从分子运动的角度，通过对不同分子沉降过程的量化计算，发现不同污染物沉降速率的差异，由此提出了一种包含污染物化学成分的有效洁净度的概念。有效洁净度从描述物质沉降过程的输运方程出发，通过计算不同理化性质的污染物分子沉降速率对不同污染物进行区分，并将该信息与原标准下的洁净度信息结合。使用美国国家标准与技术学会(NIST)数据库提供的数据代入有效洁净度理论，计算了几种主要污染物的有效洁净度数值，计算结果与法国LIL激光装置中有代表性的污染物的沉降速率及曝光后形成污染的程度进行了对比，与实验观测基本吻合。

Based on the current cleanliness standards, the definition of cleanliness only considers the size and the density of contaminations, ignoring the effects of different particles in laser-induced damage threshold. This article puts forward the effective cleanliness method, which contains the information of different chemical components in contaminations. The effective cleanliness method bases on the mass-transporting equation, combining with the previous standards. The calculation considers the molecular-level difference of contaminants of various classes. The result of the calculation on chemicals of the most amounts in LIL matches the experiment, proving the validity of this method. The effective cleanliness method provides a brand new assessment standard of contamination control in large laser engineering.