Aerosol Particles in the Middle Troposphere over the Northwestern Pacific

Ikegami, Machiko; Okada, Kikuo; Zaizen, Yuji; Makino, Yukio

doi:10.2151/jmsj1965.71.4_517

Cited by 20 publications

(7 citation statements)

References 27 publications

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“…AAC tent with the surface feature of the particles found in the SEM images of Figure 5; the mineral particles surrounded by traces of rings (Figure 5b) contained water-soluble compounds, whereas those unsurrounded (Figure 5a) did not. Sulfate-coated mineral particles have been found in the free troposphere ($4 km in altitude) over Japan [Iwasaka et al, 1988] and over the North Pacific Ocean [Ikegami et al, 1993]. Okada et al [1987Okada et al [ , 1990 have reported that these coated mineral particles are frequently present in the surface atmosphere in Japan during Asian dust events.…”

Section: Aerosol Morphology and Chemical Compositionmentioning

confidence: 99%

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

et al. 2003

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[1] The vertical distributions of tropospheric aerosol properties were measured during the Asian dust event over central Japan (35°-36°N, 136°-137°E), using a ground-based Raman lidar and aircraft-based instruments on 23 April 1996. The lidar measured enhancements of aerosol backscattering below an altitude of 4 km and between 5 and 8 km where the total aerosol linear depolarization ratio showed peaks of 12-15% and the relative humidities were $30%. The aircraft measurements showed that the aerosol particles consisted primarily of irregularly shaped mineral dusts and sea salts with a mode radius (r m ) of $1 mm and sulfates with r m $ 0.1 mm over the measured height range of 0.6-5.5 km. Electron microscopic analyses suggest that $77% of the mineral particles were coated with a solution at 1.8 km and that the fraction of coated particles decreased with height. The aerosol backscattering coefficients (b a ), calculated from the airborne optical particle counter (OPC) data, were smaller than the lidar-derived values by $30% above 3.1 km and by $44% below that altitude. The difference was attributable to the horizontal and temporal inhomogeneities of the aerosol properties between the measurement sites and to the uncertainty in b a , particularly for the coarse particles calculated from the OPC data. The aerosol depolarization ratios (d a ) estimated from the OPC data showed the same increase as those obtained with the lidar above 4.1 km. This suggests that the proportion of backscattering by coarse particles to total particles primarily controlled the d a measured with the lidar in that region.

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Section: Aerosol Morphology and Chemical Compositionmentioning

confidence: 99%

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

et al. 2003

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“…Asian dust-storm particles originating mainly in the desert and loess areas in China are transported widely to the atmosphere over Japan in spring (e. g., Ishizaka and Ono, 1982;Iwasaka et al, 1983;Kai et al, 1988;Murayama, 1988;Ikegami et al, 1993) and the North Pacific Ocean (Duce et al, 1980;Shaw, 1980;Uematsu et al, 1983). Asian duststorm particles act as efficient light extinction particles (Arao and Ishizaka, 1986) and ice nuclei (Isono et al, 1959).…”

Section: Introductionmentioning

confidence: 99%

Formation of Asian Dust-Storm Particles Mixed Internally with Sea Salt in the Atmosphere

Niimura

Okada²,

Fan

et al. 1998

Journal of the Meteorological Society of Japan

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In the spring of 1991, individual aerosol particles were collected on electron microscopic grids in Beijing (China) and Nagasaki (Japan). In order to study the change in the chemical composition of Asian duststorm particles during transport, the dust particles were examined using an electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer. An isentropic backward-trajectory analysis was carried out in order to obtain the transport path of the dust-storm particles. Spatial distributions of clouds by the Geostationary Meteorological Satellite (GMS) were also used in order to examine the presence of clouds along the transport path.Asian dust-storm particles mixed internally with sea salt (mixed particles) ranged from 16 to 100% among the dust particles in the air over Nagasaki. For the two cases that the same dust-storm events were observed in Beijing and Nagasaki, dust-storm particles containing sea salt were present abundantly in Nagasaki in a case that the air would have been influenced largely by clouds in the maritime atmosphere during the transport. It is suggested that these mixed dust-storm particles were formed by cloud processes.

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“…S. Bucci et al: Aerosol particle optical properties in the Po Valley -Mechanisms explaining the increase in scattering of mineral dust particles, along with a reduction of their depolarization ratio, can also be hypothesized (Ikegami et al, 1993;Murayama et al, 1999;Sassen et al, 2002;Zhou et al, 2002;Nee et al, 2007). It should be emphasized that, during the analysed case study, high relative humidity values (80 % or more) are observed in the lowermost non-depolarizing layer (see Fig.…”

Section: Mean Daily Variabilitymentioning

confidence: 83%

Vertical distribution of aerosol optical properties in the Po Valley during the 2012 summer campaigns

et al. 2018

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Abstract. Studying the vertical distribution of aerosol particle physical and chemical properties in the troposphere is essential to understand the relative importance of local emission processes vs. long-range transport for column-integrated aerosol properties (e.g. the aerosol optical depth, AOD, affecting regional climate) as well as for the aerosol burden and its impacts on air quality at the ground. The main objective of this paper is to investigate the transport of desert dust in the middle troposphere and its intrusion into the planetary boundary layer (PBL) over the Po Valley (Italy), a region considered one of the greatest European pollution hotspots for the frequency that particulate matter (PM) limit values are exceeded. Events of mineral aerosol uplift from local (soil) sources and phenomena of hygroscopic growth at the ground are also investigated, possibly affecting the PM concentration in the region as well. During the PEGASOS 2012 field campaign, an integrated observing–modelling system was set up based on near-surface measurements (particle concentration and chemistry), vertical profiling (backscatter coefficient profiles from lidar and radiosoundings) and Lagrangian air mass transport simulations by FLEXPART model. Measurements were taken at the San Pietro Capofiume supersite (44°39′ N, 11°37′ E; 11 m a.s.l.), located in a rural area relatively close to some major urban and industrial emissive areas in the Po Valley. Mt. Cimone (44°12′ N, 10°42′ E; 2165 m a.s.l.) WMO/GAW station observations are also included in the study to characterize regional-scale variability. Results show that, in the Po Valley, aerosol is detected mainly below 2000 m a.s.l. with a prevalent occurrence of non-depolarizing particles ( > 50 % throughout the campaign) and a vertical distribution modulated by the PBL daily evolution. Two intense events of mineral dust transport from northern Africa (19–21 and 29 June to 2 July) are observed, with layers advected mainly above 2000 m, but subsequently sinking and mixing in the PBL. As a consequence, a non-negligible occurrence of mineral dust is observed close to the ground ( ∼ 7 % of occurrence during a 1-month campaign). The observations unambiguously show Saharan dust layers intruding the Po Valley mixing layer and directly affecting the aerosol concentrations near the surface. Finally, lidar observations also indicate strong variability in aerosol on shorter timescales (hourly). Firstly, these highlight events of hygroscopic growth of anthropogenic aerosol, visible as shallow layers of low depolarization near the ground. Such events are identified during early morning hours at high relative humidity (RH) conditions (RH  > 80 %). The process is observed concurrently with high PM1 nitrate concentration (up to 15 µg cm−3) and hence mainly explicable by deliquescence of fine anthropogenic particles, and during mineral dust intrusion episodes, when water condensation on dust particles could instead represent the dominant contribution. Secondly, lidar images show frequent events (mean daily occurrence of ∼  22 % during the whole campaign) of rapid uplift of mineral depolarizing particles in afternoon–evening hours up to 2000 m a.s.l. height. The origin of such particles cannot be directly related to long-range transport events, being instead likely linked to processes of soil particle resuspension from agricultural lands.

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Aerosol Particles in the Middle Troposphere over the Northwestern Pacific

Cited by 20 publications

References 27 publications

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

Formation of Asian Dust-Storm Particles Mixed Internally with Sea Salt in the Atmosphere

Vertical distribution of aerosol optical properties in the Po Valley during the 2012 summer campaigns

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