Glassy aerosols with a range of compositions nucleate ice heterogeneously at cirrus temperatures 1School of Earth and Environment, University of Leeds, UK
25 Sep 2012
2School of Chemistry, University of Leeds, UK
3Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Germany
Received: 20 Mar 2012 – Published in Atmos. Chem. Phys. Discuss.: 10 Apr 2012 Abstract. Atmospheric secondary organic aerosol (SOA) is likely to exist in a
semi-solid or glassy state, particularly at low temperatures and humidities.
Previously, it has been shown that glassy aqueous citric acid aerosol is
able to nucleate ice heterogeneously under conditions relevant to cirrus in
the tropical tropopause layer (TTL). In this study we test if glassy aerosol
distributions with a range of chemical compositions heterogeneously nucleate
ice under cirrus conditions. Three single component aqueous solution
aerosols (raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA) and
levoglucosan) and one multi component aqueous solution aerosol (raffinose
mixed with five dicarboxylic acids and ammonium sulphate) were studied in
both the liquid and glassy states at a large cloud simulation chamber. The
investigated organic compounds have similar functionality to oxidised
organic material found in atmospheric aerosol and have estimated
temperature/humidity induced glass transition thresholds that fall within
the range predicted for atmospheric SOA. A small fraction of aerosol
particles of all compositions were found to nucleate ice heterogeneously in
the deposition mode at temperatures relevant to the TTL (<200 K).
Raffinose and HMMA, which form glasses at higher temperatures, nucleated ice
heterogeneously at temperatures as high as 214.6 and 218.5 K respectively.
We present the calculated ice active surface site density, ns, of the
aerosols tested here and also of glassy citric acid aerosol as a function of
relative humidity with respect to ice (RHi). We also propose a
parameterisation which can be used to estimate heterogeneous ice nucleation
by glassy aerosol for use in cirrus cloud models up to ~220 K.
Finally, we show that heterogeneous nucleation by glassy aerosol may
compete with ice nucleation on mineral dust particles in mid-latitudes
Revised: 17 Aug 2012 – Accepted: 29 Aug 2012 – Published: 25 Sep 2012
Citation: Wilson, T. W., Murray, B. J., Wagner, R., Möhler, O., Saathoff, H., Schnaiter, M., Skrotzki, J., Price, H. C., Malkin, T. L., Dobbie, S., and Al-Jumur, S. M. R. K.: Glassy aerosols with a range of compositions nucleate ice heterogeneously at cirrus temperatures, Atmos. Chem. Phys., 12, 8611-8632, doi:10.5194/acp-12-8611-2012, 2012.