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Particulate Size Distribution in the Haze and Non-Haze Episodes at Shijiazhuang City, China

Aimed at detecting the particulate size distributions in the typical air pollution city of Shijiazhuang, China, this research collected samples in haze episode and non-haze episode separately and found the difference between the two situations. In non-haze episode, the average size distribution is a U-shape curve both lifting at the size minimum and maximum, with slightly higher frequency in the size below 0.65μm (grade 1 and grade 2); but in haze episode, the frequency of 0.43~0.65μm (grade 2) and 0.65~1.1μm (grade 3) increase evidently. By the correlation coefficient calculation, the mass concentration of PM0.43~0.65 has strong negative relationship with visibility range, which should be responsible for the low visibility formation. The fitting function demonstrates that the mass concentration of PM0.43~0.65 must be limited below 0.117 mg/m3 if the visibility range reaches 10km (“medium”), and below 0.006 mg/m3 over 19km (“good”). And there is a inflection point around 0.01 mg/m3 of PM0.43~0.65 as for the visiblity variation, in which the visiblity range decreases rapidly with slight increase of PM0.43~0.65 when below 0.001 mg/m3. PM0.43~0.65 is conclusively regarded as the feature size of particulate responsible for the haze formation in Shijiazhuang, China.