Seasonal Variation in Size Distributions for Major Ionic Species in the Atmospheric Aerosol

Abstract

Aerosol size distribution were determined in Chiba City by Andersen sampler from April 1987 to March 1988 for the major ionic species (H⁺, NH₄⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, SO₄^2-, NO₃^- and Cl^-) and TSP (Total Suspended Particles). The seasonal variations in concentrations and size distributions have been investigated.
The size distributions of TSP and each of the ionic species were bimodal throughout the year. The size distribution of these ions were divided into four patterns, one variant pattern with season and three variant ones throughout the year:
(1) fine-mode dominant in the summer and coarse-mode dominant in the winter for NO₃^- and Cl^-.(2) fine-mode dominant for SO₄^2-, NH₄, K⁺ and H⁺.(3) coarse-mode dominant for Na⁺, Ca²⁺, and Mg²⁺.(4) both-mode dominant for TSP.
There was no seasonal variation in concentration for SO₄^2-, K⁺. But the concentration of Na⁺ increased in the summer and those of NO₃^-, Cl^-, NH₄⁺, Ca²⁺, Mg²⁺ and H⁺ increased in the winter.
In the fine-mode the sum of ionic species (neq/m³) increased in the winter and decreased in the summer, but in the coarse-mode the seasonal variation was not observed.