Estimation of contributions of NO2 and PAN to total atmospheric deposition of oxidized nitrogen across Eastern Canada

Total oxidized nitrogen (N) dry deposition fluxes have been estimated for a 1-year period at seven eastern Canadian rural sites using observed air concentrations of nitric acid (HNO3) and particle nitrate (NO 3), modelled air concentrations of nitrogen dioxide (NO2) and peroxyacetyl nitrate (PAN), and modelled dry deposition velocities. The calculated annual dry N deposition fluxes range from 0.8 to 4 kg N ha(-1) depending on location. HNO3 is estimated to contribute at most 47-68% of the total, while conservative estimates for NO2 indicate it contributes 12-36% of the total. Smaller contributions are from NO3 (12-20%) and PAN (3-16%). The NO2 contribution to total N dry deposition is higher at locations closer to NO, emission sources (e.g., over and downwind of urban areas) than that at remote locations. Available rural NO2 measurements indicate that the modelled NO2 concentrations (from which dry deposition of NO2 is calculated) are low. With adjustments for this bias, the NO2 contribution to total dry N flux can be higher than 50%, implying that NO2 dry deposition is more important over a greater land area than previously believed and likely more important than HNO3 over some areas. Combining our calculated dry deposition totals with monitored wet deposition produces an estimate of total annual N deposition ranging from 3 to 8 kg N ha(-1), depending on location, with 25-60% contributed by dry deposition. If NO2 and PAN dry deposition are excluded, then total N deposition is underestimated by 7-30%, depending on location, suggesting that previous estimates that have not included NO2 have underestimated dry and total N deposition substantially. Crown Copyright (c) 2005 Published by Elsevier Ltd. All rights reserved.