In this paper, we investigate the role of in situ new particle production in the central Canadian sub-Arctic and Arctic as part of the TOPSE experiment. Airborne measurements conducted primarily in the free troposphere were made from 50¿ to 90¿W longitude and 60¿ to 85¿N latitude during the period from February to May 2000. Data pertinent to this paper include 3--4 nm diameter (Dp) particles, ultrafine condensation nuclei (Dp > 3 nm), fine particles (0.2 < Dp < 3 ¿m), and the possible nucleation precursor, sulfuric acid, and its precursor, sulfur dioxide. For data averaged over this period, most species showed little evidence for a latitudinal trend. Fine aerosol number concentrations, however, showed a slight increase with latitude. The evolution of various species concentrations over the period of the study show that fine particles also had a consistent temporal trend, increasing at all altitudes from February to May, whereas sulfur dioxide at the surface tended to peak in late March. Ultrafine condensation nuclei and 3--4 nm particles showed no temporal trends. Little evidence for in situ new particle production was observed during the study, except for one atypical event where SO2 concentrations were 3.5 ppbv, 2 orders of magnitude higher than typical levels. This paper cannot address the question of whether the observed condensation nuclei were produced in situ by a low particle production rate or transported from lower latitudes.