Abstract
Abstract. Biological aerosol particles have become increasingly important for atmospheric study, but continuous measurements at high time and size resolution have not been available until recently. Here we report seasonal cycles of fluorescent biological aerosol particles (FBAP) from the boreal forest in Hyytiälä, Finland (18 months) and the semi-arid Manitou Experimental Forest, Colorado (10 months). FBAP at both locations were observed to be highest in summer and lowest in winter, increasing by factors of 12 and 5 between these seasons, respectively. In addition to the low temperatures and reduced sunlight during winter, we suggest that snow cover inhibited FBAP release from local terrestrial surfaces and that more extensive snow cover at the Finland site contributed to lower winter FBAP concentrations. Average size distributions at each site exhibited peaks between 1.5 and 6 μm in aerodynamic diameter. The Finland site consistently showed a dominant, narrow FBAP peak at ~ 3 μm in addition to discreet modes at ~ 1.5 and ~ 5 μm, whereas the Colorado site showed broader peaks at 1.5 and 5 μm, suggesting different modes of biological particles at the two sites. FBAP concentrations in both locations were shown to correlate with daily patterns of relative humidity (RH) during each season. Also during summer at each site, average FBAP concentration scaled with RH, but at the Finland site RH values above ~ 82% led to a significant decrease in FBAP concentration. We hypothesize that this is due to dew formation that inhibits bioparticle release. Lastly we show that rain during summer at each location led to pronounced increases in both fluorescent and total particle concentrations with FBAP peak particle size at ~ 2 μm and concentration scaling with rain intensity. We suggest that these particles are primarily fungal spores and other bioparticles lofted from splashing of rain droplets hitting soil and leaf surfaces. During the summer at the Colorado site we consistently observed a mode of ~ 4 μm particles appearing several hours after rain events that we suggest are fungal spores actively emitted when ambient conditions are most advantageous for spread and germination. The pronounced patterns of fluorescent bioparticles observed here suggest that parameterizations of both daily and seasonal cycles will be important to accurately reflect bioparticle emissions in future studies of atmospheric bioaerosols and their potential effects on clouds and precipitation.
Highlights
Biogenic gases and particles are released into the atmosphere from every region and ecosystem of the planet and contribute significantly to many Earth, atmospheric, and human systems
The ultraviolet aerodynamic particle sizer (UV-APS) was operated at each sampling location for a minimum of 10 months to evaluate the respective seasonal cycles of total and fluorescent biological particles
Environmental factors were expected to lower the concentration of airborne biological particles due to the reduced biological activity during winter and the reduced ability of microorganisms to become lofted to the air because of the snow coverage barrier
Summary
Biogenic gases and particles are released into the atmosphere from every region and ecosystem of the planet and contribute significantly to many Earth, atmospheric, and human systems. Small particles of biological origin (e.g. pollen grains, spores of fungi and plants, bacteria, and cellular debris) emitted directly into the atmosphere, called primary biological aerosol particles (PBAP), can range in size from approximately 0.1 to 100 μm and may be suspended for minutes to days (Womack et al, 2010; Després et al, 2012). While global estimates are uncertain, reports suggest that classes of PBAP exist in typical ambient concentrations of ∼ 104 m−3 and often represent tens of percent of coarse particle number (Després et al, 2012 and references therein). PBAP play important roles in local and regional environments, but have been observed after atmospheric transport of thousands of kilometers over land and oceans Schumacher et al.: Seasonal cycles of fluorescent biological aerosol particles
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
