Coal fly ash: linking immersion freezing behavior and physicochemical particle properties
<p>To date, only a few studies have investigated the potential of coal fly ash particles to trigger heterogeneous ice nucleation in cloud droplets. The presented measurements aim at expanding the sparse dataset and improving process understanding of how physicochemical particle properties...
| Main Authors: | , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-10-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/13903/2018/acp-18-13903-2018.pdf |
| Summary: | <p>To date, only a few studies have investigated the
potential of coal fly ash particles to trigger heterogeneous ice nucleation
in cloud droplets. The presented measurements aim at expanding the sparse
dataset and improving process understanding of how physicochemical particle
properties can influence the freezing behavior of coal fly ash particles
immersed in water.</p><p>Firstly, immersion freezing measurements were performed with two single
particle techniques, i.e., the Leipzig Aerosol Cloud Interaction Simulator
(LACIS) and the SPectrometer for Ice Nuclei (SPIN). The effect of suspension
time on the efficiency of the coal fly ash particles when immersed in a cloud
droplet is analyzed based on the different residence times of the two
instruments and employing both dry and wet particle
generation. Secondly, two
cold-stage setups, one using microliter sized droplets (Leipzig Ice
Nucleation Array) and one using nanoliter sized droplets (WeIzmann
Supercooled Droplets Observation on Microarray setup) were applied.</p><p>We found that coal fly ash particles are comparable to mineral dust in their
immersion freezing behavior when being dry generated. However, a significant
decrease in immersion freezing efficiency was observed during experiments
with wet-generated particles in LACIS and SPIN. The efficiency of
wet-generated particles is in agreement with the cold-stage measurements. In
order to understand the reason behind the deactivation, a series of chemical
composition, morphology, and crystallography analyses (single particle mass
spectrometry, scanning electron microscopy coupled with energy dispersive
X-ray microanalysis, X-ray diffraction analysis) were performed with dry- and
wet-generated particles. From these investigations, we conclude that
anhydrous CaSO<sub>4</sub> and CaO – which, if investigated in pure form, show the
same qualitative immersion freezing behavior as observed for dry-generated
coal fly ash particles – contribute to triggering heterogeneous ice nucleation
at the particle–water interface. The observed deactivation in contact with
water is related to changes in the particle surface properties which are
potentially caused by hydration of CaSO<sub>4</sub> and CaO. The contribution of coal
fly ash to the ambient population of ice-nucleating particles therefore
depends on whether and for how long particles are immersed in cloud droplets.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |