Fig. 3: Indoor concentrations and PM I/O ratio.

a PM_2.5 (yellow) and PM₁₀ (blue) at four stations in the morning (rush hour), noon (non-rush hour), and evening (rush hour) across four seasons; b the I/O ratios of PM_2.5 (yellow) and PM₁₀ (blue) at four stations in the morning, noon, and evening across four seasons.