The long-range transport of birch (Betula) pollen from Poland and Germany causes significant pre-season concentrations in Denmark

Diurnal pattern of Poaceae and Betula pollen flight in Central Europe

In Central Europe the most common allergies are provoked by grass or birch pollen allergens. We determined the intra-daily behavior of airborne pollen grains of grasses (Poaceae) and birch (Betula ssp.) in Central Europe, based on data obtained from a network of automatic pollen monitors over Europe (www.pollenscience.eu). Our aim was to determine the time of day when the lowest concentrations occur, to provide allergic individuals the optimal time to ventilate their homes. The study was carried out in three Central European capitals, Berlin (Germany), Paris-Saclay (France), and Luxembourg (Luxembourg), as well as in eight stations in Germany (Altötting, Feucht, Garmisch-Partenkirchen, Hof, Marktheidenfeld, Mindelheim, Munich and Viechtach). The diurnal rhythm of these eleven locations was analyzed for either the complete, first week, peak week, peak day and last week of the pollen season. The data studied were reported as pollen/m3 measured in 3 h periods. Stations were classified as city, semi-populated or countryside areas using land-use and population density criteria. Grass pollen has a more pronounced diurnal rhythm than birch pollen concentrations. A significant difference was observed when comparing day (6-21 h) versus night (21-6 h) for all stations. No difference was detected between city and countryside for both pollen types, although for Poaceae a longer period of maximum concentrations was observed in big cities and higher day/night-time differences were registered in the countryside (6.4) than in cities (3.0). The highest pollen concentrations were observed between 9 and 18 h for grass, but the rhythm was less pronounced for birch pollen. For allergic individuals who want to bring in fresh air in their homes, we recommend opening windows after 21 h, but even better early in the morning between 6 and 9 h before pollinations (re)starts.

Impact of meteorological parameters and air pollutants on airborne concentration of Betula pollen and Bet v 1 allergen

The intensity of birch pollen season is expressed by seasonal pollen integral (SPIn, the sum of the mean daily pollen concentration during the birch pollination period) and the amount of Bet v 1 allergen released per birch pollen grain expressed by pollen allergen potency (PAP). Betula pollen and Bet v 1 allergen were simultaneously measured in the air of Bratislava from 2019 to 2022 by using two Burkard traps (Hirst-type and cyclone) in order to evaluate the causes of the seasonal variation in the SPIn and PAP levels. The highest SPIn (19,975 pollen/m3) was observed in 2022 and the lowest one (1484 pollen/m3) in 2021. The average daily PAP level (4.0 pg Bet v 1/pollen) was highest in 2019 and lowest (2.5 pg Bet v 1/pollen) in 2020. We found that seasonal variation in SPIn was associated mainly with the changes in environmental conditions during the pre-season period, whereas the year-to-year variation in PAP levels was attributed to environmental conditions during both pre- and in-season periods. Our results indicate that rainy weather in June 2020 and cold overcast weather in January‒February 2021 resulted in low SPIn in 2021. On the other hand, dry weather in June 2021 and warm weather in January‒February 2022 resulted in high SPIn in 2022. The low average daily PAP level in 2020 was associated with (1) low levels of gaseous air pollutants in March, when the ripening of pollen takes place; (2) an earlier start of the birch main pollen season (MPS); and (3) dry weather during the MPS. On the other hand, high PAP level in 2019 was associated with higher levels of air pollutants in March and during the MPS.

Birch pollen-The unpleasant herald of spring

Type I respiratory allergies to birch pollen and pollen from related trees of the order Fagales are increasing in industrialized countries, especially in the temperate zone of the Northern hemisphere, but the reasons for this increase are still debated and seem to be multifaceted. While the most important allergenic molecules of birch pollen have been identified and characterized, the contribution of other pollen components, such as lipids, non-allergenic immunomodulatory proteins, or the pollen microbiome, to the development of allergic reactions are sparsely known. Furthermore, what also needs to be considered is that pollen is exposed to external influences which can alter its allergenicity. These external influences include environmental factors such as gaseous pollutants like ozone or nitrogen oxides or particulate air pollutants, but also meteorological events like changes in temperature, humidity, or precipitation. In this review, we look at the birch pollen from different angles and summarize current knowledge on internal and external influences that have an impact on the allergenicity of birch pollen and its interactions with the epithelial barrier. We focus on epithelial cells since these cells are the first line of defense in respiratory disease and are increasingly considered to be a regulatory tissue for the protection against the development of respiratory allergies.

Constructing a pollen proxy from low-cost Optical Particle Counter (OPC) data processed with Neural Networks and Random Forests

Pollen allergies affect a significant proportion of the global population, and this is expected to worsen in years to come. There is demand for the development of automated pollen monitoring systems. Low-cost Optical Particle Counters (OPCs) measure particulate matter and have attractive advantages of real-time high time resolution data and affordable costs. This study asks whether low-cost OPC sensors can be used for meaningful monitoring of airborne pollen. We employ a variety of methods, including supervised machine learning techniques, to construct pollen proxies from hourly-average OPC data and evaluate their performance, holding out 40 % of observations to test the proxies. The most successful methods are supervised machine learning Neural Network (NN) and Random Forest (RF) methods, trained from pollen concentrations collected from a Hirst-type sampler. These perform significantly better than using a simple particle size-filtered proxy or a Positive Matrix Factorisation (PMF) source apportionment pollen proxy. Twelve NN and RF models were developed to construct a pollen proxy, each varying by model type, input features and target variable. The results show that such models can construct useful information on pollen from OPC data. The best metrics achieved (Spearman correlation coefficient = 0.85, coefficient of determination = 0.67) were for the NN model constructing a Poaceae (grass) pollen proxy, based on particle size information, temperature, and relative humidity. Ability to distinguish high pollen events was evaluated using F1 Scores, a score reflecting the fraction of true positives with respect to false positives and false negatives, with promising results (F1 ≤ 0.83). Model-constructed proxies demonstrated the ability to follow monthly and diurnal trends in pollen. We discuss the suitability of OPCs for monitoring pollen and offer advice for future progress. We demonstrate an attractive alternative for automated pollen monitoring that could provide valuable and timely information to the benefit of pollen allergy sufferers.

Aircraft surveys for air eDNA: probing biodiversity in the sky

Air is a medium for dispersal of environmental DNA (eDNA) carried in bioaerosols, yet the atmosphere is mostly unexplored as a source of genetic material encompassing all domains of life. In this study, we designed and deployed a robust, sterilizable hardware system for airborne nucleic acid capture featuring active filtration of a quantifiable, controllable volume of air and a high-integrity chamber to protect the sample from loss or contamination. We used our hardware system on an aircraft across multiple height transects over major aerosolization sources to collect air eDNA, coupled with high-throughput amplicon sequencing using multiple DNA metabarcoding markers targeting bacteria, plants, and vertebrates to test the hypothesis of large-scale genetic presence of these bioaerosols throughout the planetary boundary layer in the lower troposphere. Here, we demonstrate that the multi-taxa DNA assemblages inventoried up to 2,500 m using our airplane-mounted hardware system are reflective of major aerosolization sources in the survey area and show previously unreported airborne species detections (i.e., Allium sativum L). We also pioneer an aerial survey flight grid standardized for atmospheric sampling of genetic material and aeroallergens using a light aircraft and limited resources. Our results show that air eDNA from terrestrial bacteria, plants, and vertebrates is detectable up to high altitude using our airborne air sampler and demonstrate the usefulness of light aircraft in monitoring campaigns. However, our work also underscores the need for improved marker choices and reference databases for species in the air column, particularly eukaryotes. Taken together, our findings reveal strong connectivity or mixing of terrestrial-associated eDNA from ground level aerosolization sources and the atmosphere, and we recommend that parameters and indices considering lifting action, atmospheric instability, and potential for convection be incorporated in future surveys for air eDNA. Overall, this work establishes a foundation for light aircraft campaigns to comprehensively and economically inventory bioaerosol emissions and impacts at scale, enabling transformative future opportunities in airborne DNA technology.

A Modified Spectroscopic Approach for the Real-Time Detection of Pollen and Fungal Spores at a Semi-Urban Site Using the WIBS-4+, Part I

The real-time monitoring of primary biological aerosol particles (PBAP) such as pollen and fungal spores has received much attention in recent years as a result of their health and climatic effects. In this study, the Wideband Integrated Bioaerosol Sensor (WIBS) 4+ model was evaluated for its ability to sample and detect ambient fungal spore and pollen concentrations, compared to the traditional Hirst volumetric method. Although the determination of total pollen and fungal spore ambient concentrations are of interest, the selective detection of individual pollen/fungal spore types are often of greater allergenic/agricultural concern. To aid in this endeavour, modifications were made to the WIBS-4 instrument to target chlorophyll fluorescence. Two additional fluorescence channels (FL4 and FL5 channels) were combined with the standard WIBS channels (FL1, FL2, FL3). The purpose of this modification is to help discriminate between grass and herb pollen from other pollen. The WIBS-4+ was able to successfully detect and differentiate between different bioaerosol classes. The addition of the FL4 and FL5 channels also allowed for the improved differentiation between tree (R² = 0.8), herbaceous (R² = 0.6) and grass (R² = 0.4) pollen and fungal spores (R² = 0.8). Both grass and herbaceous pollen types showed a high correlation with D type particles, showing strong fluorescence in the FL4 channel. The additional fluorescent data that were introduced also improved clustering attempts, making k-means clustering a comparable solution for this high-resolution data.

Drivers of the release of the allergens Bet v 1 and Phl p 5 from birch and grass pollen

The drivers affecting the Pollen Allergen Potency (PAP, amount of allergen released per pollen) are sparsely known. Betula and Poaceae airborne pollen are the two main allergenic pollen in the World. Airborne pollen and their allergens Bet v 1 and Phl p 5 were simultaneously measured from 2010 to 2015 in Davos (Switzerland) and Munich (Germany) by using volumetric traps and ChemVol cascade impactors. Daily variations in PAP were analysed in PM_>10 and PM_2.5-10 air fractions and generalized additive models were created to explain which factors determine PAP, including meteorological parameters and inorganic pollutants. 87.1 ± 13.9% of Bet v 1 and 88.8 ± 15.5% of Phl p 5 was detected in the fraction PM_>10 where most pollen grains were collected. Significantly higher PAP for grasses (3.5 ± 1.9 pg Phl p 5/pollen grain) were observed in Munich than in Davos (2.4 ± 1.5 pg/pollen grain, p < 0.001), but not for Betula (2.5 ± 1.6 pg Bet v 1/pollen grain in Munich and 2.3 ± 1.7 in Davos, N.S.). PAP varied between days, years and location, and increased along the pollen season for Poaceae, but remaining constant for Betula. Free allergens (allergens observed in the fraction with limited pollen, PM_{2.5- 10}) were recorded mostly at the beginning or at the end of the pollen season, being linked to higher humidity and rainy days. Also, PAP was higher when the airborne pollen concentrations increased rapidly after one day of low/moderate levels. Our findings show that pollen exposure explains allergen exposure only to a limited extend, and that day in the season, geographic location and some weather conditions need to be considered also to explain symptoms of allergic individuals.

Aerobiological modelling II: A review of long-range transport models

The long-range atmospheric transport models of pollen and fungal spores require four modules for their development: (i) Meteorological module: which contain the meteorological model, and it can be coupled to transport model with the same output configuration (spatio-temporal resolution), or uncoupled does not necessarily have the same output parameters. (ii) Emission module: settles the mass fluxes of bioaerosol, it can be done with a complex parameterization integrating phenological models and meteorological factors or by a simple emission factor. (iii) Sources of emission module, specifically refers to forestry/agronomy maps or, in the case of herbs and fungi, to potential geographical areas of emission. Obtaining the highest possible resolution in these maps allows establishing greater reliability in the modelling. (iv) Atmospheric transport module, with its respective established output parameters. The review and subsequent analysis presented in this article, were performed on published electronic scientific articles from 1998 to 2016. Of a total of 101 models applied found in 64 articles, 33 % performed forward modelling (using 15 different models) and 67 % made backward modelling (with three different models). The 88 % of the cases were applied to pollen (13 taxa) and 12 % to fungal spores (3 taxa). Regarding the emission module, 22 % used parametrization (four different parameters) and 10 % emission factors. The most used transport model was HYSPLIT (59 %: 56 % backward and 3 % forward) following by SILAM 10 % (all forward). Main conclusions were that the models of long-range transport of pollen and fungal spores had high technical-scientific requirements to development and that the major limitations were the establishment of the flow and the source of the emission.

A Review of the Respiratory Health Burden Attributable to Short-Term Exposure to Pollen

Respiratory diseases such as asthma, allergic rhinitis (AR) and chronic obstructive pulmonary disease (COPD) affect millions worldwide and pose a significant global public health burden. Over the years, changes in land use and climate have increased pollen quantity, allergenicity and duration of the pollen season, thus increasing its impact on respiratory disease. Many studies have investigated the associations between short-term ambient pollen (i.e., within days or weeks of exposure) and respiratory outcomes. Here, we reviewed the current evidence on the association between short-term outdoor pollen exposure and thunderstorm asthma (TA), asthma and COPD hospital presentations, general practice (GP) consultations, self-reported respiratory symptoms, lung function changes and their potential effect modifiers. The literature suggests strong evidence of an association between ambient pollen concentrations and almost all respiratory outcomes mentioned above, especially in people with pre-existing respiratory diseases. However, the evidence on sub-clinical lung function changes, COPD, and effect modifiers other than asthma, hay fever and pollen sensitisation are still scarce and requires further exploration. Better understanding of the implications of pollen on respiratory health can aid healthcare professionals to implement appropriate management strategies.

Potential contribution of distant sources to airborne Betula pollen levels in Northeastern Iberian Peninsula

Betula (birch) pollen is one of the most important causes of respiratory allergy in Northern and Central Europe. While birch trees are abundant in Central, Northern, and Eastern Europe, they are scarce in the Mediterranean territories, especially in the Iberian Peninsula (IP), where they grow only in the northern regions and as ornamental trees in urban areas. However, the airborne birch pollen patterns in Catalonia (Northeastern IP) show abrupt high concentrations in areas with usually low local influence. The intensity of the derived health problems can be increased by outbreaks due to long-range pollen transport. The present work evaluates the different potential contributions to Catalonia from the main source regions: Pyrenees, Cantabria, and the forests of France and Central Europe. To this end, we computed the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) back trajectories of air masses associated with the main Betula pollen peaks occurring simultaneously over different Catalan monitoring stations, and we studied their provenance over a 15-year period. The Vielha aerobiological station on the northern slopes of the Central Pyrenees was used to identify the dates of the pollen season in the Pyrenean region. In order to better understand the role of the Pyrenees, which is the nearest of the four birch forested regions, we classified the pollen peaks in the other Catalan stations into three groups based on the relationship between the peak and the pollen season in the Pyrenees. Our analysis of back-trajectory residence time, combined with the associated pollen concentration, reveals that two principal routes other than the Pyrenean forest sustain the northerly fluxes that enter Catalonia and carry significant concentrations of Betula pollen. This study has also allowed quantifying the differentiated contributions of the potential source regions. In addition, the Weather Research Forecast (WRF) mesoscale model has been used to study three specific episodes. Both models, HYSPLIT and WRF, complement each other and have allowed for better understanding of the main mechanisms governing the entry of birch pollen to the region.

Atmospheric transport reveals grass pollen dispersion distances

Identifying the origin of bioaerosols is of central importance in many biological disciplines, such as human health, agriculture, forestry, aerobiology and conservation. Modelling sources, transportation pathways and sinks can reveal how bioaerosols vary in the atmosphere and their environmental impact. Grass pollen are particularly important due to their widely distributed source areas, relatively high abundance in the atmosphere and high allergenicity. Currently, studies are uncertain regarding sampler representability between distance and sources for grass pollen. Using generalized linear modelling, this study aimed to analyse this relationship further by answering the question of distance-to-source area contribution. Grass pollen concentrations were compared between urban and rural locations, located 6.4 km apart, during two years in Worcestershire, UK. We isolated and refined vegetation areas at 100 m × 100 m using the 2017 CEH Crop Map and conducted atmospheric modelling using HYSPLIT to identify which source areas could contribute pollen. Pollen concentrations were then modelled with source areas and meteorology using generalized linear mixed-models with three temporal variables as random variation. We found that the Seasonal Pollen Integral for grass pollen varied between both years and location, with the urban location having higher levels. Day of year showed higher temporal variation than the diurnal or annual variables. For the urban location, grass source areas within 30 km had positive significant effects in predicting grass pollen concentrations, while source areas within 2-10 km were important for the rural one. The source area differential was likely influenced by an urban-rural gradient that caused differences in the source area contribution. Temperature had positive highly significant effects on both locations while precipitation affected only the rural location. Combining atmospheric modelling, vegetation source maps and generalized linear modelling was found to be a highly accurate tool to identify transportation pathways of bioaerosols in landscape environments.

Air Pollution Affecting Pollen Concentrations through Radiative Feedback in the Atmosphere

Episodes with high air pollution and large amounts of aeroallergens expose sensitive individuals to a health damaging cocktail of atmospheric particles. Particulate matter (PM) affects the radiative balance and atmospheric dynamics, hence affecting concentrations of pollutants. The aim of the study is to estimate feedback between meteorology and particles on concentrations of aeroallergens using an extended version of the atmospheric model WRF-Chem. The extension, originally designed for PM and dust, concerns common aeroallergens. We study a birch pollen episode coinciding with an air pollution event containing Saharan dust (late March to early April 2014), using the model results, pollen records from Southern UK and vertical profiles of meteorological observations. During the episode, increased concentrations of birch pollen were calculated over the European continent, causing plumes transported towards the UK. The arrival of these plumes matched well with observations. The lowest parts of the atmospheric boundary layer demonstrate a vertical profile that favours long distance transport, while the pollen record shows pollen types that typically flower at another time. The model calculations show that feedback between meteorology and particles changes pollen concentrations by ±30% and in some cases up to 100%. The atmospheric conditions favoured meteorological feedback mechanisms that changed long distance transport of air pollution and aeroallergens.

The Effect of Seasonal Priming on Specific Inhalation Challenges With Birch and Grass Allergen Among Persons With Allergic Rhinitis

Objectives: Allergic diseases are prevalent in the working population, and work-related airborne pollen exposure might be substantial, especially among outdoor workers, resulting in work-exacerbated effects. Seasonal exposure to pollen may induce a priming effect on the allergic bronchial response resulting in exaggerated effects at the end of the natural pollen season. This was previously observed among people with asthma but may also be of importance for persons with allergic rhinitis. In this study, we examined the effect of seasonal priming on bronchial responsiveness among young adults with allergic rhinitis and no or mild asthma. In addition, we explored the association between the baseline characteristics of participants and the severity of bronchoconstriction. Finally, we evaluated the application of a novel non-linear regression model to the log-dose-response curves.

Material and methods: In a crossover design, 36 participants underwent specific inhalation challenges (SICs) with either grass or birch allergen outside and at the end of the pollen season. The differences in bronchial response were evaluated by comparing the dose-response profiles and PD₂₀ estimates derived by applying a non-linear regression model.

Results: The results showed that 12 of the 19 grass pollen-exposed participants had a lower PD₂₀ at the end of the season compared with the outside season. For birch, this was true for nine out of the 17 participants. However, no statistically significant effects of the seasonal pollen exposure were found on neither the shape nor the magnitude of the modeled dose-response curves for either birch allergen, p = 0.77, or grass allergen, p = 0.45. The model depicted a good fit for the data. Among the baseline characteristics, only the size of the skin prick test for grass allergen was associated with PD₂₀.

Conclusion: This study does not support a priming effect of pollen exposure on the bronchial response from the natural seasonal exposure levels of grass or birch allergens among young adults with allergic rhinitis.

Organic and aqueous extraction of lipids from birch pollen grains exposed to gaseous pollutants

The lipid fraction of birch pollen grains (BPGs) is not yet fully described, although pollen lipid molecules may play a role in the allergic immune response. The mechanisms by which atmospheric pollutants modify allergenic pollen grains (PGs) are also far from being elucidated despite high potential effects on allergic sensitization. This work is a contribution to a better description of the lipid profile (both external and cytoplasmic) of BPGs and of alterations induced by gaseous air pollutants. Several lipid extractions were performed using organic and aqueous solvents on BPGs following exposure to ozone and/or nitrogen dioxide and under conditions favoring the release of internal lipids. Ozone reacted with alkenes to produce aldehydes and saturated fatty acids, while nitrogen dioxide was shown to be unreactive with lipids. NO₂ exhibited a protective effect against the reactivity of alkenes with ozone, probably by competition for adsorption sites. The decreased reactivity of ozone during simultaneous exposure to NO₂/O₃ raised the possibility of a Langmuir-Hinshelwood mechanism. Oxidation reactions induced by exposure of BPGs to ozone did not substantially modify the extraction of lipids by aqueous solvent, suggesting that the bioaccessibility of lipids was not modified by oxidation. On the contrary, the rupture of PGs appeared to be a key factor in enhancing the bioaccessibility of bioactive lipid mediators (linoleic and α-linolenic acids) in an aqueous solution. The internal lipid fraction of BPGs has specific characteristics compared with external lipids, with more abundant hexadecanoic acid, tricosanol, and particularly unsaturated fatty acids (linoleic and α-linolenic acids). Several mechanisms of action of gaseous pollutants on allergenic pollen were identified in this study: gaseous air pollutants can (i) modify the external lipid fraction by reactivity of alkenes, (ii) adsorb on the surface of PGs and be a source of oxidative stress after inhalation of PGs, and (iii) promote the release of cytoplasmic bioactive lipids by facilitating pollen rupture.

Numerical modelling of birch pollen dispersion in Canada

Simulating allergenic tree pollen is important to protect sensitive population and to support bioaerosols monitoring effort. Using the regional air quality model GEM-MACH, a simulation was conducted adopting two new main hypotheses: 1) the use of vertical correlation concept to force the vertical dispersion (a method normally used in tracer data assimilation) and, 2) the use of a puff instead of a continuous pollen release. The simulation was compared with pollen observations in Montreal and with the corresponding statistical forecasts (issued daily by the Weather Network) at several locations in the province of Quebec and elsewhere. The comparison with the simulation was found satisfactory (outperform forecasts based on persistence or pollen calendar and is also superior to numerical simulation of tree pollen done elsewhere in North America). Simulation shows that, for the 2012 pollen season, the majority (88%) of the Betula pollen measured in Montreal originated from the Laurentides region. Another result of scientific importance obtained here is that Betula pollen episodes (observed or simulated birch pollen) in Montreal occur only when the average daily temperature is in the range of 10° to 18 °C. This research is considered as a first step in forecasting bioaerosols in Canada within an air quality model.

A First Pre-season Pollen Transport Climatology to Bavaria, Germany

Climate impacts on the pollen season are well-described however less is known on how frequently atmospheric transport influences the start of the pollen season. Based on long-term phenological flowering and airborne pollen data (1987–2017) for six stations and seven taxa across Bavaria, Germany, we studied changes in the pollen season, compared pollen and flowering season start dates to determine pollen sources, and analyzed the likelihood of pollen transport by HYSPLIT back trajectories. Species advanced their pollen season more in early spring (e.g., Corylus and Alnus by up to 2 days yr⁻¹) than in mid spring (Betula, Fraxinus, Pinus); Poaceae and Artemisia exhibited mixed trends in summer. Annual pollen sums mainly increased for Corylus and decreased for Poaceae and Artemisia. Start of pollen season trends largely deviated from flowering trends, especially for Corylus and Alnus. Transport phenomena, which rely on comparisons between flowering and pollen dates, were determined for 2005–2015 at three stations. Pre-season pollen was a common phenomenon: airborne pollen was predominantly observed earlier than flowering (median 17 days) and in general, in 63% of the cases (except for Artemisia and Poaceae, and the alpine location) the pollen sources were non-local (transported). In 54% (35%) of these cases, back trajectories confirmed (partly confirmed) the pre-season transport, only in 11% of the cases transport modeling failed to explain the records. Even within the main pollen season, 70% of pollen season start dates were linked to transport. At the alpine station, non-local pollen sources (both from outside Bavaria as well as Bavarian lowlands) predominated, in only 13% of these cases transport could not be confirmed by back trajectories. This prominent role of pollen transport has important implications for the length, the timing, and the severity of the allergenic pollen season, indicating only a weak dependency on flowering of local pollen sources.

Modelling grass pollen levels in Belgium

Biogenic aerosols such as airborne grass pollen affect the public health badly by putting additional distress on people already suffering from cardiovascular and respiratory diseases. In Belgium, daily airborne pollen concentrations are monitored offline at a few sites only, hampering the timely coverage of the country and short-term forecasts. Here we apply the Chemistry Transport Model SILAM to the Belgian territory to model the spatio-temporal airborne grass pollen levels near the surface based on bottom-up inventories of grass pollen emissions updated with the Copernicus land monitoring Service grassland map of 2015. Transport of aerosols in SILAM is driven by ECMWF ERA5 meteorological data. The emitted grass pollen amounts in SILAM are computed by the multiplication of the grass pollen source map with the release rate determined by the seasonal shape production curve during the grass flowering period. The onset and offset of this period follow a location-dependent prescribed calendar days. Here we optimize the grass pollen seasonal start and end in SILAM by comparing a 2008-2018 time series of daily airborne grass pollen concentrations from the Belgian aerobiological surveillance network with the simulations. The effect of the spatial distribution of grass pollen sources is quantified by constructing pollen source-receptor relations using model simulations with varying grass pollen emissions in five areas of the model domain as input. Up to 33% of the airborne grass pollen in one area was transport from others areas inside Belgium. Adjusting the start and end of the grass pollen season improved the model performance substantially by almost doubling the correlation with local observations. By introducing the temporal scaling of the inter-seasonal pollen amounts in the model, an additional R² increase up to 22% was obtained. Further improvements can be made by including more detailed grass pollen sources and more dynamic start and end dates of the pollen season.

Allergy to oak pollen in North America

Background: Oak pollen is an important allergen in North America. The genus Quercus (oak) belongs to the family Fagaceae under the order Fagales. Objective: The objective of this article was to narratively review the oak pollen season, clinical and epidemiologic aspects of allergy to oak pollen, oak taxonomy, and oak allergen cross-reactivity, with a focus on the North American perspective. Methods: A PubMed literature review (no limits) was conducted. Publications related to oak pollen, oak-related allergic rhinitis with or without conjunctivitis, and oak-related allergic asthma were selected for review. Results: Oak species are common throughout the United States and contribute up to 50% to overall atmospheric pollen loads. Mean peak oak pollen counts can reach >2000 grains/m³. The start of the oak pollen season generally corresponds to the seasonal shift from winter to spring based on latitude and elevation, and may begin as early as mid February. The duration of the season can last > 100 days and, in general, is longer at lower latitudes. In the United States, ∼30% of individuals with allergy are sensitized to oak. The oak pollen season correlates with increased allergic rhinitis symptom-relieving medication use and asthma-related emergency department visits or hospitalizations. Oak falls within the birch homologous group. Extensive immunologic cross-reactivity has been demonstrated between oak pollen and birch pollen allergens, and, more specifically, their major allergens Que a 1 and Bet v 1. The cross-reactivity between oak and birch has implications for allergy immunotherapy (AIT) because guidelines suggest selecting one representative allergen within a homologous group for AIT, a principle that would apply to oak. Conclusion: Allergy to oak pollen is common in North America and has a substantial clinical impact. Oak pollen allergens are cross-reactive with birch pollen allergens, which may have implications for AIT.

The Impact of Climate Change on Pollen Season and Allergic Sensitization to Pollens

Pollens are a major cause of seasonal allergic diseases. Weather may alter the production of pollens. Increased atmospheric temperatures lead to earlier pollination of many plants and longer duration of pollination, resulting in extended pollen seasons, with early spring or late winter. Longer pollen seasons increase duration of exposure, resulting in more sensitization, and higher pollen concentrations may lead to more severe symptoms. Climate changes in contact to pollens may affect both allergic sensitization and symptom prevalence with severity. The future consequences of climate change, however, are speculative, because the influence on humans, is complex.

High Ambrosia pollen concentrations in Poland respecting the long distance transport (LDT)

High Ambrosia pollen concentrations in Poland rather rarely come from the local sources. The aim of this study was to define the temporal and spatial differences of the high Ambrosia pollen concentrations by creating models for the pollen transport from the distant sources. This study was thought to determine the direction of the air masses inflow into Poland, carrying Ambrosia pollen, from areas of the bordering countries with the pollen concentrations higher than iSTOTEN_n Poland. Pollen and meteorological datasets at 8 monitoring sites in Poland, and daily pollen concentrations at 11 sites in the Czech Republic, 5 sites in Slovakia and 3 sites in Ukraine were analysed recently. Days with concentrations ≥10 Pollen/m³ and concurrent meteorological situations were analysed in great deal. The HYSPLIT model was applied to compute backward trajectories up to 4 days backward (96 h) and at three altitudes: 20, 500 and 1000 m above ground level (a.g.l.). High pollen concentrations occur most frequently when the air masses inflow into Poland from southerly (S, SE, SW, 44%) and easterly (E, 6%) directions and in no advection situations (25%). In years with the highest frequency of days over 10 Pollen/m³, the prevailing directions of the pollen influx into Poland were from the South (2004-2006, 2008, 2011) but in one year (2014) from the East. Trajectories for the studied period show that air masses come most frequently from Slovakia and the Czech Republic. Sometimes, the Ambrosia pollen transport happens from Ukraine.

Is allergy immunotherapy with birch sufficient to treat patients allergic to pollen of tree species of the birch homologous group?

Pollen from various Fagales tree species prolongs the season and makes tree pollen allergy a major health problem. Despite involving the same causative allergens, allergy immunotherapy (AIT) treatment habits differ significantly across different geographical regions. Diagnosis and treatment with AIT in patients allergic to tree pollen were discussed by a group of German medical experts who give practical recommendations based on the available data. Regulatory perspective: According to current guidelines on allergen products, birch pollen are the representative allergen source of the birch homologous group including several Fagales trees based on sequence and structural similarity of their allergen proteins. Immunological perspective: A high level of IgE cross-reactivity towards allergens from the birch homologous group has been observed in basic research and clinical trials. Clinical perspective: Clinical trial data show that the efficacy of birch pollen AIT is not only related to birch pollen allergy but extends to pollen from other trees, especially alder, hazel and oak. In order to optimize diagnosis and treatment of tree pollen allergy, the experts recommend to focus diagnosis and respective treatment with AIT primarily to birch as the representative allergen of the Fagales tree homologous group, but further diagnostics may be needed for some patients to determine adequate treatment.

Potential of Birch (Betula pendula Roth and B. pubescens Ehrh.) for Forestry and Forest-Based Industry Sector within the Changing Climatic and Socio-Economic Context of Western Europe

Five commercial tree species comprise nearly 80% of the forest standing stock volume in Western Europe. Nowadays, there is a strong need to consider a wider diversity of tree species, as evidenced by the impact of climate change and the forest health crises over the past decades. In this context, this study focuses on the potential of birch (Betula pendula Roth and Betula pubescens Ehrh.), a neglected indigenous species, for forestry and the forest-based industry sector. We have therefore compiled, analyzed, and discussed literature regarding the strengths and weaknesses of the species and the opportunities and threats of its use for this purpose. Among the strengths, birch tolerates various climates and sites, and high genetic variability promotes its adaptability. Birch improves forest resilience by colonizing forest gaps and quickly increasing soil functioning and biodiversity. Birch is also remarkably resistant to game overpopulation-associated damage. Large-sized logs are produced within relatively short periods with proper silvicultural treatment, and the wood characteristics allow versatile and valuable uses, as shown in Northern Europe. However, its weaknesses include high sensitivity to crown competition and to wood rot as challenges for silviculture. Among the opportunities, birch is well-suited to the global changes with its adaptability to climate change and its possible integration in diverse productive mixed tree stands. In the context of societal evolutions and customer perceptions, birch wood could play an increasing role in the building and furniture sectors, and among non-wood forest products. In Western Europe, the main obstacle to birch development is the lack of information on the wood uses and, consequently, the lack of interest among forest managers and wood processing professionals, which have led to a poor quality of the resource and to insufficient demand for its wood. Moreover, its fast height growth can affect the vitality of other species in mixed stands. Our analysis highlighted the potential of birch in the Western European forestry considering societal, ecological, and economic purposes in a changing climatic and socio-economic context and the need to (i) develop opportunities for industrial uses of birch wood, (ii) inform forest owners, managers, and industrial professionals about the potential value of birch, and (iii) define silvicultural guidelines.

Forecasting the seasonal pollen index by using a hidden Markov model combining meteorological and biological factors

The seasonal pollen index (SPI) is a continuing concern within the fields of aerobiology, ecology, botany, and epidemiology. The SPI of anemophilous trees, which varies substantially from year to year, reflects the flowering intensity. This intensity is regulated by two factors: weather conditions during flower formation and the inner resource for assimilation. A deterministic approach has to date been employed for predicting SPI, in which the forecast is made entirely by parameters. However, given the complexity of the masting mechanism (which has intrinsic stochastic properties), few attempts have been made to apply a stochastic model that considers the inter-annual SPI variation as a stochastic process. We propose a hidden Markov model that can integrate the stochastic process of mast flowering and the meteorological conditions influencing flower formation to predict the annual birch pollen concentration. In experiments conducted, the model was trained and validated by using data in Hokkaido, Japan covering 22 years. In the model, the hidden Markov sequence was assigned to represent the recurrence of mast years via a transition matrix, and the observation sequences were designated as meteorological conditions in the previous summer, which are governed by hidden states with emission distribution. The proposed model achieved accuracies of 83.3% in the training period and 75.0% in the test period. Thus, the proposed model can provide an alternative perspective toward the SPI forecast and probabilistic information of pollen levels as a useful reference for allergy stakeholders.

Lidar-Derived Tree Crown Parameters: Are They New Variables Explaining Local Birch (Betula sp.) Pollen Concentrations?

Birch trees are abundant in central and northern Europe and are dominant trees in broadleaved forests. Birches are pioneer trees that produce large quantities of allergenic pollen efficiently dispersed by wind. The pollen load level depends on the sizes and locations of pollen sources, which are important for pollen forecasting models; however, very limited work has been done on this topic in comparison to research on anthropogenic air pollutants. Therefore, we used highly accurate aerial laser scanning (Light Detection and Ranging—LiDAR) data to estimate the size and location of birch pollen sources in 3-dimensional space and to determine their influence on the pollen concentration in Poznań, Poland. LiDAR data were acquired in May 2012. LiDAR point clouds were clipped to birch individuals (mapped in 2012–2014 and in 2019), normalised, filtered, and individual tree crowns higher than 5 m were delineated. Then, the crown surface and volume were calculated and aggregated according to wind direction up to 2 km from the pollen trap. Consistent with LIDAR data, hourly airborne pollen measurements (performed using a Hirst-type, 7-day volumetric trap), wind speed and direction data were obtained in April 2012. We delineated 18,740 birch trees, with an average density of 14.9/0.01 km2, in the study area. The total birch crown surface in the 500–1500 m buffer from the pollen trap was significantly correlated with the pollen concentration aggregated by the wind direction (r = 0.728, p = 0.04). The individual tree crown delineation performed well (r2 ≥ 0.89), but overestimations were observed at high birch densities (> 30 trees/plot). We showed that trees outside forests substantially contribute to the total pollen pool. We suggest that including the vertical dimension and the trees outside the forest in pollen source maps have the potential to improve the quality of pollen forecasting models.

Influence of a Municipal Solid Waste Landfill on the Surrounding Environment: Landfill Vegetation as a Potential Risk of Allergenic Pollen

When the landfill use comes to end, important subsequent steps include aftercare, safety assurance, and ecological regeneration. Landfill revegetation is cost-effective and eco-friendly approach in the management of landfill areas, which serves the purpose of stabilization and provides a pleasant landscape. There are various vegetation types that can be planted, yet grass species are often used for low-cost reasons. Plants can be important sources of air pollution, particularly by grass pollen. The main goal of our study was to identify plant species that produce allergenic pollen. Long-term vegetation monitoring took place on three sites in the growing seasons of years 2008–2018. Studied objects were landfills located in the Czech Republic. The vegetation was assessed using a floristic survey of identified plant species. Plant species that produced allergens were recorded. During the monitoring, 298 plant species were determined. Plant species with allergenic pollen have a considerable share in the landfill vegetation. Thus, landfills are potential sources of various kinds of allergenic pollen. Moreover, our results indicated that there are three periods of pollen production: early spring, late spring, and early summer; late summer; and autumn. The second period is typical for the production of highly allergenic pollen by grasses. Most detected plant species with allergenic pollen are common for all monitored sites, which demonstrates that the vegetation of landfills is a significant source of allergenic pollen.

Predicting the start, peak and end of the Betula pollen season in Bavaria, Germany

Betula pollen is frequently found in the atmosphere of central and northern Europe. Betula pollen are health relevant as they cause severe allergic reactions in the population. We developed models of thermal requirements to predict start, peak and end dates of the Betula main pollen season for Bavaria (Germany). Betula pollen data of one season from 19 locations were used to train the models. Estimated dates were compared with observed dates, and the errors were spatially represented. External validation was carried out with time series datasets of 3 different locations (36years in total). RESULTS: The temperature requirements to detonate the main pollen season proved non-linear. For the start date model (error of 8,75days during external validation), daily mean temperatures above a threshold of 10°C from 28th of February onwards were the most relevant. The peak model (error of 3.58days) takes into account mean daily temperatures accumulated since the first date of the main pollen season in which the daily average temperature exceeded 11°C. The end model (error of 3.75days) takes into account all temperatures accumulated since the start of the main pollen season. CONCLUSION: These models perform predictions that enable the allergic population to better manage their disease. With the established relationship between temperatures and pollen season dates, changes in the phenological behaviour of Betula species due to climate change can be also estimated in future studies by taking into account the different climate scenarios proposed by previous climate change studies.

Detecting distant sources of airborne pollen for Poland: Integrating back-trajectory and dispersion modelling with a satellite-based phenology

Airborne pollen might be transported over thousands of kilometres, which has important ecological, evolutionary and clinical consequences. The long-distance transport (LDT) of birch (Betula sp.) pollen has been described in detail for northern Europe. However, a comprehensive analysis of this transport from other European regions is lacking. This study focused on the post-seasonal LDT of birch pollen to Poland (central Europe), with special attention paid to determining potential source areas of pollen and describing the causal mechanism favouring LDT episodes. Pollen monitoring (1997-2016) was conducted in Poznań and Rzeszów (500 km away from each other) using volumetric traps. The LDT episodes were characterized by analysing the (1) bi-hourly backward air mass trajectories using the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT); (2) sea level pressure (SLP) and 500 hPa geopotential height (z500) anomalies; and (3) patterns of the Enhanced Vegetation Index to determine the birch flowering time along the moving air mass trajectories. The potential locations of birch populations within broadleaved forests were estimated with GLOBCOVER data. Finally, the movement of pollen emitted from potential source areas was simulated using the HYSPLIT dispersion model. LDT episodes were mainly recorded in the first fortnight of May. The main source areas of pollen to Poland were western Russia, Belarus and to a lesser extent the eastern Baltic republics and the Scandinavian Peninsula. In most cases, a high-pressure centre located over Scandinavia and an elevated z500 over Germany-Denmark-Sweden favoured pollen transport. On average, the post-seasonal LDT episodes of birch pollen to Poland occur almost every year (Poznań) or every second year (Rzeszów). The episodes are highly variable in time; thus, the pollen concentration may unexpectedly cause allergy symptoms in sensitized patients. In some cases, these episodes may be extremely severe, thereby prolonging and strengthening the exposure to birch pollen allergens.

Population structure of Betula albosinensis and Betula platyphylla: evidence for hybridization and a cryptic lineage

BACKGROUND AND AIMS

Differences in local abundance and ploidy level are predicted to impact the direction of introgression between species. Here, we tested these hypotheses on populations of Betula albosinensis (red birch) and Betula platyphylla (white birch) which were thought to differ in ploidy level, the former being tetraploid and the latter diploid.

METHODS

We sampled 391 birch individuals from nine localities in China, and classified them into species based on leaf morphology. Twelve nuclear microsatellite markers were genotyped in each sample, and analysed using principal coordinates analysis and STRUCTURE software. We compared the effects of two different methods of scoring polyploid genotypes on population genetic analyses. We analysed the effect of ploidy, local species abundance and latitude on levels of introgression between the species.

KEY RESULTS

Leaf morphology divided our samples into red and white birch, but genetic analyses unexpectedly revealed two groups within red birch, one of which was tetraploid, as expected, but the other of which appeared to have diploid microsatellite genotypes. Five individuals were identified as early-generation hybrids or backcrosses between white birch and red birch and five were identified between red birch and 'diploid' red birch. Cline analysis showed that levels of admixture were not significantly correlated with latitude. Estimated genetic differentiation among species was not significantly different between determined tetraploid and undetermined tetraploid genotypes.

CONCLUSIONS

Limited hybridization and gene flow have occurred between red birch and white birch. Relative species abundance and ploidy level do not impact the direction of introgression between them, as genetic admixture is roughly symmetrical. We unexpectedly found populations of apparently diploid red birch and this taxon may be a progenitor of allotetraploid red birch populations. Incomplete lineage sorting may explain patterns of genetic admixture between apparently diploid and allotetraploid red birch.

Oak pollen seasonality and severity across Europe and modelling the season start using a generalized phenological model

Oak pollen seasons are relatively unexplored in large parts of Europe despite producing allergens and being a common tree in both continental and northern parts. Many studies are concentrated only on the Iberian Peninsula. In this study, the seasonal pattern of oak pollen in Europe was analysed using 10 observation sites, ranging from Spain to Sweden. The magnitude of peaks and annual pollen integral together with season-length were studied and substantially higher pollen levels and longer seasons were found in Spain. Two northern sites in Denmark and Sweden showed high oak pollen peaks together with two sites in Spain and United Kingdom. The study also tested four common definitions of season start and applied a generalized phenological model for computing the start of the pollen season. The most accurate definition for a European-wide description of the observed oak pollen start was when the cumulative daily average pollen count reached 50 grains per cubic meter. For the modelling of the start a thermal time method based on Growing Degree Day (GDD) was implemented, utilizing daily temperatures and a generalized approach to identify model parameters applicable to all included sites. GDD values varied between sites and generally followed a decreasing gradient from south to north, with some exceptions. Modelled onsets with base temperatures below 7 °C matched well with observed onsets and 76% of the predictions differed ≤4 days compared to observed onsets when using a base temperature of 2 °C. Base temperatures above 7 °C frequently predicted onsets differing >1 week from the observed. This general approach can be extended to a larger area where pollen observations are non-existent. The presented work will increase the understanding of oak pollen variation in Europe and provide knowledge of its phenology, which is a critical aspect both for modelling purposes on large-scale and assessing the human exposure to oak allergens.

Transport pathway and source area for Artemisia pollen in Beijing, China

Artemisia pollen is an important allergen responsible for allergic rhinitis in Beijing, China. To explore the transport pathways and source areas of Artemisia pollen, we used Burkard 7-day traps to monitor daily pollen concentrations in 2016 in an urban and suburban locality. Backward trajectories of 24- and 96-h and their cluster analysis were performed to identify transport pathways of Artemisia pollen using the HYSPLIT model on 0.5° × 0.5° GADS meteorological data. The potential source contribution function (PSCF) and concentration weighted trajectory (CWT) were calculated to further identify the major potential source areas at local, regional, and long-range scales. Our results showed significant differences in Artemisia pollen concentration between urban and suburban areas, attributed to differences in plant distribution and altitude of the sampling locality. Such differences arisen from both pollen emission and air mass movements, hence pollen dispersal. At local or regional scales, source area of northwestern parts of Beijing City, Hebei Province and northern and northwestern parts of Inner Mongolia influenced the major transport pathways of Artemisia pollen. Transport pathway at a long-range scale and its corresponding source area extended to northwestern parts of Mongolia. The regional-scale transport affected by wind and altitude is more profound for Artemisia pollen at the suburban than at the urban station.

Mapping allergenic pollen vegetation in UK to study environmental exposure and human health

Allergenic pollen is produced by the flowers of a number of trees, grasses and weeds found throughout the UK. Exposure to such pollen grains can exacerbate pollen-related asthma and allergenic conditions such as allergic rhinitis (hay fever). Maps showing the location of these allergenic taxa have many applications: they can be used to provide advice on risk assessments; combined with health data to inform research on health impacts such as respiratory hospital admissions; combined with weather data to improve pollen forecasting systems; or as inputs to pollen emission models. In this study we present 1km resolution maps of 12 taxa of trees, grass and weeds found in the UK. We have selected the main species recorded by the UK pollen network. The taxa mapped in this study were: Alnus (alder), Fraxinus (ash), Betula (birch), Corylus (hazel), Quercus (oak), Pinus (pine) and Salix (willow), Poaceae (grass), Artemisia (mugwort), Plantago (plantain), Rumex (dock, sorrels) and Urtica (nettle). We also focus on one high population centre and present maps showing local level detail around the city of London. Our results show the different geographical distributions of the 12 taxa of trees, weeds and grass, which can be used to study plants in the UK associated with allergy and allergic asthma. These maps have been produced in order to study environmental exposure and human health, although there are many possible applications. This novel method not only provides maps of many different plant types, but also at high resolution across regions of the UK, and we uniquely present 12 key plant taxa using a consistent methodology. To consider the impact on human health due to exposure of the pollen grains, it is important to consider the timing of pollen release, and its dispersal, as well as the effect on air quality, which is also discussed here.

Pollen exposure and hospitalization due to asthma exacerbations: daily time series in a European city

Exposure to pollen can contribute to increased hospital admissions for asthma exacerbation. This study applied an ecological time series analysis to examine associations between atmospheric concentrations of different pollen types and the risk of hospitalization for asthma in London from 2005 to 2011. The analysis examined short-term associations between daily pollen counts and hospital admissions in the presence of seasonal and long-term patterns, and allowed for time lags between exposure and admission. Models were adjusted for temperature, precipitation, humidity, day of week, and air pollutants. Analyses revealed an association between daily counts (continuous) of grass pollen and adult hospital admissions for asthma in London, with a 4-5-day lag. When grass pollen concentrations were categorized into Met Office pollen 'alert' levels, 'very high' days (vs. 'low') were associated with increased admissions 2-5 days later, peaking at an incidence rate ratio of 1.46 (95%, CI 1.20-1.78) at 3 days. Increased admissions were also associated with 'high' versus 'low' pollen days at a 3-day lag. Results from tree pollen models were inconclusive and likely to have been affected by the shorter pollen seasons and consequent limited number of observation days with higher tree pollen concentrations. Future reductions in asthma hospitalizations may be achieved by better understanding of environmental risks, informing improved alert systems and supporting patients to take preventive measures.

Relationships between airborne pollen grains, wind direction and land cover using GIS and circular statistics

Airborne bio-aerosol content (mainly pollen and spores) depends on the surrounding vegetation and weather conditions, particularly wind direction. In order to understand this issue, maps of the main land cover in influence areas of 10km in radius surrounding pollen traps were created. Atmospheric content of the most abundant 14 pollen types was analysed in relation to the predominant wind directions measured in three localities of SW of Iberian Peninsula, from March 2011 to March 2014. Three Hirst type traps were used for aerobiological monitoring. The surface area for each land cover category was calculated and wind direction analysis was approached by using circular statistics. This method could be helpful for estimating the potential risk of exposure to various pollen types. Thus, the main land cover was different for each monitoring location, being irrigated crops, pastures and hardwood forests the main categories among 11 types described. Comparison of the pollen content with the predominant winds and land cover shows that the atmospheric pollen concentration is related to some source areas identified in the inventory. The study found that some pollen types (e.g. Plantago, Fraxinus-Phillyrea, Alnus) come from local sources but other pollen types (e.g. Quercus) are mostly coming from longer distances. As main conclusions, airborne particle concentrations can be effectively split by addressing wind with circular statistics. By combining circular statistics and GIS method with aerobiological data, we have created a useful tool for understanding pollen origin. Some pollen loads can be explained by immediate surrounding landscape and observed wind patterns for most of the time. However, other factors like medium or long-distance transport or even pollen trap location within a city, may occasionally affect the pollen load recorded using an air sampler.

Co-occurrence of Artemisia and Ambrosia pollen seasons against the background of the synoptic situations in Poland

The Asteraceae family is one of the largest families, comprising 67 genera and 264 species in Poland. However, only a few genera, including Artemisia and Ambrosia are potential allergenic sources. The aim of the study was to estimate how often and to what degree Artemisia and Ambrosia pollen seasons co-occur intensifying human health risk, and how synoptic situations influence frequency of days with high pollen concentrations of both taxa. Artemisia and Ambrosia pollen data were collected, using the volumetric method, at 8 sites in Poland. Daily concentrations of Artemisia pollen equal to 30 grains or more and Ambrosia pollen equal to 10 grains or more were accepted as high values. Concentrations of more than 10 pollen grains were defined as high in the case of Ambrosia because its allergenicity is considered higher. High concentrations were confronted with synoptic situations. Analysis was performed on the basis of two calendars on circulation types of atmosphere in Poland (Niedźwiedź, 2006, 2015). Co-occurrence of Artemisia and Ambrosia pollen seasons is being found most often, when Ambrosia pollen season starts in the first half of August. If it happens in the last 10 days of August high pollen concentrations of Artemisia and Ambrosia do not occur at the same days. At three sites (Sosnowiec, Rzeszów, Lublin) high Ambrosia pollen concentrations during the Artemisia pollen season appear more often than in other sites under question. The high Artemisia pollen concentrations occur, when continental or polar maritime old air masses inflow into Poland. The impact of air masses on high Ambrosia pollen concentrations depends on site localizations. It is likely, that in the south-eastern part of Poland high Ambrosia pollen concentrations result from the pollen transport from east-south-south-westerly directions and the local sources. Co-occurrence of both taxa pollen seasons depends on the air masses inflow and appears more often in a south-eastern part of Poland.

Estimating the abundance of airborne pollen and fungal spores at variable elevations using an aircraft: how high can they fly?

Airborne pollen and fungal spores are monitored mainly in highly populated, urban environments, for allergy prevention purposes. However, their sources can frequently be located outside cities' fringes with more vegetation. So as to shed light to this paradox, we investigated the diversity and abundance of airborne pollen and fungal spores at various environmental regimes. We monitored pollen and spores using an aircraft and a car, at elevations from sea level to 2,000 m above ground, in the region of Thesssaloniki, Greece. We found a total of 24 pollen types and more than 15 spore types. Pollen and spores were detected throughout the elevational transect. Lower elevations exhibited higher pollen concentrations in only half of plant taxa and higher fungal spore concentrations in only Ustilago. Pinaceae and Quercus pollen were the most abundant recorded by airplane (>54% of the total). Poaceae pollen were the most abundant via car measurements (>77% of the total). Cladosporium and Alternaria spores were the most abundant in all cases (aircraft: >69% and >17%, car: >45% and >27%, respectively). We conclude that pollen and fungal spores can be diverse and abundant even outside the main source area, evidently because of long-distance transport incidents.

Source regions of ragweed pollen arriving in south-western Poland and the influence of meteorological data on the HYSPLIT model results

We have investigated the relationship between the inflow of air masses and the ragweed pollen concentration in SW Poland (Wrocław) for a 10-year period of 2005-2014. The HYSPLIT trajectory model was used to verify whether episodes of high concentrations can be related to regions outside of the main known ragweed centres in Europe, like Pannonian Plain, northern Italy and Ukraine. Furthermore, we used two different meteorological data sets (the global GDAS data set and from the WRF mesoscale model; the meteorological parameters were: U and V wind components, temperature and relative humidity) into HYSPLIT to evaluate the influence of meteorological input on calculated trajectories for high concentration ragweed episodes. The results show that the episodes of high pollen concentration (above 20 pm^-3) represent a great part of total recorded ragweed pollen in Wrocław, but occur rarely and not in all years. High pollen episodes are connected with air masses coming from south and south-west Europe, which confirms the existence of expected ragweed centres but showed that other centres near Wrocław are not present. The HYSPLIT simulations with two different meteorological inputs indicated that footprint studies on ragweed benefit from a higher resolution meteorological data sets.

Are the Pyrenees a barrier for the transport of birch (Betula) pollen from Central Europe to the Iberian Peninsula?

This work provides a first assessment of the possible barrier effect of the Pyrenees on the atmospheric transport of airborne pollen from Europe to the North of the Iberian Peninsula. Aerobiological data recorded in three Spanish stations located at the eastern, central and western base of the Pyrenees in the period 2004-2014 have been used to identify the possible long range transport episodes of Betula pollen. The atmospheric transport routes and the origin regions have been established by means of trajectory analysis and a source receptor model. Betula pollen outbreaks were associated with the meteorological scenario characterized by the presence of a high-pressure system overm over Morocco and Southern Iberian Peninsula. France and Central Europe have been identified as the probable source areas of Betula pollen that arrives to Northern Spain. However, the specific source areas are mainly determined by the particular prevailing atmospheric circulation of each location. Finally, the Weather Research and Forecasting model highlighted the effect of the orography on the atmospheric transport patterns, showing paths through the western and easternmost lowlands for Vitoria-Gasteiz and Bellaterra respectively, and the direct impact of air flows over Vielha through the Garona valley.

The relationship between birch pollen, air pollution and weather types and their effect on antihistamine purchase in two Swedish cities

Exposure to elevated air pollution levels can aggravate pollen allergy symptoms. The aim of this study was to investigate the relationships between airborne birch (Betula) pollen, urban air pollutants NO₂, O₃ and PM₁₀ and their effects on antihistamine demand in Gothenburg and Malmö, Sweden, 2006-2012. Further, the influence of large-scale weather pattern on pollen-/pollution-related risk, using Lamb weather types (LWTs), was analysed. Daily LWTs were obtained by comparing the atmospheric pressure over a 16-point grid system over southern Sweden (scale ~3000 km). They include two non-directional types, cyclonic (C) and anticyclonic (A) and eight directional types depending on the wind direction (N, NE, E…). Birch pollen levels were exceptionally high under LWTs E and SE in both cities. Furthermore, LWTs with dry and moderately calm meteorological character (A, NE, E, SE) were associated with strongly elevated air pollution (NO₂ and PM₁₀) in Gothenburg. For most weather situations in both cities, simultaneously high birch pollen together with high air pollution had larger over-the-counter (OTC) sales of antihistamines than situations with high birch pollen alone. LWTs NE, E, SE and S had the highest OTC sales in both cities. In Gothenburg, the city with a higher load of both birch pollen and air pollution, the higher OTC sales were especially obvious and indicate an increased effect on allergic symptoms from air pollution. Furthermore, Gothenburg LWTs A, NE, E and SE were associated with high pollen and air pollution levels and thus classified as high-risk weather types. In Malmö, corresponding high-risk LWTs were NE, E, SE and S. Furthermore, occurrence of high pollen and air pollutants as well as OTC sales correlated strongly with vapour pressure deficit and temperature in Gothenburg (much less so in Malmö). This provides evidence that the combination of meteorological properties associated with LWTs can explain high levels of birch pollen and air pollution. Our study shows that LWTs represent a useful tool for integrated daily air quality forecasting/warning.

The long-range transport of Pinaceae pollen: an example in Kraków (southern Poland)

High Pinaceae pollen concentrations in the air and on the surface of puddles before the main pollen season started were observed in Kraków (southern Poland) in May 2013. The paper presents the results of detailed studies of the composition and source of the "yellow rain" in 2013, and as a comparison, the Pinaceae pollen concentrations and samples collected from the ground surface in 2014 were considered. The air samples were collected using the volumetric method (Hirst-type device), while pollen grains sampled from the ground surface were processed using a modified Erdtman acetolysis method. Finally, all samples were studied using a light microscope. In 2013, the period of higher Abies, Picea and Pinus pollen concentrations was observed from the 5 to 12 of May, earlier than the main pollen season occurred. The presence of rainfall on the 12 and 13 of May 2013 caused the pollen deposition on the ground surface, where the prevalence of Pinaceae pollen was found. The synoptic situation and the analysis of the back-trajectories and air mass advection at the beginning of May 2013 indicated that Pinaceae pollen grains could have been transported from Ukraine, Romania, Hungary and Slovakia. In contrast, Pinaceae pollen grains deposited on the ground surface as a "yellow" film in May 2014, originated from local sources.

Airborne Microalgae: Insights, Opportunities, and Challenges

Airborne dispersal of microalgae has largely been a blind spot in environmental biological studies because of their low concentration in the atmosphere and the technical limitations in investigating microalgae from air samples. Recent studies show that airborne microalgae can survive air transportation and interact with the environment, possibly influencing their deposition rates. This minireview presents a summary of these studies and traces the possible route, step by step, from established ecosystems to new habitats through air transportation over a variety of geographic scales. Emission, transportation, deposition, and adaptation to atmospheric stress are discussed, as well as the consequences of their dispersal on health and the environment and state-of-the-art techniques to detect and model airborne microalga dispersal. More-detailed studies on the microalga atmospheric cycle, including, for instance, ice nucleation activity and transport simulations, are crucial for improving our understanding of microalga ecology, identifying microalga interactions with the environment, and preventing unwanted contamination events or invasions.

Potential sources of airborne Alternaria spp. spores in South-west Spain

Fungi belonging to the genus of Alternaria are recognised as being significant plant pathogens, and Alternaria allergens are one of the most important causes of respiratory allergic diseases in Europe. This study aims to provide a detailed and original analysis of Alternaria transport dynamics in Badajoz, SW Spain. This was achieved by examining daily mean and hourly observations of airborne Alternaria spores recorded during days with high airborne concentrations of Alternaria spores (>100 s m(-3)) from 2009 to 2011, as well as four inventory maps of major Alternaria habitats, the overall synoptic weather situation and analysis of air mass transport using Hybrid Single Particle Lagrangian Integrated Trajectory model and geographic information systems. Land use calculated within a radius of 100 km from Badajoz shows that crops and grasslands are potentially the most important local sources of airborne Alternaria spores recorded at the site. The results of back trajectory analysis show that, during the examined four episodes, the two main directions where Alternaria source areas were located were: (1) SW-W; and (2) NW-NE. Regional scale and long distance transport could therefore supplement the airborne catch recorded at Badajoz with Alternaria conidia originating from sources such as crops and orchards situated in other parts of the Iberian Peninsula.

Tree pollen allergens-an update from a molecular perspective

It is estimated that pollen allergies affect approximately 40% of allergic individuals. In general, tree pollen allergies are mainly elicited by allergenic trees belonging to the orders Fagales, Lamiales, Proteales, and Pinales. Over 25 years ago, the gene encoding the major birch pollen allergen Bet v 1 was the first such gene to be cloned and its product characterized. Since that time, 53 tree pollen allergens have been identified and acknowledged by the WHO/IUIS allergen nomenclature subcommittee. Molecule‐based profiling of allergic sensitization has helped to elucidate the immunological connections of allergen cross‐reactivity, whereas advances in biochemistry have revealed structural and functional aspects of allergenic proteins. In this review, we provide a comprehensive overview of the present knowledge of the molecular aspects of tree pollen allergens. We analyze the geographic distribution of allergenic trees, discuss factors pivotal for allergic sensitization, and describe the role of tree pollen panallergens. Novel allergenic tree species as well as tree pollen allergens are continually being identified, making research in this field highly competitive and instrumental for clinical applications.

Trends in atmospheric concentrations of weed pollen in the context of recent climate warming in Poznań (Western Poland)

A significant increase in summer temperatures has been observed for the period 1996-2011 in Poznań, Poland. The phenological response of four weed taxa, widely represented by anemophilous species (Artemisia spp., Rumex spp. and Poaceae and Urticaceae species) to this recent climate warming has been analysed in Poznań by examining the variations in the course of airborne pollen seasons. Pollen data were collected by 7-day Hirst-type volumetric trap. Trends in pollen seasons were determined using Mann-Kendall test and Sen's slope estimator, whereas the relationships between meteorological and aerobiological data were established by Spearman's rank correlation coefficient. Significant trends in pollen data were detected. The duration of pollen seasons of all analysed taxa increased (from +2.0 days/year for Urticaceae to +3.8 days/year for Rumex), which can be attributed to a delay in pollen season end dates rather than earlier start dates. In addition, the intensity of Artemisia pollen seasons significantly decreased and correlates with mean July-September daily minimum temperatures (r = -0.644, p < 0.01). In contrast, no significant correlations were found between temperature and characteristics of Rumex pollen seasons. The results of this study show that observed shifts in weed pollen seasons in Poznań, i.e. longer duration and later end dates, might be caused by the recorded increase in summer temperature. This influence was the strongest in relation to Artemisia, which is the taxon that flowers latest in the year. The general lack of significant correlations between Rumex and Urticaceae pollen seasons and spring and/or summer temperature suggests that other factors, e.g. land use practices, could also be partially responsible for the observed shifts in pollen seasons.

Exploring the spatio-temporal relationship between two key aeroallergens and meteorological variables in the United Kingdom

Constructing accurate predictive models for grass and birch pollen in the air, the two most important aeroallergens, for areas with variable climate conditions such as the United Kingdom, require better understanding of the relationships between pollen count in the air and meteorological variables. Variations in daily birch and grass pollen counts and their relationship with daily meteorological variables were investigated for nine pollen monitoring sites for the period 2000-2010 in the United Kingdom. An active pollen count sampling method was employed at each of the monitoring stations to sample pollen from the atmosphere. The mechanism of this method is based on the volumetric spore traps of Hirst design (Hirst in Ann Appl Biol 39(2):257-265, 1952). The pollen season (start date, finish date) for grass and birch were determined using a first derivative method. Meteorological variables such as daily rainfall; maximum, minimum and average temperatures; cumulative sum of Sunshine duration; wind speed; and relative humidity were related to the grass and birch pollen counts for the pre-peak, post peak and the entire pollen season. The meteorological variables were correlated with the pollen count data for the following temporal supports: same-day, 1-day prior, 1-day mean prior, 3-day mean prior, 7-day mean prior. The direction of influence (positive/negative) of meteorological variables on pollen count varied for birch and grass, and also varied when the pollen season was treated as a whole season, or was segmented into the pre-peak and post-peak seasons. Maximum temperature, sunshine duration and rainfall were the most important variables influencing the count of grass pollen in the atmosphere. Both maximum temperature (pre-peak) and sunshine produced a strong positive correlation, and rain produced a strong negative correlation with grass pollen count in the air. Similarly, average temperature, wind speed and rainfall were the most important variables influencing the count of birch pollen in the air. Both wind speed and rain produced a negative correlation with birch pollen count in the air and average temperature produced a positive correlation.

Identification of potential sources of airborne Olea pollen in the Southwest Iberian Peninsula

This study aims to determine the potential origin of Olea pollen recorded in Badajoz in the Southwest of the Iberian Peninsula during 2009-2011. This was achieved using a combination of daily average and diurnal (hourly) airborne Olea pollen counts recorded at Badajoz (south-western Spain) and Évora (south-eastern Portugal), an inventory of olive groves in the studied area and air mass trajectory calculations computed using the HYSPLIT model. Examining olive pollen episodes at Badajoz that had distinctly different diurnal cycles in olive pollen in relation to the mean, allowed us to identify three different scenarios where olive pollen can be transported to the city from either distant or nearby sources during conditions with slow air mass movements. Back trajectory analysis showed that olive pollen can be transported to Badajoz from the West on prevailing winds, either directly or on slow moving air masses, and from high densities of olive groves situated to the Southeast (e.g. Andalucía). Regional scale transport of olive pollen can result in increased nighttime concentrations of this important aeroallergen. This could be particularly important in Mediterranean countries where people can be outdoors during this time due to climate and lifestyle. Such studies that examine sources and the atmospheric transport of pollen are valuable for allergy sufferers and health care professionals because the information can be incorporated into forecasts, the outputs of which are used for avoiding exposure to aeroallergens and planning medication. The results of studies of this nature can also be used for examining gene flow in this important agricultural crop.

Pollen season and climate: is the timing of birch pollen release in the UK approaching its limit?

In light of heightened interest in the response of pollen phenology to temperature, we investigated recent changes to the onset of Betula (birch) pollen seasons in central and southern England, including a test of predicted advancement of the Betula pollen season for London. We calculated onset of birch pollen seasons using daily airborne pollen data obtained at London, Plymouth and Worcester, determined trends in the start of the pollen season and compared timing of the birch pollen season with observed temperature patterns for the period 1995-2010. We found no overall change in the onset of birch pollen in the study period although there was evidence that the response to temperature was nonlinear and that a lower asymptotic start of the pollen season may exist. The start of the birch pollen season was strongly correlated with March mean temperature. These results reinforce previous findings showing that the timing of the birch pollen season in the UK is particularly sensitive to spring temperatures. The climate relationship shown here persists over both longer decadal-scale trends and shorter, seasonal trends as well as during periods of 'sign-switching' when cooler spring temperatures result in later start dates. These attributes, combined with the wide geographical coverage of airborne pollen monitoring sites, some with records extending back several decades, provide a powerful tool for the detection of climate change impacts, although local site factors and the requirement for winter chilling may be confounding factors.

Prediction of the birch pollen season characteristics in Cracow, Poland using an 18-year data series

The aim of the study was to construct the model forecasting the birch pollen season characteristics in Cracow on the basis of an 18-year data series. The study was performed using the volumetric method (Lanzoni/Burkard trap). The 98/95 % method was used to calculate the pollen season. The Spearman's correlation test was applied to find the relationship between the meteorological parameters and pollen season characteristics. To construct the predictive model, the backward stepwise multiple regression analysis was used including the multi-collinearity of variables. The predictive models best fitted the pollen season start and end, especially models containing two independent variables. The peak concentration value was predicted with the higher prediction error. Also the accuracy of the models predicting the pollen season characteristics in 2009 was higher in comparison with 2010. Both, the multi-variable model and one-variable model for the beginning of the pollen season included air temperature during the last 10 days of February, while the multi-variable model also included humidity at the beginning of April. The models forecasting the end of the pollen season were based on temperature in March-April, while the peak day was predicted using the temperature during the last 10 days of March.

Development of a regional-scale pollen emission and transport modeling framework for investigating the impact of climate change on allergic airway disease

Exposure to bioaerosol allergens such as pollen can cause exacerbations of allergenic airway disease (AAD) in sensitive populations, and thus cause serious public health problems. Assessing these health impacts by linking the airborne pollen levels, concentrations of respirable allergenic material, and human allergenic response under current and future climate conditions is a key step toward developing preventive and adaptive actions. To that end, a regional-scale pollen emission and transport modeling framework was developed that treats allergenic pollens as non-reactive tracers within the WRF/CMAQ air-quality modeling system. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model was used to generate a daily pollen pool that can then be emitted into the atmosphere by wind. The STaMPS is driven by species-specific meteorological (temperature and/or precipitation) threshold conditions and is designed to be flexible with respect to its representation of vegetation species and plant functional types (PFTs). The hourly pollen emission flux was parameterized by considering the pollen pool, friction velocity, and wind threshold values. The dry deposition velocity of each species of pollen was estimated based on pollen grain size and density. An evaluation of the pollen modeling framework was conducted for southern California for the period from March to June 2010. This period coincided with observations by the University of Southern California's Children's Health Study (CHS), which included O₃, PM_2.5, and pollen count, as well as measurements of exhaled nitric oxide in study participants. Two nesting domains with horizontal resolutions of 12 km and 4 km were constructed, and six representative allergenic pollen genera were included: birch tree, walnut tree, mulberry tree, olive tree, oak tree, and brome grasses. Under the current parameterization scheme, the modeling framework tends to underestimate walnut and peak oak pollen concentrations, and tends to overestimate grass pollen concentrations. The model shows reasonable agreement with observed birch, olive, and mulberry tree pollen concentrations. Sensitivity studies suggest that the estimation of the pollen pool is a major source of uncertainty for simulated pollen concentrations. Achieving agreement between emission modeling and observed pattern of pollen releases is the key for successful pollen concentration simulations.