Based on 1983-1987 conventional environment monitoring data from the city of Yinchuan of Ningxia,a systematic analysis is performed of the mass concentration characteristics of atmospheric Inhalable Particulate Matter(IPM),and analysis results indicate that the proportions of PM_2.5 particles in the total IPM in winter heating months are considerably higher than those in spring sandstorm period and non-heating months.The IPM mass concentration spectral distribution exhibits a peak at particle diameter 0.58 μm in four seasons of a year.PM_2.5particles make >50 % contribution to wintertime IPM,indicating that coal burning is the major emission source for fine particles that are responsible for the most severe contamination of the season.IPM size distribution displays multiple-peaks in different seasons for different functional blocks,which result from the interactions among differing-mode particles.In windy and sandy spring and non-heating summer and autumn the mass median diameter of IPM are greater than those in winter.The σ_g is however the smallest in heating winter,revealing that the divergent degree of IPM particle diameters in winter is minimum.