Inhalable elemental carbon (EC) concentrations at eight MWCNT facilities. The mean, with error bars representing the upper and lower range, of measured EC concentration (μg/m3) with background correction. The figure was adapted from data previously published, sites A, C-F , while including 3 additional sites, L, J, and O. The studied sites were identified in a manner to be consistent with nomenclature of specific sites. For example, site B was a single-walled carbon nanotube facility and therefore excluded.