The increased application of volatilityanaly sis to determine the composition and structure of sub-micron aerosol requires that the thermal behaviour of chemicallycomplex aerosol be understood. Presented here is a volatilitystudy , utilising a tandem volatilitydierential mobilityanaly ser (TVDMA), of 30, 50, and 70 nm radii, internallymixed, aerosol containing ionic-salts, acids, organics, and carbon. Evidence of some size-dependent behaviour was observed with several of the single component aerosol. Internallymixed aerosol displayed complex thermal behaviours that were dependent on both size and the volume mixing ratio of source solutions


Volatility analysis of aerosol uses the principle that
as a particle is heated it will lose mass/size by either
mechanical breakdown (shattering) or by undergoing a
phase transition. The characteristic temperatures at which
these events occur being dependent on the chemical
species present in the particle.
The resultant variation observed in the particle spectra
provide an insight into both the degree of internal/external
mixing of the aerosol population and the partitioning of
chemical species with size. To date this analysis has
been purely qualitative (Jennings and O’Dowd, 1990;
Jennings et al., 1991; O’Dowd et al., 1992; Brooks et al.,
2002);


Volatility analysis relies on the fact that manydierent aerosol species are volatile at characteristic temperatures. Put simply, as the temperature of the aerosol is increased particles lose mass as their chemical constituents volatilise resulting in changes in the size spectrum. Consider the simplest mixing scenario of an externallymixed aerosol comprising two species A and B (the volatilisation temperature of B is lower than that of A). Fig. 1 shows two possible externally mixed populations and the eect on the size spectrum of heating. Although not in the remit of this study, the externally mixed case is included in this introductory discussion for completeness and clariHcation purposes.


The use of the volatility technique has been to provide
an insight into the chemical species present within an
aerosol population, how the composition varies with size,
and a handle on the mixing state, but not in general for
the quantitative retrieval of species mass loadings. This
study has shown that mass loadings retrieved using the
VACC agree well with those acquired from an AMS.
Unlike the AMS, the VACC was also able to indicate the
mixing state of species with size, and the source species
of the ions. When compared to externally mounted instrumentation,
the ambient temperature behaviour of the
volatility spectra indicated that inlet losses and transport
losses arising from tubing runs and an aspirated
plenum have been minimized and aerosol entering the
volatility system can be considered as a true representation
of the external aerosol population being sampled.
This analysis has shown that reliable quantitative
aerosol composition data are retrievable from the VACC
unit.




Size-differentiated volatility analy sis of internally mixed laboratory-generated aerosol
B.J. Brooks, M.H. Smith, M.K. Hill, & C.D. O’Dowd
Aerosol Science 33 (2002) 555–579

Brooks , B.J., McQuaid, J.B., Smith, M, Crosier, J., Williams, P.I, Coe, H. & Osborne, S., 2007, "Inter-Comparison of VACC & AMS derived Nitrate, Sulphate and Ammonium Aerosol Loadings during ADRIEX", Q. J. R. Meteorol. Soc., 133, 77-84.

Jennings SG, O’Dowd CD. 1990. Volatility of aerosol at Mace Head
on the west coast of Ireland. J. Geophys. Res. 95: 13937–13948.

Jennings SG, O’Dowd CD, O’Connor TC, McGovern FM. 1991.
Physical characteristics of the ambient aerosol at Mace Head. Atmos.
Environ. 25A: 557–562.

Lesins G, Chlylek P, Lohmann U. 2002. A study of internal and
external mixing scenarios and its effect on aerosol optical properties
and radiative forcing. J. Geophys. Res. 107: (D10), 4094.

O’Dowd CD, Jennings SG, Smith MH, Cooke WF. 1992. A high
temperature volatility technique for determination of atmospheric
aerosol composition. J. Aerosol Sci. 23: 5905–5908.