scholarly journals Complex refractive indices in the near-ultraviolet spectral region of biogenic secondary organic aerosol aged with ammonia

2014 ◽  
Vol 16 (22) ◽  
pp. 10629-10642 ◽  
Author(s):  
J. M. Flores ◽  
R. A. Washenfelder ◽  
G. Adler ◽  
H. J. Lee ◽  
L. Segev ◽  
...  
Keyword(s):  
Refractive Index ◽  
Spectral Region ◽  
Secondary Organic Aerosol ◽  
Complex Refractive Index ◽  
Organic Aerosol ◽  
Refractive Indices ◽  
Near Ultraviolet ◽  
Ultraviolet Spectral Region ◽  
P Distribution

Distribution of the number of N atoms and the change in the complex refractive index of unreacted and NH3-aged limonene SOA.

scholarly journals Evolution of the complex refractive index in the near UV spectral region in ageing secondary organic aerosol

2014 ◽  
Vol 14 (3) ◽  
pp. 4149-4187 ◽  
Author(s):  
J. M. Flores ◽  
D. F. Zhao ◽  
L. Segev ◽  
P. Schlag ◽  
A. Kiendler-Scharr ◽  
...  
Keyword(s):  
Refractive Index ◽  
Physical Properties ◽  
Spectral Region ◽  
Secondary Organic Aerosol ◽  
Ageing Time ◽  
Complex Refractive Index ◽  
Organic Aerosol ◽  
Photochemical Degradation ◽  
Optical Extinction ◽  
Biogenic Voc

Abstract. The chemical and physical properties of secondary organic aerosol (SOA) formed by the photochemical degradation of biogenic and anthropogenic volatile organic compounds (VOC) are yet poorly constrained. The evolution of the complex refractive index (RI) of SOA, formed from purely biogenic VOC and mixtures of biogenic and anthropogenic VOC was studied over a diurnal cycle in the SAPHIR photochemical outdoor chamber in Jülich, Germany. The correlation of RI with SOA chemical and physical properties such as oxidation level and volatility was examined. The RI was retrieved by a newly developed broadband cavity enhanced spectrometer for aerosol optical extinction measurements in the near UV spectral region (360 to 420 nm). Chemical composition and volatility of the particles were monitored by a high resolution time of flight aerosol mass spectrometer, and a volatility tandem differential mobility analyzer. SOA was formed by ozonolysis of either (i) a mixture of biogenic VOC (α-pinene and limonene), (ii) biogenic VOC mixture with subsequent addition of an anthropogenic VOC (p-xylene-d10), or (iii) a mixture of biogenic and anthropogenic VOC. The SOA aged by ozone / OH reactions up to 29.5 h was found to be non-absorbing in all cases. The SOA with p-xylene-d10 showed an increase of the scattering component of the RI correlated with an increase of the O / C ratio and with an increase in the SOA density. There was a greater increase in the scattering component of the RI when the SOA was produced from the mixture of biogenic VOCs and anthropogenic VOC than from the sequential addition of the VOCs after the approximate same ageing time. The increase of the scattering component was inversely correlated with the SOA volatility. Two RI retrievals determined for the pure biogenic SOA showed a constant RI for up to 5 h of ageing. Mass spectral characterization shows the three types of the SOA formed in this study have significant amount of semivolatile components. The influence of anthropogenic VOCs on the oxygenated organic aerosol, and the atmospheric implications are discussed.

scholarly journals Evolution of the complex refractive index in the UV spectral region in ageing secondary organic aerosol

2014 ◽  
Vol 14 (11) ◽  
pp. 5793-5806 ◽  
Author(s):  
J. M. Flores ◽  
D. F. Zhao ◽  
L. Segev ◽  
P. Schlag ◽  
A. Kiendler-Scharr ◽  
...  
Keyword(s):  
Refractive Index ◽  
Physical Properties ◽  
Spectral Region ◽  
Secondary Organic Aerosol ◽  
Ageing Time ◽  
Complex Refractive Index ◽  
Organic Aerosol ◽  
Photochemical Degradation ◽  
Optical Extinction ◽  
Biogenic Voc

Abstract. The chemical and physical properties of secondary organic aerosol (SOA) formed by the photochemical degradation of biogenic and anthropogenic volatile organic compounds (VOC) are as yet still poorly constrained. The evolution of the complex refractive index (RI) of SOA, formed from purely biogenic VOC and mixtures of biogenic and anthropogenic VOC, was studied over a diurnal cycle in the SAPHIR photochemical outdoor chamber in Jülich, Germany. The correlation of RI with SOA chemical and physical properties such as oxidation level and volatility was examined. The RI was retrieved by a newly developed broadband cavity-enhanced spectrometer for aerosol optical extinction measurements in the UV spectral region (360 to 420 nm). Chemical composition and volatility of the particles were monitored by a high-resolution time-of-flight aerosol mass spectrometer, and a volatility tandem differential mobility analyzer. SOA was formed by ozonolysis of either (i) a mixture of biogenic VOC (α-pinene and limonene), (ii) biogenic VOC mixture with subsequent addition of an anthropogenic VOC (p-xylene-d10), or (iii) a mixture of biogenic and anthropogenic VOC. The SOA aged by ozone/OH reactions up to 29.5 h was found to be non-absorbing in all cases. The SOA with p-xylene-d10 showed an increase of the scattering component of the RI correlated with an increase of the O / C ratio and with an increase in the SOA density. There was a greater increase in the scattering component of the RI when the SOA was produced from the mixture of biogenic VOCs and anthropogenic VOC than from the sequential addition of the VOCs after approximately the same ageing time. The increase of the scattering component was inversely correlated with the SOA volatility. Two RI retrievals determined for the pure biogenic SOA showed a constant RI for up to 5 h of ageing. Mass spectral characterization shows the three types of the SOA formed in this study have a significant amount of semivolatile components. The influence of anthropogenic VOCs on the oxygenated organic aerosol as well as the atmospheric implications are discussed.

scholarly journals Real refractive indices and volatility of secondary organic aerosol generated from photooxidation and ozonolysis of limonene, α-pinene and toluene

2013 ◽  
Vol 13 (15) ◽  
pp. 7711-7723 ◽  
Author(s):  
H. Kim ◽  
S. E. Paulson
Keyword(s):  
Refractive Index ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Refractive Indices ◽  
Radical Scavenger ◽  
Hydrocarbon Oxidation ◽  
Aerosol Composition ◽  
Genetic Algorithm Method ◽  
Oxidation Chemistry ◽  
532 Nm

Abstract. Thermodenuding particles can provide insights into aerosol composition and may be a way to create particles in laboratory chambers that better mimic the atmosphere. The relative volatility of secondary organic aerosol (SOA) was investigated by evaporating organics from the particles using a thermodenuder (TD) at temperatures between ∼60 and 100 °C. Volatility was influenced by the parent hydrocarbon, oxidation chemistry and relative humidity (RH). For SOA generated from ozonolysis, limonene had lower volatility than α-pinene, and OH scavengers had no influence on volatility. For photooxidation, α-pinene SOA was slightly more volatile than limonene SOA. Increasing RH also modestly increased volatility, while toluene SOA was unaffected by heating to 98 °C. For both α-pinene and limonene, the concentration of NOx and the HC / NOx ratio had no discernible effect on SOA volatility. Refractive indices for the original and denuded particles were retrieved from polar nephelometer measurements using parallel and perpendicular polarized 532 nm light. Retrievals were performed with a genetic algorithm method using Mie–Lorenz scattering theory and measured particle size distributions. Retrieved refractive indices for the SOA before thermodenuding varied between 1.35 and 1.61 depending on several factors, including parent hydrocarbon, oxidation chemistry, and SOA generation temperature. For high NOx SOA, as particles shrink, their refractive index returns to the value of the corresponding size particles before heating (limonene) or slightly higher (α-pinene). For low NOx however, the resulting refractive index is 0.05 ± 0.02 lower than the corresponding size undenuded particles. Additionally, for α-pinene SOA from ozonolysis with OH radical scavenger, resulting refractive indices were higher by about 0.03 after heating. Consistent with no change in size, refractive indices of toluene SOA were unaffected by heating. Finally, refractive index data available to date are reviewed, leading to the suggestion that the most representative values for mr at λ =532 nm for biogenic and anthropogenic SOA are 1.44 and 1.55, respectively.

Direct measurement of the complex refractive index in the extreme ultraviolet spectral region using diffraction from a nanosphere array

2008 ◽  
Vol 93 (23) ◽  
pp. 231103 ◽  
Author(s):  
B. Mills ◽  
C. F. Chau ◽  
E. T. F. Rogers ◽  
J. Grant-Jacob ◽  
S. L. Stebbings ◽  
...  
Keyword(s):  
Refractive Index ◽  
Direct Measurement ◽  
Spectral Region ◽  
Extreme Ultraviolet ◽  
Complex Refractive Index ◽  
Ultraviolet Spectral Region

scholarly journals Effects of SO<sub>2</sub> on optical properties of secondary organic aerosol generated from photooxidation of toluene under different relative humidity conditions

2020 ◽  
Vol 20 (7) ◽  
pp. 4477-4492 ◽  
Author(s):  
Wenyu Zhang ◽  
Weigang Wang ◽  
Junling Li ◽  
Chao Peng ◽  
Kun Li ◽  
...  
Keyword(s):  
Climate Change ◽  
Refractive Index ◽  
Optical Properties ◽  
Secondary Organic Aerosol ◽  
Aldol Condensation ◽  
Complex Refractive Index ◽  
Organic Aerosol ◽  
Atmospheric Conditions ◽  
Radiative Balance ◽  
Dry Conditions

Abstract. Secondary organic aerosol (SOA) has great impacts on air quality, climate change and human health. The composition and physicochemical properties of SOA differ greatly because they form under different atmospheric conditions and from various precursors as well as differing oxidation. In this work, photooxidation experiments of toluene were performed under four conditions (dry, dry with SO2, wet and wet with SO2) to investigate the effect of SO2 under different relative humidities on the composition and optical properties of SOA at wavelengths of 375 and 532 nm. According to our results, the increase in humidity enhances not only light absorption but also the scattering property of the SOA. Oligomers formed through multiphase reactions might be the reason for this phenomenon. Adding SO2 slightly lowers the real part of the complex refractive index, RI(n), of toluene-derived SOA (RI(n)dry,SO2<RI(n)dry, RI(n)wet,SO2<RI(n)wet), which might be a result of the partitioning of low-oxidation-state products. The imaginary part of the complex refractive index, RI(k), is enhanced under dry conditions with SO2 compared to that of only dry conditions, which might be due to acid-catalyzed aldol condensation reactions. Wet conditions with SO2 shows the combined effect of SO2 and humidity. The extinction properties of toluene-derived SOA under wet conditions with SO2 increased by approximately 30 % compared to that of toluene-derived SOA formed under dry conditions. Our results suggest that various atmospheric conditions will affect the composition and optical proprieties of SOA, which has significant implications for evaluating the impacts of SOA on the rapid formation of regional haze, global radiative balance and climate change.

scholarly journals Real refractive indices and volatility of secondary organic aerosol generated from photooxidation and ozonolysis of limonene, α-pinene and toluene

2013 ◽  
Vol 13 (1) ◽  
pp. 1949-1977 ◽  
Author(s):  
H. Kim ◽  
S. E. Paulson
Keyword(s):  
Refractive Index ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Refractive Indices ◽  
Radical Scavenger ◽  
Hydrocarbon Oxidation ◽  
Aerosol Composition ◽  
Discernible Effect ◽  
Genetic Algorithm Method ◽  
Oxidation Chemistry

Abstract. Thermodenuding particles can provide insights into aerosol composition, and may be a way to create particles in laboratory chambers that better mimic the atmosphere. The volatility of secondary organic aerosol (SOA) was investigated by evaporating organics from the particles using a thermodenuder (TD) at temperatures between ~ 60 and 100 °C. Volatility was influenced by the parent hydrocarbon, oxidation chemistry and relative humidity (RH). For SOA generated from ozonolysis, limonene had lower volatility than α-pinene, and OH scavengers had no influence on volatility. For photooxidation, α-pinene SOA was slightly more volatile than limonene SOA and increasing RH also modestly increased volatility, while toluene SOA was unaffected by heating to 98 °C. For both α-pinene and limonene, the concentration of NOx and the HC/NOx ratio had no discernible effect on SOA volatility. Refractive indices for the original and denuded particles were retrieved from polar nephelometer measurements using parallel and perpendicular polarized 532 nm light. Retrievals were performed with a genetic algorithm method using Mie-Lorenz scattering theory and measured particle size distributions. Retrieved refractive indices for the SOA before thermodenuding varied between 1.35 and 1.61 depending on several factors, including parent hydrocarbon, oxidation chemistry, and SOA generation temperature. For high NOx SOA, as particles shrink, their refractive index returns to the value of the corresponding size particles before heating (limonene) or slightly higher (α-pinene). For low NOx however, the resulting refractive index is 0.05 ± 0.02 lower than the corresponding size undenuded particles. Additionally, for α-pinene SOA from ozonolysis with OH radical scavenger, resulting refractive indices were higher by about 0.03 after heating. Consistent with no change in size, refractive indices of toluene SOA were unaffected by heating. Finally, refractive index data available to date are reviewed and resulting in suggestions an mr for biogenic SOA of 1.44 and 1.55 for anthropogenic SOA as the most representative values.

scholarly journals Relating hygroscopicity and optical properties to chemical composition and structure of secondary organic aerosol particles generated from the ozonolysis of α-pinene

2014 ◽  
Vol 14 (7) ◽  
pp. 10543-10596 ◽  
Author(s):  
C. Denjean ◽  
P. Formenti ◽  
B. Picquet-Varrault ◽  
E. Pangui ◽  
P. Zapf ◽  
...  
Keyword(s):  
Optical Properties ◽  
Secondary Organic Aerosol ◽  
Complex Refractive Index ◽  
Glassy State ◽  
Particle Surface ◽  
Chemical Properties ◽  
Organic Aerosol ◽  
Atomic Ratio ◽  
Scattering Coefficient ◽  
Size Growth

Abstract. Secondary Organic Aerosol (SOA) were generated from the ozonolysis of α-pinene in the CESAM simulation chamber. The formation and ageing of the SOA were studied by following their optical, hygroscopic and chemical properties. The optical properties investigated by determining the particle Complex Refractive Index (CRI). The hygroscopicity was quantified by measuring the effect of RH on particle size (Growth Factor, GF) and scattering coefficient (f(RH)). The oxygen to carbon (O : C) atomic ratio of the particle surface and bulk were used as a sensitive parameter to correlate the changes in hygroscopic and optical properties of the SOA composition in CESAM. The real CRI at 525 nm wavelength decreased from 1.43–1.60 (±0.02) to 1.32–1.38 (±0.02) during the SOA formation. The decrease in real CRI correlates with a decrease in the O : C ratio of SOA from 0.68 (±0.20) to 0.55 (±0.16). In contrast, the GF stayed roughly constant over the reaction time, with values of 1.02–1.07 (±0.02) at 90% (±4.2) RH. Simultaneous measurements of O : C ratio of the particle surface revealed that the SOA was not composed of a homogeneous mixture, but with less oxidised species at the surface which would limit the water adsorption onto particle. In addition, an apparent change of both mobility diameter and scattering coefficient with increasing RH from 0 to 30% was observed for SOA after 16 h reaction. We postulate that this change could be due to a change in the viscosity of the SOA from a predominantly glassy state to a predominantly liquid state.

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