and high-molecular weight components. Photolysis of nitrous oxide (N2O) was used to simulate NOx-dependent photochemical aging of tar balls in the OFR. Under high NOx conditions, photochemical aging lead to the formation of organic-nitrates, increased oxidation degree and increased absorption for the tar ball aerosols. These observations suggest that secondary organic nitrate formation compensates the bleaching by photolysis and OH radical photooxidation to eventually regain some absorption of aged tar balls aerosols. The atmospheric implication and climatic effects from tar balls upon various oxidation processes are briefly discussed.

scholarly journals Stimuli responsive dynamic transformations in supramolecular gels

2021 ◽  
Author(s):  
Santanu Panja ◽  
Dave J. Adams
Keyword(s):  
Chemical Properties ◽  
Physical And Chemical Properties ◽  
Stimuli Responsive ◽  
Dynamic Changes ◽  
Supramolecular Gels ◽  
Self Assembled ◽  
Physical And Chemical ◽  
And Chemical Properties

Stimuli responsive dynamic changes in the networks of self-assembled gels result in an alteration of physical and chemical properties of the gel with time.

scholarly journals Laboratory studies of fresh and aged biomass burning aerosols emitted from east African biomass fuels – Part 1 – Optical properties

2020 ◽  
Author(s):  
Damon M. Smith ◽  
Marc N. Fiddler ◽  
Rudra Pokhrel ◽  
Solomon Bililign
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Chemical Properties ◽  
Urban Environments ◽  
Laboratory Studies ◽  
Aerosol Formation ◽  
East African ◽  
Extinction Cross Section ◽  
Photochemical Aging ◽  
And Chemical Properties

Abstract. An accurate measurement of optical properties of aerosols is critical for quantifying the effect of aerosols on climate. Uncertainties persist and measurement results vary significantly. Biomass burning (BB) aerosols have been extensively studied through both field and laboratory environments for North American fuels to understand the changes in optical and chemical properties as a function of aging. There is a clear research need for a wider sampling of fuels from different regions of the world for laboratory studies. This work represents the first such study the optical and chemical properties of three wood fuel samples used commonly for domestic use in east Africa. In general, combustion temperature plays a major role on the optical properties of the emitted aerosols. For fuels combusted at 800 °C SSA values are in the range between 0.287 and 0.439 while the SSA for fuels combusted at 500 °C, the range between 0.66 and 0.769. There is a clear but very small dependence of SSA on fuel type, with eucalyptus producing aerosol with higher SSA than olive and acacia. A significant increase in the scattering and extinction cross-section (mostly dominated by scattering) was observed, indicating the occurrence of chemistry, even during dark aging for combustion at 500 °C. This fact can't be explained by the heterogeneous chemistry and we hypothesized secondary organic aerosol formation as a potential phenomenon happing during dark aging. After 12 h of photochemical aging, BB aerosol becomes highly scattering with SSA values above 0.9, which can be attributed to oxidation in the chamber. Due to the very low number concentration of aerosols during aging studies of combustion at 800 °C, the results were inconclusive. We also attempted to simulate polluted urban environments by ejecting VOCs and BB aerosol into the chamber, but no distinct difference was observed, since measurements were done 12 hours after injection of VOCs.

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