No abstract

Ship-borne measurements of ambient aerosols were conducted during an 11 937 km cruise over the Arctic Ocean (cruise 1) and the Pacific Ocean (cruise 2). A frequent nucleation event was observed during cruise 1 under marine influence, and the abundant organic matter resulting from the strong biological activity in the ocean could contribute to the formation of new particles and their growth to a detectable size. Concentrations of particle mass and black carbon increased with increasing continental influence from polluted areas. During cruise 1, multiple peaks of hygroscopic growth factor (HGF) of 1.1-1.2, 1.4, and 1.6 were found, and higher amounts of volatile organic species existed in the particles compared to that during cruise 2, which is consistent with the greater availability of volatile organic species caused by the strong oceanic biological activity (cruise 1). Internal mixtures of volatile and nonhygroscopic organic species, nonvolatile and less-hygroscopic organic species, and nonvolatile and hygroscopic nss-sulfate with varying fractions can be assumed to constitute the submicrometer particles. On the basis of elemental composition and morphology, the submicrometer particles were classified into C-rich mixture, S-rich mixture, C/S-rich mixture, Na-rich mixture, C/P-rich mixture, and mineral-rich mixture. Consistently, the fraction of biological particles (i.e., P-containing particles) increased when the ship traveled along a strongly biologically active area.

Cloud condensation nuclei (CCN) activation of black carbon (BC) particles coated with different amounts of inorganic (sulfuric acid) and organic (levoglucosan or succinic acid) compounds was investigated. An evaporation-condensation method was used to produce coated BC particles, and the volume fractions of coating species were measured using the tandem differential mobility analyzer method. Furthermore, the CCN activation of the coated BC particles was measured using a differential mobility analyzer-CCN counter method. Coating with both aforementioned compounds engendered the activation of the BC particles as CCN at a supersaturation of 0.5%. Sulfuric acid coating was associated with the highest CCN activation fraction (= CCN/condensation nuclei), followed by levoglucosan coating and then succinic acid coating; this indicates that the water solubility of the coating compounds played a crucial role in the CCN activation of the coated BC particles. In general, the CCN activation fraction of the coated BC particles increased with the volume fraction of the coating species, but the manner of increase differed with the coating compounds and generation method. A premixed solution method was also used to produce mixed BC particles, and among the coating compounds, sulfuric acid was associated with the highest CCN activation fraction. For a given volume fraction, sulfuric-acid-coated BC particles produced using the premixed solution method showed a higher CCN activation fraction compared with those obtained using the evaporation-condensation method, and this was due to the presence of residual water in the sulfuric-acid-coated BC particles produced using the premixed solution method.

No abstract

Mass concentrations of chemical constituents (organics, nitrate, sulfate, ammonium, chloride, and black carbon (BC)) and the number size distribution of submicrometer particles in the ambient atmosphere were continuously measured in urban Gwangju, Korea, during the Megacity Air Pollution Studies (MAPS)-Seoul campaign. Organics (9.1 μg/m3) were the most dominant species, followed by sulfate (4.7 μg/m3), nitrate (3.2 μg/m3), ammonium (2.6 μg/m3), and BC (1.3 μg/m3) in submicrometer particles (particulate matter less than 1 μm (PM1)). The potential source regions of the sulfate were located in the South and East regions of China and South and East regions of Korea, while local sources were responsible for the elevated BC concentration. Diurnal variation showed that concentrations of organics, nitrate, ammonium, chloride, and BC decreased with increasing mixing layer and wind speed (dilution effect), while sulfate and oxidized organics increased possibly due to their strong photochemical production in the afternoon. During the campaign, an elevated mass concentration of PM1 (PM1 event) and number concentration (nanoparticle formation (NPF) event) were observed (one PM1 event and nine NPF events out of 28 days). The PM1 event occurred with Western and Southwestern air masses with increasing sulfate and organics. Long-range transported aerosols and stagnant meteorological conditions favored the elevated mass concentration of submicrometer particles. Most of the NPF events took place between 10:00 and 14:00, and the particle growth rates after the initial nanoparticle formation were 7.2–11.0 nm/h. The times for increased concentration of nanoparticles and their growth were consistent with those for elevated sulfate and oxidized organics in submicrometer particles under strong photochemical activity.