AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Black Carbon Hygroscopicity at a Rural Site in the UK
JAMES ALLAN, Dantong Liu, Michael Flynn, Dominique Young, James Whitehead, Gordon McFiggans, Hugh Coe, Zoe Fleming, University of Manchester
Abstract Number: 624 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Black Carbon (BC) is recognised as a highly potent climate forcing agent, particularly on regional scales, however the exact magnitude of its forcing potential is highly uncertain, partly due to uncertainties in its atmospheric lifetime. It is therefore important to understand the atmospheric processes and timescales by which hydrophobic BC particles obtain hygroscopic coatings, which makes them more susceptible to scavenging and in turn, wet deposition. In order to study these processes, an intensive campaign was carried out at the Weybourne Atmospheric Observatory, a coastal, rural site in the UK during the summer of 2011. During this period, the site was influenced by a variety of polluted airmasses of different ages from the UK and mainland Europe.
As part of a suite of measurements, a hygroscopicity tandem differential mobility analyser (HTDMA) coupled with a single particle soot photometer (SP2) was used to study the growth factors of particles while quantifying their BC content and compared to composition data measured using a Soot Particle Aerosol Mass Spectrometer (SP-AMS). The growth spectra of BC-containing particles at 90% RH showed an expected non-hygroscopic mode corresponding to unmodified soot particles and an additional ‘more hygroscopic’ mode with a growth factor of up to 1.5. This mode sometimes became dominant during periods of high ammonium nitrate concentrations. Attempts at quantitatively predicting the growth based the available composition data and the Zdanovskii-Stokes-Robinson (ZSR) mixing rule produced satisfactory results within the limitations of the measurements. These data demonstrate the importance of nitrate in the atmospheric BC lifecycle and can be used to inform approaches used in higher-level modelling.