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

Projections of the start of the airborne pollen season in Barcelona (NE Iberian Peninsula) over the 21st century

The effects of global warming are numerous and recent studies reveal that they can affect the timing of pollination. Temperature is the meteorological variable that presents a clearer relationship with the start of the pollination season of most of the observed airborne pollen taxa. In Catalonia, in the last fifty years, the average annual air temperature has increased by +0.23 °C/decade, and the local warming has been slightly higher than the one on a global scale. Projections point to an increase in temperature in the coming decades, which would be more marked towards the middle of the century. To analyse the effect of the increase in temperature due to global warming on the starting date of pollen season in Barcelona, a forecasting model has been applied to a set of projected future temperatures estimated by the European RESCCUE project. This model, largely used in the literature, is based on determining the thermal needs of the plant for the pollen season to begin. The model calibration to obtain the initial parameters has been made by using 20 years of pollen data (2000-2019), and the model effectiveness has subsequently been tested through an internal evaluation over the period of the calibration and an external evaluation on 4 years not included in the calibration (2020-2023). The mean bias error in the internal calibration ranged between -0.4 and - 0.6 days, and between +0.5 and - 8.3 in the external one, depending on the taxon. The results of the application of the model to the temperature projections over the 21st century point to a progressive advancement in the pollination dates of several pollen types abundant in the city, allergenic most of them. These advances ranged, at the end of the century, between 15 and 27 days, depending on the climate model, for the scenario of the highest concentrations (RCP8.5) and between 7 and 12 days for the emissions stabilization scenario (RCP4.5).

Influence of synoptic meteorology on airborne allergenic pollen and spores in an urban environment in Northeastern Iberian Peninsula

The influence of the most frequent patterns of synoptic circulation on the dynamics of airborne pollen/spores recorded at the Barcelona Aerobiological Station (BCN) was analysed. Six pollen types (Platanus, Cupressaceae, Olea, Poaceae, Urticaceae and Amaranthaceae), and one fungal spore (Alternaria) were selected for their high allergenic effect in sensitive people. Six synoptic meteorological patterns were identified through cluster analysis of sea level pressure fields as the main responsible of the weather conditions in the Iberian Peninsula. The local meteorological conditions in Barcelona associated with each one of the synoptic types were also stablished. Different statistical methods were applied to analyse possible relationships between concentrations and timing of the recorded aerobiological particles and specific synoptic types. The study, focused in the 19-year period 2001-2019, shows that one of the scenarios, frequent in winter and linked to high stability and air-mass blockage, registered the highest mean and median values for Platanus and Cupressaceae, but it was not very relevant for the other taxa. It was also this scenario that turned out to be the most influent on the pollination timing showing a significant influence on the start occurrence of Urticaceae flowering and on the peak date of Platanus. On the other hand, the most frequent synoptic type in the period, relevant in spring and summer, was linked to sporadic episodes of levels considered to be of high risk of allergy to Platanus, Poaceae, and Urticaceae pollen, and Alternaria fungal spore. This synoptic pattern, characterized by the presence of the Azores anticyclone and the Atlantic low located in the north of the United Kingdom, was associated with high temperatures, low relative humidity and moderate winds from the NW in Barcelona. The identification of an interaction between synoptic meteorology and pollen/spore dynamics will allow better abatement measures, reducing adverse health effects on sensitive population.

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.

Alder pollen concentrations in the air during snowfall

The focus of our study was airborne alder pollen because it is one of the main causes of inhalant allergies in many countries in the Northern Hemisphere. The main research setback was pollen concentrations during snowfall. Analyses from a 21-year database showed that the hourly patterns of occurrence of airborne Alnus pollen during snowfall differ. Snowfall can cause a decrease in pollen concentrations in the air that may persist for several hours. However, during the snowfall period of 2018, an increase in pollen concentrations was observed. High temperatures during the days preceding snowfall stimulate thermal currents, and pollen could become airborne. During snowfall, airborne pollen grains are supposedly washed out of the atmosphere and numerous pollen grains are deposited on the snow surface. Hypotheses about the long-distance transport of pollen have also been verified. Back-trajectory analysis has revealed that air masses from Belarus and Ukraine were transported to Rzeszow. We found that the influence of snowfall on pollen concentrations is ambiguous and individuals prone to allergies also notice symptoms on days with snowfall and temperatures below zero.

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.

Assessment of the potential real pollen related allergenic load on the atmosphere of Porto city

The knowledge of the allergen content in the atmosphere is a useful tool to stablish the risk allergy warnings for the sensitive people. In Portugal the main airborne allergenic pollen come from trees (such as Betula or Olea), grasses or weeds (mainly Urticaceae). The present study sought the quantification of the Bet v 1, Ole e 1, Lol p1 and Par j1-2 aeroallergen concentration as well as how weather variables influence in the pollen and allergen concentration in Porto city. Aerobiological study was carried out by a Hirst-type volumetric sampler for pollen collection and a Burkard Cyclone sampler for the aeroallergens. A regression analysis between pollen and allergens was conducted for the identification the allergenic risk days. High Pollen Allergen Potency in the atmosphere was observed considering the low levels of airborne pollen detected. A significant and positive correlation has been obtained between pollen and aeroallergen values with the temperatures whereas the correlation was negative with relative humidity, rainfall and wind speed. Back trajectory methodology was applied in order to analyse the discordances between pollen and allergen maximum concentrations. The analysis showed that when the pollen and allergen peaks were registered on the same day, air masses always comes from the continent. However, when the peaks do not coincide, the air mass comes from the continent in the case of the pollen peak and from the sea for the allergen peak. This behaviour can be a consequence of the high humidity in the air masses from the sea, which can benefit the allergen release from pollen grains. In our study it was observed that the available traditional information for allergenic Type I patients, corresponding to the amount of pollen grains in the bioaerosol, do not accurately identify the real allergenic load in the air.