Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities
To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates wi...
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doaj-de3b01f723744a64b7dc41aee832e9ed2020-11-24T22:33:49ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242016-07-01168817883010.5194/acp-16-8817-2016Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacitiesM. Song0M. Song1P. F. Liu2S. J. Hanna3R. A. Zaveri4K. Potter5Y. You6S. T. Martin7S. T. Martin8A. K. Bertram9Department of Chemistry, University of British Columbia, Vancouver, BC, CanadaDepartment of Earth and Environmental Sciences, Chonbuk National University, Jeollabuk-do, Republic of KoreaJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USADepartment of Chemistry, University of British Columbia, Vancouver, BC, CanadaAtmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USASchool of Chemistry, University of Bristol, Bristol, UKDepartment of Chemistry, University of British Columbia, Vancouver, BC, CanadaJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USADepartment of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USADepartment of Chemistry, University of British Columbia, Vancouver, BC, CanadaTo improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as <i>α</i>-pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2 × 10<sup>−1</sup> to ∼ 6 × 10<sup>6</sup> Pa s from 30 to 90 % RH, and greater than ∼ 2 × 10<sup>8</sup> Pa s (similar to or greater than the viscosity of tar pitch) for RH ≤ 17 %. These viscosities correspond to Stokes–Einstein-equivalent diffusion coefficients for large organic molecules of ∼ 2 × 10<sup>−15</sup> cm<sup>2</sup> s<sup>−1</sup> for 30 % RH, and lower than ∼ 3 × 10<sup>−17</sup> cm<sup>2</sup> s<sup>−1</sup> for RH ≤ 17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1–5 h for 30 % RH, and higher than ∼ 100 h for RH ≤ 17 %. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be well-mixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00–17:00 LT) during certain times of the year.https://www.atmos-chem-phys.net/16/8817/2016/acp-16-8817-2016.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
M. Song M. Song P. F. Liu S. J. Hanna R. A. Zaveri K. Potter Y. You S. T. Martin S. T. Martin A. K. Bertram |
spellingShingle |
M. Song M. Song P. F. Liu S. J. Hanna R. A. Zaveri K. Potter Y. You S. T. Martin S. T. Martin A. K. Bertram Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities Atmospheric Chemistry and Physics |
author_facet |
M. Song M. Song P. F. Liu S. J. Hanna R. A. Zaveri K. Potter Y. You S. T. Martin S. T. Martin A. K. Bertram |
author_sort |
M. Song |
title |
Relative humidity-dependent viscosity of secondary organic material from
toluene photo-oxidation and possible implications for organic particulate
matter over megacities |
title_short |
Relative humidity-dependent viscosity of secondary organic material from
toluene photo-oxidation and possible implications for organic particulate
matter over megacities |
title_full |
Relative humidity-dependent viscosity of secondary organic material from
toluene photo-oxidation and possible implications for organic particulate
matter over megacities |
title_fullStr |
Relative humidity-dependent viscosity of secondary organic material from
toluene photo-oxidation and possible implications for organic particulate
matter over megacities |
title_full_unstemmed |
Relative humidity-dependent viscosity of secondary organic material from
toluene photo-oxidation and possible implications for organic particulate
matter over megacities |
title_sort |
relative humidity-dependent viscosity of secondary organic material from
toluene photo-oxidation and possible implications for organic particulate
matter over megacities |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2016-07-01 |
description |
To improve predictions of air quality, visibility, and climate change,
knowledge of the viscosities and diffusion rates within organic particulate
matter consisting of secondary organic material (SOM) is required. Most
qualitative and quantitative measurements of viscosity and diffusion rates
within organic particulate matter have focused on SOM particles generated
from biogenic volatile organic compounds (VOCs) such as <i>α</i>-pinene and isoprene. In this study, we
quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K
of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The
viscosities of toluene-derived SOM were 2 × 10<sup>−1</sup> to ∼ 6 × 10<sup>6</sup> Pa s from 30 to 90 % RH, and greater than
∼ 2 × 10<sup>8</sup> Pa s (similar to or greater than the
viscosity of tar pitch) for RH ≤ 17 %. These viscosities
correspond to Stokes–Einstein-equivalent diffusion coefficients for large
organic molecules of ∼ 2 × 10<sup>−15</sup> cm<sup>2</sup> s<sup>−1</sup> for
30 % RH, and lower than
∼ 3 × 10<sup>−17</sup> cm<sup>2</sup> s<sup>−1</sup> for RH ≤ 17 %.
Based on these estimated diffusion coefficients, the mixing time of large
organic molecules within 200 nm toluene-derived SOM particles is 0.1–5 h
for 30 % RH, and higher than ∼ 100 h for RH ≤ 17 %. As
a starting point for understanding the mixing times of large organic
molecules in organic particulate matter over cities, we applied the mixing
times determined for toluene-derived SOM particles to the world's top 15 most
populous megacities. If the organic particulate matter in these megacities is
similar to the toluene-derived SOM in this study, in Istanbul, Tokyo,
Shanghai, and São Paulo, mixing times in organic particulate matter during
certain periods of the year may be very short, and the particles may be
well-mixed. On the other hand, the mixing times of large organic molecules in
organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be
long and the particles may not be well-mixed in the afternoon
(15:00–17:00 LT) during certain times of the year. |
url |
https://www.atmos-chem-phys.net/16/8817/2016/acp-16-8817-2016.pdf |
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