Limits...
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

Dependence of the extinction efficiencies of the polydispersed SOA particles on the surface mean diameter at a wavelength of 532 nm and the retrieved RIs for the following.(a) the L1, L2, L5 and L7 low-NOx experiments; (b) the classical high-NOx experiments; (c) the HONO experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4017213&req=5

f3: Dependence of the extinction efficiencies of the polydispersed SOA particles on the surface mean diameter at a wavelength of 532 nm and the retrieved RIs for the following.(a) the L1, L2, L5 and L7 low-NOx experiments; (b) the classical high-NOx experiments; (c) the HONO experiments.

Mentions: Fig. 3a depicts the dependence of Qext on the surface mean diameter and the retrieved RIs of the BTEX SOAs under the low-NOx condition. The concentrations of hydrocarbon and oxidant are identical. The temperature and relative humidity (RH) conditions are similar (with a fluctuation of <2°C and <4% RH, respectively). As illustrated in the figure, the measured extinction efficiencies generally conform to the Mie scattering curves, and the RI values are in the range of 1.45–1.52. Studies that explore the RIs of these four aromatic hydrocarbons under low-NOx conditions are lacking; therefore, only limited data can be contrasted. Note that the m-xylene SOA has the largest RI value at 1.52, followed by the ethylbenzene SOA at 1.478, the benzene SOA at 1.464 and the toluene SOA, which has the smallest RI value at 1.45. It is well known that hydrocarbons react with OH to produce RO2, and the RO2 can then react with HO2, NO and RO251. Under this condition, there is no detectable NO; therefore, we can attribute these RI values to the RIs of the BTEX SOAs generated through the RO2 + RO2 and RO2 + HO2 pathways. The different RI values are attributed to the different components of the products. Although undergoing similar reaction pathways under the low-NOx condition, m-xylene tends to produce products with high RI values. The data also reveal that the benzene SOA particles are smaller in size than the other particles, leading to markedly smaller final extinction efficiencies. This result is likely due to the different structure of the precursors. With no alkyl group attached to the benzene ring, benzene is less reactive than the other alkyl-substituted aromatics34.


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)

Dependence of the extinction efficiencies of the polydispersed SOA particles on the surface mean diameter at a wavelength of 532 nm and the retrieved RIs for the following.(a) the L1, L2, L5 and L7 low-NOx experiments; (b) the classical high-NOx experiments; (c) the HONO experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Dependence of the extinction efficiencies of the polydispersed SOA particles on the surface mean diameter at a wavelength of 532 nm and the retrieved RIs for the following.(a) the L1, L2, L5 and L7 low-NOx experiments; (b) the classical high-NOx experiments; (c) the HONO experiments.
Mentions: Fig. 3a depicts the dependence of Qext on the surface mean diameter and the retrieved RIs of the BTEX SOAs under the low-NOx condition. The concentrations of hydrocarbon and oxidant are identical. The temperature and relative humidity (RH) conditions are similar (with a fluctuation of <2°C and <4% RH, respectively). As illustrated in the figure, the measured extinction efficiencies generally conform to the Mie scattering curves, and the RI values are in the range of 1.45–1.52. Studies that explore the RIs of these four aromatic hydrocarbons under low-NOx conditions are lacking; therefore, only limited data can be contrasted. Note that the m-xylene SOA has the largest RI value at 1.52, followed by the ethylbenzene SOA at 1.478, the benzene SOA at 1.464 and the toluene SOA, which has the smallest RI value at 1.45. It is well known that hydrocarbons react with OH to produce RO2, and the RO2 can then react with HO2, NO and RO251. Under this condition, there is no detectable NO; therefore, we can attribute these RI values to the RIs of the BTEX SOAs generated through the RO2 + RO2 and RO2 + HO2 pathways. The different RI values are attributed to the different components of the products. Although undergoing similar reaction pathways under the low-NOx condition, m-xylene tends to produce products with high RI values. The data also reveal that the benzene SOA particles are smaller in size than the other particles, leading to markedly smaller final extinction efficiencies. This result is likely due to the different structure of the precursors. With no alkyl group attached to the benzene ring, benzene is less reactive than the other alkyl-substituted aromatics34.

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