(A) FDG distribution in various peripheral tissues induced by insulin. Representative axial, coronal, sagittal images of mice from FA versus PM_2.5 exposure (n = 4) are shown. PET/CT showing specific BATs that were assessed in this study (ROI placement in BAT in axial, coronal, and sagittal PET images and overlaid on CT images), and localization of specific tissues was established utilizing CT scans. Bar plots indicate mean FDG uptake level of BAT and other metabolic organs from mice exposed to FA versus PM_2.5 (n = 4). (B) Representative TEM photomicrographs acquired from the section of the BAT from mice exposed to FA and PM_2.5 for 24 weeks (n = 2). Bar plots represent mean mitochondrial number and size per image field. Higher magnification (scale bars: 0.5 μm) of mitochondria shows lamellar cristae in FA-exposed and tubular cristae structure in PM_2.5-exposed mice. Lower magnification (scale bars: 2 μm) micrographs demonstrate the accumulation of lipid droplets in mitochondria. Bar plots represent the mean number of lipid droplets and their size per image field. Data were collected across 48 fields of view for 2 mice per group. (C) Heatmap indicates 24-hour circadian variation (ZT0 to ZT20) of thermogenic, metabolic, and antioxidant gene expression in BAT tissues (n = 3). Data are presented as fold change relative to the baseline (FA at ZT0) and the heatmap shows the mean value at each time point. Statistical significance was determined using an unpaired, 2-tailed Student’s t test, with P < 0.05 considered significant when comparing each ZT point between groups. (D) Describes the batokine mRNA expression levels in BAT from mice exposed to FA versus PM_2.5 for 24 weeks (n = 5). Data are provided as mean ± SEM. *P < 0.05 versus FA-exposed mice by unpaired, 2-tailed Student’s t test.