Airborne microorganisms transported from forested areas can influence cloud formation by forming ice nuclei. However, the vertical transportation of airborne microorganisms over forested areas is not ...well understood. We collected aerosols at three heights, ground (2 m), canopy top (20 m), and above canopy (500 m) during the summer, fall and winter, to analyze the airborne microbial communities that were distributed vertically over the forest. During summer and fall, the microbial particles maintained similar concentrations in the forest zone (canopy top and ground) and decreased to 1/10th of the microbial concentration in the above canopy area. The particle concentrations in winter indicated efficient vertical mixing below 500 m. High-throughput DNA sequencing revealed that the airborne microbial communities were composed of terrestrial and phyllospheric species associated with the degradation of decaying plant litters. Regardless of the three seasons, the above canopy was dominated by atmospheric stress-resistant bacteria from the phyla Actinobacteria and Firmicutes. Unlike bacteria, the mushroom-type fungal members of Agaricomycetes grew in relative abundance above the canopy, primarily throughout the summer and winter, while mold-type fungal Dothideomycetes species were often found at all three heights during the fall. The Fusarium, Pseudomonas, and Bacillus isolates, which were obtained from air samples at three heights, indicated high activities of ice nucleation in the water-drop freezing assay. Therefore, ice-nucleating microbial taxa likely originated from fungal and bacterial communities in the soil litter and plant surfaces of the phyllospheric environments.
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•Bioaerosols were collected from ground to high altitude at the forest environments.•Terrestrial and phyllospheric bacteria were dominated vertically over forest.•Mushroom- and mold-type fungi in airborne fungal communities changed seasonally.•Ice-nucleating microorganisms were obtained from the aerosols at heights of 500 m.
Amplified Trace Gas Removal in the Troposphere Hofzumahaus, Andreas; Rohrer, Franz; Lu, Keding ...
Science (American Association for the Advancement of Science),
06/2009, Volume:
324, Issue:
5935
Journal Article
Peer reviewed
The degradation of trace gases and pollutants in the troposphere is dominated by their reaction with hydroxyl radicals (OH). The importance of OH rests on its high reactivity, its ubiquitous ...photochemical production in the sunlit atmosphere, and most importantly on its regeneration in the oxidation chain of the trace gases. In the current understanding, the recycling of OH proceeds through HO₂ reacting with NO, thereby forming ozone. A recent field campaign in the Pearl River Delta, China, quantified tropospheric OH and HO₂ concentrations and turnover rates by direct measurements. We report that concentrations of OH were three to five times greater than expected, and we propose the existence of a pathway for the regeneration of OH independent of NO, which amplifies the degradation of pollutants without producing ozone.
We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012. During the ...survey periods from 2012 to 2015, the activity concentrations of radiocaesium in air ranged from approximately 10
to 10
Bq per m
and were higher in the warm season than in the cold season. Electron microscopy showed that the particles collected on filters in summer were predominantly of biological origin (bioaerosols), with which the observed radiocaesium activity concentration varied. We conducted an additional aerosol analysis based on fluorescent optical microscopic observation and high-throughput DNA sequencing technique to identify bioaerosols at Namie in 2015 summer. The concentrations of bioaerosols fluctuated the order of 10
particles per m
, and the phyla Basidiomycota and Ascomycota (true Fungi) accounted for approximately two-thirds of the bioaerosols. Moreover, the fungal spore concentration in air was positively correlated with the radiocaesium concentration at Namie in summer 2016. The bioaerosol emissions from Japanese mixed forests in the temperate zone predominately included fungal cells, which are known to accumulate radiocaesium, and should be considered an important scientific issue that must be addressed.
Resuspension of 137Cs from the contaminated ground
surface to the atmosphere is essential for understanding the environmental
behaviors of 137Cs and estimating external and inhalation exposure of
...residents. Kajino et al. (2016) assessed the 137Cs resuspension flux
from bare soil and forest ecosystems in eastern Japan in 2013 using a numerical
simulation constrained by surface air concentration measurements. However,
the simulation was found to underestimate the observed deposition amounts by
2 orders of magnitude. The reason for this underestimation is that the
simulation assumed that resuspended 137Cs is carried by submicron
aerosols, which have low deposition rates. Based on the observational
indications that soil dust and bioaerosols are the major carriers of
resuspended 137Cs, a new simulation is performed with higher deposition
rates constrained by both surface concentrations and deposition amounts. In
the new estimation, the total areal annual resuspension of 137Cs in
2013 is 25.7 TBq, which is equivalent to 0.96 % of the initial deposition
(2.68 PBq). Due to the rapid deposition rates, the annual redeposition
amount is also large at 10.6 TBq, approximately 40 % of the resuspended
137Cs. The resuspension rate through the atmosphere (0.96 % yr−1)
seems slow, but it (2.6 × 10−5 d−1) may not be negligibly
small compared to the actual decreasing trend of the ambient gamma dose rate
obtained in Fukushima Prefecture after the radioactive decay of 137Cs
plus 134Cs in 2013 is subtracted (1.0–7.9 × 10−4 d−1): resuspension can account for 1 %–10 % of the decreasing rate due
to decontamination and natural decay through land surface processes. The
current simulation underestimated the 137Cs deposition in Fukushima
city in winter by more than an order of magnitude, indicating the presence
of additional resuspension sources. The site of Fukushima city is surrounded
by major roads. Heavy traffic on wet and muddy roads after snow removal
operations could generate superlarge (approximately 100 µm in
diameter) road dust or road salt particles, which are not included in the
model but might contribute to the observed 137Cs at the site.
The deposition of insoluble radiocesium-bearing microparticles (CsMPs), which were released from the Fukushima Daiichi Nuclear Power Plant (F1NPP) accident in March 2011, has resulted in the ...widespread contamination of eastern Japan. Obviously, these deposited insoluble CsMPs may become the secondary contamination sources by atmospheric migration or other environmental transferring process; however, the understanding of the transport mechanism remains non-elucidation, and the relevant evidence has not been directly provided. This study, for the first time, provides the direct evidence for the resuspension of these insoluble CsMPs to the atmosphere from (1) proximity of
137
Cs radioactivity and resemblance of the morphology and the elemental compositions of CsMPs in the samples of soil and aerosol derived from the same sampling site, (2) the special characteristics of the resuspended CsMPs of which the ratios of Na/Si, K/Si and/or Cs/Si were smaller than those from the initially released CsMPs collected at either long distance or near F1NPP, which can be ascribed to the slowly natural corrosion of CsMPs by the loss of the small amount of soluble contents in CsMPs, and (3) high CsMPs concentration of 10 granules/g in the surface soil of our sampling site and high resuspension frequency of CsMPs in spring when predominant suspended particles were soil dust. Specifically, 15 single CsMPs were successfully isolated from the aerosol filters collected by unmanned high-volume air samplers at a severely polluted area in Fukushima Prefecture, about 25 km away from F1NPP, from January 2015 to September 2019. The mean diameter of these CsMPs was 1.8 ± 0.5 μm, and the average
137
Cs radioactivity was 0.35 ± 0.23 Bq/granule. The contribution rate of the resuspended CsMPs to the atmospheric radiocesium was estimated from the ratio of
137
Cs radioactivity of a single CsMP to that of the aerosol filter to be of 23.9 ± 15.3%. There has been no considerable decreasing trend in the annual CsMP resuspension frequency.
On March 11, 2011, the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident occurred and large amounts of radionuclides were discharged into the atmosphere. We have operated continuous aerosol ...samplings at four locations in Japan from the accident until the end of 2011. The activities of 90Sr and 137Cs in the aerosol samples were measured using low background liquid scintillation counters and high-purity germanium detectors, respectively. The atmospheric 90Sr and 137Cs concentrations decreased exponentially during 2011. The time variation of the 90Sr/137Cs ratio was obtained, and we found that the ratio rose from 1.2 × 10–3 in March to 1.3 × 10–1 in August 2011. One reason for the increase in the 90Sr/137Cs ratio could be the change in the primary emission source of activity at the FDNPP, which occurred near June 2011.
Even after 7 years of the nuclear accident that occurred in 2011 at the Fukushima Dai-ichi nuclear power plant (F1NPP), high levels of 137Cs have been detected in ambient aerosols from some polluted ...areas of Fukushima. Higher levels of radionuclides were often observed in the atmosphere during and after rain events. We presume that biological processes such as fungal activity associated with higher relative humidity may be involved with a possible emission of radioactivity to the atmosphere, which was originally emitted from the F1NPP accident and was deposited over the ground, forest, soil, etc. Here, we report, for the first time, relationships of 137Cs and organic tracers of fungal spores (i.e., arabitol, mannitol and trehalose) in the aerosol samples collected from Fukushima, Japan. Although we found twice-higher concentrations of 137Cs at nighttime than at daytime, fungal spore tracers did not show a consistent trend to 137Cs, that is, organic tracers at nighttime were similar with those at daytime or were even higher in daytime. This study has not clearly demonstrated that fungal spores are the important source of high levels of 137Cs at nighttime. The current unclear relationship is probably associated with the sampling strategy (four consecutive days with a sampling on/off program for day/nighttime samples) taken in this campaign, which may have caused a complicated meteorological situation.
Black carbon (BC), brown carbon, and light‐absorbing iron oxides (FeOx) aerosols affect Earth's energy budget through their strong absorption of solar radiation. FeOx aerosols can also affect global ...biogeochemical cycles through their role as a nutrient for oceanic phytoplankton. However, observational data for these aerosols required for evaluating their effects using global models are scarce, especially for FeOx. Here, we summarize and compare the data sets of BC and FeOx from five ground‐based and three aircraft observation campaigns conducted in the East Asian and Arctic regions during the 2009–2018 period acquired using a modified single‐particle soot photometer. In these campaigns, >80% of FeOx‐containing aerosols in the 170–270 nm FeOx core size range had microphysical features indicating an anthropogenic origin. The particle size distribution for each of the BC and FeOx was similar in all of the data sets except for those dominated by fresh urban pollution or pristine Arctic air. The campaign‐averaged mass concentrations of FeOx and BC were ~60–360 ng/m3 and ~240–1,300 ng/m3, respectively, in East Asia, and ~6 ng/m3 and ~20–30 ng/m3, respectively, in the Arctic. The campaign‐averaged FeOx/BC mass concentration ratio varied within a narrow range of 0.2–0.6 in both East Asian and Arctic regions. In every campaign, FeOx, BC, and carbon monoxide were tightly correlated with each other with similar slope to the urban campaigns (around Tokyo), implying the spatiotemporal variation of anthropogenic FeOx emission around northern middle‐to‐high latitudes is similar to those of anthropogenic BC and CO emissions.
Key Points
Mass concentrations of anthropogenic iron oxide (FeOx) were at least 20% of those of black carbon (BC) in both East Asia and the Arctic
FeOx, BC, and carbon monoxide were tightly correlated with each other in both East Asia and the Arctic
Particle size distributions of both FeOx and BC were presented and compared in detail
In this study, the potential natural sources of secondary radiocesium isotope (134Cs and 137Cs) emissions were investigated, with a focus on n-alkanes, a characteristic bioaerosol compound. ...Monitoring was performed to obtain a time series of aerosol, samples, from winter 2013 to summer 2014, and size-resolved aerosol samples in 2012 and 2014. Samples were collected from the area heavily contaminated after the Fukushima Daiichi Nuclear Power Plant accident in March 2011. A correlation analysis of radiocesium, n-alkanes, and black carbon concentrations was performed to identify the contributions of aerosols from biogenic and anthropogenic sources. Biogenic n-alkanes exhibited similar concentration ranges except for spring 2014. The continuous input of biogenic n-alkanes is characteristic of a sampling site surrounded by forest, where pollen dispersion increased the concentration of biogenic n-alkanes in spring 2014. On the other hand, anthropogenic n-alkane concentrations were significantly increased in spring and summer 2014 (>50 ng/m3), compared with those prior to winter 2014 (<20 ng/m3). This anthropogenic n-alkane increase represents the beginning of reconstruction near the area. The carbon preference index (CPI) clearly showed biogenic n-alkanes with coarse-sized particles (CPI > 3), and more anthropogenic n-alkanes were contained in fine particle aerosols. Our results showed that radiocesium and biogenic n-alkane concentrations in seasonal and size-resolved aerosol samples have a partially positive correlation, which supports the hypothesis that the secondary emissions of radionuclides occurred in the forested areas.
In situ measurements of nitrogen dioxide (NO₂) concentrations were conducted at an urban site in Tokyo (35°71′N, 139°76′E), Japan during the summers of 2007–2009. A chemiluminescence instrument ...equipped with a molybdenum oxide converter (Mo-CL) and a laser-induced fluorescence (LIF) instrument were used simultaneously for determining the ambient NO₂ concentrations. A tight linear correlation between the NO₂ concentrations determined by the LIF and Mo-CL techniques was evident except for high ozone concentration periods over 50 ppbv. During the high ozone episodes, correlation plots of the NO₂ concentrations between Mo-CL and LIF techniques indicated an overestimation of Mo-CL NO₂. To examine in detail the systematic differences between two techniques, a thermal dissociation laser-induced fluorescence (TD-LIF) instrument was employed in the summer of 2009 to measure total peroxy nitrates (ΣPNs) and total reactive nitrogen (NOz). We found that the ΣPNs concentrations correlated well with the discrepancies in NO₂ concentrations determined by the Mo-CL and LIF techniques. This result suggests that peroxy nitrate species significantly contribute to the observed interference in the Mo-CL measurements under high O₃ concentrations in our observation at the urban site in Tokyo.
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