A task-based analysis of black carbon exposure in Iowa farmers during harvest. - Stapleton, Emma M.; O'Shaughnessy, Patrick T.; Locke, Sarah J.; Altmaier, Ralph W.; Hofmann, Jonathan N.; Beane Freeman, Laura E.; Thorne, Peter S.; Jones, Rena R.; Friesen, Melissa C. (Journal of Occupational & Environmental Hygiene, 2018)