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Optical properties of secondary organic aerosols generated by photooxidation of aromatic hydrocarbons.

Li K, Wang W, Ge M, Li J, Wang D - Sci Rep (2014)

Bottom Line: The retrieved RIs at 532 nm for the SOAs range from 1.38-1.59, depending on several factors, such as different precursors and NOx levels.The RIs of the SOAs are altered differently as the NOx concentration increases as follows: the RIs of the SOAs derived from benzene and toluene increase, whereas those of the SOAs derived from ethylbenzene and m-xylene decrease.Finally, by comparing the experimental data with the model values, we demonstrate that the models likely overestimate the RI values of the SOA particles to a certain extent, which in turn overestimates the global direct radiative forcing of the organic particles.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China.

ABSTRACT
The refractive index (RI) is the fundamental characteristic that affects the optical properties of aerosols, which could be some of the most important factors influencing direct radiative forcing. The secondary organic aerosols (SOAs) generated by the photooxidation of benzene, toluene, ethylbenzene and m-xylene (BTEX) under low-NOx and high-NOx conditions are explored in this study. The particles generated in our experiments are considered to be spherical, based on atomic force microscopy (AFM) images, and nonabsorbent at a wavelength of 532 nm, as determined by ultraviolet-visible light (UV-Vis) spectroscopy. The retrieved RIs at 532 nm for the SOAs range from 1.38-1.59, depending on several factors, such as different precursors and NOx levels. The RIs of the SOAs are altered differently as the NOx concentration increases as follows: the RIs of the SOAs derived from benzene and toluene increase, whereas those of the SOAs derived from ethylbenzene and m-xylene decrease. Finally, by comparing the experimental data with the model values, we demonstrate that the models likely overestimate the RI values of the SOA particles to a certain extent, which in turn overestimates the global direct radiative forcing of the organic particles.

No MeSH data available.


Related in: MedlinePlus

RIs of the different SOA particles, and the comparison between the experimental data and the model values.The BTEX data are the current results; the toluene result (inverted triangle) is from Nakayama et al.20, and the data of the BVOCs are from Kim et al.252627. The blue boxes are the results of the low-NOx experiments; the red boxes are the results of the classical high-NOx experiments, and the green boxes are the results of the HONO experiments. The three BVOCs are limonene (cyan), α-pinene (pink) and β-pinene (dark yellow). The three lines are the RI values of organic aerosols in different models: the blue dash/dot line is for the ULAQ; the green dotted line is for MIRAGE; and the black dashed line is for ECHAM4, GOCART, GISS, Sprintars and Grantour51.
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f6: RIs of the different SOA particles, and the comparison between the experimental data and the model values.The BTEX data are the current results; the toluene result (inverted triangle) is from Nakayama et al.20, and the data of the BVOCs are from Kim et al.252627. The blue boxes are the results of the low-NOx experiments; the red boxes are the results of the classical high-NOx experiments, and the green boxes are the results of the HONO experiments. The three BVOCs are limonene (cyan), α-pinene (pink) and β-pinene (dark yellow). The three lines are the RI values of organic aerosols in different models: the blue dash/dot line is for the ULAQ; the green dotted line is for MIRAGE; and the black dashed line is for ECHAM4, GOCART, GISS, Sprintars and Grantour51.

Mentions: As illustrated in Fig. 6, we compared our experimental data to the model values. The RI values of the SOA generated by BVOCs measured by Kim et al.242526 and the data of the toluene SOA measured by Nakayama et al.21 are also shown in this figure. The three lines are the values of real RIs of seven common models60. ECHAM4, GOCART, GISS, Sprintars and Grantour perform better than ULAQ and MIRAGE compared with the laboratory studies. Nearly all of the experimental data are lower than the model values, regardless of whether the SOAs are generated by biological or anthropogenic VOCs. Kim et al. have noted that changing the RI value from 1.4 to 1.5 can produce an increase in the radiative forcing by at least 12% for non-absorbing particles25. Because aromatic hydrocarbons, limonene, α-pinene and β-pinene contribute most of the SOA content, current models may overestimate the RI values of organic aerosols to a certain extent.


Optical properties of secondary organic aerosols generated by photooxidation of aromatic hydrocarbons.

Li K, Wang W, Ge M, Li J, Wang D - Sci Rep (2014)

RIs of the different SOA particles, and the comparison between the experimental data and the model values.The BTEX data are the current results; the toluene result (inverted triangle) is from Nakayama et al.20, and the data of the BVOCs are from Kim et al.252627. The blue boxes are the results of the low-NOx experiments; the red boxes are the results of the classical high-NOx experiments, and the green boxes are the results of the HONO experiments. The three BVOCs are limonene (cyan), α-pinene (pink) and β-pinene (dark yellow). The three lines are the RI values of organic aerosols in different models: the blue dash/dot line is for the ULAQ; the green dotted line is for MIRAGE; and the black dashed line is for ECHAM4, GOCART, GISS, Sprintars and Grantour51.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4017213&req=5

f6: RIs of the different SOA particles, and the comparison between the experimental data and the model values.The BTEX data are the current results; the toluene result (inverted triangle) is from Nakayama et al.20, and the data of the BVOCs are from Kim et al.252627. The blue boxes are the results of the low-NOx experiments; the red boxes are the results of the classical high-NOx experiments, and the green boxes are the results of the HONO experiments. The three BVOCs are limonene (cyan), α-pinene (pink) and β-pinene (dark yellow). The three lines are the RI values of organic aerosols in different models: the blue dash/dot line is for the ULAQ; the green dotted line is for MIRAGE; and the black dashed line is for ECHAM4, GOCART, GISS, Sprintars and Grantour51.
Mentions: As illustrated in Fig. 6, we compared our experimental data to the model values. The RI values of the SOA generated by BVOCs measured by Kim et al.242526 and the data of the toluene SOA measured by Nakayama et al.21 are also shown in this figure. The three lines are the values of real RIs of seven common models60. ECHAM4, GOCART, GISS, Sprintars and Grantour perform better than ULAQ and MIRAGE compared with the laboratory studies. Nearly all of the experimental data are lower than the model values, regardless of whether the SOAs are generated by biological or anthropogenic VOCs. Kim et al. have noted that changing the RI value from 1.4 to 1.5 can produce an increase in the radiative forcing by at least 12% for non-absorbing particles25. Because aromatic hydrocarbons, limonene, α-pinene and β-pinene contribute most of the SOA content, current models may overestimate the RI values of organic aerosols to a certain extent.

Bottom Line: The retrieved RIs at 532 nm for the SOAs range from 1.38-1.59, depending on several factors, such as different precursors and NOx levels.The RIs of the SOAs are altered differently as the NOx concentration increases as follows: the RIs of the SOAs derived from benzene and toluene increase, whereas those of the SOAs derived from ethylbenzene and m-xylene decrease.Finally, by comparing the experimental data with the model values, we demonstrate that the models likely overestimate the RI values of the SOA particles to a certain extent, which in turn overestimates the global direct radiative forcing of the organic particles.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China.

ABSTRACT
The refractive index (RI) is the fundamental characteristic that affects the optical properties of aerosols, which could be some of the most important factors influencing direct radiative forcing. The secondary organic aerosols (SOAs) generated by the photooxidation of benzene, toluene, ethylbenzene and m-xylene (BTEX) under low-NOx and high-NOx conditions are explored in this study. The particles generated in our experiments are considered to be spherical, based on atomic force microscopy (AFM) images, and nonabsorbent at a wavelength of 532 nm, as determined by ultraviolet-visible light (UV-Vis) spectroscopy. The retrieved RIs at 532 nm for the SOAs range from 1.38-1.59, depending on several factors, such as different precursors and NOx levels. The RIs of the SOAs are altered differently as the NOx concentration increases as follows: the RIs of the SOAs derived from benzene and toluene increase, whereas those of the SOAs derived from ethylbenzene and m-xylene decrease. Finally, by comparing the experimental data with the model values, we demonstrate that the models likely overestimate the RI values of the SOA particles to a certain extent, which in turn overestimates the global direct radiative forcing of the organic particles.

No MeSH data available.


Related in: MedlinePlus