Measurement report: The effect of aerosol chemical composition on light scattering due to the hygroscopic swelling effect
<p>Liquid water in aerosol particles has a significant effect on their optical properties, especially on light scattering, whose dependence on chemical composition is investigated here using measurements made in southern Beijing in 2019. The effect is measured by the particle light scattering...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/9977/2021/acp-21-9977-2021.pdf |
| Summary: | <p>Liquid water in aerosol particles has a significant effect on
their optical properties, especially on light scattering, whose dependence
on chemical composition is investigated here using measurements made in
southern Beijing in 2019. The effect is measured by the particle light
scattering enhancement <span class="inline-formula"><i>f</i></span>(RH), where RH denotes the relative humidity, which
is found to be positively and negatively impacted by the proportions of
inorganic and organic matter, respectively. Black carbon is also negatively
correlated. The positive impact is more robust when the inorganic matter
mass fraction was smaller than 40 % (<span class="inline-formula"><i>R</i>=0.93</span>, <span class="inline-formula"><i>R</i></span>: the Pearson's correlation
coefficient), becoming weaker as the inorganic matter mass fraction gets
larger (<span class="inline-formula"><i>R</i>=0.48</span>). A similar pattern was also found for the negative impact
of the organic matter mass fraction. Nitrate played a more significant role
in aerosol hygroscopicity than sulfate in Beijing. However, the
deliquescence point of ambient aerosols was at about RH <span class="inline-formula">=</span> 80 % when the
ratio of the sulfate mass concentration to the nitrate mass concentration of
the aerosol was high (mostly higher than <span class="inline-formula">∼</span> 4). Two schemes to
parameterize <span class="inline-formula"><i>f</i></span>(RH) were developed to account for the deliquescent and
non-deliquescent effects. Using only one <span class="inline-formula"><i>f</i></span>(RH) parameterization scheme to fit
all <span class="inline-formula"><i>f</i></span>(RH) processes incurs large errors. A piecewise parameterization scheme
is proposed, which can better describe deliquescence and reduces
uncertainties in simulating aerosol hygroscopicity.</p> |
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| ISSN: | 1680-7316 1680-7324 |