Atmospheric measurements of peroxyacetyl nitrate and other organic nitrates at high latitudes: Possible sources and sinks

Abstract

Aircraft measurements of peroxyacetyl nitrate (PAN) and other important reactive nitrogen species (NO, NO2, HNO3, peroxypropionyl nitrate (PPN), CH3ONO2, NOy) were performed at high latitudes over North America and Greenland during July–August 1988, at all altitudes between 0 and 6 km as part of an Arctic Boundary Layer Expedition (ABLE 3A). Complementing these were measurements of C1 to C5 hydrocarbons, O3, chemical tracers (C2Cl4, CO), and important meteorological parameters. PAN was found to be an important reactive nitrogen species in the free troposphere, with 95% of the mixing ratios falling in the range of 5 to 450 ppt. PAN increased systematically with height with mixing ratios of 100–700 ppt at 6 km and 0–50 ppt in the boundary layer. The free tropospheric PAN reservoir was present over the entire high‐latitude region sampled (50° to 82°N latitude and 60° to 160°W longitude). In the boundary layer, PAN mixing ratios were higher over land than over the North Pacific Ocean. Significant levels of PAN were measured within stratospheric intrusions, forest fire plumes, and episodes of remote pollution. Other organic nitrates such as PPN and CH3ONO2 were found to be a small fraction of PAN (0–10%). PAN and O3 were strongly correlated both in their fine and gross structures, and the latitudinal distribution of PAN in the free troposphere followed that of O3. A two dimensional global photochemical model is used to compare measurements and model results. Model simulations, correlations between reactive nitrogen species (e.g. PAN and NOy) and anthropogenic tracers (C2H2, CO, C2Cl4), and the composition of NOy itself support the view that the reactive nitrogen measured during ABLE 3 A is predominantly of anthropogenic origin with a minor stratospheric component. Transported industrial pollution, biomass burning, and the unique seasonal dynamics of the Arctic/sub‐Arctic region play a dominant role in defining this reactive nitrogen abundance. This PAN (and NOy) reservoir may contribute to the summertime maximum in deposited nitrate observed over Greenland.