Vertical profiles in NO₃ and N₂O₅ measured from an aircraft: Results from the NOAA P-3 and surface platforms during the New England Air Quality Study 2004

The nocturnal nitrogen oxides, NO₃ and N₂O₅, are important to the chemical transformation and transport of NO_x, O₃ and VOC. Their concentrations, sources and sinks are known to be vertically stratified in the nighttime atmosphere. In this paper, we report vertical profiles for NO₃ and N₂O₅ measured from an aircraft (the NOAA P-3) as part of the New England Air Quality Study in July and August 2004. The aircraft data are compared to surface measurements made in situ from a ship and by long-path DOAS. Consistent with previous, vertically resolved studies of NO₃ and N₂O₅, the aircraft measurements show that these species occur at larger concentrations and are longer lived aloft than they are at the surface. The array of in situ measurements available on the P-3 allows for investigation of the mechanisms that give rise to the observed vertical gradients. Selected vertical profiles from this campaign illustrate the role of biogenic VOC, particularly isoprene and dimethyl sulfide, both within and above the nocturnal and/or marine boundary layer. Gradients in relative humidity and aerosol surface may also create a vertical gradient in the rate of N₂O₅ hydrolysis. Low-altitude intercepts of power plant plumes showed strong vertical stratification, with plume depths of 80 in. The efficiency of N₂O₅ hydrolysis within these plumes was an important factor determining the low-level NO_x and O₃ transport or loss at night. Averages of nocturnal O₃, NO₂, NO₃ and N₂O₅ binned according to altitude were consistent with the trends from individual profiles. While production rates of NO₃ peaked near the surface, lifetimes of NO₃ and N₂O₅ were maximum aloft, particularly in the free troposphere. Variability in NO₃ and N₂O₅ was large and exceeded that of NO₂ or O₃ because of inhomogeneous distribution of NO_x emissions and NO₃ and N₂O₅ sinks.