Eddy covariance fluxes of peroxyacetyl nitrates (PANs) and NOy to a coniferous forest

up to approximately � 14 ng N m � 2 s � 1 . The average daytime flux peaked at � 6.0 ng N m � 2 s � 1 and accounted for � 20% of the daytime NOy flux. Calculations suggest minimum daytime surface resistances for PAN in the range of 70–130 s m � 1 .I t was estimated that approximately half of daytime uptake was through plant stomates. Average PAN deposition velocities, Vd(PAN), showed a daytime maximum of � 10.0 mm s � 1 ; however, deposition did not cease during nighttime periods. Vd(PAN) was highly variable at night and increased when canopy elements were wet from either precipitation or dew formation. Diel patterns of deposition velocity of MPAN and PPN were similar to that of PAN. These results suggest that deposition of PAN, at least to coniferous forest canopies, is much faster than predicted with current deposition algorithms. Although deposition of PAN is unlikely to compete with thermal dissociation during warm summer periods, it will likely play an important role in removing PAN from the atmosphere in colder regions or during winter. The fate of PAN at the surface and within the plants remains unknown, but may present a previously ignored source of nitrogen to ecosystems.