Airborne peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) measurements during TRACT 1992

Airborne PAN and PPN measurements with high spatial resolution were made during the TRACT 1992 intensive campaign. Relationships between PAN, PPN, ozone and reactive nitrogen species are discussed. PPN mixing ratios are found to be typically 12 per cent of the PAN mixing ratios. PAN was always tightly correlated with CO, and in most cases with ozone, in agreement with a simple photochemical box model which was run with input parameters representative of the flight situations. The observed PPN/PAN ratios were lower than predicted by the box model. This may be due to an overestimation of 2-pentene emissions which were used as input to the model, and/or to the omission of isoprene and other biogenic hydrocarbons. The observed PAN/NOy ratios in photochemically aged air masses exceeded both model predictions and previous observations. This inconsistency is most likely due to HNO3 losses in the aircraft sampling line.