Participants: Colson, Daum, Doskey, Gaffney, Kleinman, Moses, Newman, Polissar, Springston, Wang

Status of the G-1

The Gulfstream I (G-1) aircraft, which serves as a DOE Research Aircraft Facility, is presently under going routine maintenance and special work to repair corrosion damage to the right wing. The plane has been out of service since mid December. It is expected to return to the Pacific Northwest National Laboratory (PNNL) in mid December and be available for future ACP service by early January. No other maintenance that would take the G-1 out of service for an extended period is expected for the remainder of FY 1997. Most routine maintenance is done locally at the PNNL hangar in Pasco, Washington.

The timing of major routine maintenance, which can only be done offsite, is expected to occur on an annual basis near the end of the fiscal year. This usually takes on the order of two weeks. Whether additional work and down-time is required depends on the outcome of mandated visual and nondestructive testing inspections.

On a longer time horizon, downtime for engine and propeller overhauls will be needed. If we manage to fly between 100 and 150 hours per year, the first round of overhauls would be in FY 1999 and another in 2000. By planning these ahead of time, the actual down time can be as short as a few weeks.

Field Experiment Planning

Field work involving the DOE Research Aircraft Facility in FY 1997 appears to be limited to brief test flights of various instruments being developed for use on the G-1. These flights will take place out of Pasco, Washington, sometime during the late spring or summer months. Paul Doskey will be testing his VOC gas chromatograph. Jeff Gaffney may be testing his new PAN and NO₂ device. If both instruments are ready at the same time, they can be test flown together. Other investigators who wish to also do test flying this year should contact Rich Barchet as soon as possible.

There was some discussion of field experiments beyond the 1997 time frame. Four classes of field studies were proposed:

Nocturnal chemistry. These studies would focus on quantifying the role of chemical reactions that dominate the nighttime chemistry of polluted environments (urban and rural). These reactions deplete O₃ at night and shift reactive nitrogen from NO_x to HONO, the NO₃ radical, and N₂O₅. Those compounds then can photolyze and react when the sun comes up and add to the O₃ production potential for the next day. Measurements of HNO₃, HONO, N₂O₅, and NO₃ radical would be needed to fully understand the nighttime chemistry. Field studies would probably be carried out in the eastern part of the United States during the summer, preferably in conjunction with programs making surface measurements.

Regional oxidant variability. These studies would be similar to those conducted in conjunction with the Southern Oxidant Study in Nashville, Tennessee, and the NARSTO-Northeast field study, in which the G-1 operated out of East Hampton, New York. The focus would be on establishing the variability in the distribution of O₃, its precursors and it co-pollutants on regional scales. Air quality and meteorological modeling would be used to interpret the sparse spatial sampling obtained from an aircraft. Issues related to regional scale vertical and horizontal transport of pollutants, source-receptor relationships, and NO_x-VOC limitation are among those that could be investigated in these studies. A full suite of trace gas measurements would be required to close the NO_y budget and establish VOC speciation. Field work could be done in several geographical areas in order to characterize the variability of oxidant chemistry in different parts of the United States, again during the summer.

Aerosol and oxidants. These studies would focus on determining the role of aerosols in O₃ chemistry. Measurements of aerosol number concentration, size distribution, and chemical composition (bulk and single particle) would be required in addition to those measurements needed to establish the oxidant chemistry. Instruments for making the aerosol measurements may need testing at surface sites prior to deployment on the G-1. Such studies would probably be conducted in the northeastern United States where the O₃ problem is most severe, however, there may be other locations in which aerosols and ozone are considered air quality problems that must be dealt with simultaneously.

Aerosols and climate. These field studies would emphasize the connection between the chemical composition and size of aerosols, their interaction with shortwave and longwave radiant energy, and their ability to act as condensation nuclei in clouds. By focusing on the chemical composition aspects of the aerosol-climate problem, we could bring ACP expertise to bear on a problem that is usually out of the realm of the climate research program at DOE. To do this work effectively would require collaboration with scientists in the Atmospheric Radiation Measurements program and utilization of the aerosol measuring facilities now at the Southern Great Plains Cloud and Radiation Testbed site in north central Oklahoma.

Linking our aircraft-based field work with research groups active at well described surface sites could prove mutually beneficial. Aerosol work at the SGP CART site noted above is one example. Other possible collaborations could be with Harvard (the Harvard Experimental Forest), Notre Dame (an eco-research park in northern Wisconsin), North Carolina State University (Mount Mitchell in the southern Appalachian mountains), and University of Washington (Cheeka Peak on the western coast of the Olympic Peninsula) among others.

Instrumentation

Barchet reviewed the status of the various instruments presently available on or planned for the G-1 aircraft (see tables below). Three categories of instrumentation needs were identified: faster response, new species, and improved devices.

The call for faster response chemical sensors is driven by the need to resolve from measurements made on the G-1 the small-scale spatial variations in pollutant concentration at the edges of plumes from point sources and those that are the result of convective mixing processes in the boundary layer. Response times need to be on the order of one second for O₃, less than one minute for PAN, one second for CO. For many chemicals, existing technology has been pushed to the limit; a technological break-through will be needed to achieve the desired response time.

To expand ACP research into new areas will require measurements of species heretofore not being measured or not being measured adequately. Among those mentioned at the workshop are HONO, NO₃ radicals, HO_x radicals, and integrated hydrocarbon reactivity that is relatively fast and continuous. The next generation of mass spectrometers may be able to detect many compounds of interest but little information was available on the range of compounds that could be measured.

It was relatively easy to generate a long list of improved devices for use within the ACP and on the G-1. Several of these were in support of a greater emphasis on aerosol studies: a nephelometer regulated at various relative humidities (RHs) to standardize the RH at which optical characteristics are measured; a differential mobility analyzer for aircraft operation; a single particle chemical analyzer (probably for surface operation initially); an improved inlet system for sampling aerosols with the G-1; and an organic aerosol collector. Improvements to the radiometric measurements made on the G-1 were also suggested: addition of Multifilter Rotating Shadowband Radiometer sensor heads for upwelling and downwelling solar radiation; UV radiometers with narrower wavelength ranges; and a system for the direct measurement of actinic flux. Also suggested was an upgrade of the data acquisition system on the G-1 to include screens for monitoring instrumentation performance at several locations in the cabin, an increase in the number of data channels; and a lighter weight and lower power basic system.

Endnotes

Although the breakout session discussions addressed many of its objectives, we did not come to closure on specific recommendation for future field studies. With most current ACP projects now in their final year and new proposals to be written this spring, few came prepared to really define new field studies. However, as was pointed out in the concluding plenary session, we need to lay out some field studies that can be the focal point for future ACP proposals. The advantage to DOE of selecting one or more of these as the center of the ACP's future field work would be that ACP investigators would have a clear target for the next round of proposals. Then DOE would not be faced with coordinating field work proposed for many different sites with many different objectives.

Another area of lack of closure was prescribing a plan for how the ACP would be able to realize the improvements called for in its suite of ground and airborne instruments. Here, too, there is need for prioritization and coordination between research groups.