Observation of daytime N₂O₅ in the marine boundary layer during New England Air Quality Study–Intercontinental Transport and Chemical Transformation 2004

Abstract

The nitrate radical, NO 3 , and dinitrogen pentoxide, N 2 O 5 , are key reactive nocturnal nitrogen oxides in the troposphere. The daytime impact of NO 3 and N 2 O 5 , however, is restricted by photochemical recycling of NO 3 to NO 2 and O 3 . In this paper, we report daytime measurements of N 2 O 5 on board the NOAA research vessel Ronald H. Brown in the Gulf of Maine during the New England Air Quality Study–Intercontinental Transport and Chemical Transformation (NEAQS‐ITCT) campaign in the summer of 2004. Daytime N 2 O 5 mixing ratios of up to 4 pptv were observed, consistent with predictions from a steady state analysis. Predicted and observed NO 3 mixing ratios were below the instrumental detection limit of ∼1 pptv; the average calculated concentration was 0.09 pptv. Important impacts of daytime NO 3 and N 2 O 5 in the marine boundary layer included increased rates of VOC oxidation (in particular dimethyl sulfide) and enhanced NO x to HNO 3 conversion, both of which scaled with the available NO x . Smaller effects of daytime NO 3 and N 2 O 5 included chemical destruction of O 3 and a shift of the NO 2 :NO ratio. Because the rates of heterogeneous conversion of N 2 O 5 and NO 3 to HNO 3 scale with the surface area available for uptake, the importance of daytime fog is discussed.