Abstract
An analysis of coastal meteorological mechanisms facilitating the transit pollution plumes emitted from sources in the Northeastern U.S. was based on observations from the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 field campaign. Particular attention was given to the relation of these plumes to coastal transport patterns in lower tropospheric layers throughout the Gulf of Maine (GOM), and their contribution to large-scale pollution outflow from the North American continent. Using measurements obtained during a series of flights of the National Oceanic & Atmospheric Administration (NOAA) WP-3D and the National Aeronautics and Space Administration (NASA) DC-8, a unique quasi-Lagrangian case study was conducted for a freshly emitted plume emanating from the New York City source region in late July 2004. The development of this plume stemmed from the accumulation of boundary layer pollutants within a coastal residual layer, where weak synoptic conditions allowed for its advection into the marine troposphere and transport by a mean southwesterly flow. Upon entering the GOM, analysis showed that the plume layer vertical structure evolved into an internal boundary layer form, with signatures of steep vertical gradients in temperature, moisture and wind speed often resulting in periodic turbulence. This structure remained well-defined during the plume study, allowing for the detachment of the plume layer from the surface and minimal plume-sea surface exchange. In contrast, shear driven turbulence within the plume layer facilitated lateral mixing with other low-level plumes during its transit. This turbulence was periodic and further contributed to the high spatial variability in trace gas mixing ratios. Further influences of the turbulent mixing were observed in the impact of the plume inland as observed by the Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) air quality network. This impact was seen as extreme elevations of surface ozone and CO levels, equaling the highest observed that summer.
Highlights
The composition and dynamics associated with pollution plumes released from coastal source regions are of eminent importance to regional air quality and larger scale continental outflow
20 July and 22 July to provide a quasi-Lagrangian vantage point of a fresh plume emitted from the New York City (NYC) source region as it transited through the Gulf of Maine (GOM) and into the Western North Atlantic
The 7/20 plume case study was characteristic of a low-flowing fresh plume, detached from the surface and ventilated into shallow tropospheric layers under mild synoptic conditions
Summary
The composition and dynamics associated with pollution plumes released from coastal source regions are of eminent importance to regional air quality and larger scale continental outflow. Real et al [22] and Cain et al [23] added to this Lagrangian approach, advancing new insights into the processes influencing the plume’s chemical transformation and ozone production in particular based upon photochemical model simulations These authors advanced that potential errors in their Lagrangian analyses may have derived from uncertainties in the lower tropospheric wind fields used to force the trajectory forecasts and diagnose mixing and transport in their simulations. Specific objectives of our study were to employ these observations in a quasi-Lagrangian manner to investigate the composition and dynamics of such regional plumes, influences of the local marine atmospheric boundary layer (MABL) on plume transport, and the contribution of such plumes to North American continental outflow.
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