Abstract
Abstract. As a part of the AMAZE-08 campaign during the wet season in the rainforest of central Amazonia, an ultraviolet aerodynamic particle sizer (UV-APS) was operated for continuous measurements of fluorescent biological aerosol particles (FBAP). In the coarse particle size range (> 1 μm) the campaign median and quartiles of FBAP number and mass concentration were 7.3 × 104 m−3 (4.0–13.2 × 104 m−3) and 0.72 μg m−3 (0.42–1.19 μg m−3), respectively, accounting for 24% (11–41%) of total particle number and 47% (25–65%) of total particle mass. During the five-week campaign in February–March 2008 the concentration of coarse-mode Saharan dust particles was highly variable. In contrast, FBAP concentrations remained fairly constant over the course of weeks and had a consistent daily pattern, peaking several hours before sunrise, suggesting observed FBAP was dominated by nocturnal spore emission. This conclusion was supported by the consistent FBAP number size distribution peaking at 2.3 μm, also attributed to fungal spores and mixed biological particles by scanning electron microscopy (SEM), light microscopy and biochemical staining. A second primary biological aerosol particle (PBAP) mode between 0.5 and 1.0 μm was also observed by SEM, but exhibited little fluorescence and no true fungal staining. This mode may have consisted of single bacterial cells, brochosomes, various fragments of biological material, and small Chromalveolata (Chromista) spores. Particles liquid-coated with mixed organic-inorganic material constituted a large fraction of observations, and these coatings contained salts likely from primary biological origin. We provide key support for the suggestion that real-time laser-induce fluorescence (LIF) techniques using 355 nm excitation provide size-resolved concentrations of FBAP as a lower limit for the atmospheric abundance of biological particles in a pristine environment. We also show some limitations of using the instrument for ambient monitoring of weakly fluorescent particles < 2 μm. Our measurements confirm that primary biological particles, fungal spores in particular, are an important fraction of supermicron aerosol in the Amazon and that may contribute significantly to hydrological cycling, especially when coated by mixed inorganic material.
Highlights
Biogenic gases and particles emitted into the atmosphere by plants and organisms on the Earth’s surface can have a wideranging influence on a number of natural systems and are important for study by a multitude of scientific disciplines
The second half can be characterized as representing clean air masses that were relatively free of biomass burning and mineral dust plumes (Chen et al, 2009; Martin et al, 2010a) and is more representative of pristine emissions directly from the forest (Poschl et al, 2010)
Occasional periods of high total particle concentrations still occurred during this period, but these periods were much shorter in duration and much weaker than events during the first three weeks of February (Fig. 1a, c)
Summary
Biogenic gases and particles emitted into the atmosphere by plants and organisms on the Earth’s surface can have a wideranging influence on a number of natural systems and are important for study by a multitude of scientific disciplines. PBAP can be living or dead and their size can span physical dimensions of a few nanometers to hundreds of micrometers They are crucial to the reproductive processes of many organisms because they spread genetic material over long distances. In part motivated by the desire to constrain the understanding of the geographic spread and climatic importance of PBAP, a number of recent works have presented regional or global modeling studies of biological particles in the atmosphere (Helbig et al, 2004; Burrows et al, 2009a, b; Heald and Spracklen, 2009; Hoose et al, 2010; Sesartic and Dallafior, 2011; Sesartic et al, 2012) These are important steps in determining the effects that bioaerosols have on various Earth and human systems, but uncertainties in measurements input to these models are still large
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