The University of Maryland aircraft flew as scheduled Thursday May 3 (RF-05 & RF-06) and Friday May 4 (RF-07 & RF-08). The objectives of these 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) 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, and may be summarized as follows:
AM Flight: take off at 0830 EDT/1230 UT from College Park, MD (CGS) and spirals performed over Luray, VA (W45); Winchester, VA (OKV); and Cumberland, MD (CBE) where we landed for refueling. This pattern characterized early/mid-morning conditions within the planetary boundary layer (PBL) and lower free troposphere at the western boundaries of Maryland and Virginia. Flight data quantified remnant overnight and synoptic-scale transport aloft which would be expected to advect into Maryland and Virginia during the day, mixing into the developing PBL facilitated by ridge-induced subsidence. Surface data from the SNP Big Meadows air quality site (Elev. 1100 m MSL) - often very useful for forecasting in VA and MD - were evaluated against airborne in situ observations.
PM Flight: take off at 1330/1730 from CBE and spirals performed over Fort Meade, MD (FME); Harford Co., MD (0W3) and Easton, MD (ESN). This pattern characterized the developing PBL during the day, including the result of convective mixing of remnant pollution and ozone/haze precursors. Flight data provided direct airborne in situ information over FME to compare with profiler winds and virtual temperature, and quantified urban corridor precursor input, photochemical ozone and haze formation, and pollution transport aloft.

Widespread 8-hr NAAQS ozone exeedences were reported in VA and MD during both days during this unseasonally warm mini-episode. Preliminary results for the research flights follow. On May 3rd AM (RF-05) the western boundary was characterized by a tight inversion over the Shenandoah Valley around 600 m MSL (~300 m AGL) trapping substantial CO and SO₂ in the near-surface layer overnight. This has been observed in the region under these conditions by this group in the past, and while perhaps being significant in terms of convective lifting and westerly transport later in the day, probably at the very least presents a public health issue to residents of the Shenandoah Valley. Ozone aloft was relatively constant at 80-85 ppbv with altitude between the nocturnal inversion and a second subsidence inversion at ~2400 m MSL. Ozone at 1100 m MSL over W45 was 83 ppbv consistent with SNP Big Meadows ozone 87 ppbv at 0900 EDT as reported by Dan Salkovitz at VADEQ. The flight later that day May 3rd PM (RF-06) saw moderate haze throughout Maryland west of the Chesapeake Bay. Highest ozone observed was 115 ppbv aloft at 350 m AGL over the northernmost Chesapeake Bay northeast (downwind) of Baltimore City with ozone around 100 ppbv from the surface to 1200 m MSL northeast of Baltimore. Moderate seasonable humidity (40-60%) throughout all altitude levels and geographic areas studied may have kept ozone levels aloft below the 1-hr NAAQS.
The May 4th AM (RF-07) flight was characterized by generally more hazy conditions - again with widespread 8-hr ozone NAAQS exceedences - until sporadic late-afternoon storms broke the weather pattern. The boundary areas of northwestern VA and western MD were again characterized by precursors in the near surface layer, and elevated remnant ozone throughout the upper levels. Ozone of ~85 ppbv was reported at 1100 m MSL over W45, again consistent with 91 ppbv recorded at Big Meadows in SNP concurrently (SNP data again courtesy of Dan Salkovitz, VADEQ). Amazingly, ozone at 85-90 ppbv was observed over CBE from 2.0-3.0 km MSL - regional air quality at levels above the 8-hr standard coming into the area early in the day! The May 4th PM (RF-08) flight saw haze intensifying early reducing visibility, coupled with prefrontal cumulus buildups, which made flying a challenge at times. Again highest ozone aloft was observed downwind of Baltimore over Harford Co., with ozone ~90 ppbv from near the surface to 1500 m MSL. Ozone of ~105 ppbv was again observed aloft (350 m AGL) over the upper Chesapeake Bay near Aberdeen, MD - northeast and downwind of Baltimore City. A number of localized and short-lived severe storm cells moved through the area late afternoon (~2000 UT) breaking the pattern and terminating the episode locally.

In summary, in interesting early-season event where substantial evidence for regional-scale transport of criteria pollutants and haze from the west to Virginia and Maryland was acquired. Seasonably low humidity possibly saved a particularly severe ozone exceedence.

Doddridge