© 2017 Elsevier Ltd Particulate matter exposure may cause adverse health effects. Although ultrafine particulate matter (UFP) is hypothesised to be particularly health relevant, the number of studies into personal UFP exposure is limited. Aim To increase insight where and when most UFP exposure occurs, in terms of exposure levels and peaks in microenvironments, time of day and activities, to support development of abatement strategies to reduce exposure. Methods UFP exposure and GPS tracks were recorded continuously for 5 days in 12 healthy volunteers. GPS data was processed to assign context information, and linked to UFP data. Results Participants spent most time indoors ( > 90%), mainly at home (approx. 80%). Mean particle number concentration (particles/cm 3 ) was highest in motorized transport (20.5 × 10 3 ), followed by other indoor environments (16.5 × 10 3 ), and lower at home (11.2 × 10 3 ) and walking outdoors (9.0 × 10 3 ). Due to the large proportion of time spent indoors, exposure indoors contributed most to total exposure (nearly 90%). Exposure during motorized transport showed a speed dependency, most likely linked to exposure on larger busier roads. Using a 95th percentile cut-off for concentration elevations lasting at least 5 min for peak-detection, 98 peaks were identified, mainly during daytime. These contributed substantially to total exposure (25%) while accounting for only 3.4% of total time. Of this peak contribution 88% occurred indoors (mainly at home) and 12% outdoors. Conclusions UFP exposure shows clear differences between microenvironments. Peaks contribute substantially to total exposure. Measures to prevent peak exposures could contribute to substantial exposure reduction.