In situ and remote-sensing measurements of the mean microphysical and optical properties of industrial pollution aerosol during ADRIEX

Abstract

ABSTRACT:We present a summary of the principal physical and optical properties of aerosol particles using the FAAM BAE-146 instrumented aircraft during ADRIEX between 27 August and 6 September 2004, augmented by sunphotometer, lidar and satellite retrievals. Observations of anthropogenic aerosol, principally from industrial sources, were concentrated over the northern Adriatic Sea and over the Po Valley close to the aerosol sources. An additional flight was also carried out over the Black Sea to compare east and west European pollution. Measurements show the single-scattering albedo of dry aerosol particles to vary considerably between 0.89 and 0.97 at a wavelength of 0.55 µm, with a campaign mean within the polluted lower free troposphere of 0.92. Although aerosol concentrations varied significantly from day to day and during individual days, the shape of the aerosol size distribution was relatively consistent through the experiment, with no detectable change observed over land and over sea. There is evidence to suggest that the pollution aerosol within the marine boundary layer was younger than that in the elevated layer. Trends in the aerosol volume distribution show consistency with multiple-site AERONET radiometric observations. The aerosol optical depths derived from aircraft measurements show a consistent bias to lower values than both the AERONET and lidar ground-based radiometric observations, differences which can be explained by local variations in the aerosol column loading and by some aircraft instrumental artefacts. Retrievals of the aerosol optical depth and fine-mode (<0.5 µm radius) fraction contribution to the optical depth using MODIS data from the Terra and Aqua satellites show a reasonable level of agreement with the AERONET and aircraft measurements.  Crown

Aerosol scattering and absorption during the EUCAARI-LONGREX flights of the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146: can measurements and models agree?

“…Density differences between the components can also play a role. The ADRIEX campaign in Northern Italy using the same measurement platform (but a different methodology and some different instrumentation) found a value of 3.5±1.2 m 2 g −1 for ambient industrial aerosol with a large nitrate component but a higher organic mass fraction (Osborne et al, 2007); again this is consistent with our value within the measurement uncertainties.…”

“…Only the instrumentation that is particularly relevant for optical property studies is described here. More comprehensive discussion of the full instrumentation can be found in Johnson et al (2000) and Osborne et al (2007). The size range and estimated accuracy of the instruments used in this paper is summarised in Table 2.…”

“…Volume weighted mixing is often used to combine optical properties (for external mixtures) or refractive indices and density prior to scattering calculations (for internal mixtures) of aerosol components such as sulphates or black carbon (BC) (e.g. Chylek et al, 1988;Osborne et al, 2007;Cook et al, 2007). It is important to quantify the uncertainty with which we know firstly the refractive indices of individual aerosols as measured in the laboratory, and secondly, how mixing the components affects scattering and absorption.…”

“…As a result, the amount of BC used in the "model" aerosol has often been tuned to give closure on single scattering albedo as derived from in-situ scattering and absorption measurements. Cook et al (2007) and Osborne et al (2007) apply this technique to data from the FAAM platform, using filter measurements to check the consistency of the mass of BC required. However, the filter measurements themselves carry large uncertainties for low concentrations of BC.…”

Intercomparison of VACC- and AMS-derived nitrate, sulphate and ammonium aerosol loadings during ADRIEX

“…A detailed description of both instruments can be found in Osborne et al (2007). The combined PCASP/SID provides the number concentration characteristics of the aerosol sampled by the internally mounted Volatile Aerosol Concentration and Composition (VACC) and Aerosol Mass Spectrometer (AMS) instruments.…”