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WIND TUNNEL EVALUATION OF AN AIRCRAFT-BORNE SAMPLING SYSTEM
Citation:
Irshrad, H., A. McFarland, M S. Landis, AND R. K. STEVENS. WIND TUNNEL EVALUATION OF AN AIRCRAFT-BORNE SAMPLING SYSTEM. AEROSOL SCIENCE AND TECHNOLOGY 38(4):311-321, (2004).
Impact/Purpose:
The overall research objective of this task is to improve our understanding of the emission, transport, transformation, and deposition of atmospheric mercury. Information garnered from this research is used to improve and evaluate EPA deterministic models that are used to investigate the (i) relative impact to local, regional, and global sources to atmospheric mercury deposition, and (ii) benefits of various emission reduction scenarios.
Specifically, individual research project objectives are listed below:
(1) Evaluate the ability of speciated mercury (Hg0, Hg2+, HgP) measurements to aid source apportionment models in identifying anthropogenic source contributions to atmospheric mercury deposition
(2) Elucidate the contribution of coal combustion sources to observed mercury wet deposition in the Ohio River Valley
(3) Obtain atmospheric profiles (200 - 12,000 ft) of speciated ambient mercury off the south Florida Coast
- Evaluate the role of long range transport of RGM to Florida in the marine free troposphere.
- Identify any vertical mercury gradients that might indicate the presence of rapid mercury chemistry in air or in cloud water.
(4) Conduct research at Mauna Loa Observatory to elucidate elemental mercury oxidation in the remote marine free troposphere.
(5) Conduct laboratory kinetics experiments to determine the rate constants of elemental mercury oxidation to gaseous inorganic divalent mercury species from atmospheric halide species (e.g. BrO, ClO).
Description:
The US Environmental Protection Agency (EPA), the Florida Department of Environmental Protection (FLDEP), and Texas A&M University collaborated in the design, construction, and testing of a unique highly cross-linked Teflon coated inlet and manifold gas and aerosol sampling system that are being used in EPA aircraft atmospheric pollution characterization studies. The aircraft-borne ambient sampling system consists of a Teflon coated shrouded probe coupled to a Teflon coated aluminum manifold that are designed to collect reactive gases (e.g., mercury and halide species) and aerosols for subsequent analysis and characterization. The shrouded inlet probe was tested for particle transmission ratios in a high-speed aerosol wind tunnel. An existing wind tunnel was upgraded from a maximum wind speed of 13.4 m/s (48 km/h or 30 miles/hr) to 50.5 m/s (182 km/h or 113 miles/hr) to test this probe. The wind tunnel was evaluated for compliance with the criteria of ANSI 13.1 to establish the acceptability of its use in testing probes. The results demonstrated that the velocity and tracer gas concentration profiles were within the specified limits. A well characterized ThermoAndersen Shrouded Probe (Model RF-2-112) was also tested to check tunnel performance and test methodology. The results obtained from these tests are in close agreement with data published earlier.
The aircraft-borne shrouded probe showed a transmission ratio of about 0.76 at 45 m/s (162 km/h or 100 miles/hr) for 10 m aerodynamic diameter particles at a sampling flow rate of 90 L/min. To improve the transmission ratio of the sampling probe, the sampling flow rate was reduced to 80 L/min and the air speed increased to 50.5 m/s, which increased the transmission ratio to about 0.9 for 10 m particles. Further reduction of the flow rate to 60 L/min increased the transmission to 1.2. The Teflon coated manifold downstream of the shrouded probe, was statically tested for transmission ratio at flow rates of 90 L/min and 30 L/min. The results were a transmission ratio about 0.80 for 10 m aerodynamic diameter particles. The combination of the shrouded probe operated at 60 L/min with a transmission ratio of 1.2 and the manifold with its transmission of 0.8, will give an overall transmission of about unity for 10 um aerodynamic diameter particles at a flight speed of 50.5 m/s.
These findings suggest that shrouded probes can be used for low speed (~100 miles/hr) aircraft applications. The transmission ratio of these probes is a significant improvement over the conventional aircraft-mounted, sharp-edged isokinetic diffuser-type inlets.
This manuscript has been subjected to Agency Review and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.