Airborne Characterization of the Chemical, Optical, and Meteorological Properties, and Origins of a Combined Ozone-Haze Episode over the Eastern United States

Abstract

Airborne observations of trace gases, particle size distributions, and particle optical properties were made during a constant altitude transect from New Hampshire to Maryland on 14 August 2002, the final day of a multiday haze and ozone (O₃) episode over the Mid-Atlantic and northeastern United States. These observations, together with chemical, meteorological, and dynamical analyses, suggest that a simple two-reservoir model, composed of the lower free troposphere (LFT), where photochemical processes are accelerated and removal via deposition does not occur, and the planetary boundary layer (PBL), where most precursor species are injected, may realistically represent the physics and chemistry of severe, multiday haze and O₃ episodes over the Mid-Atlantic and Northeast. Correlations among O₃, potential temperature (θ), the scattering Ångström exponent (α), and relative humidity (RH) suggest that high concentrations of O₃ and relatively large, internally mixed sulfate and black carbon (BC) particles were produced in the LFT. Conversely, the PBL contained less O₃ and more externally mixed, primary sulfate and BC particles than the LFT. Backward trajectories indicate source regions in the Midwest and Mid-Atlantic urban corridor, with southerly transport up the urban corridor augmented by the Appalachian lee trough and nocturnal low-level jet.