Evaluation statistics (µg/m3) for the exposure assessment methods.

aN is the number of surveillance-oriented sites used for PM pollution modeling.bA constant trend is implied by ordinary kriging.cThe optimal assessment method is indicated. When models rank similarly in terms of performance, the simpler specification that reproduces important features of the empirical variogram is deemed optimal.a. 变量aN为用于颗粒物（Particulate Matter，PM）污染建模的监测导向站点的数量。 b. 普通克里金法（Ordinary Kriging）隐含恒定趋势。 c. 已明确最优评估方法：当多个模型的性能排名相近时，能够重现经验变异函数关键特征的更简洁设定形式，将被认定为最优模型。