Dust characteristics over the North Pacific observed through shipboard measurements during the ACE-Asia experiment

To examine the diversity of chemical and physical properties of aerosol particles, in particular dust, over the North Pacific, aerosols were collected along ∼32°N latitude between 140°E and 170°W longitude aboard the NOAA R/V Ronald H. Brown during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) in the spring 2001. A total of 11,482 aerosol particles were examined through individual-particle analysis. Results indicate that dust particles over this region were dominated primarily by Si-rich particles, including aluminosilicates that contain Fe. Fe is also present as separate Fe-rich particles. Additional common particle types include Ca- and S-rich particles; many of the later appear to represent soil-derived calcium carbonate and its reaction products whereas the former are predominantly reaction products of sea salt and sulfate. Particles are often aggregates of different types including pollution-derived substances and highly heterogeneous, both internally and externally. Dust particles are non-spherical, having circularities from 1.0 up to 4.5, suggesting the high degree of complexity of particle shape. The majority of dust particles were dominated by particles with median diameters from 0.67 to 1.26 μm. However, dust particles with diameters of 5 μm or even larger do exist associated with those events of dust originated from Asian desert areas. The existence of soot and Fe-rich particles over this region indicates the influence of fossil fuel sources in Asia. Aerosol Fe from both Asian desert and fossil fuel combustion may contribute to the nutrient Fe in the surface waters of the North Pacific basin. Therefore, the transport of Asian dust associated with species of fossil fuel burning in the spring may play an important role in altering the natural composition of aerosols over the North Pacific.