Nucleation-mode particle pool and large increases in <i>N</i><sub>cn</sub> and <i>N</i><sub>ccn</sub> observed over the northwestern Pacific Ocean in the spring of 2014
<p>Determination of the updated concentrations of atmospheric particles (<span class="inline-formula"><i>N</i><sub>cn</sub></span>) and the concentrations of cloud condensation nuclei (<span class="inline-formula"><i>N</i&g...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/8845/2019/acp-19-8845-2019.pdf |
| Summary: | <p>Determination of the updated concentrations of atmospheric
particles (<span class="inline-formula"><i>N</i><sub>cn</sub></span>) and the concentrations of cloud condensation nuclei
(<span class="inline-formula"><i>N</i><sub>ccn</sub></span>) over the northwestern Pacific Ocean (NWPO) are important to
accurately evaluate the influence of aerosol outflow from the Asian
continent on the climate by considering the rapid changes in emissions of
air pollutants therein. However, field observations in the last two decades
are scarce. We conducted a cruise campaign over the NWPO to simultaneously
measure <span class="inline-formula"><i>N</i><sub>cn</sub></span>, <span class="inline-formula"><i>N</i><sub>ccn</sub></span> and the size distribution of aerosol particles
from day of year (DOY) 81 to DOY 108 of 2014. The mean values of <span class="inline-formula"><i>N</i><sub>ccn</sub></span>
at supersaturation (SS) of levels 0.2 % and 0.4 % were <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.68</mn><mo>±</mo><mn mathvariant="normal">0.38</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">3</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="84pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="686d8131701e122c575a6f7b19971d41"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-8845-2019-ie00001.svg" width="84pt" height="14pt" src="acp-19-8845-2019-ie00001.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1.1</mn><mo>±</mo><mn mathvariant="normal">0.67</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">3</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="78pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="60297161ccf1b4c85ab862a3bd654183"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-8845-2019-ie00002.svg" width="78pt" height="14pt" src="acp-19-8845-2019-ie00002.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>−3</sup></span>, respectively, with an average of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">2.8</mn><mo>±</mo><mn mathvariant="normal">1.0</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">3</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="72pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="780f93c4987a9f58c44aedb9e905d9bf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-8845-2019-ie00003.svg" width="72pt" height="14pt" src="acp-19-8845-2019-ie00003.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>−3</sup></span> for <span class="inline-formula"><i>N</i><sub>cn</sub></span> during the cruise over the NWPO.
All are approximately 1 order of magnitude larger than spring observations
made during the preceding two decades in the remote marine atmosphere. The
larger values, against the marine natural background reported in the
literature, imply an overwhelming contribution from continental inputs. The
calculated activity ratios (ARs) of the cloud condensation nuclei (CCN) were
<span class="inline-formula">0.30±0.11</span> and <span class="inline-formula">0.46±0.19</span> at SS levels of 0.2 % and 0.4 %,
respectively, which are almost the same as those of upwind semi-urban sites.
High <span class="inline-formula"><i>N</i><sub>ccn</sub></span> and CCN activities were observed from DOY 98 to DOY 102, when
the oceanic zone received even stronger continental input. Excluding biomass
burning (BB) and dust aerosols, good correlation between <span class="inline-formula"><i>N</i><sub>ccn</sub></span> at
0.4 % SS and the number concentrations of > 60 nm particles
(<span class="inline-formula"><i>N</i><sub>>60 nm</sub></span>) was obtained during the entire cruise period, with a
slope of 0.98 and <span class="inline-formula"><i>R</i><sup>2</sup>=0.94</span>, and the corresponding
effective hygroscopicity parameter (<span class="inline-formula"><i>κ</i></span>) was estimated to be 0.40. A
bimodal size distribution pattern of the particle number concentration was
generally observed during the entire campaign when the <span class="inline-formula"><i>N</i><sub>>90 nm</sub></span> varied
largely. However, the <span class="inline-formula"><i>N</i><sub><30 nm</sub></span>, accounting for approximately
one-third of the total number concentration, varied narrowly, and two NPF
events associated with vertical transport were observed. This implies that a
pool of nucleation-mode atmospheric particles is aloft. BB and dust events
were observed over the NWPO, but their aerosol contributions to <span class="inline-formula"><i>N</i><sub>cn</sub></span> and
<span class="inline-formula"><i>N</i><sub>ccn</sub></span> were minor (i.e., 10 % or less) on a monthly timescale.</p> |
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| ISSN: | 1680-7316 1680-7324 |