Masahiro Nagatani

Polar stratospheric clouds observed by lidar over Spitsbergen in the winter of 1994/1995: Liquid particles and vertical “sandwich” structure

Polar stratospheric clouds (PSCs) were observed by lidar at Ny-Alesund, Spitsbergen, in December 1994 and January 1995. The backscattering coefficient at wavelengths of 1064 and 532 nm and the depolarization ratio at 532 nm of PSCs were measured by the lidar system. The stratospheric temperature was below the estimated frost point of nitric acid tri-hydrate (NAT) in the winter of 1994/1995. PSCs were observed more frequently in this low-temperature period than in previous winters since 1991. The characteristics of the PSCs were very variable but had a noticeable vertical “sandwich” structure in January in which a layer of liquid PSC particles at the altitude around 20 km existed between the two solid particle layers. The wavelength dependence of the backscattering shows that the size of both liquid and solid particles was larger than the average size of background stratospheric aerosols. Lidar observations of the liquid layer particles show characteristics in qualitative agreement with those expected from model PSC particles grown in ternary solutions of H2SO4, HNO3, and H2O with a temperature decrease. However, the observed backscattering coefficient and its wavelength dependence indicate that PSC particles require further growth than that predicted by the ternary solution model at temperature where most HNO3 molecules in the surrounding atmosphere are considered to be condensed on PSCs.

Changes in ionic constituents of free tropospheric aerosol particles obtained at Mt. Norikura (2770 m a.s.l.), central Japan, during the Shurin period in 2000

Abstract Free tropospheric aerosols and O 3 concentrations with meteorological parameters were observed at the Norikura Cosmic-Ray Observatory ( 2770 m a.s.l.) near the top of Mt. Norikura, central Japan from 1 September to 8 October 2000. The study period represents the Shurin period in Japan, which is a transition period of dominant air masses over Japan. Automated air sampling was conducted during nighttime: from 00 midnight to 06 a.m. every day to collect free tropospheric aerosols particles under subsidence air flow condition over the mountain. Results of ionic concentrations suggested that the observation period was divided into 2 periods: one was higher equivalent ratios (>1) of non-sea salt (nss) SO 4 2− /NH 4 + until 17 September and the other was slightly above unity of the ratio after that. O 3 concentrations also shifted simultaneously to higher and stable conditions. Concentrations of oxalate, nssK + , and nssCa 2+ were also higher in the later period. Molar ratios of nssSr/nssCa and nssMg/nssCa in the samples were about 0.0024 and 0.172, respectively. These values were very close to ratios found in the desert area in China. Backward air trajectory analysis for the period of high nssCa 2+ suggested that Asian dust with pollutants were not only transported in spring but also in fall from the Asian continent to the free troposphere over Japan.

Vertical variations of sea-salt modification in the boundary layer of spring Arctic during the ASTAR 2000 campaign

Abstract Airborne and ground-based aerosol/gas measurements were carried out in Svalbard between mid-March and mid-April 2000. From the viewpoint of vertical features of sea-salt modification in the lower troposphere (1500 m) of the Arctic spring, more than 1000 individual sea-salt particles were analyzed with scanning electron microscopy energy dispersive X-ray spectrometry (SEM-EDX) in the present study. Individual particle analysis suggested a vertical gradient of sea-salt modification in fine sea-salt particles with an altitude of 59–1485 m above sea level (asl), e.g. chlorine liberation rates of 33.0% (212 m asl) and 81.0% (1266 m asl) on 15 March, and 72.7% (100 m asl), 83.8% (495 m asl) and 95.8% (1411 m asl) on 26 March. Sea salts may be dominantly modified with SO2 and SO42− under Arctic haze conditions with higher SO2 concentration (≥2 nmol m−3), whereas they are dominantly modified with NO3− and reactive nitrogen oxides under Arctic background conditions, with [HNO3] of 0.15–1.3 nmol m−3 and [SO2] of 0.04–2 nmol m−3. Vertical trends in sea-salt modification suggested that it makes a significant contribution to the formation of reactive halogen species in the upper boundary layer and the lower free troposphere of the spring Arctic.

Nature of Atmospheric Aerosols over the Desert Areas in the Asian Continent: Chemical State and Number Concentration of Particles Measured at Dunhuang, China

Measurements of aerosol were made in August and October 2001, and January 2002, at Dunhuang, China (40°00′N, 94°30′E), to understand the nature of atmosphericparticles over the desert areas in the Asian continent. Balloon-borne measurements with an optical particle counter suggested that particle size and concentration had a noticeable peak in size range of super micron in not only the boundary mixing layer but also the free troposphere. Thickness of the boundary mixing layer, from distributions of particle concentration, was about 4 km in summer (17 August 2001), about2.5 km in fall (17 October 2001), and about 3 km in winter (11 January 2002), which suggest active mixing of particles near the boundary in summer. Number-size distribution of particleshowed a noticeable peak in the super micron particles size range inthe mixing boundary layer: 0.4–2 particles cm-3 at diameter>1.2 μm in summer, 0.05–4 particles cm-3 at diameter >1.2 μm in fall, and 0.1–5 particles cm-3 at diameter>1.2 μm in winter. In winter strong inversion of atmospherictemperature was found in the height range from the boundary to about 3 km and vertical distribution of particle concentration well corresponded with the temperature distribution. Chemical elements of individual aerosols, which were collectedin the boundary layer atmosphere at Dunhuang (18 October 2001) were analyzed with an electron microscope equipped with EDX. Thosesingle particle analysis suggested that most of the particles with supermicron size were soil particles, and those particles had littlesulfate on its surface. This is a very important different point,comparing with the chemical state of soil particles, which weretransported from the desert area of China to Japan, and showed frequentlythe existence of sulfate on the particle surface. Therefore, it isstrongly suggested that dust particles can be chemically modifiedduring their long-range transport from desert areas to Japan.

Pool of dust particles over the asian continent: Balloon-borne optical particle counter and ground-based lidar measurements at Dunhuang, China

Measurements of aerosols were made in 2001 and 2002 at Dunhuang (40°00′N, 94°30′E), China to understand the nature of atmospheric particles over the desert areas in the Asian continent. Balloon-borne measurements with an optical particle counter suggested that particle size and concentration had noticeable peaks in super micron size range not only in the boundary mixing layer but also in the free troposphere. Super-micron particle concentration largely decreased in the mid tropopause (from 5 to 10 km; above sea level, a.s.l.). Lidar measurements made during August 2002 at Dunhuang suggested the possibility that mixing of dust particles occurred from near the ground to about 6km even under calm weather conditions, and a large depolarization ratio of particulate matter was found in the aerosol layer. The top of the aerosol layer was found at heights of nearly 6km (a.s.l.). It is strongly suggested that nonspherical dust particles (Kosa particles) frequently diffused in the free atmosphere over the Taklamakan desert through small-scale turbulences and are possible sources of dust particles of weak Kosa events that have been identified in the free troposphere not only in spring but also in summer over Japanese archipelago. Electron microscopic experiments of the particles collected in the free troposphere confirmed that coarse and nonspherical particles observed by the mineral particle were major components of coarse mode (diameter larger than 1 μm) below about 5 km over Dunhuang, China.

Temporal variation of water-soluble ions of free tropospheric aerosol particles over central Japan

Free tropospheric aerosol particles were collected at Mt. Norikura (36.1°N, 137.5°E, 2770 m a.s.l.) in Japan during May.October in 2001 and 2002. An automated sequential daily nighttime (00-06 a.m.) sampler collected free tropospheric aerosols. Average, median, SD, minimum and maximum concentrations of total ionic weight of the 114 samples were, respectively, 3.9, 2.8, 3.7, 0.2 and 23.2 μg m-3 Transport conditions were analysed using backward air trajectory with precipitation amounts along the trajectory. Results suggest that low aerosol mass concentration causes are (1) descending trajectories and (2) precipitation scavenging during transport without contacting boundary layer atmosphere until arrival. It is suggested that, without precipitation scavenging after entrainment into the free troposphere, aerosol transport from active emissions at the surface enhances mass concentration at Mt. Norikura. Average concentrations of NO3-, non-sea-salt (nss)K+ and C2O4 2- are high in March.June and low in winter. The highest average nssSO42-. concentration occurs in summer; it is high from spring through fall. Seasonal variation of NH4+ concentrations resembles that of nss SO4 2-, but the concentrations molar ratio (NH4 +/nssSO42-) is high (ca. 2) in spring and decreases to 1 in winter. Seasonal variation of NH4+ + NH3 concentration agrees with that of NH3 emissions in China.

Features in Number Concentration-Size Distributions of Aerosols in the Free Atmosphere over the Desert Areas in the Asian Continent: Balloon-Borne Measurements at Dunhuang, China

Vertical changes of aerosol concentration and size in the freetroposphere over the Asian desert areas were firstly observed using a balloon-borne optical particle counter at DunHuang, China (40°00′N, 94°30′E) (17 August and 17 October 2001, and 11 January 2002). In the free troposphere highly concentrated aerosol layers were frequentlyobserved, suggesting the importance of regional scale particletransportation over the Asian continent. Concentration ofparticles with a diameter larger than 0.15 μm was about 5–10particles cm-3 in the free troposphere.Particle number-size distribution in the free troposphereshows important contribution of super micron particles. Regionalscale transportation, in addition to diffusion of soil particlesfrom the lower atmosphere to the free troposphere through localand small scale air motions, is suggested by backward trajectoryanalysis of air masses containing super micron particles. The importance of horizontal transport of coarse size particles in the free troposphere was strongly suggested.Thickness of the boundary mixing layer, from distributions ofparticle concentration, was about 4 km in summer (17 August 2001)and apparently higher than the height of layers in fall (17 October2001) and in winter (11 January 2002), which suggest an active mixingof particles near the boundary in summer. In winter measurement(11 January 2002), strong inversion was found in the vertical profile of temperature, suggesting cold ground surface and vertically stable atmosphere near the ground.