People are exposed to ultrafine (UF, dp<100nm) and nanoparticles (NPs, dp<50nm) under a variety of circumstances, including occupational and on-road exposure. In urban areas, an increasingly important exposure worldwide occurs during commute in roads and freeways, and while walking on roadside near vehicular traffic. To date, very limited information is available for in-cabin UF and NP measurements. We report in-cabin measurements of particle number concentration (#/cm(3)) acquired with an all new water-based condensation particle counter (WCPC) while driving in Los Angeles roads and freeways. Our results show dramatic increases in particle number concentration when driving from local streets onto freeways. The highest on-board cabin particle number concentration, about 3.0 x 10(5) particle/cm(3), was observed, with all windows open, while driving on a major truck route with up to 25% heavy-duty diesels; the lowest particle number concentration, similar to 2.0 x 10(3) particle/cm(3), was observed when the vehicle was parked with windows closed and engine off.
