Measurements and modeling of surface–atmosphere exchange of microorganisms in Mediterranean grassland

Abstract

Abstract. Microbial aerosols (mainly composed of bacterial and fungal cells) may constitute up to 74 % of the total aerosol volume. These biological aerosols are not only relevant to the dispersion of pathogens, but they also have geochemical implications. Some bacteria and fungi may, in fact, serve as cloud condensation or ice nuclei, potentially affecting cloud formation and precipitation and are active at higher temperatures compared to their inorganic counterparts. Simulations of the impact of microbial aerosols on climate are still hindered by the lack of information regarding their emissions from ground sources. This present work tackles this knowledge gap by (i) applying a rigorous micrometeorological approach to the estimation of microbial net fluxes above a Mediterranean grassland and (ii) developing a deterministic model (the PLAnET model) to estimate these emissions on the basis of a few meteorological parameters that are easy to obtain. The grassland is characterized by an abundance of positive net microbial fluxes and the model proves to be a promising tool capable of capturing the day-to-day variability in microbial fluxes with a relatively small bias and sufficient accuracy. PLAnET is still in its infancy and will benefit from future campaigns extending the available training dataset as well as the inclusion of ever more complex and critical phenomena triggering the emission of microbial aerosol (such as rainfall). The model itself is also adaptable as an emission module for dispersion and chemical transport models, allowing further exploration of the impact of landcover-driven microbial aerosols on the atmosphere and climate.

Bioaerosol field measurements: Challenges and perspectives in outdoor studies

“…These are not direct measurements, as the estimation depends on the parameterization of the diffusivity coefficient. Varying results were obtained by this technique, which may in many cases be associated with the choice of specific parameterization and the errors associated with the cultivationdependent techniques used to quantify concentrations (Carotenuto et al 2017;Mayol et al 2014;Crawford et al 2014;Huffman et al 2013;Lighthart and Shaffer 1994;Lindemann and Upper 1985;Lindemann et al 1982). The gradient method also tends to fail in specific cases such as under canopies, as in forests, due to the formation of counter gradients (Baldocchi, Hincks, and Meyers 1988).…”

The global impact of bacterial processes on carbon mass

“…Near the ground, typical concentrations of total airborne bacteria range from ∼ 10 2 to 10 6 cells m −3 , depending on the emission source (Burrows et al, 2009b) and on temporal, meteorological, or other environmental conditions influencing its propensity to emit particles to the air (Carotenuto et al, 2017;Huffman et al, 2013;Lighthart, 1997;Lighthart and Shaffer, 1995). Atmospheric mixing tends to homoge-B.…”

“…2 Data and assumptions on bacterial processes in clouds 2.1 Atmospheric concentrations of bacterial cells Burrows et al (2009a, b) have summarized data on number concentrations and emission fluxes of bacteria above various ecosystems on the Earth's surface. These ecosystems represent lumped categories based on the original classification by Olson et al (1992).…”

Microbial composition in seasonal time series of free tropospheric air and precipitation reveals community separation

“…Most aerobiology studies are restricted to groundbased sampling within the planetary boundary layer (PBL) or focus on extreme events such as heat events and dust storms Jeon et al 2011;Maki et al 2017;Gat et al 2017;Fierer et al 2008;Bowers et al 2013), civilization and health related questions, like disease spread (Park et al 2014;Adams et al 2015;Di Giulio et al 2010;Kelley and Gilbert 2013;Hagan et al 1995;Polymenakou 2012;Griffin 2007;Brown and Hovmøller 2002) or pollen events (Burge 2002;Damialis et al 2015;Ziello et al 2012;Clot 2003;Jäger 2000;Gioulekas et al 2004;Sofiev et al 2013;Hamaoui-Laguel et al 2015). Microbial composition in air masses within the PBL is affected by ground emissions and mixing of air masses (Bowers et al 2011;Carotenuto et al 2017;Burrows et al 2009a, b). Within the PBL (upper boundary around 100-1000 m above ground level, AGL), vertical mixing of air masses over mountainous terrain is driven by ground turbulence, thermal convection and dynamic forcing with strong diurnal and seasonal variations in elevation AGL and mixing force (Rotach et al 2015).…”