REACTIVE NITROGEN-OXIDES AND OZONE ABOVE A TAIGA WOODLAND

Measurements of reactive nitrogen oxides (NOx and NOy) and ozone (03) were made in the planetary boundary layer (PBL) above a taiga woodland in northern Quebec, Canada, during June-August, 1990, as part of NASA Artic Boundary Layer Expedition (ABLE) 3B. Levels of nitrogen oxides and 03 were strongly modulated by the synoptic scale meteorology that brought air from various source regions to the site. Industrial pollut ion from the Great Lakes region of the U.S. and Canada appears to be a major source for periodic elevation of NOx, NOy, and O-3. We find tha t NO/NO2 ratios at this site at midday were approximately 50% those ex pected from a simple photochemical steady state between NCx and O-3, i n contrast to our earlier results from the ABLE 3A tundra site. The di fference between the taiga and tundra sites is likely due to much larg er emissions of biogenic hydrocarbons (particularly isoprene) from the taiga vegetation. Hydrocarbon photooxidation leads to relatively rapi d production of peroxy radicals, which convert NO to NO2, at taiga sit e. Ratios of NOx to NOy were typically 2-3 times higher in the PBL dur ing ABLE 3B than during ABLE 3A. This is probably the result of high P AN levels and suppressed formation of HNO3 from NO2 due to high levels of biogenic hydrocarbons at the ABLE 3B site.