Abstract
Abstract. Scattering and absorption by aerosol in anthropogenically perturbed air masses over Europe has been measured using instrumentation flown on the UK's BAe-146-301 large Atmospheric Research Aircraft (ARA) operated by the Facility for Airborne Atmospheric Measurements (FAAM) on 14 flights during the EUCAARI-LONGREX campaign in May 2008. The geographical and temporal variations of the derived shortwave optical properties of aerosol are presented. Values of single scattering albedo of dry aerosol at 550 nm varied considerably from 0.86 to near unity, with a campaign average of 0.93 ± 0.03. Dry aerosol optical depths ranged from 0.030 ± 0.009 to 0.24 ± 0.07. An optical properties closure study comparing calculations from composition data and Mie scattering code with the measured properties is presented. Agreement to within measurement uncertainties of 30% can be achieved for both scattering and absorption, but the latter is shown to be sensitive to the refractive indices chosen for organic aerosols, and to a lesser extent black carbon, as well as being highly dependent on the accuracy of the absorption measurements. Agreement with the measured absorption can be achieved either if organic carbon is assumed to be weakly absorbing, or if the organic aerosol is purely scattering and the absorption measurement is an overestimate due to the presence of large amounts of organic carbon. Refractive indices could not be inferred conclusively due to this uncertainty, despite the enhancement in methodology compared to previous studies that derived from the use of the black carbon measurements. Hygroscopic growth curves derived from the wet nephelometer indicate moderate water uptake by the aerosol with a campaign mean f(RH) value (ratio in scattering) of 1.5 (range from 1.23 to 1.63) at 80% relative humidity. This value is qualitatively consistent with the major chemical components of the aerosol measured by the aerosol mass spectrometer, which are primarily mixed organics and nitrate and some sulphate.
Highlights
Atmospheric aerosol has a “direct effect” on climate through the scattering and absorption of radiation and “indirect effects” via changes to cloud microphysics and properties
Fol12lowing Morgan et al (2010a), the EUCAARI LONGREX3 period can be divided into 3 parts based on the dominant meteorology: LONGREX-1 (6–8 May 2008, flights B362–4 366) is defined by approximately zonal flow from east to5 west; during LONGREX-2 (10–14 May 2008, flights B369–6 B374) the strong anticyclone was centered over Denmark and northern Germany resulting in more strongly curving anticyclonic flow; whilst LONGREX-3 (19–20 May, flights B379–380) was characterized by building high pressure following the passage of a weak frontal system across northern Europe with predominantly easterly flow
Assuming that the horizontal variability experienced during profiles is similar to that observed during 15 min straight and level runs (SLRs) runs, the uncertainty in scattering is around 30 % and this results in an uncertainty of 30 % in optical depth estimated by this method
Summary
Atmospheric aerosol has a “direct effect” on climate through the scattering and absorption of radiation and “indirect effects” via changes to cloud microphysics and properties. Highwood et al.: Aerosol scattering and absorption during the EUCAARI-LONGREX flights of composition) as a function of wavelength, the size distribution, the influence of relative humidity and the mixing state (internal or external) These properties are included in, or predicted by, aerosol transport models, and regional and global climate models and used in satellite retrieval algorithms for aerosol optical depth or other quantities. For the first time from this platform we are able to perform optical property closure studies without tuning the black carbon amount, and to quantify the degree to which we can bring models and measurements of aerosol scattering and absorption into agreement.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
