Peroxyacetyl nitrate (PAN) concentrations in the Antarctic troposphere measured during the Photochemical Experiment at Neumayer (PEAN'99)

Because investigations of PAN at higher southern latitudes are very scarce, we measuredsurface PAN concentrations for the first time in Antarctica. During the PhotochemicalExperiment at Neumayer (PEAN'99) campaign mean surface PAN mixing ratios of(13 ± 7) pptv and maximum values of 48 pptv were found. When these PAN mixing ratioswere compared to the sum of NOx and inorganic nitrate they were found to be equal orhigher. Low ambient air temperatures and low PAN concentrations caused a slowhomogeneous PAN decomposition rate of approximately 5 x 10^-2 pptv hr^-1. These slowdecay rates were not sufficient to firmly establish the simultaneously observed NOxconcentrations. In addition, low concentration ratios of [HNO3] / [NOx] imply that thephotochemical production of NOx within the snow pack can influence surface NOx mixingratios in Antarctica. Alternate measurements of PAN mixing ratios at two different heightsabove the snow surface were performed to derive fluxes between the lower troposphereand the underlying snow pack using calculated friction velocities. Most of the concentrationdifferences were below the precision of the measurements. Therefore, only an upper limitfor the PAN flux of ± 1 x 10^13 molecules m^-2 s^-1 without a predominant direction canbe estimated. However, PAN fluxes below this limit can still influence both the transfer ofnitrogen compounds between atmosphere and ice, and the PAN budget in higher southernlatitudes