Nitric oxide in the boundary-layer at South Pole during the Antarctic Tropospheric Chemistry Investigation (ANTCI)

The vertical distribution of nitric oxide (NO) was investigated by profiling from a tethered balloon platform during the 2003 Antarctic Tropospheric Chemistry Investigation (ANTCI) at South Pole (SP), Antarctica. The lower atmosphere was probed between the surface and 120 m height by pulling air from an inlet attached to the balloon through a thin-wall, 135 m-long Teflon sampling line and by analyzing NO in this airflow with a ground-borne monitor. Losses and conversion of NO during the 2–4-min residence time in the sampling line were on average on the order of 6–16%, providing a feasible approach for the measurement of vertical NO profiles under SP conditions. NO was found to be highly variable within the lowest 100 m of the atmosphere. Greatly enhanced NO mixing ratios were constrained to a shallow (20–50 m height) air layer nearest to the surface, above which NO rapidly dropped to its mixed boundary layer background levels. Concurrent measurements of ozone and meteorological conditions provide insight into linkages between the ongoing snowpack and boundary layer nitrogen oxides (NOx=NO+NO2) and ozone chemistry. Since [OH] and [HO2] are non-linearly coupled to absolute levels of NOx, their concentrations and the rate of ozone production are expected to similarly show appreciable changes on small vertical scales during conditions with enhanced [NOx].