Transport and outflow to the North Atlantic in the lower marine troposphere during ICARTT 2004

Abstract

An analysis of pollution plumes emitted from sources in the Northeastern US 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 NOAA WP-3D and the 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 initial development of this plume stemmed from the accumulation of boundary layer pollutants within a coastal residual layer where weak synoptic forcing triggered its advection by mean southwesterly flow. As the plume tracked into 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 thus minimal deposition and plume-sea surface exchange. In contrast, lateral mixing with other low-level plumes was significant during its transit and facilitated in part by persistent shear driven turbulence which further contributed to the high spatial variability in trace gas mixing ratios. The impact of the plume inland was assessed using observations from the AIRMAP air quality network. This impact was noticeably detected as a contribution to poor surface ozone conditions and significant elevations of other major pollutants to levels equaling the highest observed that summer. Further contributions to larger-scale outflow across the North Atlantic was also observed and analyzed

The Land‐Sea Breeze of the Red Sea: Observations, Simulations, and Relationships to Regional Moisture Transport

“…The prevailing stability of the stratification within offshore IBLs further provides for detachment from the surface once a continental air mass passes into the marine LT. This enables an efficient means for LT transport of trace gases and aerosols/dust over regional to intercontinental distances (Angevine et al, ; Dacre et al, ; Davis et al, ; Davis et al, ).…”

Meteorological factors controlling low-level continental pollutant outflow across a coast

“…The air mass was broader and related to pollution outflow from a wider area of the East Coast, rather than the tight plume related to the strong emissions in the New York area (which would not be represented in the tracer simulations). Vertical profiles of a wide range of measurements are also shown in Davis et al (2012) from the same three flights, but the segments shown do not correspond to the Lagrangian intercepts identified by Methven et al (2006). Consequently the time evolution is not as apparent as shown in Fig.…”

“…However, there were marked episodes of cross-coastal pollutant transport, some of which were observed by research aircraft as the air crossed the Atlantic to the Azores and Europe (Methven et al, 2006;Owen et al, 2006). Chemical processing following air masses for several days during these ICARTT Lagrangian cases has been examined in detail by Real et al (2008); Lee et al (2011);Cain et al (2012); Davis et al (2012).…”

“…They named it the ICARTT Lagrangian Case 3, and it has been used to examine long-range transport and chemical transformation (Real et al, 2008;Cain et al, 2012). The near-range chemical evolution of the air mass has been examined by several authors including Lee et al (2011) and Davis et al (2012). Here, segments of three NOAA WP-3D flights following the air mass on consecutive days are used to compare the time evolution of observed vertical profiles of trace gases with the idealised tracer simulation.…”

“…The box model is sufficiently simple to have analytic solutions, but is also capable of describing the diurnal and synoptic timescale variability in tracers in the mesoscale model. Stratified layers of pollutants over oceans have been observed by many studies (Paluch et al, 1992;Müller et al, 2001;Davis et al, 2012). Pollutants exported above the marine BL (MBL) have longer lifetimes (Dickerson et al, 1999), allowing more efficient long-range transport of pollutants (VanCuren et al, 2005;Holzer and Hall, 2007).…”