Large increases in N<sub>cn</sub> and N<sub>ccn</sub> together with a nucleation-modeparticle pool over the northwestern Pacific Ocean in the spring of 2014

Abstract

<p><strong>Abstract.</strong> The updated concentrations of atmospheric particles (N<sub>cn</sub>) and the concentrations of cloud condensation nuclei (N<sub>ccn</sub>) over the northwestern Pacific Ocean (NWPO) were important to accurately evaluate the influence of aerosol outflow from the Asian continent on the climate by considering rapid changes in emissions of air pollutants therein. However, field observations were scarce in the last two decades. We conducted a cruise campaign over the NWPO to simultaneously measure N<sub>cn</sub>, N<sub>ccn</sub> and the size distribution of aerosol particles from DOY 81 to DOY 108 of 2014. The mean values of N<sub>ccn</sub> at supersaturation (SS) of 0.2 % and 0.4 % were 0.68 ± 0.38×10<sup>3</sup> cm<sup>−3</sup> and 1.1 ± 0.67×10<sup>3</sup> cm<sup>−3</sup>, respectively, with an average for Ncn of 2.8 ± 1.0×10<sup>3</sup> cm<sup>−3</sup> during the cruise over the NWPO, which were all approximately one order of magnitude larger than spring observations from two decades ago in the atmosphere of remote marine areas. The higher values, against the marine natural background reported in the literature, implied an overwhelming contribution from continental inputs. The calculated CCN activity ratios were 0.30 ± 0.11 and 0.46 ± 0.19 at SS of 0.2 % and 0.4 %, respectively, which were almost the same as those of upwind semi-urban sites. High N<sub>ccn</sub> and CCN activities were observed from DOY 98 to 102, when the oceanic zone received even stronger continental inputs. During the whole cruise period with the exclusion of biomass burning and dust aerosols, a good correlation between N<sub>ccn</sub> at 0.4 % SS and the number concentrations of > 60 nm particles (N<sub>> 60 nm</sub>), with the slope of 0.98 and R<sup>2</sup> = 0.94, was obtained, and the corresponding effective hygroscopicity parameter (<i>k</i>) was estimated as 0.40. The bimodal size distribution pattern of the particle number concentration was generally observed during the entire campaign when the N<sub>> 90 nm</sub> varied largely. However, the N<sub>< 30 nm</sub>, accounting for approximately 1 / 3 of the total number concentration, varied narrowly, and two NPF events associated with vertical transport were observed, implying a pool of nucleation mode atmospheric particles aloft. Biomass burning (BB) and dust events were observed over the NWPO, but the contributions of BB and dust aerosols to N<sub>cn</sub> and N<sub>ccn</sub> were minor (i.e., 10 % or less) on the monthly time scale.</p>