[1] Observations of aerosol constituents and acidic gases in the Antarctic area were carried out at Syowa (39.58°E, 69.00°S) in 1997 and1998 and Dome Fuji stations (39.62°E, 77.37°S) in 1997. Sea-salt concentrations decreased to background levels in the summer at both Syowa (Na + , 4 nmol m À3 ) and Dome Fuji (Na + , $0.44 nmol m À3 on average). During the winter, blizzard and strong wind may cause an increase of sea-salt particles at Syowa, whereas long-range transport from the boundary layer at midlatitudes and coastal Antarctic regions may contribute significantly to the increase in sea-salt particles observed at Dome Fuji. Particulate Cl À and Br À are liberated preferentially from sea-salt particles at Syowa and Dome Fuji in the summer. The molar ratio of Cl À /Na + and Br À /Na + at Syowa decreased to $0.5 and %0, respectively, in summer. At Dome Fuji more Cl À tend to be liberated from sea-salt particles thorough heterogeneous NO 3 À formation. The concentrations of gaseous chlorine species (mostly HCl) and bromine species ranged from 0.2 to 5.3 nmol m À3 and below detection limit (BDL) to 1.5 nmol m À3 , respectively, corresponding to sea-salt modification. In the present study, SO 4 2À depletion due to mirabilite formation was observed not only at Syowa but also at Dome Fuji. This evidence suggests that SO 4 2À depletion might occur through sublimation on snow surfaces in addition to seawater freezing. At Syowa, sea-salt fractionation relating to Mg 2+ , K + , and Ca 2+ was also observed mostly under strong wind conditions.

Abstract. Atmospheric aerosol particles and acidic gases were collected at Ny-Alesund, Norwegian high Arctic, in winter (December -March) of 1994/1995, 1995/1996 and 1996/1997 to understand the sink processes of atmospheric inorganic nitrate and reactive nitrogen oxides. At•nospheric inorganic nitrates were mostly present as particulate NO3-in the coarse mode defined as diameter >2.3 jim) of which major constituents were sea-salt compounds such as Na + and C1-. The number fraction of coarse aerosol particles containing NO3-increased in aged oceanic air masses. The internal mixing between sea-salt particles and inorganic nitrates revealed by individual particle analysis implies that uptake of gaseous HNO3 and/or formation of particulate NO3' through heterogeneous processes occurs on sea-salt particles. A simple uptake model was used to estimate the production rate of particulate NO3-due to these processes. Model calculations showed that the formation of particulate NO3-was mainly due to the uptake of gaseous HNO3 on sea-salt particles in winter Arctic. However, the heterogeneous formation from N:Os and NO3 also makes an important contribution to the formation of particulate NO3-under no and/or weak solar radiation in winter Arctic (polar night). Thus the heterogeneous formation of NO3-on sea-salt particles may play an important role as a sink of reactive nitrogen oxide in winter Arctic.

[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.

Deposition of water‐insoluble dust was measured in winter snow deposited at Murododaira (2450 m) on the western flank of Mount Tateyama in central Japan. An analysis of temporal variation in atmospheric aerosol concentration, incremental snow height and concentration of dust in the snow cover suggests that wet deposition is the major process in forming thicker dust layers in the snow cover at Mount Tateyama. Dust layers in the snow cover contain Ca‐rich materials typically found in Asian dust (Kosa) particles. Volume size distributions of dust particles in the snow showed single and bi‐modal structures having volume median diameters from 6–21 μm. Dust profiles in snow cover over the last 6 yr reveal frequent sporadic high dust concentrations in spring and large year‐to‐year variations in the amount deposited. The average amount of dust deposition (7.7 g m−2) from winter to spring at the site was close to the long‐term averages of annual flux obtained from sea sediment near Japan, implying that dusty precipitation in spring contributes to annual deposition of aeolian mineral dust.

Number‐size distribution of atmospheric aerosol particles and O3 concentration were measured at Murododaira (36.6N, 137.6E, 2450 m above sea level (asl)) on the western flank of Mt. Tateyama in central Japan from January 1999 to November 2002. This study used nighttime data from 2400 to 0500 hours (local time) on the basis of analysis of their diurnal variation to characterize free tropospheric aerosols and O3 over Japan. The O3 concentration shows small variability (standard deviation of 4 ppbv) with the mean value of 40 ppbv in winter (October to February), large variability (8 ppbv) with the higher mean value of 51 ppbv in spring (March to May), and large variability (14 ppbv) with the lower mean value of 32 ppbv in summer (June to September). Highest monthly mean volume concentration (2.7 μm3/cm3) of accumulation particles (0.3 μm < D < 1.0 μm) was observed in June, while the mean value in winter (October to February) was 0.7 μm3/cm3. On the basis statistics of backward air trajectory analyses, a stagnant airflow in summer over the coastal areas of the Yellow Sea and near Japan is inferred to be a suitable meteorological condition to form enhanced volume concentration of accumulation particles during transport. Associating with the seasonal changes in the dominant air trajectories, SO2 emission from Miyakejima volcano since August 2000 is also an important source of the summer enhancement of accumulation particles. Highest monthly mean volume concentration (11.2 μm3/cm3) of coarse particles (D > 1.0 μm) was found in April, which was about 10 times higher than the mean value of 1.2 μm3/cm3 from summer to winter. Variability of daily nighttime volume concentrations of the coarse particles was high (standard deviation of 13.6 μm3/cm3) in spring and low (about 2 μm3/cm3) in the rest of the year. High volume concentration with large variability of the coarse particles in spring is caused by frequent arrival of Kosa (yellow dust) particles from the Asian continent. Rapid enhancement of coarse volume concentration was often observed to increase as much as 30 times within 3 hours during Kosa phenomena. The year 2001 had particularly strong Kosa activity with a prolonged season starting early January and ending early July.

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.

Sampling of atmospheric aerosol particles was carried out at Syowa station, Antarctica (39.58°E, 69.00°S) in 1998. For a better understanding of sea‐salt chemistry in the coastal Antarctic regions, individual sea‐salt particles were analysed using a scanning electron microscope equipped with energy dispersive X‐ray spectrometer (SEM‐EDX). Individual particle analysis indicates that more sea‐salt particles were modified in fine particles (0.2–2 μm in diameter) through heterogeneous reactions mainly with gaseous sulfur species in the summer and reactive nitrogen oxides in the winter–spring. In particular, sea‐salt particles in the coastal Antarctic atmosphere may be modified by heterogeneous reactions with not only SO2 and H2SO4 but also volatile sulfur species (e.g. CH3SO3H, DMS and DMSO) derived from bioactivity on the ocean surface during the summer. Also, low air temperature and a larger extent of sea ice offshore Syowa probably enhanced release of fractionated sea‐salt particles (S‐rich, Mg‐rich, K‐rich and Ca‐rich) from the surface of snow and sea ice, particularly in September–October 1998. In addition, we attempt to estimate the scavenging rate of atmospheric sulfur species and reactive nitrogen oxides by dry deposition of sea‐salt particles. Our estimation suggests that the upper limit of the scavenging rate of atmospheric sulfur species by sea‐salt particles could rise to approximately 0.5 nmol m−2 day−1 at Syowa station during the summer. This value corresponded to about 30% of the concentration of particulate sulfur species such as non‐sea‐salt (nss)‐SO2−4 and CH3SO−3 and ∼10% of total atmospheric sulfur species (nss‐SO2−4, CH3SO−3 and SO2). In contrast, the estimated NO−3 scavenging rate by sea‐salt particles was ∼0.2 nmol m−2 day−1, which is similar to the dry deposition rate of HNO3+N2O5 (approximately 0.2–0.3 nmol m−2 day−1). Hence, sea‐salt particles probably play an important role as scavengers of acidic species in the coastal Antarctic regions.

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