Composition of Individual Particles in the Lower Troposphere Determined by Microprobe Technique

Abstract

Aerosol particles were collected with impaction technique at altitudes up to 3.0 km over three different locations in Japan: urban area (Nagoya), mountain (Mt. Norikura) and ocean (South Okinawa region). Individual aerosol particles larger than 0.5 μm in diameter (at 0 percent relative humidity) were analyzed with an electron microprobe. Elemental composition for silicon, sodium, and sulfur contained in collected particles were as follows: (1) Over Nagoya and its vicinity, the aerosol consisted often of particles rich in silicon and/or sulfur in and above mixing layer. (2) At the summit of Mt. Norikura, the aerosol consisted of particles rich in sulfur when convective activities were strong, whereas particles containing silicon and sulfur in large relative weight fractions and sodium in very small amount during nocturnal subsidence conditions. (3) Over the South Okinawa region, two regimes were clearly delineated: The aerosol consisted mainly of particles having the composition similar to the composition of sea water in marine layer, whereas particles having large relative weight fractions of silicon and/or sulfur as compared with the composition of sea water above the marine layer. The relative contribution of silicate, sea salt, and sulfate components in individual particles was estimated from the elemental composition for silicon, sodium, and sulfur contained in their particles. The result of these analysis suggests that mixed large particles (d≥0.5μm) containing silicate and sulfate in large relative weight fractions and sea salt in a minor constituent distribute widely in the free atmosphere over the Japanese Islands from Honshu to Okinawa.