Influence of natural and anthropogenic aerosols on cloud base droplet size distributions in clouds over the South China Sea and West Pacific
<p>Cumulus clouds are common over maritime regions. They are important regulators of the global radiative energy budget and global hydrologic cycle, as well as a key contributor to the uncertainty in anthropogenic climate change projections due to uncertainty in aerosol–cloud interactions. The...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/8959/2023/acp-23-8959-2023.pdf |
| Summary: | <p>Cumulus clouds are common over maritime regions. They are
important regulators of the global radiative energy budget and global
hydrologic cycle, as well as a key contributor to the uncertainty in anthropogenic
climate change projections due to uncertainty in aerosol–cloud interactions.
These interactions are regionally specific owing to their strong influences
on aerosol sources and meteorology. Here, our analysis focuses on the
statistical properties of marine boundary layer (MBL) aerosol chemistry and
the relationships of MBL aerosol to cumulus cloud properties just above
cloud base as sampled in 2019 during the NASA Cloud, Aerosol and Monsoon
Processes Philippines Experiment (CAMP<span class="inline-formula"><sup>2</sup></span>Ex). The aerosol and clouds were
sampled by instruments on the NASA P-3 aircraft over three distinct maritime
regions around the Philippines: the West Pacific, the South China Sea, and
the Sulu Sea.</p>
<p>Our analysis shows three primary sources influenced the aerosol chemical
composition: clean marine (ocean source), industrial (Southeast Asia,
Manila, and cargo and tanker ship emissions), and biomass burning (Borneo
and Indonesia). The clean marine aerosol chemical composition had low values
of all sampled chemical signatures, specifically median values of 2.2 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span> of organics (ORG), 2.3 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span> of <span class="inline-formula">SO<sub>4</sub></span>, 0.3 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span> of <span class="inline-formula">NO<sub>3</sub></span>, 1.4 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span> of <span class="inline-formula">NH<sub>4</sub></span>, 0.04 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span> of Cl, and 0.0074 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span> of refractory black
carbon (BC). Chemical signatures of the other two aerosol source regions
were industrial, with elevated <span class="inline-formula">SO<sub>4</sub></span> having a median value of 6.1 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span>, and biomass burning, with elevated median concentrations
of ORG 21.2 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span> and BC 0.1351 <span class="inline-formula">µg</span> m<span class="inline-formula"><sup>−3</sup></span>. Based on
chemical signatures, the industrial component was primarily from ship
emissions, which were sampled within 60 km of ships and within projected
ship plumes. Normalized cloud droplet size distributions in clouds sampled
near the MBL passes of the P-3 showed that clouds impacted by industrial and
biomass burning contained higher concentrations of cloud droplets, by as
much as 1.5 orders of magnitude for diameters <span class="inline-formula"><</span> 13 <span class="inline-formula">µm</span>
compared to clean marine clouds, while at size ranges between 13.0–34.5 <span class="inline-formula">µm</span> the median concentrations of cloud droplets in all aerosol
categories were nearly an order of magnitude less than the clean marine
category. In the droplet size bins centered at diameters <span class="inline-formula">></span> 34.5 <span class="inline-formula">µm</span> concentrations were equal to, or slightly exceeded, the
concentrations of the clean marine clouds. These analyses show that
anthropogenic aerosols generated from industrial and biomass<span id="page8960"/> burning sources
significantly influenced cloud base microphysical structure in the
Philippine region enhancing the small droplet concentration and reducing the
concentration of mid-sized droplets.</p> |
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| ISSN: | 1680-7316 1680-7324 |