<p><strong>Abstract.</strong> Aerosol particles in marine atmosphere have been shown to significantly affect cloud formation, atmospheric optical properties, and climate change. However, high temporal and spatial resolved atmospheric measurements over sea are currently sparse, limiting our understanding of aerosol properties in marine atmosphere. In this study, a ship-based cruise campaign was conducted over northern South China Sea (SCS) region (19&#176;37&#8242;&#8201;N to 22&#176;43&#8242;&#8201;N, 113&#176;44&#8242;&#8201;E to 118&#176;12&#8242;&#8201;E) during summertime 2018. Chemical compositions of the non-refractory PM1 (NR-PM1), particle number size distribution (PNSD) and size-resolved cloud condensation nuclei (CCN) activity (at supersaturation ss&#8201;=&#8201;0.18&#8201;%, 0.34&#8201;%, and 0.59&#8201;%) were measured by a time-of-flight aerosol chemical speciation monitor (ToF-ACSM), and the combination of a cloud condensation nuclei counter (CCNc) and a scanning mobility particle sizer (SMPS), respectively. Overall, aerosol particles exhibited a unimodal distribution (centering at 60&#8764;80&#8201;nm) and dominated by sulfate (~46&#8201;%) in the NR-PM1, similar to the characteristic of previously-reported background marine aerosols. Two polluted episodes were respectively observed at the beginning (P1, 6th&#8211;8th August) and at the end (P2, 25th&#8211;26th August) of the campaign and both were characterized by high particle number concentrations (NCN) which were shown to originate from local emissions or pollutants from long range transport. Two relatively clean periods (C1, 9th&#8211;10th and C2, 19th&#8211;21st August) prior to and after tropical storm Bebinca (11th&#8211;15th August) were also classified due to substantial removal of pollutants by strong winds and rainfalls accompanying with the storm. A value of about 0.4 for aerosol hygroscopicity parameter &#954; measured in this study falls in a range of values (i.e., 0.2&#8211;1.0) reported previously for urban atmosphere and for remote marine atmosphere. </p> <p> The concentrations of trace gases (i.e., O<sub>3</sub>, CO, NO<sub>X</sub>) and particles (NCN and NCCN at ss&#8201;=&#8201;0.34&#8201;%) were elevated at the end of the campaign and decreased with the offshore distance, suggesting important impacts of anthropogenic emissions from the inland Pearl River Delta (PRD) region on the northern SCS. A good correlation between NOX concentration and NCN implies similar sources (e.g., heavy ship, traffic, and biomass burning) for NOx and particles. The results showed that the NCCN/NCN,tot and the &#954; values obtained from the CCNc measurement (ss&#8201;=&#8201;0.34&#8201;%) had no clear correlation either with the offshore distance or with the concentrations of the particles. Back trajectory analysis showed that the air pollutants originated from local emissions and from inland China continent via long range transport during P1 and P2, respectively. In addition, the air was affected by air masses from southwest and from Indo-China Peninsula during the clean C1 and C2 periods respectively. Chemical composition measurements showed an increase of organic mass fraction and no obviously different &#954; values were obtained from CCN measurements during C2 and P2, implying that the air masses carried pollutants from local sources during long range transport from Indo-China Peninsula and from the inland China continent respectively during the above two periods. Our study highlights dynamical variations of particle properties and the impact of long range transport from the China continent and Indo-China Peninsula on the northern SCS region during summertime.</p>
Abstract. Aerosol particles in marine atmosphere have been shown to significantly affect cloud formation, atmospheric optical properties, and climate change. However, high temporally and spatially resolved atmospheric measurements over the sea are currently sparse, limiting our understanding of aerosol properties in marine atmosphere. In this study, a ship-based cruise campaign was conducted over the northern South China Sea (SCS) region during summertime 2018. The chemical composition of non-refractory PM1 (NR-PM1), the particle number size distribution (PNSD), and size-resolved cloud condensation nuclei (CCN) activity were measured by a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) and the combination of a cloud condensation nuclei counter (CCNc) and a scanning mobility particle sizer (SMPS). Overall, aerosol particles exhibited a unimodal distribution centering at 60–80 nm and the chemical composition of the NR-PM1 was dominated by sulfate (∼ 46 %), which likely originated from anthropogenic emissions rather than dimethyl sulfide (DMS) oxidation. Two polluted episodes (P1 and P2) were observed, and both were characterized by high particle number concentrations (NCN) which originated from local emissions and from emissions in inland China via long-range transport. The concentrations of trace gases (i.e., O3, CO, NOx) and particles (NCN and NCCN at ss = 0.34 %) were elevated during P2 at the end of the campaign and decreased with offshore distance, further suggesting important impacts of anthropogenic emissions from the inland Pearl River Delta (PRD) region. Two relatively clean periods (C1 and C2) prior to and after tropical storm Bebinca were classified and the air was affected by air masses from the southwest and from the Indo-Chinese Peninsula, respectively. Chemical composition measurements showed an increase in organic mass fraction during P2 compared to C2; however, no obviously different κ values were obtained from the CCNc measurements, implying that the air masses carried pollutants from local sources during long-range transport. We report an average value of about 0.4 for the aerosol hygroscopicity parameter κ, which falls within the literature values (i.e., 0.2–1.0) for urban and remote marine atmosphere. In addition, our results showed that the CCN fraction (NCCN∕NCN, tot) and the κ values had no clear correlation either with the offshore distance or with concentrations of the particles. Our study highlights dynamical variations in particle properties and the impact of long-range transport from continental China and the Indo-Chinese Peninsula on the northern SCS region during summertime.
A 1‐month field campaign (May 29–June 29, 2018) was conducted at a mountain site (862 m above sea level) on the Wudang Mountains in China. The particle number size distribution (3–400 nm), size‐resolved cloud condensation nuclei (CCN, at 0.2% and 0.8% SS), and nonrefractory PM1 chemical composition were measured, respectively. The occurrence of the three chosen new particle formation (NPF) events (June 4, 7, and 11) was facilitated by southwest or west winds with a speed of about 3–4 m s−1. The hygroscopicity parameter (κ) value of newly grown particles varied in a wide range (0.25–0.8) during the events, leading to large uncertainties (−98% to 38%) on the NCCN prediction compared to the campaign. During growth of the newly formed particles for the three events, condensation of sulfuric acid vapor accounts for 14%–42%, 2%–8%, and 3%–9%, respectively, indicating that organic vapors may play an important role in particle growth. For plume‐type events with rapid growth, the observed high CCN activity (i.e., June 7 event) may be explained by the contribution of amines and depression of surface tension in the presence of organic surfactants during particle growth. Our study demonstrates that the contribution of NPF to CCN concentration is modulated by many key factors including growth rate, hygroscopicity, concentrations of new particles and preexisting particles, and variation of those factors from one event to another leads to large uncertainties on the CCN prediction.
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