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Critical periods for PM2.5 (n = 1,334) at selected density levels: (A) 50% (yellow): (–90, –72), (47, 181), and (246, 272); (B) 75% (blue): (–90, –75), (91, 139), and (249, 272); and (C) 90% (red): (–90, –84), (109, 128), and (253, 262). The vertical dotted lines indicate the start-end pair days of critical periods.
