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In this study, we characterized personal exposure to fine particulate matter (PM 2.5 ), black carbon (BC), and nicotine in pregnant women in Hidalgo County, where the hospitalization rates of childhood asthma are the highest in the state of Texas. The measurements were conducted over three non-consecutive sampling days for 17 participants in their third trimester. Measurements were partitioned into four microenvironments, i.e., Residential, Vehicular, Commercial, and Other, on the basis of GPS coordinates and temperature and humidity measurements. The daily average PM 2.5 mass concentration was 24.2 (standard deviation=22.0) μg/m 3 , with the highest daily mass concentration reaching 126.0μg/m 3 . The daily average BC concentration was 1.44 (SD=0.82) μg/m 3 , ranging from 0.5 to 5.4μg/m 3 . Hair nicotine concentrations were all near the detection level (i.e., 49.2pg/mg), indicating that the participants were not routinely exposed to tobacco smoke. The Residential microenvironment contributed dominantly to the mass concentration since the participants chiefly remained at home and cooking activities contributed significantly to the total PM 2.5 . When compared to an ambient monitoring station, the person-specific PM 2.5 was frequently more than double the ambient measurement (10.4μg/m 3 overall), revealing that even in regions where ambient concentrations are below national standards, individuals may be still be exposed to elevated PM 2.5 mass concentrations., (Copyright © 2018 Elsevier B.V. All rights reserved.)