64 Biological Activity in Clouds: From the Laboratory to the Model
405
acid in the aqueous phase (~75%) that is now undersaturated in formic acid; aqueous
formic acid is then degraded mainly by the ferryl ion and HO
• .
Effect of Biodegradation Rates:
The time evolution of the 4 target species present similar behavior than what was
observed for the Ref-sum and Ref-win cases (i.e. without considering biodegradation). But when looking more carefully in Fig. 64.2 at the details of their sources
and sinks including biodegradation rates, the contribution of biodegradation appears
clearly. In all cases, biodegradation sink is more important at nighttime. Biodegradation is globally more efficient during summer as explained by the biodegradation
rates lower in the winter case (5 °C) in comparison to the summer case (17 °C).
In the Ref-sum-bio case, formic acid concentration decreases in comparison to
the Ref-sum. At the end of the simulation time, the concentration is reduced by
a 20%. H 2 O 2 concentrations are not significantly modified by the implementation
of biodegradation rates. In summer, formic acid during the day is degraded by the
microorganisms significantly (~35%) and the mass transfer is reduced from 72 to
40%. During the night, this effect is amplified with the biodegradation process becoming dominant (60%) and the mass transfer becoming negligible. The biological activity degrades the H 2 O 2 during the day and the night but in a lesser extent (7 and 12%,
respectively).
Microorganisms are considered as biological catalysts that may compete with
chemical reactivity and with photochemistry features in cloud waters, in particular.
The results indicate that this biological activity has to be considered in cloud chemistry model since this modify the way the molecules are degraded both in the gas and
the aqueous phases.
QUESTIONER: Paul Makar
QUESTION: The microorganisms degrade short chain organic acids? What do they
produce? Do they make more molecular mass organic compounds?
ANSWER: Yes, they are also to degrade short chain organic compounds such as
carboxylic acids because most of them can enter into the central metabolisms of
several microorganisms, and these metabolites can be used to maintain energy levels
through the production of ATP to synthesize larger molecules and produce biomass
(proteins, nucleic acids, etc.).
QUESTIONER: Silvia Trini Castelli
QUESTION: What is the lifetime of the microorganisms, bacteria residing in the
cloud?
ANSWER: Once in the cloud, the living bacteria are able to survive to this harsh
medium. However, the viability of microorganisms in clouds could be altered by
environmental factors such as exposition to H 2 O 2 , solar light, osmotic shocks and
freeze-thaw cycles. Recent study from Joly et al. [4] have shown (https://doi.org/10.
1016/j.atmosenv.2015.07.009) that the survival depends on the microorganism and
on the stress; free-thaw appears to be the most stringent factor. See also the work
from Amato et al. [1] (https://doi.org/10.5194/acp-15-6455-2015).
405
acid in the aqueous phase (~75%) that is now undersaturated in formic acid; aqueous
formic acid is then degraded mainly by the ferryl ion and HO
• .
Effect of Biodegradation Rates:
The time evolution of the 4 target species present similar behavior than what was
observed for the Ref-sum and Ref-win cases (i.e. without considering biodegradation). But when looking more carefully in Fig. 64.2 at the details of their sources
and sinks including biodegradation rates, the contribution of biodegradation appears
clearly. In all cases, biodegradation sink is more important at nighttime. Biodegradation is globally more efficient during summer as explained by the biodegradation
rates lower in the winter case (5 °C) in comparison to the summer case (17 °C).
In the Ref-sum-bio case, formic acid concentration decreases in comparison to
the Ref-sum. At the end of the simulation time, the concentration is reduced by
a 20%. H 2 O 2 concentrations are not significantly modified by the implementation
of biodegradation rates. In summer, formic acid during the day is degraded by the
microorganisms significantly (~35%) and the mass transfer is reduced from 72 to
40%. During the night, this effect is amplified with the biodegradation process becoming dominant (60%) and the mass transfer becoming negligible. The biological activity degrades the H 2 O 2 during the day and the night but in a lesser extent (7 and 12%,
respectively).
Microorganisms are considered as biological catalysts that may compete with
chemical reactivity and with photochemistry features in cloud waters, in particular.
The results indicate that this biological activity has to be considered in cloud chemistry model since this modify the way the molecules are degraded both in the gas and
the aqueous phases.
QUESTIONER: Paul Makar
QUESTION: The microorganisms degrade short chain organic acids? What do they
produce? Do they make more molecular mass organic compounds?
ANSWER: Yes, they are also to degrade short chain organic compounds such as
carboxylic acids because most of them can enter into the central metabolisms of
several microorganisms, and these metabolites can be used to maintain energy levels
through the production of ATP to synthesize larger molecules and produce biomass
(proteins, nucleic acids, etc.).
QUESTIONER: Silvia Trini Castelli
QUESTION: What is the lifetime of the microorganisms, bacteria residing in the
cloud?
ANSWER: Once in the cloud, the living bacteria are able to survive to this harsh
medium. However, the viability of microorganisms in clouds could be altered by
environmental factors such as exposition to H 2 O 2 , solar light, osmotic shocks and
freeze-thaw cycles. Recent study from Joly et al. [4] have shown (https://doi.org/10.
1016/j.atmosenv.2015.07.009) that the survival depends on the microorganism and
on the stress; free-thaw appears to be the most stringent factor. See also the work
from Amato et al. [1] (https://doi.org/10.5194/acp-15-6455-2015).