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Atmospheric particles of biological origin, also referred to as bioaerosols or primary biological aerosol particles (PBAP), are important to various human health and environmental systems. There has been a recent steep increase in the frequency of published studies utilizing commercial instrumentation based on ultraviolet laser/light-induced fluorescence (UV-LIF), such as the WIBS (wideband integrated bioaerosol sensor) or UV-APS (ultraviolet aerodynamic particle sizer), for bioaerosol detection both outdoors and in the built environment. Significant work over several decades supported the development of the general technologies, but efforts to systematically characterize the operation of new commercial sensors have remained lacking. Specifically, there have been gaps in the understanding of how different classes of biological and non-biological particles can influence the detection ability of LIF instrumentation. Here we present a systematic characterization of the WIBS-4A instrument using 69 types of aerosol materials, including a representative list of pollen, fungal spores, and bacteria as well as the most important groups of non-biological materials reported to exhibit interfering fluorescent properties. Broad separation can be seen between the biological and non-biological particles directly using the five WIBS output parameters and by taking advantage of the particle classification analysis introduced by Perring et al. (2015). We highlight the importance that particle size plays on observed fluorescence properties and thus in the Perring-style particle classification. We also discuss several particle analysis strategies, including the commonly used fluorescence threshold defined as the mean instrument background (forced trigger; FT) plus 3 standard deviations (σ) of the measurement. Changing the particle fluorescence threshold was shown to have a significant impact on fluorescence fraction and particle type classification. We conclude that raising the fluorescence threshold from FT + 3σ to FT + 9σ does little to reduce the relative fraction of biological material considered fluorescent but can significantly reduce the interference from mineral dust and other non-biological aerosols. We discuss examples of highly fluorescent interfering particles, such as brown carbon, diesel soot, and cotton fibers, and how these may impact WIBS analysis and data interpretation in various indoor and outdoor environments. The performance of the particle asymmetry factor (AF) reported by the instrument was assessed across particle types as a function of particle size, and comments on the reliability of this parameter are given. A comprehensive online supplement is provided, which includes size distributions broken down by fluorescent particle type for all 69 aerosol materials and comparing threshold strategies. Lastly, the study was designed to propose analysis strategies that may be useful to the broader community of UV-LIF instrumentation users in order to promote deeper discussions about how best to continue improving UV-LIF instrumentation and results.

Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). The measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.The CCN measurements were continuously cycled through 10 levels of supersaturation (S  =  0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S  =  1.10 % to 172 nm at S  =  0.11 %. The particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode (κAit  =  0.14 ± 0.03), higher values for the accumulation mode (κAcc  =  0.22 ± 0.05), and an overall mean value of κmean  =  0.17 ± 0.06, consistent with high fractions of organic aerosol.The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. We find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.

The Amazon rainforest is a sensitive ecosystem experiencing the combined pressures of progressing deforestation and climate change. Its atmospheric conditions oscillate between biogenic and biomass burning (BB) dominated states. The Amazon further represents one of the few remaining continental places where the atmosphere approaches pristine conditions during occasional wet season episodes. The Amazon Tall Tower Observatory (ATTO) has been established in central Amazonia to investigate the complex interactions between the rainforest ecosystem and the atmosphere. Physical and chemical aerosol properties have been analyzed continuously since 2012. This paper provides an in-depth analysis of the aerosol's optical properties at ATTO based on data from 2012 to 2017. The following key results have been obtained. The aerosol scattering and absorption coefficients at 637 nm, σsp,637 and σap,637, show a pronounced seasonality with lowest values in the clean wet season (mean ± SD: σsp,637=7.5±9.3 M m−1; σap,637=0.68±0.91 M m−1) and highest values in the BB-polluted dry season (σsp,637=33±25 M m−1; σap,637=4.0±2.2 M m−1). The single scattering albedo at 637 nm, ω0, is lowest during the dry season (ω0=0.87±0.03) and highest during the wet season (ω0=0.93±0.04). The retrieved BC mass absorption cross sections, αabs, are substantially higher than values widely used in the literature (i.e., 6.6 m2 g−1 at 637 nm wavelength), likely related to thick organic or inorganic coatings on the BC cores. Wet season values of αabs=11.4±1.2 m2 g−1 (637 nm) and dry season values of αabs=12.3±1.3 m2 g−1 (637 nm) were obtained. The BB aerosol during the dry season is a mixture of rather fresh smoke from local fires, somewhat aged smoke from regional fires, and strongly aged smoke from African fires. The African influence appears to be substantial, with its maximum from August to October. The interplay of African vs. South American BB emissions determines the aerosol optical properties (e.g., the fractions of black vs. brown carbon, BC vs. BrC). By analyzing the diel cycles, it was found that particles from elevated aerosol-rich layers are mixed down to the canopy level in the early morning and particle number concentrations decrease towards the end of the day. Brown carbon absorption at 370 nm, σap,BrC,370, was found to decrease earlier in the day, likely due to photo-oxidative processes. BC-to-CO enhancement ratios, ERBC, reflect the variability of burnt fuels, combustion phases, and atmospheric removal processes. A wide range of ERBC between 4 and 15 ng m−3 ppb−1 was observed with higher values during the dry season, corresponding to the lowest ω0 levels (0.86–0.93). The influence of the 2009/2010 and 2015/2016 El Niño periods and the associated increased fire activity on aerosol optical properties was analyzed by means of 9-year σsp and σap time series (combination of ATTO and ZF2 data). Significant El Niño-related enhancements were observed: in the dry season, σsp,637 increased from 24±18 to 48±33 M m−1 and σap, 637 from 3.8±2.8 to 5.3±2.5 M m−1. The absorption Ångström exponent, åabs, representing the aerosol absorption wavelength dependence, was mostly <1.0 with episodic increases upon smoke advection. A parameterization of åabs as a function of the BC-to-OA mass ratio for Amazonian aerosol ambient measurements is presented. The brown carbon (BrC) contribution to σap at 370 nm was obtained by calculating the theoretical BC åabs, resulting in BrC contributions of 17 %–29 % (25th and 75th percentiles) to σap 370 for the entire measurement period. The BrC contribution increased to 27 %–47 % during fire events under El Niño-related drought conditions from September to November 2015. The results presented here may serve as a basis to understand Amazonian atmospheric aerosols in terms of their interactions with solar radiation and the physical and chemical-aging processes that they undergo during transport. Additionally, the analyzed aerosol properties during the last two El Niño periods in 2009/2010 and 2015/2016 offer insights that could help to assess the climate change-related potential for forest-dieback feedbacks under warmer and drier conditions.

Size-resolved measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted over a full seasonal cycle at the remote Amazon Tall Tower Observatory (ATTO, March 2014–February 2015). In a preceding companion paper, we presented annually and seasonally averaged data and parametrizations (Part 1; Pöhlker et al., 2016a). In the present study (Part 2), we analyze key features and implications of aerosol and CCN properties for the following characteristic atmospheric conditions: Empirically pristine rain forest (PR) conditions, where no influence of pollution was detectable, as observed during parts of the wet season from March to May. The PR episodes are characterized by a bimodal aerosol size distribution (strong Aitken mode with DAit ≈ 70 nm and NAit ≈ 160 cm−3, weak accumulation mode with Dacc ≈ 160 nm and Nacc≈ 90 cm−3), a chemical composition dominated by organic compounds, and relatively low particle hygroscopicity (κAit≈ 0.12, κacc ≈ 0.18). Long-range-transport (LRT) events, which frequently bring Saharan dust, African biomass smoke, and sea spray aerosols into the Amazon Basin, mostly during February to April. The LRT episodes are characterized by a dominant accumulation mode (DAit ≈ 80 nm, NAit ≈ 120 cm−3 vs. Dacc ≈ 180 nm, Nacc ≈ 310 cm−3), an increased abundance of dust and salt, and relatively high hygroscopicity (κAit≈ 0.18, κacc ≈ 0.35). The coarse mode is also significantly enhanced during these events. Biomass burning (BB) conditions characteristic for the Amazonian dry season from August to November. The BB episodes show a very strong accumulation mode (DAit ≈ 70 nm, NAit ≈ 140 cm−3 vs. Dacc ≈ 170 nm, Nacc ≈ 3400 cm−3), very high organic mass fractions (∼ 90 %), and correspondingly low hygroscopicity (κAit≈ 0.14, κacc ≈ 0.17). Mixed-pollution (MPOL) conditions with a superposition of African and Amazonian aerosol emissions during the dry season. During the MPOL episode presented here as a case study, we observed African aerosols with a broad monomodal distribution (D ≈ 130 nm, NCN,10 ≈ 1300 cm−3), with high sulfate mass fractions (∼ 20 %) from volcanic sources and correspondingly high hygroscopicity (κ< 100 nm ≈ 0.14, κ>100nm≈ 0.22), which were periodically mixed with fresh smoke from nearby fires (D ≈ 110 nm, NCN,10 ≈ 2800 cm−3) with an organic-dominated composition and sharply decreased hygroscopicity (κ<150nm≈ 0.10, κ>150nm≈ 0.20). Insights into the aerosol mixing state are provided by particle hygroscopicity (κ) distribution plots, which indicate largely internal mixing for the PR aerosols (narrow κ distribution) and more external mixing for the BB, LRT, and MPOL aerosols (broad κ distributions). The CCN spectra (CCN concentration plotted against water vapor supersaturation) obtained for the different case studies indicate distinctly different regimes of cloud formation and microphysics depending on aerosol properties and meteorological conditions. The measurement results suggest that CCN activation and droplet formation in convective clouds are mostly aerosol-limited under PR and LRT conditions and updraft-limited under BB and MPOL conditions. Normalized CCN efficiency spectra (CCN divided by aerosol number concentration plotted against water vapor supersaturation) and corresponding parameterizations (Gaussian error function fits) provide a basis for further analysis and model studies of aerosol–cloud interactions in the Amazon.

Primary biological aerosol particles (PBAPs) in the atmosphere are highly relevant for the Earth system, climate, and public health. The analysis of PBAPs, however, remains challenging due to their high diversity and large spatiotemporal variability. For real-time PBAP analysis, light-induced fluorescence (LIF) instruments have been developed and widely used in laboratory and ambient studies. The interpretation of fluorescence data from these instruments, however, is often limited by a lack of spectroscopic information. This study introduces an instrument – the Spectral Intensity Bioaerosol Sensor (SIBS; Droplet Measurement Technologies (DMT), Longmont, CO, USA) – that resolves fluorescence spectra for single particles and thus promises to expand the scope of fluorescent PBAP quantification and classification. The SIBS shares key design components with the latest versions of the Wideband Integrated Bioaerosol Sensor (WIBS) and the findings presented here are also relevant for the widely deployed WIBS-4A and WIBS-NEO as well as other LIF instruments. The key features of the SIBS and the findings of this study can be summarized as follows. Particle sizing yields reproducible linear responses for particles in the range of 300 nm to 20 µm. The lower sizing limit is significantly smaller than for earlier commercial LIF instruments (e.g., WIBS-4A and the Ultraviolet Aerodynamic Particle Sizer; UV-APS), expanding the analytical scope into the accumulation-mode size range. Fluorescence spectra are recorded for two excitation wavelengths (λex=285 and 370 nm) and a wide range of emission wavelengths (λmean=302–721 nm) with a resolution of 16 detection channels, which is higher than for most other commercially available LIF bioaerosol sensors. Fluorescence spectra obtained for 16 reference compounds confirm that the SIBS provides sufficient spectral resolution to distinguish major modes of molecular fluorescence. For example, the SIBS resolves the spectral difference between bacteriochlorophyll and chlorophyll a and b. A spectral correction of the instrument-specific detector response is essential to use the full fluorescence emission range. Asymmetry factor (AF) data were assessed and were found to provide only limited analytical information. In test measurements with ambient air, the SIBS worked reliably and yielded characteristically different spectra for single particles in the coarse mode with an overall fluorescent particle fraction of ∼4 % (3σ threshold), which is consistent with earlier studies in comparable environments.

Fluorescent dyed polystyrene latex spheres (PSLs) are commonly used for characterization and calibration of instruments detecting fluorescence signals from particles suspended in the air and other fluids. Instruments like the Ultraviolet Aerodynamic Particle Sizer (UV-APS) and the Waveband Integrated Bioaerosol Sensor (WIBS) are widely used for bioaerosol research, but these instruments present significant technical and physical challenges requiring careful characterization with standard particles. Many other research communities use flow cytometry and other instruments that interrogate fluorescence from individual particles, and these also frequently rely on fluorescent PSLs as standards. Nevertheless, information about physical properties of commercially available PSLs provided by each manufacturer is generally proprietary and rarely available, making their use in fluorescence validation and calibration very difficult. This technical note presents an overview of steady-state fluorescence properties of fluorescent and non-fluorescent PSLs, as well as of polystyrene-divinylbenzene (PS-DVB) particles, by using on- and offline spectroscopic techniques. We show that the “fluorescence landscape” of PSLs is more complex than the information typically provided by manufacturers may imply, especially revealing multimodal emission patterns. Furthermore, non-fluorescent PSLs also exhibit defined patterns of fluorescent emission originating from a mixture of polystyrene and detergents, which becomes a crucial point for fluorescence threshold calibrations and qualitative comparison between instruments. By comparing PSLs of different sizes, but doped with the same dye, changes in emission spectra from bulk solutions are not immediately obvious. On a single-particle scale, however, fluorescence intensity values increase with increasing particle size. No significant effect in the fluorescence signatures was detectable by comparing PSLs in dry vs. wet states, indicating that solvent water may only play a minor role as a fluorescence quencher. Because information provided by manufacturers of commercially available PSLs is generally very limited, we provide the steady-state excitation–emission matrices (EEMs) of PSLs as open-access data within the Supplement. Detergent and solvent effects are also discussed in order to provide information not available elsewhere to researchers in the bioaerosol and other research communities. These data are not meant to serve as a fundamental library of PSL properties because of the variability of fluorescent properties between batches and as a function of particle aging and agglomeration. The data presented, however, provide a summary of spectral features which are consistent across these widely used fluorescent standards. Using these concepts, further checks will likely be required by individual researchers using specific lots of standards.

Non-methane hydrocarbons (NMHCs) such as ethane and propane are significant atmospheric pollutants and precursors of tropospheric ozone, while the Middle East is a global emission hotspot due to  extensive oil and gas production. Here we compare in situ hydrocarbon measurements, performed around the Arabian Peninsula, with global model simulations that include current emission inventories (EDGAR) and state-of-the-art atmospheric circulation and chemistry mechanisms (EMAC model). While measurements of high mixing ratios over the Arabian Gulf are adequately simulated, strong underprediction by the model was found over the northern Red Sea. By examining the individual sources in the model and by utilizing air mass back-trajectory investigations and Positive Matrix Factorization (PMF) analysis, we deduce that Red Sea Deep Water (RSDW) is an unexpected, potent source of atmospheric NMHCs. This overlooked underwater source is comparable with total anthropogenic emissions from entire Middle Eastern countries, and significantly impacts the regional atmospheric chemistry. The Middle East is known to emit large amounts of non-methane hydrocarbon pollutants to the atmosphere, but the sources are poorly characterized. Here the authors discover a new source—deep water in the Red Sea—and calculate that its emissions exceed rates of several high gas-production countries.

The Amazon rain forest experiences the combined pressures from human-made deforestation and progressing climate change, causing severe and potentially disruptive perturbations of the ecosystem's integrity and stability. To intensify research on critical aspects of Amazonian biosphere–atmosphere exchange, the Amazon Tall Tower Observatory (ATTO) has been established in the central Amazon Basin. Here we present a multi-year analysis of backward trajectories to derive an effective footprint region of the observatory, which spans large parts of the particularly vulnerable eastern basin. Further, we characterize geospatial properties of the footprint regions, such as climatic conditions, distribution of ecoregions, land cover categories, deforestation dynamics, agricultural expansion, fire regimes, infrastructural development, protected areas, and future deforestation scenarios. This study is meant to be a resource and reference work, helping to embed the ATTO observations into the larger context of human-caused transformations of Amazonia. We conclude that the chances to observe an unperturbed rain forest–atmosphere exchange at the ATTO site will likely decrease in the future, whereas the atmospheric signals from human-made and climate-change-related forest perturbations will increase in frequency and intensity.

Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German–Brazilian cooperative aircraft campaign ACRIDICON–CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (global precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September–October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5–72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.

Radiotherapy is a powerful cure for several types of solid tumours, but its application is often limited because of severe side effects in individual patients. With the aim to find biomarkers capable of predicting normal tissue side reactions we analysed the radiation responses of cells from individual head and neck tumour and breast cancer patients of different clinical radiosensitivity in a multicentric study. Multiple parameters of cellular radiosensitivity were analysed in coded samples of peripheral blood lymphocytes (PBLs) and derived lymphoblastoid cell lines (LCLs) from 15 clinical radio-hypersensitive tumour patients and compared to age- and sex-matched non-radiosensitive patient controls and 15 lymphoblastoid cell lines from age- and sex- matched healthy controls of the KORA study. Experimental parameters included ionizing radiation (IR)-induced cell death (AnnexinV), induction and repair of DNA strand breaks (Comet assay), induction of yH2AX foci (as a result of DNA double strand breaks), and whole genome expression analyses. Considerable inter-individual differences in IR-induced DNA strand breaks and their repair and/or cell death could be detected in primary and immortalised cells with the applied assays. The group of clinically radiosensitive patients was not unequivocally distinguishable from normal responding patients nor were individual overreacting patients in the test system unambiguously identified by two different laboratories. Thus, the in vitro test systems investigated here seem not to be appropriate for a general prediction of clinical reactions during or after radiotherapy due to the experimental variability compared to the small effect of radiation sensitivity. Genome-wide expression analysis however revealed a set of 67 marker genes which were differentially induced 6 h after in vitro-irradiation in lymphocytes from radio-hypersensitive and non-radiosensitive patients. These results warrant future validation in larger cohorts in order to determine parameters potentially predictive for clinical radiosensitivity.