Seasonal Changes of Total Suspended Particles in the Air of 15 Big Cities in Northern Parts of China
北方15个大型城市总悬浮颗粒物的季节变化

One-year (from July of 1998 to June of 1999) monitoring data on air quality of 15 big cities in northern parts of China are analyzed Analysis indicates that: (1) major pollutant in the air of big cities except Beijing is total suspended particles, i e , TSP, and the yearly averaged occurrence frequency of TSP is between 70% and 100%; (2) II-level-air-quality occurrence frequency is always high in the summer and fall and low in the spring and winter for each big city due to influence of local factors (terrain, vegetation distributions, meteorological conditions and anthropogenic activities); (3) III-air-quality occurrence frequency has not all the same seasonal changes for different cities owing to influence of local factors and transport of TSP among neighboring cities; (4) IV-or-V-air-quality occurrence frequency is always high in the spring and winter and low in the summer and autumn because during the spring and winter strong wind often occurs in the Northern or Northwestern China and causes long-range transport of dust or sand produced in the arid or desert area This implies that due-fixing forest is extremely needed strengthening in the area