Atmospheric aerosols may be solid or liquid and vary in size from 0.002 to 100 μm. They can be either emitted directly into the atmosphere as primary aerosol (such as sea salt, dust, etc.), or formed in-situ from chemical reactions occurring in the atmosphere, which are referred to as secondary aerosols. Secondary aerosols that have an organic precursor are referred to as secondary organic aerosols (SOAs).

SOAs are formed from the photodegradation of volatile organic compounds in the atmosphere. Volatile organic compounds can be released from man-made sources such as vehicles and industry, which are referred to as anthropogenic sources. Similarly, volatile organic compounds can be emitted from vegetation in which case they are referred to as biogenic emissions. More SOA is produced from biogenic than from anthropogenic sources. Some of the more abundant SOA precursor compounds in ambient air are illustrated in Figure 1.

Isoprene a-pinene b-pinene 1,3-Butadiene  Toluene
Fig. 1: Some of the more dominant SOA precursor compounds in ambient air.

Environmental chamber experiments allow researchers to isolate photooxidation reactions that produce SOA. The decomposition of precursor compounds and products can be monitored with a range of instruments, thereby allowing SOA formation pathways to be identified. CSIRO’s chamber facility has been used extensively to study the SOA forming potential and formation mechanisms of a number of species. The influence of the physical and chemical parameters on SOA formation can also be evaluated using chamber experiments. Physical parameters like the amount of ultraviolet light present, the relative humidity and temperature have been shown to have an influence on the amount of SOA formed in a given system.

As a result of the chamber experiments, computer models have been developed to either predict the mass of SOA produced in the ambient environment, or to map the formation routes and to identify possible species involved in the formation of SOA from a specific compound. This project has examined different types and applications of models. A detailed near explicit model has been developed to estimate the quantity and composition of SOA produced from the photooxidation of isoprene.

Fig. 2: An internal view of CSIRO’s chamber facility.

Lila Singh, Michael Box, Dennys Angove, Robert Hynes, Merched Azzi, and Martin Cope.

For more information, go to:
http://www.det.csiro.au/science/e_e/e_e_topics.htm#modelling