Aerosols in the atmosphere - Air Pollution Modeling and Its Application - page 411

4. New Developments in Biophysicochemistry

Several studies have shown that primary biological aerosol (PBA) represent a
significant fraction of air particulate matter and hence affect the microstructure
and water uptake of aerosol particles (Möhler et al., 2007; Bauer et al., 2008).
Moreover, airborne micro-organisms, namely fungal spores and bacteria, can
transform chemical constituents of the atmosphere by metabolic activity. Recent
studies have emphasized the viability of bacteria and metabolic degradation of
organic substances in cloud water (Amato et al., 2007; Deguillaume et al., 2008).

Radical chemistry Observed metabolic pathways

C 1 Carboxylic acids

Methanol Methanol Acetate Lactate Succinate

Carboxylic
acids

Formaldehyde Formaldehyde Pyruvate Fumarate

Formiate Formiate

CO 2 CO 2

Fig. 2. Transformations of organic compounds by photochemical pathways (on the left side) and
by biochemical pathways (on the right side) observed in the laboratory for organic compounds
with one carbon atom and for carboxylic acids (Deguillaume et al., 2008)

Figure 2 illustrates the similarities between the radical chemistry within clouds
and observed metabolic ways of bacteria collected in cloud water. The degradation
of carboxylic acids leads to a final release of CO 2 with similar active intermediate
molecules.
The M2C2 model is suitable to include explicit photochemistry with biological
degradation processes. The objective will be to evaluate the global potential of
microorganisms present in cloud water on the degradation of relevant chemical
compounds. Those microorganisms will be considered as one category of aerosol
particles and kinetic constants of biological degradation will be introduced as a
function of environmental conditions and compared with photochemical rates.
Laboratory studies are developing biodegradation parameterizations as a function
of environmental conditions that will be incorporated in the M2C2 model. In the
future, simulations of various cloud events under different environmental conditions
will allow us to generalize the effect of microorganisms on cloud photochemistry.