Summertime distribution of PAN and other reactive nitrogen species in the northern high‐latitude atmosphere of eastern Canada

Aircraft measurements of key reactive nitrogen species (NO, NO 2 , HNO 3 , PAN, PPN, NO 3 ‐, NO y ), C 1 to C 6 hydrocarbons, acetone, O 3 , chemical tracers (C 2 Cl 4 CO), and important meteorological parameters were performed over eastern Canada during July to August 1990 at altitudes between 0 and 6 km as part of an Arctic Boundary Layer Expedition (ABLE3B). In the free troposphere, PAN was found to be the single most abundant reactive nitrogen species constituting a major fraction of NO y and was significantly more abundant than NO x and HNO 3 . PAN and O 3 were well correlated both in their fine and gross structures. Compared to data previously collected in the Arctic/subarctic atmosphere over Alaska (ABLE3A), the lower troposphere (0–4 km) over eastern Canada was found to contain larger reactive nitrogen and anthropogenic tracer concentrations. At higher altitudes (4–6 km) the atmospheric composition was in many ways similar to what was seen over Alaska and supports the view that a large‐scale reservoir of PAN (and NO y ) is present in the upper troposphere over the entire Arctic/subarctic region. The reactive nitrogen budget based on missions conducted from the North Bay site (missions 2–10) showed a small shortfall, whereas the budget for data collected from the Goose Bay operation (missions 11–19) showed essential balance. It is calculated that 15–20 ppt of the observed NO x may find its source from the available PAN reservoir. Meteorological considerations as well as relationships between reactive nitrogen and tracer species suggest that the atmosphere over eastern Canada during summer is greatly influenced by forest fires and transported industrial pollution.