During our aerosol measurement program at Syowa Station, Antarctica, in 2004–2007, some low‐visibility (haze) phenomena were observed during winter–spring under conditions with low winds and without drifting snow and fog. During “Antarctic haze” phenomena, the number concentration of aerosol particles and black carbon concentration increased by 1 to 2 orders higher relative to background conditions at Syowa Station, whereas surface O3 concentration dropped simultaneously, especially after polar sunrise. Chemical analysis showed that major aerosol constituents in the haze phenomena were sea salt (e.g., Na+, Cl−). Trajectory analysis and the Navy Aerosol Analysis and Prediction System model showed that plumes from biomass burning in South America and southern Africa were transported to Syowa Station, on the Antarctic coast, because of the eastward (occasionally westward) approach of cyclones in the Southern Ocean and subsequent poleward flow. This poleward flow from midlatitudes of the plume and injection of sea‐salt particles during the transport might engender Antarctic haze phenomena at Syowa Station. Differences of O3 concentration between the background and the haze conditions tended to be larger in spring (after polar sunrise) than in winter. Enhancement of sea‐salt particles in the haze events can serve important roles in providing additional sources of reactive halogen species.

[1] Seasonal changes in the vertical structure of free tropospheric aerosols over east Asia, on the basis of aircraft-borne and lidar measurements, and on the pathway of the longrange transport of Asian dust particles inferred from isentropic trajectory analysis are discussed. Aircraft-borne measurements held in situ in the free troposphere over central Japan in 2000-2001 revealed a small in scale yet steady transport of dust in the lowermiddle free troposphere (2-6 km altitude) during spring including days with no evident dust outbreak. Such dust, found as background, was observed even in summer in the regions higher than 4 km under the influence of remaining westerly winds but not in the lower regions. From a series of lidar observations over Nagoya (35°N, 137°E), Japan, noticeable changes in aerosol characteristics were obtained in the free troposphere from spring to summer. Taklimakan desert is suggested as possible important source of the background dust.

This study focuses on providing a direct insight into the process by which sulfate is formed on mineral dust surface in the actual atmosphere. Six sets of aerosol measurements were conducted in the outskirts of Beijing, China, in 2002-2003 using a tethered balloon. The mineralogy of individual dust particles, as well as its influence on the S (sulfur) loadings was investigated by SEM-EDX analysis of the directly collected particles.The mixed layer in the urban atmosphere was found to be quite low (500-600 m), often appearing as a particle dense stagnant layer above the surface. It is suggested that mineral dust is a common and important fraction of the coarse particles in Beijing (35-68%), and that it is relatively enriched with Calcite (>28%).An exceptional amount of S was detected in the mineral particles, which can be explained neither by their original composition, nor by coagulation processes between the submicron sulfates and the dust. Heterogeneous uptake of gaseous SO 2 , and its subsequent oxidation on dust was suggested as the main pathway that has actually taken place in the ambient environment. The mineral class found with the largest number of particles containing S was Calcite, followed by Dolomite, Clay, Amphibole etc., Feldspar, and Quartz. Among them, Calcite and Dolomite showed distinctly higher efficiency in collecting sulfate than the other types.A positive correlation was found with the number of S containing particles and the relative humidity. Calcite in particular, since almost all of its particles was found to contain S above 60% r.h. On the other hand, the active uptake of SO 2 by the carbonates was not suggested in the free troposphere downwind, and all the mineral classes exhibited similar S content. Relative humidity in the free troposphere was suggested as the key factor controlling the SO 2 uptake among the mineral types. In terms of sulfate loadings, the relationship was not linear, but rather increased exponentially as a function of relative humidity. The humidity-dependent uptake capacity of mineral types altogether showed an intermediate value of 0.07 gSO 2− 4 g −1 mineral at 30% r.h. and 0.40 gSO 2− 4 g −1 mineral at 80%, which is fairly consistent with laboratory experiments.

Number‐size distributions of atmospheric aerosol particles of 9–300 nm diameter were observed along with SO2 and NH3 concentrations at Mount Norikura, Japan (36.1°N, 137.5°E, 2770 m asl), during September 2001 and August–September 2002. Particle size distributions between the free troposphere and the mixed layer were measured at the site under local wind system conditions, comprising downslope mountain and upslope valley winds. The local wind system was well developed under clear‐sky conditions and was determined according to temporal variation of the water vapor mixing ratio at the site. Nucleation mode particles were observed on 4 of 23 clear‐sky days during our observation periods. Nucleation mode particles were observed in the mixed layer air, but never in the free tropospheric air, suggesting that new particle formation occurred in the air transported from the mixed layer. Nucleation‐mode‐particle growth rates during new particle formation events were 2.6–3.1 nm h−1. Preexisting particle concentrations on event days were about half those of nonevent sunny days on average, but no positive correlation was found between the events and either SO2 or NH3 concentrations. The events always occurred in a cold air mass advected from the north behind cold fronts. Horizontal advection of the northern cold air mass might bring a clean air mass with low preexisting particle concentration in the mixed layer and trigger a new particle formation event at Mount Norikura.

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.

No abstract

Number‐size distributions of free tropospheric aerosol particles of 9–300‐nm diameter were observed at Mt. Norikura (36.1°N, 137.5°E, 2770 m a.s.l.) in central Japan in August and September 2002. We observed two distinct air masses transported from over the Pacific Ocean and continental Asia. Size distributions of aerosol particles were analyzed in terms of their relation to the air mass transportation pathway, cumulative precipitation amount in the air mass for the last 24 h, and local precipitation rate. Particle concentrations of the accumulation mode range (100–300 nm) decreased by an order of magnitude when cumulative precipitation amount increased from 0 to 20 mm. The cumulative precipitation amount is suggested as an important factor to modify the size distribution by decreasing particle concentration. Considering data for air masses without experience of precipitation scavenging before arrival, concentrations of accumulation mode particles were almost identical (approximately 400 cm−3) in air masses transported from over the Pacific Ocean and continental Asia. Concentration of Aitken mode particles was high (890 cm−3 as a median value) in the air mass subsiding from over the subtropical Pacific Ocean (> 4 km a.s.l.). Based on the relationship with the controlling factors described above, this study provides number‐size distribution parameters of free tropospheric aerosol particles in the west Pacific area.

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 SO 2 and SO 2− 4 under Arctic haze conditions with higher SO 2 concentration (≥2 nmol m −3 ), whereas they are dominantly modified with NO − 3 and reactive nitrogen oxides under Arctic background conditions, with [HNO 3 ] of 0.15-1.3 nmol m −3 and [SO 2 ] 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.