In-situ Measurements of NO3 and N2O5 During NEAQS 2002

During the New England Air Quality Study (NEAQS) 2002 campaign, nighttime chemistry of nitrogen oxides was studied through direct, in-situ measurements of NO₃ and N₂O₅ via cavity ring-down spectroscopy. The measurements were taken off the coast of the Northeast U.S. aboard the NOAA research vessel Ronald H. Brown. The marine boundary layer is a unique environment in which to observe chemical transformations occurring in polluted air masses advected from land over the ocean. Data are available for 17 nights of observations of these two compounds; their mixing ratios varied from the instrumental detection limit of 0.5 pptv (5 s average) to maximum values of 140 pptv for NO₃ and 1.5 ppbv for N₂O₅. Respective average mixing ratios were 17 and 84 pptv during nighttime hours for these two compounds. The combination of these observations with measurements of mixing ratios of other important trace gases, aerosols properties and composition, and meteorological data allowed for detailed analysis of NO₃ and N₂O₅ lifetimes and relevant sink chemistry for these compounds. Model calculations are used to illustrate the interconversion of nitrogen oxide compounds near sunset and sunrise.