The influence of traffic-related air pollution on indoor residential exposure is not well characterized in homes with high natural ventilation in low-income countries. Additionally, domestic allergen exposure is unknown in such populations. We conducted a pilot study of 25 homes in peri-urban Lima, Peru to estimate the effects of roadway proximity and season on residential concentrations. Indoor and outdoor concentrations of particulate matter (PM2.5), nitrogen dioxide (NO2), and black carbon (BC) were measured OPEN ACCESS Int. J. Environ. Res. Public Health 2015, 12 13467 during two seasons, and allergens were measured in bedroom dust. Allergen levels were highest for dust mite and mouse allergens, with concentrations above clinically relevant thresholds in over a quarter and half of all homes, respectively. Mean indoor and outdoor pollutant concentrations were similar (PM2.5: 20.0 vs. 16.9 μg/m3, BC: 7.6 vs. 8.1 μg/m3, NO2: 7.3 vs. 7.5 ppb), and tended to be higher in the summer compared to the winter. Road proximity was significantly correlated with overall concentrations of outdoor PM2.5 (rs = −0.42, p = 0.01) and NO2 (rs = −0.36, p = 0.03), and outdoor BC concentrations in the winter (rs = −0.51, p = 0.03). Our results suggest that outdoor-sourced pollutants significantly influence indoor air quality in peri-urban Peruvian communities, and homes closer to roadways are particularly vulnerable
