Fig 10 - uploaded by Audrey Lallement
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Dans un contexte de réchauffement climatique, une compréhension des mécanismes atmosphériques influençant le bilan radiatif terrestre est nécessaire. Les nuages peuvent participer à un refroidissement mais des incertitudes demeurent sur ces systèmes qui sont encore mal connus (notamment la composition de leur fraction organique). Depuis toujours, s...
Citations
... However, the resulting k Bact values (i.e., rate divided by substrate concentration) are all on the order of k Bact ≤ 10 −13 L cell −1 s −1 , which appears to represent an upper limit for the organics that have been investigated for metabolic activity in clouds. A much lower constant was derived from experiments with less oxygenated compounds such as phenol (Lallement, 2017). ...
... k Bact (L cell −1 s −1 ) 10 −13 10 −15 10 −13 k Bact,min was derived for microbial activity towards phenol (Lallement, 2017). k Bact,max was derived from experiments using cloud water and is valid for the microbial activity of various highly oxygenated compounds. ...
Many recent studies have identified biological material as a major
fraction of ambient aerosol loading. A small fraction of these bioaerosols
consist of bacteria that have attracted a lot of attention due to their role
in cloud formation and adverse health effects. Current atmospheric models
consider bacteria as inert quantities and neglect cell growth and
multiplication. We provide here a framework to estimate the production of
secondary biological aerosol (SBA) mass in clouds by microbial cell growth
and multiplication. The best estimate of SBA formation rates of 3.7 Tg yr−1 is comparable to previous model estimates of the primary emission
of bacteria into the atmosphere, and thus this might represent a previously
unrecognized source of biological aerosol material. We discuss in detail the
large uncertainties associated with our estimates based on the rather sparse
available data on bacteria abundance, growth conditions, and properties.
Additionally, the loss of water-soluble organic carbon (WSOC) due to
microbial processes in cloud droplets has been suggested to compete under
some conditions with WSOC loss by chemical (OH) reactions. Our estimates
suggest that microbial and chemical processes might lead to a global loss of
WSOC of 8–11 and 8–20 Tg yr−1, respectively. While
this estimate is very approximate, the analysis of the uncertainties
and ranges of all parameters suggests that high concentrations of
metabolically active bacteria in clouds might represent an efficient sink
for organics. Our estimates also highlight the urgent need for more data
concerning microbial concentrations, fluxes, and activity in the atmosphere
to evaluate the role of bacterial processes as net aerosol sinks or sources on
various spatial and temporal scales.
... rate divided by substrate concentration) are all on the order of kBact ~10 -13 L cell -1 s -1 which appears to represent an upper limit for the organics that have been investigated for metabolic activity in clouds. A much lower constant was derived from experiments with less oxygenated compounds such as phenol (Lallement, 2017). 395 ...
... The assumption of LWC is not needed if it is assumed that all bacteria-containing particles act as CCN. kBact [L cell -1 s -1 ]10 -13 10 -15 10 -13 kBact,min was derived for microbial activity towards phenol(Lallement, 2017). kBact,max was derived from experiments using cloud water and is valid for the microbial activity various highly oxygenated compounds. ...
Many recent studies have identified biological material as a major fraction of ambient aerosol loading. A small fraction of these bioaerosols consist of bacteria that have attracted a lot of attention due to their role in cloud formation and adverse health effects. Current atmospheric models consider bacteria as inert quantities and neglect cell growth and multiplication. We provide here a framework to estimate the production of secondary biological aerosol (SBA) mass in clouds by microbial cell growth and multiplication. The best estimate of SBA formation rates of 3.7 Tg yr⁻¹ are comparable to previous model estimates of the primary emission of bacteria into the atmosphere, and thus might represent a previously unrecognized source of biological aerosol material. We discuss in detail the large uncertainties associated with our estimates based on the rather sparse available data on bacteria abundance, growth conditions and properties. Additionally, the loss of water-soluble organic carbon (WSOC) due to microbial processes in cloud droplets has been suggested to compete under some conditions with WSOC loss by chemical (OH) reactions. Our estimates suggest that microbial and chemical processes might lead to a global loss of WSOC of 8–11 Tg yr⁻¹ and 8–20 Tg yr⁻¹, respectively. While also this estimate is very approximate, the analysis of the uncertainties and ranges of all parameters gives hints about the conditions under which microbial processes cannot be neglected as organic carbon sinks in clouds. Our estimates also highlight the urgent needs for more data concerning microbial concentrations, fluxes and activity in the atmosphere to evaluate the role of bacterial processes as net aerosol sink or source on various spatial and temporal scales.
