Episodic removal of NOy species from the marine boundary layer over the North Atlantic

Measurements of ozone, carbon monoxide, NOy, NOx, HNO3, particulate NO3-, PAN, PPN, and alkyl nitrates were made at Chebogue Point, Nova Scotia, during July, August, and September 1993, and measurements of ozone, carbon monoxide, NOx and NOy were made at Sable Island, Nova Scotia, during August and September 1993 as part of the North Atlantic Regional Experiment (NARE). Periods of photochemical pollution were observed during which concentrations of the above species were elevated relative to average conditions. The best indicator of the extent of impact was found to be the sum of the C-1-C-4 alkyl nitrates. The removal of PAN and PPN by fog droplets through thermal decomposition and subsequent uptake of the peroxyacetyl and peroxypropionyl radicals (PA and PP) was suggested by loss of PAN and PPN during fog. The effect of this chemistry on NOy species in the marine environment will need to be considered. The loss of inorganic nitrate (HNO3 and particulate NO3-), PAN (and to a minor extent PPN) resulted in deviation of the O-3 versus NOy-NOx correlations from that observed in eastern North America.