Nucleation-mode particle pool and large increases in <i>N</i>_cn and <i>N</i>_ccn observed over the northwestern Pacific Ocean in the spring of 2014

• Main Authors: J. Wang, Y. Shen, K. Li, Y. Gao, H. Gao, X. Yao
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-07-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/8845/2019/acp-19-8845-2019.pdf

<p>Determination of the updated concentrations of atmospheric particles (<span class="inline-formula"><i>N</i>_cn</span>) and the concentrations of cloud condensation nuclei (<span class="inline-formula"><i>N</i>_ccn</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>_cn</span>, <span class="inline-formula"><i>N</i>_ccn</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>_ccn</span> at supersaturation (SS) of levels 0.2&thinsp;% and 0.4&thinsp;% 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>&thinsp;cm<span class="inline-formula">⁻³</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>&thinsp;cm<span class="inline-formula">⁻³</span> for <span class="inline-formula"><i>N</i>_cn</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&thinsp;% and 0.4&thinsp;%, respectively, which are almost the same as those of upwind semi-urban sites. High <span class="inline-formula"><i>N</i>_ccn</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>_ccn</span> at 0.4&thinsp;% SS and the number concentrations of &gt;&thinsp;60&thinsp;nm particles (<span class="inline-formula"><i>N</i>_&gt;60 nm</span>) was obtained during the entire cruise period, with a slope of 0.98 and <span class="inline-formula"><i>R</i>²=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>_&gt;90 nm</span> varied largely. However, the <span class="inline-formula"><i>N</i>_&lt;30 nm</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>_cn</span> and <span class="inline-formula"><i>N</i>_ccn</span> were minor (i.e., 10&thinsp;% or less) on a monthly timescale.</p>