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

Federico Carotenuto,Cindy E. Morris,Christel Leyronas,Georg Wohlfahrt,Teodoro Georgiadis,Beniamino Gioli,Franco Miglietta,Marianna Nardino

doi:10.5194/acp-17-14919-2017

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 land-cover-driven microbial aerosols on the atmosphere and climate.

Highlights

Vegetated land surfaces, and plant leaves in particular, harbor a large number of microorganisms that can be transported by wind
With multiple campaigns this study investigated the behavior of a Mediterranean grassland from the point of view of microbial emissions
Behave as a passive tracer in the absence of significant aerodynamic effects: such conditions were tested during field campaigns using literature relationships between friction velocity and size of transported particles

Summary

Introduction

Plant leaves in particular, harbor a large number of microorganisms that can be transported by wind. Up to 107 bacteria per square centimeter are present on leaf surfaces (Morris et al, 2004), and plant materials are considered the largest source of fungal spores in the atmosphere (Burge, 2002). All of these organisms can be transported into the atmosphere by wind (Delort et al, 2010), as was shown experimentally in an artificial wind gust chamber (Lighthart et al, 1993). Living and dead microorganisms are part of primary biolog-

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