Feature Article Earozoru Kenkyu, 26 4, 326 331 2011 1 Soot-Containing Particles in the Atmosphere: Modifications of Morphology and Mixing States with Water-Soluble Materials Sayako UEDA 1 * Received 31 May 2011 Accepted 10 November 2011 Abstract This study focused on modification effects of soot-containing particles by aging and incloud scavenging processes. Morphological features and mixing states with water-soluble materials of soot-containing particles collected at two observation sites were analyzed by a transmission electron microscopy (TEM) with extraction of water-soluble materials. To elucidate the aging effects after their transport from megacities, we obtained aerosol samples for continental outflow at Cape Hedo, Okinawa in March 2008. Most soot-containing particles (0.2 0.7 μm) were mixed with water-soluble materials. Some soot-containing particles were found as clustered particles in multiple small (ca. 0.3 μm) spheroids. They were attributed to coagulation of solid spheroidal particles. At Mt. Tateyama (2300 m a.s.l.) in June 2007, cloud interstitial particles were measured using fog (>10 μm)-cut inlets. During fog condition under high precipitation (2 6 mm/hr), most of cloud interstitial particles (0.3 0.5 μm) were less- or non-hygroscopic particles. The results of TEM analysis suggested that most of the cloud interstitial particles were soot particles without water-soluble materials. These observation results suggested that morphological modification with coagulation process under high aerosol concentration and population change of the particles with in-cloud scavenging process are key processes controlling morphology and mixing states of soot-containing particles in the atmosphere. These changes of soot-containing particles must be considered when estimating direct radiation effect of aerosols from megacities and assessing climatic effects by long range transport of soot aerosols. Keywords : Atmospheric Aerosol, Microscopic Analysis, Aging Process, Coagulation, In-Cloud Scavenging. 1,2 1 162-0825 1-3 1 Tokyo University of Science 1-3 Kagurazaka Shinjuku Tokyo 162-0825 * Corresponding Author. E-mail: ueda@rs.tus.ac.jp (S. Ueda) 2010 3,4 5,6 326 56
7 2 2008 3 8 3 2007 6 2300 m 9 4 nm 10 Okada 11 Pt/Pd arctan 0.5 Pt/Pd 0.1 0.5 μm Optical Particle Counter OPC, KC-18; Rion Particle Soot Absorption Photometer PSAP Radiance Research BC 0.5 μm 0.5 μm 88 0.56 μm less-grown LG OPC 9 Takami 12 Takiguchi 13 Q-AMS; Aerodyne Research PM 1.0 1 5 6 Fig. 1 Fig. 1 Temporal variations of (a) potential area of air mass origin, (b) volume concentrations of aerosols for 0.1 0.5 μm diameter and sampling times (A F with bars) and (c) size-segregated black carbon mass concentration. Vol. 26 No. 4 2011 57 327
BC 24 26 28 Fig. 1 B, D, F BC 0.3 μm 0.3 μm Fig. 1 A-F Fig. 2 Fig. 2a 10 nm Type 1 Fig. 2c 0.3 μm Type 5 Fig. 2a c Type 1 Type 5 10 nm Fig. 2a Fig. 2 Electron micrographs before and after water dialysis for Type 1 5 particles: (a), (b), (c) and (d) before water dialysis; (a ), (b ), (c ), and (d ) after dialysis with water for the same regions of (a), (b), (c), and (d). White arrows indicate morphological types. White dotted lines represent dimensions of particles before water dialysis. Black arrows indicate insoluble-soot cores. Fig. 2a 100 0.2 0.4 μm 2 25% 0.4 0.7 μm 14 59% 1% 80 0.2 0.7 μm 5 Type 1 Type 2 Type 3 Type 4 Type 5 0.3 μm X Type 1 C Type 2 3 4 5 S Q-AMS Cl - NO 3- SO 2-4 NH 4+ SO 2-4 NH 4+ 90% SO 2-4 Type 2 3 4 5 Fig. 3a A C Type 2 3 B D E F 0.4 μm Type 4 0.4 μm Type 5 Type 5 Type 4 Q-AMS A C NH 4 HSO 4 B D E F (NH 4 ) 2 SO 4 A C NH 4 HSO 4 39% 14 B D E F (NH 4 ) 2 SO 4 80% 15 Fig. 3b A C Type 2 3 B D E F 0.4 μm Type 4 0.4 μm Type 5 Fig. 3a Type 5 0.3 μm 16 328 58
Fig. 3 Number proportions of morphological types of (a) particles and (b) soot-containing particles, for samples A F. Numbers above columns show the number of particles observed. 10 μm LG Fig. 4 1 2 Fig. 4b 2 6 mm/hr 6 22 0.3 0.5 μm LG 100 Fig. 4a c BC 0.4 μm Fig. 4d 0.1 0.5 μm 0.4 μm BC 70% Fig. 4e 1 mm/hr LG 50% 0.1 0.5 μm 0.4 μm BC 20 Fig. 4 I, II, III LG I, II Fig. 5 I III LG 20% II 0.1 0.5 μm 9 BC 17 19 Vol. 26 No. 4 2011 59 329
Fig. 4 Temporal variations of (a) precipitation at Kamiichi, (b) number (black and gray lines) and volume (area plot) concentrations of aerosols with 0.1 0.5 μm in diameter, (c) number fraction of LG particles with 0.3 0.5 μm in diameter, (d) black carbon mass concentration, and (e) ratio in % of black carbon volume (V BC <0.4 ) per particle volume (V p 0.1 0.5 ). Durations of rain and fog, and sampling period were shown as bars. Fig. 5 Electron micrograph of cloud interstitial samples I and II: (a, b) before and (a, b ) after dialysis with water for the same sample region. 330 60
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