基于1995年到2005年渤海湾化学耗氧量(COD)的监测数据序列,研究了渤海湾10年来COD的季节(5月、8月及10月)及年际间的变化趋势,运用极值理论研究了COD的极值分布规律,计算了COD分别超过不同污染水平的风险概率.研究结果表明:渤海湾COD季节之间变化不明显,5月、8月及10月的COD具有指数分布特征;COD年际间变化呈下降趋势,与同期COD排放变化趋势吻合;COD的污染风险概率符合Pareto型超阈值分布函数.
Based on the data of chemical oxygen demand (COD) in Bohai Bay during 1995--2005 ,the variation trend of the COD in different seasons (May,Aug and Oct ) and years was analyzed. Furthermore,using extreme value theory ,the extreme value distribution and pollution risk probability of the COD were presented. The results show that there are no apparent variations in different seasons, and the probabilities fit with exponent distribution function;the variation of COD in 10 years shows a dramatic decline which is the sequence of the COD discharge decline; the risk probability of COD fits with Pareto distribution function.