The University of Maryland research aircraft returned from Virginia yesterday afternoon after completing several days conducting research flights based out Raleigh, NC (RDU) and Richmond, VA (RIC) during an early August episode - the most severe the 2001 season thus far over the mid-Atlantic region.

Spiral locations and heights are detailed in the research flight summary for 2001.

A brief summary of preliminary results follows:
The RF-55 Tuesday 08/07 AM flight was a ferry from MD to RDU, performing a transect en route over southern MD, central VA and northern NC at around 2.5 Kft. Weather conditions were clear with moderate planetary boundary layer (PBL) haze and visibility around 4-5 miles. Along the transect ozone dropped from moderate levels (80-90 ppbv) over MD to unseasonably low (45-60 ppbv) background values through VA and into NC. Several plumes high in SO₂ were observed throughout the transect, two of these also associated with elevated ozone suggesting in situ photochemical production. Two profiles performed near RDU (at 5W8, Siler City, NC and 5W5, Triple W, NC) showed high PBL loading of CO and SO₂ but only moderate ozone (45-60 ppbv) aloft. All instruments performed nominally.
The RF-56 Tuesday 08/07 PM flight was designed to evaluate ozone and haze production in the Raleigh, NC area, and evaluate the instrumented tall tower SE of Raleigh. PBL haze was still moderate with ~5 miles visibility, but fair weather culumus (Cu) clouds had moved in (~50% cover) with some showing slight vertical development (tops to about 8.0 Kft). Ozone was moderate throughout most of the flight at 50-70 ppbv, with highest ozone around 100 ppbv observed E of Raleigh at 2.5 Kft. All instruments performed nominally.
The RF-57 Wednesday 08/07 evening flight shifted focus from Raleigh, NC to the Richmond, VA area. The late afternoon ferry flight to RIC was conducted under mostly clear skies with a few (~10% cover) Cu clouds and moderate PBL haze with visibility 6-8 miles. Highest observed ozone was ~100 ppbv at 2.5 Kft just south of the NC-VA border. A vertical profile performed near Chesterfield Co., VA (FCI) in support of the Virginia Science Museum (VSM) profiler showed ozone around 700 pbbv throughout most of the PBL, while water vapor, CO and Bscat showed considerably more vertical structure. All instruments performed nominally.
The RF-58 flight plan on Wednesday 08/08 AM was designed to profile in the vertical west of Richmond, VA assessing any regional transport of remnant ozone and ozone/haze precursors overnight, and to evaluate the VSM profiler morning winds. Sky conditions were mostly clear with some high cirrus (Ci) to the SW, moderate to heavy PBL haze (visibility ~5 miles), and some visual evidence of stratified pollution layers above the PBL. Ozone aloft within the PBL ranged from 60-80 ppbv over Crewe (W81) and Louisa Co. (LKU) but was observed near 100 ppbv around 16Z (1200 EDT) from 500-1200 m MSL over Chesterfield Co. (FCI), probably reflecting in situ ozone production downwind of Richmond City under NE flow. All instruments performed nominally.
After a quick turnaround at RIC, the RF-59 Wednesday 08/08 PM flight plan was designed to "box" the city of Richmond, VA, performing vertical spirals upwind and downwind of the city center, as well as evaluate the VSM profiler. The PBL haze had worsened considerably since the AM flight, with visibility less than 4 miles under mostly clear skies with some (~20% cover) Cu clouds. Highest ozone observed was around 120 ppbv in a layer 1300-2000 m MSL over FCI and again on approach to land at RIC. There was evidence of considerable in situ ozone production over and downwind of Richmond City, with Louisa Co. (LKU) showing ~60 ppbv ozone aloft while ~95 ppbv throughout the PBL was observed over New Kent Co. (W96) under westerly flow as the result of a dramatic wind shift during the afternoon.
August 8, 2001 was particularly interesting as Richmond exceeded the 1-hour ozone NAAQS. The aircaft data aloft gel nicely with the VSM profiler data indicating the probability that a recirculation episode influenced Richmond, VA air quality substantially during the course of the day. Boundary layer winds began the day from the northeast and VADEQ Chesterfield Co. ozone monitor showing a substantial increase. Later in the day, winds turned westerly, presumably moving pollution located aloft over Chesterfield Co. back over Richmond City and to eastern Henrico Co. where the 1-hour exceedance occurred. This recirculation effectively enabled emissions from Richmond City to contribute to ozone/haze precursor loading twice on the same day day. All instruments performed nominally.
With substantial convection forecast for later in the day, it was decided to terminate aircraft flights with RF-60 Thursday 08/09 AM, a ferry flight from RIC back to College Park, MD. During this flight the VSM profiler data were evaluated with aircraft vertical spirals over FCI and Hanover Co. (OFP). Ozone aloft over VA was mostly moderate (50-70 ppbv) under clear skies and moderate PBL haze with visibility ~5 miles. All instruments performed nominally.

More detailed preliminary results are available from the Principal Investigator upon request.

Doddridge