Hygroscopic properties and cloud condensation nuclei activation of limonene-derived organosulfates and their mixtures with ammonium sulfate
Organosulfates have been observed as constituents of atmospheric aerosols in a wide range of environments; however their hygroscopic properties remain uncharacterised. Here, limonene-derived organosulfates with a molecular weight of 250 Da (L-OS 250) were synthesised and used for simultaneous measur...
| Main Authors: | , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-12-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/14071/2015/acp-15-14071-2015.pdf |
| Summary: | Organosulfates have been observed as constituents of atmospheric aerosols in
a wide range of environments; however their hygroscopic properties remain
uncharacterised. Here, limonene-derived organosulfates with a molecular
weight of 250 Da (L-OS 250) were synthesised and used for simultaneous
measurements with a hygroscopicity tandem differential mobility analyser
(H-TDMA) and a cloud condensation nuclei counter (CCNC) to determine the
hygroscopicity parameter, κ, for pure L-OS 250 and mixtures of
L-OS 250 with ammonium sulfate (AS) over a wide range of humidity conditions.
The κ values derived from measurements with H-TDMA decreased with
increasing particle dry diameter for all
chemical compositions investigated, indicating that κ<sub>H-TDMA</sub>
depends on particle diameter and/or
surface effects; however, it is not clear if this trend is statistically
significant. For pure L-OS 250, κ was found to increase with
increasing relative humidity, indicating dilution/solubility effects to be
significant. Discrepancies in κ between the sub- and supersaturated
measurements were observed for L-OS 250, whereas κ of AS and mixed
L-OS 250/AS were similar. This discrepancy was primarily ascribed to limited
dissolution of L-OS 250 at subsaturated conditions. In general, hygroscopic
growth factor, critical particle diameter and κ for the mixed
L-OS 250/AS particles converged towards the values of pure AS for mixtures
with ≥ 20 % w / w AS. Surface tension measurements of bulk
aqueous L-OS 250/AS solutions showed that L-OS 250 was indeed surface active,
as expected from its molecular structure, decreasing the surface tension of
solutions with 24 % from the pure water value at a L-OS 250 concentration
of 0.0025 mol L<sup>−1</sup>. Based on these surface tension measurements, we
present the first concentration-dependent parametrisation of surface tension
for aqueous L-OS 250, which was implemented to different process-level models
of L-OS 250 hygroscopicity and CCN activation. The values of κ
obtained from the measurements were compared with κ calculated
applying the volume additive Zdanovskii–Stokes–Robinson mixing rule, as
well as κ modelled from equilibrium Köhler theory with different
assumptions regarding L-OS 250 bulk-to-surface partitioning and aqueous
droplet surface tension. This study is to our knowledge the first to
investigate the hygroscopic properties and surface activity of L-OS 250;
hence it is an important first step towards understanding the atmospheric
impact of organosulfates. |
|---|---|
| ISSN: | 1680-7316 1680-7324 |