Fine (aerodynamic diameter 2.5 μm, PM2.5) and coarse particles (aerodynamic diameter 2.5 μm) were collected on glass filters (Advantec Co., Ltd., Tokyo, Japan) and quartz filters (Pall Life Sciences, Port Washington, NY, USA), respectively, in the city of Sasebo (129.79 °E, 33.10 °N) using a high volume air sampler (HV1000R, Shibata Scientific Technology, Soka, Japan) equipped with an impactor (Shibata Scientific Technology) at a flow rate of 1 m3/min for 1 week per filter. The quartz and glass filters were preheated to 250 °C for 2 h before sampling for the estimation of endotoxin level. Following sample collection, the filters were stored at −80 °C until the preparation of sample solutions.
To quantify endotoxins in fine and coarse particles, 15 % of sample filter (corresponding to 1512 m3 of air) was extracted with endotoxin-free water containing 0.025 % Tween-20 using an ultrasonic apparatus for 30 min, as previously described [22 (link),23 (link)]. The extract was centrifuged, and a portion of the supernatant was used for endotoxin analyses. A sample solution for luciferase reporter assay was extracted with distilled water from 15 % of the sample filter through ultra-sonication for 30 min, followed by centrifugation. The supernatant was lyophilized to obtain powder and resolved with culture medium before use in the luciferase reporter assay.
To quantify endotoxins in fine and coarse particles, 15 % of sample filter (corresponding to 1512 m3 of air) was extracted with endotoxin-free water containing 0.025 % Tween-20 using an ultrasonic apparatus for 30 min, as previously described [22 (link),23 (link)]. The extract was centrifuged, and a portion of the supernatant was used for endotoxin analyses. A sample solution for luciferase reporter assay was extracted with distilled water from 15 % of the sample filter through ultra-sonication for 30 min, followed by centrifugation. The supernatant was lyophilized to obtain powder and resolved with culture medium before use in the luciferase reporter assay.