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

Measurements of ozone, carbon monoxide, NO_y, NO_x, 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, NO_x and NO_y 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 C₁-C₄ 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 NO_y 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 O₃ versus NO_y-NO_x correlations from that observed in eastern North America.