Evaluating biases in filter-based aerosol absorption measurements using photoacoustic spectroscopy

Abstract

Biases in absorption coefficients measured using a filter-based absorption photometer (Tricolor Absorption Photometer, or TAP) at wavelengths of 467, 528 and 652 nm are evaluated by comparing to measurements made using photoacoustic spectroscopy (PAS). We report comparisons for ambient sampling covering a range of aerosol types including urban, fresh biomass burning and aged biomass burning. Data are also used to evaluate the performance of three different TAP correction schemes. We found that photoacoustic and filter-based measurements were well correlated, but filter-based measurements generally overestimated absorption by up to 45 %. Biases varied with wavelength and depended on the correction scheme applied. Optimal agreement to PAS data was achieved by processing the filterbased measurements using the recently developed correction scheme of Müller et al. (2014), which consistently reduced biases to 0 %-18 % at all wavelengths. The biases were found to be a function of the ratio of organic aerosol mass to light-absorbing carbon mass, although applying the Müller et al. (2014) correction scheme to filter-based absorption measurements reduced the biases and the strength of this correlation significantly. Filter-based absorption measurement biases led to aerosol single-scattering albedos that were biased low by values in the range 0.00-0.07 and absorption Ångström exponents (AAEs) that were in error by ± (0.03-0.54). The discrepancy between the filter-based and PAS absorption measurements is lower than reported in some earlier studies and points to a strong dependence of filterbased measurement accuracy on aerosol source type.

Observation of absorbing aerosols above clouds over the South-East Atlantic Ocean from the geostationary satellite SEVIRI – Part 2: Comparison with MODIS and aircraft measurements from the CLARIFY-2017 field campaign

“…To survey the full column of aerosols and characterise the aerosol-radiation interactions, a series of manoeuvres described as a Z-pattern were performed on multiple flights during the campaign (Haywood et al, 2019). These patterns start at an altitude of about 7 km with a straight level run and dropsonde deployment above the aerosol plume, followed by a 180˚ turn and a profile descent through the main aerosol layers to an altitude of around a 15 couple hundred meters above the cloud top.…”

“…For this reason, the region has been the focus of much work over the past few years. Using aircraft and surface-based instrumentation, 10 large scale field campaigns have been deployed in 2016-2018 (Zuidema et al, 2016), within the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS; , the US DOE LASIC (Layered Atlantic Smoke Interactions with Clouds; Zuidema et al, 2016), the French AEROCLO-sA (AErosol RadiatiOn and CLouds in Southern Africa; Formenti et al, 2019) and the UK CLARIFY-2017 (CLouds and Aerosol Radiative Impacts and Forcing for Year 2017, Haywood et al, 2019) programs. Airborne 15 in situ instruments, active and passive remote sensing instruments, and radiosondes as well as continuous groundbased measurements have been deployed to characterise biomass burning aerosols, clouds and radiation.…”

Vertical profiles of submicron aerosol single scattering albedo over the Indian region immediately before monsoon onset and during its development: research from the SWAAMI field campaign

“…Filter-based absorption measurements generally overestimate absorption by up to 45 % and can lead to underestimations in the SSA (up to 0.07; Davies et al, 2019). The radiative effects of these aerosols are estimated using a radiative transfer scheme taking into account the vertical distribution of extinction coefficient, SSA, pressure, temperature, water vapour and ozone.…”

“…The mean wind field at 850 hPa during different days of the campaign period(Dee et al, 2011), with colours representing the magnitude of the wind in m s −1 . The arrows indicate the direction of the mean wind.…”

Optimizing the performance of aerosol photoacoustic cells using a finite element model. Part 2: Application to a two-resonator cell

“…Traditionally, a abs have been derived from the transmission of light through a filter onto which aerosol is collected, but large uncertainties (of up to 80%) are associated with the derived values of a abs (Cappa et al 2008;Lack et al 2008Lack et al , 2009, although recent advanced correction schemes show modest biases in derived a abs values of up to 17% (Davies et al 2019). These uncertainties arise mostly from the modification of aerosol microphysical properties through interactions with a filter substrate.…”