The first in-car measurements of exposure to pollutants that cause oxidative stress during rush hour commutes has turned up potentially alarming results. The levels of some forms of harmful particulate matter inside car cabins was found to be twice as high as previously believed.Most traffic pollution sensors are placed on the ground alongside the road and take continuous samples for a 24-hour period. Exhaust composition, however, changes rapidly enough for drivers to experience different conditions inside their vehicles than these roadside sensors. Long-term sampling also misses nuanced variabilities caused by road congestion and environmental conditions.