Monthly sonde data for Lauder in Central Otago, New Zealand show profiles of aerosol backscatter from the surface to over 30 km altitude. The tropospheric data vary by season, with greater aerosol backscatter throughout the free troposphere in springtime. Aerosol mixing ratios in layers in the upper troposphere at these times are often much higher than anywhere else above the boundary layer, suggesting that they arise from horizontal transport. Ozone measurements from the sonde show correspondence in vertical structure to the backscatter data and also seasonal enhancement. The latter correlates with aerosol, but competing causes of ozone enhancement make the correspondence indistinct. High concentrations of carbon monoxide are observed by Fourier transform spectroscopy in spring, and altitude profiles derived from line shape suggest that the peak in CO occurs in the same altitude range as the aerosol enhancement.