Figure 3

Box plots of 1-second PNC measurements as a function of distance from I-93 for Somerville (a) and Dorchester/South Boston (b). The boxes represent the 25^th and 75^th percentiles of the data, the whiskers represent the 10^th and 90^th percentiles. The horizontal solid line in each box represents the median PNC; the black diamond represents the average PNC. The right side of the red line indicates distance to the east of I-93 (generally downwind), and the left side indicates distance to the west of I-93 (generally upwind).