Abstract:The PM2.5and PM2.5-10samples were collected from 14sample sites in 8cities in Haixi Urban Agglomeration. The 9water-soluble ions (F-、Cl-、NO3-、SO42-、Na+、K+、NH4+、Ca2+、Mg2+) were determined. The concentrations of PM2.5and PM10were high, and the mean value of PM2.5and PM10were 89.65and 135.65μg/m3, respectively. The PM2.5was the main composition of the PM10and the proportion of PM2.5to PM10was 66.1%. Most of the water-soluble ions in cities were associated with the PM2.5. The concentrations of water-soluble ions in Wenzhou were higher than those in other cities. The dominatant water-soluble ions were SO42-, NO3- and NH4+, which accounted for 79.6%~89.0% of total ions in PM2.5and 74.2%~83.4% in PM10. Because of the monsoon in winter, the major ions in atmospheric particles were non-sea-salt ions. The higher mass ratio of NO3-/SO42- demonstrated that the Haixi Urban Agglomeration was under combined contamination in winter.