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Stratospheric Aerosol Sampling: Effect of a Blunt-Body Housing on Inlet Sampling Characteristics

Dhaniyala, S. and Wennberg, P. O. and Flagan, R. C. and Fahey, D. W. and Northway, M. J. and Gao, R. S. and Bui, T. P. (2004) Stratospheric Aerosol Sampling: Effect of a Blunt-Body Housing on Inlet Sampling Characteristics. Aerosol Science and Technology, 38 (11). pp. 1080-1090. ISSN 0278-6826. doi:10.1080/027868290885818.

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During a campaign to study ozone loss mechanisms in the Arctic stratosphere (SOLVE), several instruments on NASA's ER-2 aircraft observed a very low number density (0.1 I^(−1)) of large, nitric-acid-containing particles that form the polar stratospheric clouds (PSCs). For effective physical and chemical characterization of these particles, the measurements from these instruments have to be intercompared and integrated. In particular, proper interpretation requires knowledge of the sampling characteristics of the particles into the instruments. Here, we present the calculation of the sampling characteristics of the one of the instruments on the ER-2, the NOAA NOy instrument. This instrument sampled ambient particles and gas from two forward-facing inlets located fore and aft on a particle-separation housing (the football) and measured total NOy in the sample. In recent studies, ambient aerosol mass has been estimated by the difference of the measurements of the two inlets with the assumption that the rear inlet observations represent the gas-phase NOy and small particles and the front inlet samples represent gas-phase NOy and all particle sizes with varied efficiency (anisokinetic sampling). This knowledge was derived largely from semiempirical relations and potential flow studies of the housing. In our study, we used CFD simulations to model the compressible flow conditions and considered noncontinuum effects in calculating particle trajectories. Our simulations show that the blunt body housing the inlets has a strong and complex interaction with the flow and particles sampled by the two inlets. The simulations show that the front inlet characteristics are influenced by the effect of the blunt body on the upstream pressure field. The rear inlet sampling characteristics are influenced both by the shape and size of the inlet and its location on the blunt body. These interactions result in calculated inlet characteristics that are significantly different from previously assumed values. Analysis of the SOLVE data, considering the ambient conditions and the calculated inlet sampling characteristics, in conjunction with thermodynamic growth modeling of super-cooled ternary solution (STS) particles, provides validation of the CFD results.

Item Type:Article
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Wennberg, P. O.0000-0002-6126-3854
Flagan, R. C.0000-0001-5690-770X
Additional Information:© 2004 American Association for Aerosol Research. Received 18 February 2004; accepted 2 September 2004. The authors would like to thank NASA Dryden for providing the photographs of the ER-2 and the NOy instrument shown in Figure 1. We would like to thank the SOLVE team for the technical and logistical help during the campaign. P. O. Wennberg thanks NASA’s UARP for funding support.
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Issue or Number:11
Record Number:CaltechAUTHORS:20150818-102244516
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59705
Deposited By: Irina Meininger
Deposited On:20 Aug 2015 16:29
Last Modified:10 Nov 2021 22:24

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