A B S T R A C T Atmospheric aerosol particles of biological origin are a very diverse group of biological materials and structures, including microorganisms, dispersal units, fragments and excretions of biological organisms. In recent years, the impact of biological aerosol particles on atmospheric processes has been studied with increasing intensity, and a wealth of new information and insights has been gained. This review outlines the current knowledge on major categories of primary biological aerosol particles (PBAP): bacteria and archaea, fungal spores and fragments, pollen, viruses, algae and cyanobacteria, biological crusts and lichens and others like plant or animal fragments and detritus. We give an overview of sampling methods and physical, chemical and biological techniques for PBAP analysis (cultivation, microscopy, DNA/RNA analysis, chemical tracers, optical and mass spectrometry, etc.). Moreover, we address and summarise the current understanding and open questions concerning the influence of PBAP on the atmosphere and climate, i.e. their optical properties and their ability to act as ice nuclei (IN) or cloud condensation nuclei (CCN). We suggest that the following research activities should be pursued in future studies of atmospheric biological aerosol particles: (1) develop efficient and reliable analytical techniques for the identification and quantification of PBAP; (2) apply advanced and standardised techniques to determine the abundance and diversity of PBAP and their seasonal variation at regional and global scales (atmospheric biogeography); (3) determine the emission rates, optical properties, IN and CCN activity of PBAP in field measurements and laboratory experiments; (4) use field and laboratory data to constrain numerical models of atmospheric transport, transformation and climate effects of PBAP.

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Abstract. Biogenic aerosols play important roles in atmospheric chemistry physics, the biosphere, climate, and public health. Here, we show that fungi which actively discharge their spores with liquids into the air, in particular actively wet spore discharging Ascomycota (AAM) and actively wet spore discharging Basidiomycota (ABM), are a major source of primary biogenic aerosol particles and components. We present the first estimates for the global average emission rates of fungal spores.Measurement results and budget calculations based on investigations in Amazonia (Balbina, Brazil, July 2001) indicate that the spores of AAM and ABM may account for a large proportion of coarse particulate matter in tropical rainforest regions during the wet season (0.7-2.3 µg m −3 ). For the particle diameter range of 1-10 µm, the estimated proportions are ∼25% during day-time, ∼45% at night, and ∼35% on average. For the sugar alcohol mannitol, the budget calculations indicate that it is suitable for use as a molecular tracer for actively wet discharged basidiospores (ABS). ABM emissions seem to account for most of the atmospheric abundance of mannitol (10-68 ng m −3 ), and can explain the observed diurnal cycle (higher abundance at night). ABM emissions of hexose carbohydrates might also account for a significant proportion of glucose and fructose in air particulate matter (7-49 ng m −3 ), but the literature-derived ratios are not consistent with the observed diurnal cycle (lower abundance at night). AAM emissions appear to account for a large proportion of potassium in air particulate matter over tropical rainforest regions during the wet season (17-43 ng m −3 ), and they can also explain the observed diurnal cycle (higher abundance at night). The results of our investigations and budget calculations for tropical rainforCorrespondence to: W. Elbert (elbert@mpch-mainz.mpg.de) est aerosols are consistent with measurements performed at other locations.Based on the average abundance of mannitol reported for extratropical continental boundary layer air (∼25 ng m −3 ), we have also calculated a value of ∼17 Tg yr −1 as a first estimate for the global average emission rate of ABS over land surfaces, which is consistent with the typically observed concentrations of ABS (∼10 3 -10 4 m −3 ; ∼0.1-1 µg m −3 ). The global average atmospheric abundance and emission rate of total fungal spores, including wet and dry discharged species, are estimated to be higher by a factor of about three, i.e. ∼1 µg m −3 and ∼50 Tg yr −1 . Comparisons with estimated rates of emission and formation of other major types of organic aerosol (∼47 Tg yr −1 of anthropogenic primary organic aerosol; 12-70 Tg yr −1 of secondary organic aerosol) indicate that emissions from fungi should be taken into account as a significant global source of organic aerosol. The effects of fungal spores and related chemical components might be particularly important in tropical regions, where both physicochemical processes in the atmosphere and biological activity at the Earth's sur...

Aerosols of biological origin play a vital role in the Earth system, particularly in the interactions between atmosphere, biosphere, climate, and public health. Airborne bacteria, fungal spores, pollen, and other bioparticles are essential for the reproduction and spread of organisms across various ecosystems, and they can cause or enhance human, animal, and plant diseases. Moreover, they can serve as nuclei for cloud droplets, ice crystals, and precipitation, thus influencing the hydrological cycle and climate. The sources, abundance, composition, and effects of biological aerosols and the atmospheric microbiome are, however, not yet well characterized and constitute a large gap in the scientific understanding of the interaction and co-evolution of life and climate in the Earth system. This review presents an overview of the state of bioaerosol research, highlights recent advances, and outlines future perspectives in terms o fbioaerosolidentification, characterization, transport, and transforma- tion processes, as well as their interactions with climate, health, and ecosystems, focusing on the role bioaerosols play in the Earth system

Abstract. Bacteria are ubiquitous in the atmosphere, with concentrations of bacterial cells typically exceeding 1×104 m−3 over land. Numerous studies have suggested that the presence of bacteria in the atmosphere may impact cloud development, atmospheric chemistry, and microbial biogeography. A sound knowledge of bacterial concentrations and distributions in the atmosphere is needed to evaluate these claims. This review focusses on published measurements of total and culturable bacteria concentrations in the atmospheric aerosol. We discuss emission mechanisms and the impacts of meteorological conditions and measurement techniques on measured bacteria concentrations. Based on the literature reviewed, we suggest representative values and ranges for the mean concentration in the near-surface air of nine natural ecosystems and three human-influenced land types. We discuss the gaps in current knowledge of bacterial concentrations in air, including the lack of reliable, long-term measurements of the total microbial concentrations in many regions and the scarcity of emission flux measurements.

[1] We collected filter samples of the atmospheric aerosol during the Southern African Regional Science Initiative (SAFARI 2000) experiment onboard the UK Met Office C-130 aircraft. The main operational area was the Atlantic Ocean offshore of Namibia and Angola, where biomass-smoke haze at least 1-2 days old was widespread. The size-fractionated aerosol samples were analyzed for the major inorganic ions, carbonaceous material (elemental and organic carbon), and elements with atomic numbers between 11 (Na) and 82 (Pb). The regional haze aerosol was composed mostly of carbonaceous aerosols (on the average, 81% of the submicron mass), with secondary inorganic aerosols (sulfate, ammonium, and nitrate) accounting for another 14%. K + and Cl À , typical pyrogenic species, constituted only 2% of the mass. The aerosol chemical data were used to estimate mass emission fluxes for various aerosol components. For African savanna/grassland burning, the estimated emission flux of carbonaceous particles ( particulate organic matter plus elemental carbon) is 14 ± 1 Tg yr À1 , and that of the nitrogen species (nitrate and ammonium) is 2 ± 2 Tg yr À1 . For the flight segments in regional haze, the mean particle scattering coefficient at 550 nm was s s = 101 ± 56 Mm À1 and the mean particle absorption coefficient s a at 565 nm averaged 8 ± 5 Mm À1 (mean single scattering albedo of 0.93 ± 0.06 at 550 nm). The dry mass scattering efficiency a s , calculated from the linear regression of the mean scattering versus the estimated submicron mass, is estimated to be between 4.2 ± and 4.6 ± 0.6 m 2 g À1 , depending on the assumptions made in calculating the aerosol mass. The dependence of the scattering enhancement ratios Ás s /ÁCO on the distance from the burning regions suggests that the evolution of particle size with time influences the light scattering efficiency. Fresh smoke was sampled during a dedicated flight in the proximity and within the plume of an active biomass burning fire. Here the enhancement ratio with respect to CO of particles in the Aitken-size range (5-100 nm diameter) was ÁN Aitken /ÁCO $25 cm À3 (STP) ppb À1 . These particles were removed rapidly after emission, and they were not detectable in the regional haze. The enhancement ratio for accumulation mode particles (0.1-1 mm diameter) ÁN Acc /ÁCO was $26-30 cm À3 (STP) ppb À1 in young smoke, and 16 ± 3 cm À3 (STP) ppb À1 in aged haze, suggesting that the number concentration of accumulation mode particles was reduced by about 41% during aging.

Salty Origins of Fresh Water Cloud droplets above the Amazonian rain forest form mostly around organic aerosols, but the source of the aerosols has been a mystery. Pöhlker et al. (p. 1075 ) report that particles rich in potassium salts emitted by Amazonian vegetation can act as the seeds for the growth of organic aerosol particles that function as condensation nuclei for water droplets. These specks of biogenic salts provide a surface for the condensation of low- or semi-volatile organic compounds formed by the atmospheric oxidation of isoprene and terpenes, molecules produced in great abundance by many kinds of Amazonian plants.

Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth's nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ∼20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ∼1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a −1 of NO-N and 0.6 Tg a −1 of HONO-N), corresponding to ∼20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate.biological soil crusts | nitric oxide | nitrous acid | nitrogen | trace gas emission