BAe146 Instrumental Corrections

This page provides some information on published papers regarding corrections and uncertainties in the nephelometer and PSAP instrument measurements. Under certain conditions it may be important to take these into account when using measurements from the BAe146 aircraft. The key points summarized below are provided with BAe146 measurements in mind and may not necessarily reflect the key point of the papers themselves.

Haywood and Osborne, 2000

Corrections to be applied to the PSAP and nephelometer for determination of the absorption coefficient, scattering coefficient and single scattering albedo, MRF Technical note No. 31

Old Met Office Technical note describing corrections to be applied to the nephelometer and PSAP based on Anderson et al., 1996 (nephelometer), Anderson and Ogren 1998 (nephelometer) and Bond et al, 1999 (PSAP). Contains several inconsistencies - should be replaced by later papers and Turnbull et al. (2010) for the PSAP.

Turnbull, 2010

PSAP Corrections

Key Message:

Details corrections to be applied to the raw PSAP data on the BAe146. Includes updates to Haywood and Osborne (2000) based on a comment by Ogren (2010) clarifying the original correction algorithms described in Bond et al., 1999.

When to take into account:

Always, when using PSAP data. Should be considered the most upto date BAe146 PSAP correction reference (as of Jan 2013).

Quirantes et al., 2008 (Q2008)

Correction factors for a total scatter/backscatter nephelometer

Key Message:

For larger particles (i.e. when the angstrom exponent, A, tends to zero), the linear relationship between Cts and A breaks down. The authors provide new relationships based on refractive index, effective size parameter and effective variance of the size distribution.

When to take into account:

when larger particles are measured (A tends to zero), such as dust and sea salt.

Heintzenberg et al., 2006 (H2006)

Intercomparisons and aerosol calibrations of 12 commercial integrating nephelometers of three manufacturers

Key Message:

Examines truncation error by comparing nephelometer measurements to Mie theory. Summarized nicely in Figure 3. Truncation (peak forward and backward scattering which is not measured by the nephelometer) varies strongly with particle size. Truncation error for total scatter, for a monodisperse size distribution, drops to around 0.66 at 1 micron diameter, and around 0.5 at 4 micron diameter. The former results in a Cts (1/0.65) value of 1.54 - higher than would be used based on A for dust measurements. This means that truncation errors can result in a large underestimate of scattering if these errors are not considered. Note that the data in Fig. 3 of Heintzenberg et al. is for monodisperse - in reality if much of the scattering originates from the submicron particles, for which there is little truncation error, the errors may be less dramatic.

When to take into account:

When a significant proportion of the size distribution is comprised of super-micron particles.

Side Note

It seems that the findings of Q2008 and H2006 result in errors in scattering in different directions to each other. H2006 shows that truncation results in 'extra' missed scattering, i.e. scattering should be higher than as calculated with AO98. Q2008 corrections typical of dust may result in 30% less scattering than AO98 (Chen et al., (2011) and Johnson and Osborne (2011)), i.e. scattering should be lower than as calculated with AO98.

Uncertainties considered in recent work on dust measurements from the nephelometer and PSAP can be found in Ryder et al., (2013), where a lower uncertainty of 3% in SSA results from the PSAP only (30% error), and a higher bound of 15% in SSA results from both PSAP and nephelometer errors (30% and 11% errors respectively).

Lack et al., (2008)

Bias in Filter-based aerosol light absorption measurements due to organic aerosol loading: Evidence from ambient measurements

Key Message:

The authors report on the accuracy of PSAP measurements related to the ratio of organic aerosol to light absorbing carbon present in the aerosol, due to 1) 'redistribution of liquid-like organic par ticulate matter around the filter surface,' and 2) 'possible coating and absorption enhancement of pre-existing absorbing particulate matter as organic aerosol deposition and redistribution occurs.' Also a reference for PSAP uncertainty to be in the range 20-30% (see also Johnson & Osborne, 2011).

When to take into account:

Points 1 and 2 are not really relevant for dust aerosol, but should be considered further for other aerosol types. Useful reference for PSAP error of 20-30%.

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