The University of Maryland aircraft flew as scheduled Wednesday June 27 through Friday June 29 (Research flights, RF-19 through -24). The objectives of this series of flights were to:
1. Evaluate MM5 forecasts produced here at METO/UMCP
2. Characterize pollutant transport aloft into the lower troposphere over MD and VA
3. Evaluate data from the air quality surface site at Shenandoah National Park (SNP), VA and MDE profiler/RASS at Fort Meade, MD

Morning and afternoon flight patterns flown each day are tabulated in the research flight summary for 2001, as already detailed in the June 26 update. The TSI Model 3563 3-wavelength (450, 550, and 700 nm) nephelometer was operated in the aircraft for the first time, providing total forward scattering of ambient sub-micron aerodynamic diameter aerosol. Preliminary results for these latest research flights follow.

On June 27 (RF-19) western boundary air quality aloft was characterized by quite low ozone around 50 ppbv, under clear sky with a few scattered Cu clouds showing very slight vertical development, and moderate haze (visability ~ 5 miles) within the planetary boundary layer (PBL). Later that day during the June 27 PM (RF-20) flight saw slightly worsening haze in the PBL and some scattered weakly-convective activity. Highest ozone observed was around 135 ppbv at 1.4 Km MSL near Annapolis, MD (ANP), with elevated ozone around 110-125 ppbv observed consistently northeast and east (downwind) of the Baltimore-Washington (B-W) corridor from about 1.0 Km to the top of the PBL. This was an interesting result given the low "regional loading" of remnant ozone and precursors observed over northwestern Virginia and western Maryland earlier in the day, and confirming substantial influence of the B-W corridor itself on in situ ozone production downwind. The TSI nephelometer worked extremely well first time up, and will be a standard component of our research flight package from now on. All other instruments performed nominally.
A similar, yet more dramatic result was observed on June 28 with the AM flight (RF-21) under clear skies and moderate/heavy PBL haze (vis. 3-5 mi). Again there was no appreciable westerly transport of remnant ozone observed along the western boundary, with ozone ranging from 55-70 ppbv throughout the lower atmosphere from the surface to around 2.3 Km. The PM flight (RF-22) later that day showed substantial ozone downwind of the B-W urban/transport corridor despite the low regional ozone load. Highest ozone observed was near 130 ppbv at 1.0 Km over Easton, MD (ESN), but ozone in the range 110-135 ppbv was observed throughout the flight path east of the B-W corridor in a well-mixed layer 0.5-1.6 Km. Easton, MD often experiences lower pollution than other locales downwind of the B-W corridor due to Chesapeake Bay breeze effects, but this was clearly not the case in this instance. Although a Code Red - Ozone Action Day was forecast for Washington and for Baltimore few surface exceedences of the 1-hr ozone NAAQS in the region were recorded. The aircraft data suggest Code Red air quality was indeed widespread throughout the region as forecast, albeit removed to regions above (0.5 Km). This particular case study may prove interesting for forecasters and modelers alike down the road. All instruments performed nominally except for the CO analyzer, which exhibited some intermittant signal spiking on the PM flight, but with minimal resultant data loss.
On June 29 (RF-23) the regional picture had changed substantially, with the effects of substantial transport of remnant ozone and ozone/haze precursors over Cumberland, MD (CBE) with ozone around 85-100 ppbv up to 1.5 Km. The PBL along the western boundary was characterized by particularly heavy haze and poor visibility. With our interest peaked on the basis of the morning results it was disappointing to have to abort the PM flight (RF-24) approximately 60 minutes after takeoff. On the traverse from CBE at around 1.0 Km ozone was 100-105 ppbv, although the area weather was deteriorating rapidly with several convective cells developing. Near Fort Meade, MD (FME) a rapidly developing thunderstorm reduced visibility to an extent precluding required operations under visual flight rules (VFR). At the same time, we experienced severe electrical malfunctions on some research instruments and aircraft avionics systems; cause is unknown, but nearby severe electrical storm activity is likely. These concurrent problems combined to force and early termination of the flight, and a direct retrun to home base at College Park, MD. The CO analyzer was extremely noisy throughout both flights, and consequently CO data are not avaialable for RF-23 and RF-24. All other instruments performed nominally.

In summary, an interesting situation June 27 and 28 where despite low regional input of remnant ozone and ozone/haze precursors quite high near-surface ozone was observed downwind of the urban corridor. These days may make for an interesting modeling scenario in the future.

Focus over the next few weeks will shift to the NARSTO Northeast Corridor Oxidant and Particle Study NE-OPS particle-oxidant project in Philadelphia, PA and supporting the Upper Ohio River Valley Project UORVP near Pittsburgh, PA and EPA Eastern Superisites consortia in Pittsburgh, PA and Baltimore, MD. Check back early in the week for details on the next flights.

Doddridge