How ship exhaust particles change cloud activity
Implications for Arctic mixed-phase clouds
Abstract
The Arctic is experiencing surface warming rates that exceed those observed at lower latitudes.
This is caused by a complex system of feedback mechanisms in the Arctic climate system and
is referred to as Arctic Amplification. Persistent mixed-phase clouds cover large areas of the
Arctic region and thus, have a substantial impact on the radiative budget in the Arctic. One
consequence of the amplified warming is that Arctic sea-ice extent has been decreasing over
the past decades. With the rapid decline in sea-ice extent, shipping activity is projected to
significantly increase due to easier accessibility and availability of shorter transportation
routes. Ships are also a significant source of atmospheric pollutants, which include greenhouse
gases, sulfur oxides (SOx) and particulate matter (PM). Increased local emissions of such
pollutants may perturb the natural state of Arctic clouds and thus, can lead to further climatic
feedbacks.
Simultaneous with climate change, the shipping sector is undergoing regulatory
changes aimed at reducing exhaust emissions of climate- and health-affecting substances. SOx
and PM emissions have been strongly linked to tens of thousands of premature deaths
worldwide. As a result, the International Maritime Organization (IMO) implemented
regulations that aim to reduce emissions of SOx and indirectly, of PM to atmosphere.
Respective IMO regulations mandate ships to either use fuels with reduced fuel sulfur content
(FSC) or to use exhaust aftertreatment systems, such as wet scrubbers, in instances where ships
continue to utilize non-compliant high sulfur content fuels. Both, FSC reduction and exhaust
wet scrubbing change physicochemical properties of exhaust particles and may therefore, lead
to climate feedbacks.
A series of laboratory engine experiments were performed to characterize
impacts of FSC reduction and exhaust wet scrubbing on the physicochemical properties of
exhaust particles. The secondary impact of compliance choices on exhaust particles’ cloud
activity, including liquid droplet and ice crystal formation, was a particular focus. Results from
laboratory experiments were subsequently implemented into a cloud-resolving large eddy
simulation model, in an effort to quantify the impact of additional ship aerosol particles on
micro- and macrophysical properties of an Arctic mixed-phase cloud.
Results presented in this study illustrate how international regulations in the
shipping sector may affect atmospheric processes. We observed that FSC reduction and wet
scrubbing have opposing effects on exhaust particles’ ability to form liquid droplets in the
atmosphere. These results are supported by observed changes in particles’ chemical mixing
states. Moreover, we find that the impact of wet scrubbing on exhaust particle properties varies
substantially between experiments and between marine engines. Wet scrubbing may lead to
particle emission profiles, which counteract the intended aims of the IMO regulation. This may
have further consequences for health- and climate-related issues.
Our modelling study suggests that ship aerosol may lead to increased cloud
droplet and decreased raindrop number concentrations. Consequently, a reduction in surface
precipitation and reduced longwave radiative surface cooling were observed. Nevertheless,
changes in cloud properties were mostly observed when ship particle number concentrations
were significantly increased and/or strongly depended on the aerosol particle properties.
Increased shipping activity in the Arctic may lead to further climate feedbacks,
but as demonstrated in this thesis, the magnitude of the induced changes strongly depends on
fuels and engines, and whether exhaust aftertreatment systems are utilized. Given continuous
changes in the shipping sector, it becomes challenging to predict how ship exhaust emissions
in the Arctic may evolve over the next decades. New regulations are emerging, and the
consequences should be studied as the Arctic is one of Earth’s most pristine and sensitive
regions, where increased shipping activity may lead to substantial environmental impacts.
Parts of work
Luis F. E. d. Santos, Kent Salo and Erik S. Thomson
Quantification and physical analysis of nanoparticle emissions from a marine
engine using different fuels and a laboratory wet scrubber. Environmental Science:
Processes & Impacts (2022), 24, 1769-1781.
https://doi.org/10.1039/D2EM00054G Luis F. E. d. Santos, Kent Salo, Xiangrui Kong, Jun Noda, Thomas Kristensen,
Takuji Ohigashi, Erik S Thomson
Changes in CCN activity of ship exhaust particles induced by fuel sulfur content
reduction and wet scrubbing. Environmental Science: Atmosphere (2023), 3, 182-
195.
https://doi.org/10.1039/D2EA00081D Luis F. E. d. Santos, Kent Salo, Xiangrui Kong, Markus Hartmann, Jonas Sjöblom,
and Erik S. Thomson
Ship aerosol emissions and marine fuel regulations: Impacts on physicochemical
properties, cloud activity and emission factors. Manuscript submitted to Journal
of Geophysical Research: Atmospheres. Under review.
https://doi.org/10.22541/essoar.170067090.01725875/v1 Luis F. E. d. Santos, Hannah C. Frostenberg, Alejandro Baró Pérez, Annica M. L.
Ekman, Luisa Ickes and Erik S Thomson
Arctic mixed-phase cloud responses from increased shipping activity. Manuscript
planned for submission to Atmospheric Chemistry and Physics.
University
University of Gothenburg. Faculty of Science
Institution
Department of Chemistry and Molecular Biology ; Institutionen för kemi och molekylärbiologi
Disputation
Friday, 2nd of February 2024, at 10:15 in room 2256 R Sandberg, Medicinaregatan 7
Date of defence
2024-02-02
luis.santos@cmb.gu.se
Date
2024-01-08Author
Escusa dos Santos, Luis Filipe
Keywords
Aerosol particles
Mixed-phase clouds
Ship emissions
Arctic
Maritime regulations
Publication type
Doctoral thesis
ISBN
978-91-8069-579-4 (PRINT)
978-91-8069-580-0 (PDF)
Language
eng