Feature

Dust particles: Travelling through the troposphere

Associate Professor Atsushi Matsuki,
Division of Natural Sciences,
Graduate School of Natural Science and
Technology,Kanazawa University, Japan.

One of Kanazawa University’s leading researchers has dedicated his career to tracing aerosols, dust and microbial particles as they travel through the atmosphere over Asia and the Pacific Ocean.

The prevailing westerly winds over Asia regularly drive dust from the continental deserts out over the sea to Japan, and sometimes as far as North America. These particles can affect air quality, sunlight levels and the distribution of pollutants, and may also disturb marine ecosystems, particularly in the aftermath of dust storm events.

Atsushi Matsuki has spent the past ten years following dust in the troposphere – the lowest few kilometers of the atmosphere - across China and Japan, studying the composition and shape of the particles as well as the chemical changes they undergo. In 2003, Matsuki and co-workers investigated the composition of dust from deserts in China, and found it began in the desert as an uncontaminated mix of minerals from the Earth’s crust. By the time these particles reached Japan, however, the researchers discovered that around 45% of particles contained sulphate that was picked up en route³.

In addition to sulphate, nitrates from human activity can also be transported by dust and deposited thousands of miles from their source. Matsuki led further studies between 2003 and 2005, using airborne data collecting techniques, to study the influence of mineral composition on the uptake of sulphate and nitrate^4,6,10. He discovered that carbonate-based dust is far more likely to accumulate sulphate and nitrate than silicate-based particles. Not only this, but Matsuki also found that carbonate-based dust was often transformed into spherical shapes by the uptake of pollutants and water vapor in the atmosphere.

Dust originating from the deserts of Asia
is regularly blown thousands of miles
west on the prevailing winds. Thanks in
part to the work of Atsushi Matsuki, the
dust particles are now known to alter
their chemical composition en route,
picking up nitrate, sulphate and sea
salts, as well as microbial particles.

These spherical particles were a crucial discovery – not only do they hold more sulphate and nitrate than ‘ordinary’ dust, but their shape changes their optical qualities as well as their ability to nucleate clouds, both influencing the amount of radiation the earth’s surface receives. Matsuki and his team were the first to highlight this phenomenon in East Asia and suggest that it should be incorporated into atmospheric models⁶.

Following on from his work on pollutants, Matsuki has also investigated the uptake of sea salt in dust travelling over the ocean. Mixing of dust with sea salt increases the size of the particles, again altering their influence on radiation and is “dependant on the vertical thermodynamic structure of the marine boundary layer.”⁹

In more recent years, Matsuki and his co-workers have expanded his expertise to include the study of aerosols and microbial particles transported by Asian desert dust^11-13. Their work on snow samples from Mount Tateyama and in the troposphere over Japan shows the presence of bacteria carried long distances by particles. Both actinobacteria, from soils and freshwater, and proteobacteria – the family of bacteria incorporating E.coli and salmonella – were found in considerable quantities.

Over the past decade, Atsushi Matsuki has made a considerable contribution to the understanding of dust transportation, the changes the particles undergo and the chemical and biological passengers they carry with them. His work in this field will continue to push Kanazawa University to the forefront of environmental research.

Publication and Affiliation

^1. D. Zhang et al. Mixture state of individual Asian dust particles at a coastal site of Qingdao, China. Atmospheric Environment 37 (2003) 3895–3901
^2. M.Mikami et al. Aeolian dust experiment on climate impact: An overview of Japan–China joint project ADEC. Global and Planetary Change 52 (2006) 142–172
^3. D. Trochkine et al. Mineral aerosol particles collected in Dunhuang, China, and their comparison with chemically modified particles collected over Japan. Journal of Geophysical Research, 108 (D23) (2003)
^4. D. Zhang et al. Mixture state and size of Asian dust particles collected at southwestern Japan in spring 2000. Journal of Geophysical Research, 108 (D24) (2003)
^5. C. E. Reeves et al. Chemical and aerosol characterisation of the troposphere over West Africa during the monsoon period as part of AMMA. Atmospheric Chemistry and Physics, 10, 7575–7601 (2010)
^6. A. Matsuki et al. Morphological and chemical modification of mineral dust: Observational insight into the heterogeneous uptake of acidic gases. Geophysical Research Letters, Vol.32 (2005)
^7. A. Matsuki et al. Cloud processing of mineral dust: direct comparison of cloud residual and clear sky particles during AMMA aircraft campaign in summer 2006. Atmospheric Chemistry and Physics, 101057–1069, (2010)
^8. A. Matsuki et al. Seasonal dependence of the long-range transport and vertical distribution of free tropospheric aerosols over east Asia: On the basis of aircraft and lidar measurements and isentropic trajectory analysis. Journal of Geophysical Research, 108 (D23) (2003)
^9. D. Zhang et al. Coarse and accumulation mode particles associated with Asian dust in southwestern Japan. Atmospheric Environment 40 (2006)
^10. Y. Iwasaka et al. Importance of dust particles in the free troposphere over the Taklamakan Desert: Electron microscopic experiments of particles collected with a balloonborne particle impactor at Dunhuang, China. Journal of Geophysical Research, 108 (D23) (2003)
^11. K. Hara et al. Heat sensitivity of ice nuclei in fresh snow collected in Kanazawa, Japan. AIP Conference Proceedings (2013)
^12. K. Kinouchi et al. Droplet sizes of activated CCN measured at Noto Peninsula, Japan, in autumn 2012. AIP Conference Proceedings (2013)
^13. T. Maki et al. Assessment of composition and origin of airborne bacteria in the free troposphere over Japan. Atmospheric Environment 74 (2013)

*corresponding author, e-mail address: matsuki＠staff.kanazawa-u.ac.jp