Improvement in the accuracy of back trajectories using WRF to identify pollen sources in southern Iberian Peninsula

Identification of Wheat Stripe Rust Inoculum Sources and Dispersal Routes Responsible for Initial Rust Establishment in Southern Henan of China

Wheat stripe rust (yellow rust), caused by Puccinia striiformis f. sp. tritici (Pst), is an important airborne disease worldwide. Pst inoculum strength in southern Henan in winter or early spring is important for spring epidemics in the main autumn-sown wheat-growing regions of China. However, there is limited knowledge about the source and time of initial infection on winter wheat in southern Henan. The first occurrence of wheat stripe rust in southern Henan was recorded annually from 2011 to 2022, from which we used the backward trajectory approach to infer the likely source of Pst inoculum responsible for the initial disease occurrence. The results suggested that the Pst inoculum responsible for initial rust established in the winter in southern Henan originated from the Gansu Pst oversummering area in China, whereas it originated from the adjacent winter Pst sporulation regions in southern Shaanxi and northwestern Hubei if Pst symptoms were first observed in early spring in southern Henan. Another possible Pst source is southern Hubei where Pst can also sporulate in the winter. Thus, early Pst development in winter in the main wheat production region in China (Henan) is likely to be caused by Pst inoculum spread from the oversummering inocula or Pst epidemics in autumn seedlings in Gansu.

Exploring the influence of meteorological conditions on the variability of olive pollen intradiurnal patterns: Differences between pre- and post-peak periods

Olive trees hold a significant economical, ecological and ornamental value, especially in the Mediterranean area. It is a wind-pollinated species emitting huge quantities of pollen with a high degree of allergenic sensitization. Andalusia region (southern Spain), where 15 % of the global olive tree population is cultivated, present a high density of this crop, reaching daily airborne olive pollen concentrations up to 6.000 pollen/m3. Although daily variations during the pollen season have been widely investigated in bibliography, factors influencing the intradiurnal dynamics of olive pollen concentrations remains underexplored in aerobiology. The present paper focuses on it, characterizing main intradiurnal patterns, identifying potential pollen source areas and the influence of wind dynamics on Córdoba city olive pollen data. The results reveal the presence of different pollen peaks at various hours of the day, depending on the stage of the pollen season (pre- and post-peak) and wind dynamics. Nevertheless, the main one is detected at midday during the pre-peak season, with secondary peaks at night, morning and late afternoon. A thorough examination of wind dynamics highlighted the significant influence of distant and local sources on the hourly pollen peaks and hence, on intradiurnal patterns. The analysis of the intradiurnal pattern associated with different air mass patterns demonstrated a considerable variability in the occurrence of peak concentrations and hence, in the contribution of sources. The characterization of surface winds confirms the substantial differences in the dynamics of atmospheric transport processes that influence the primary intradiurnal patterns of olive pollen in this region.

Computing Geographical Networks Generated by Air-Mass Movement

As air masses move within the troposphere, they transport a multitude of components including gases and particles such as pollen and microorganisms. These movements generate atmospheric highways that connect geographic areas at distant, local, and global scales that particles can ride depending on their aerodynamic properties and their reaction to environmental conditions. In this article we present an approach and an accompanying web application called tropolink for measuring the extent to which distant locations are potentially connected by air-mass movement. This approach is based on the computation of trajectories of air masses with the HYSPLIT atmospheric transport and dispersion model, and on the computation of connection frequencies, called connectivities, in the purpose of building trajectory-based geographical networks. It is illustrated for different spatial and temporal scales with three case studies related to plant epidemiology. The web application that we designed allows the user to easily perform intensive computation and mobilize massive archived gridded meteorological data to build weighted directed networks. The analysis of such networks allowed us for example, to describe the potential of invasion of a migratory pest beyond its actual distribution. Our approach could also be used to compute geographical networks generated by air-mass movement for diverse application domains, for example, to assess long-term risk of spread from persistent or recurrent sources of pollutants, including wildfire smoke.

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.

Climate change impact on fungi in the atmospheric microbiome

The atmospheric microbiome is one of the least studied microbiomes of our planet. One of the most abundant, diverse and impactful parts of this microbiome is arguably fungal spores. They can be very potent outdoor aeroallergens and pathogens, causing an enormous socio-economic burden on health services and annual damages to crops costing billions of Euros. We find through hypothesis testing that an expected warmer and drier climate has a dramatic impact on the atmospheric microbiome, conceivably through alteration of the hydrological cycle impacting agricultural systems, with significant differences in leaf wetness between years (p-value <0.05). The data were measured via high-throughput sequencing analysis using the DNA barcode marker, ITS2. This was complemented by remote sensing analysis of land cover and dry matter productivity based on the Sentinel satellites, on-site detection of atmospheric and vegetation variables, GIS analysis, harvesting analysis and footprint modelling on trajectory clusters using the atmospheric transport model HYSPLIT. We find the seasonal spore composition varies between rural and urban zones reflecting both human activities (e.g. harvest), type and status of the vegetation and the prevailing climate rather than mesoscale atmospheric transport. We find that crop harvesting governs the composition of the atmospheric microbiome through a clear distinction between harvest and post-harvest beta-diversity by PERMANOVA on Bray-Curtis dissimilarity (p-value <0.05). Land cover impacted significantly by two-way ANOVA (p-value <0.05), while there was minimal impact from air mass transport over the 3 years. The hypothesis suggests that the fungal spore composition will change dramatically due to climate change, an until now unforeseen effect affecting both food security, human health and the atmospheric hydrological cycle. Consequently the management of crop diseases and impact on human health through aeroallergen exposure need to consider the timing of crop treatments and land management, including post harvest, to minimize exposure of aeroallergens and pathogens.

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.

Medium- and long-range transport events of Alnus pollen in western Mediterranean

Alnus pollen has been frequently detected in the atmosphere of different airborne sampling sites of Southern Spain. However, Alnus sp. populations are very scarce and fragmented in the area, being restricted to a few river valleys in the southwest, and other further away regions of the Iberian Peninsula. This leads to think that the airborne pollen detected could be mainly the result of a medium- or long-distant transport. So, the aim of this study was to characterize the annual patterns of airborne Alnus pollen detected at three different locations of Malaga province, as well as to determine its possible origin, the pollen dispersion potential of these Alnus isolated populations, and their possible reproductive connectivity. Pollen sampling was conducted by means of three Hirst-type volumetric pollen traps. Samples were mounted and counted following the recommendations of the Spanish Aerobiology Network and the European Aeroallergen Society. The possible pollen sources were detected by means of a combination of meteorological information and backward air trajectories analysis. A high inter-annual variability in the annual pollen integrals was found in all the stations, favouring certain meteorological conditions a long-range transport and, therefore, causing the high concentrations detected in some specific days. Alnus pollen seems to have a heterogeneous origin with prevalence of the long-distant transport, which would suggest a possible reproductive connection among distant populations.

Understanding hourly patterns of Olea pollen concentrations as tool for the environmental impact assessment

Bioinformatics clustering application for mining of a large set of olive pollen aerobiological data to describe the daily distribution of Olea pollen concentration. The study was performed with hourly pollen concentrations measured during 8 years (2011-2018) in Extremadura (Spain). Olea pollen season by quartiles of the pollen integral in preseason (Q1: 0%-25%), in-season (Q2 and Q3: 25%-75%) and postseason (Q4: 75%-100%). Days with pollen concentrations above 100 grains/m³ were clustered according to the daily distribution of the concentrations. The factors affecting the prevalence of the different clusters were analyzed: distance to olive groves and the moment during the pollen season and the meteorology. During the season, the highest hourly concentrations during the day where between 12:00 and 14:00, while during the preseason the highest hourly concentrations were detected in the afternoon and evening hours. In the postseason the pollen concentrations were more homogeneously distributed during 9-16 h. The representation shows a well-defined hourly pattern during the season, but a more heterogeneous distribution during the preseason and postseason. The cluster dendrogram shows that all the days could be clustered in 6 groups: most of the clusters shows the daily peaks between 11:00 and 15:00 with a smooth curve (Cluster 1 and 3) or with a strong peak (2 and 5). Days included in cluster 9 shows an earlier peak in the morning (before 9:00). On the other hand, cluster 6 shows a peak in the afternoon, after 15:00. Hourly concentrations show a sharper pattern during the season, with the peak during the hours close to the emission. Out of the season, when pollen is expected to come from farther distances, the hourly peak is located later from the emission time of the trees. Significant factors for predicting the hourly pattern were wind speed and direction and the distance to the olive groves.

Deep learning-based effective fine-grained weather forecasting model

It is well-known that numerical weather prediction (NWP) models require considerable computer power to solve complex mathematical equations to obtain a forecast based on current weather conditions. In this article, we propose a novel lightweight data-driven weather forecasting model by exploring temporal modelling approaches of long short-term memory (LSTM) and temporal convolutional networks (TCN) and compare its performance with the existing classical machine learning approaches, statistical forecasting approaches, and a dynamic ensemble method, as well as the well-established weather research and forecasting (WRF) NWP model. More specifically Standard Regression (SR), Support Vector Regression (SVR), and Random Forest (RF) are implemented as the classical machine learning approaches, and Autoregressive Integrated Moving Average (ARIMA), Vector Auto Regression (VAR), and Vector Error Correction Model (VECM) are implemented as the statistical forecasting approaches. Furthermore, Arbitrage of Forecasting Expert (AFE) is implemented as the dynamic ensemble method in this article. Weather information is captured by time-series data and thus, we explore the state-of-art LSTM and TCN models, which is a specialised form of neural network for weather prediction. The proposed deep model consists of a number of layers that use surface weather parameters over a given period of time for weather forecasting. The proposed deep learning networks with LSTM and TCN layers are assessed in two different regressions, namely multi-input multi-output and multi-input single-output. Our experiment shows that the proposed lightweight model produces better results compared to the well-known and complex WRF model, demonstrating its potential for efficient and accurate weather forecasting up to 12 h.

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.

Concomitant occurrence of anthropogenic air pollutants, mineral dust and fungal spores during long-distance transport of ragweed pollen

Large-scale synoptic conditions are able to transport considerable amounts of airborne particles over entire continents by creating substantial air mass movement. This phenomenon is observed in Europe in relation to highly allergenic ragweed (Ambrosia L.) pollen grains that are transported from populations in Central Europe (mainly the Pannonian Plain and Balkans) to the North. The path taken by atmospheric ragweed pollen often passes through the highly industrialised mining region of Silesia in Southern Poland, considered to be one of the most polluted areas in the EU. It is hypothesized that chemical air pollutants released over Silesia could become mixed with biological material and be transported to less polluted regions further North. We analysed levels of air pollution during episodes of long-distance transport (LDT) of ragweed pollen to Poland. Results show that, concomitantly with pollen, the concentration of air pollutants with potential health-risk, i.e. SO₂, and PM₁₀, have also significantly increased (by 104% and 37%, respectively) in the receptor area (Western Poland). Chemical transport modelling (EMEP) and air mass back-trajectory analysis (HYSPLIT) showed that potential sources of PM₁₀ include Silesia, as well as mineral dust from the Ukrainian steppe and the Sahara Desert. In addition, atmospheric concentrations of other allergenic biological particles, i.e. Alternaria Nees ex Fr. spores, also increased markedly (by 115%) during LDT episodes. We suggest that the LDT episodes of ragweed pollen over Europe are not a "one-component" phenomenon, but are often related to elevated levels of chemical air pollutants and other biotic and abiotic components (fungal spores and desert dust).

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.

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.

Standardised index for measuring atmospheric grass-pollen emission

Grass pollen is the main cause of pollen allergy in Europe, and-given its marked allergenic potential and elevated airborne concentrations-constitutes a major public health risk. This study sought to identify the grass species triggering allergies during the highest-risk periods, and to measure the contribution of each species to airborne grass pollen concentrations. This type of research is particularly useful with a view to optimising the prevention and diagnosis of pollen allergies and developing the most effective immunological treatments. To that end, a total of 28 species potentially responsible for allergies were analysed. In order to assess the potential contribution of these species to overall airborne pollen concentrations, an index was designed (Pollen Contribution Index) based on the following parameters for each species: flowering phenology, pollen grain size (polar and equatorial axes), abundance of the species in the area and pollen production. The species contributing most to airborne pollen concentrations were, in order: Dactylis glomerata subsp. hispanica, Lolium rigidum, Trisetum paniceum and Arrhenatherum album. These species all shared certain features: small grain size (and thus greater buoyancy in air), high pollen production and considerable abundance. This Index was applied to a case study in a Mediterranean-climate area of the central Iberian Peninsula, but could equally be applied to other areas and other allergenic pollens. Findings showed that a small number of species were responsible for most airborne grass pollen.

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.

The long distance transport of airborne Ambrosia pollen to the UK and the Netherlands from Central and south Europe

The invasive alien species Ambrosia artemisiifolia (common or short ragweed) is increasing its range in Europe. In the UK and the Netherlands, airborne concentrations of Ambrosia pollen are usually low. However, more than 30 Ambrosia pollen grains per cubic metre of air (above the level capable to trigger allergic symptoms) were recorded in Leicester (UK) and Leiden (NL) on 4 and 5 September 2014. The aims of this study were to determine whether the highly allergenic Ambrosia pollen recorded during the episode could be the result of long distance transport, to identify the potential sources of these pollen grains and to describe the conditions that facilitated this possible long distance transport. Airborne Ambrosia pollen data were collected at 10 sites in Europe. Back trajectory and atmospheric dispersion calculations were performed using HYSPLIT_4. Back trajectories calculated at Leicester and Leiden show that higher altitude air masses (1500 m) originated from source areas on the Pannonian Plain and Ukraine. During the episode, air masses veered to the west and passed over the Rhône Valley. Dispersion calculations showed that the atmospheric conditions were suitable for Ambrosia pollen released from the Pannonian Plain and the Rhône Valley to reach the higher levels and enter the airstream moving to northwest Europe where they were deposited at ground level and recorded by monitoring sites. The study indicates that the Ambrosia pollen grains recorded during the episode in Leicester and Leiden were probably not produced by local sources but transported long distances from potential source regions in east Europe, i.e. the Pannonian Plain and Ukraine, as well as the Rhône Valley in France.

Airborne Quercus pollen in SW Spain: Identifying favourable conditions for atmospheric transport and potential source areas

The pollen grains of Quercus spp. (oak trees) are allergenic. This study investigates airborne Quercus pollen in SW Spain with the aim identifying favourable conditions for atmospheric transport and potential sources areas. Two types of Quercus distribution maps were produced. Airborne Quercus pollen concentrations were measured at three sites located in the Extremadura region (SW Spain) for 3 consecutive years. The seasonal occurrence of Quercus pollen in the air was investigated, as well as days with pollen concentrations ≥80Pm(-3). The distance that Quercus pollen can be transported in appreciable numbers was calculated using clusters of back trajectories representing the air mass movement above the source areas (oak woodlands), and by using a state-of-the-art dispersion model. The two main potential sources of Quercus airborne pollen captured in SW Spain are Q. ilex subsp. ballota and Q. suber. The minimum distances between aerobiological stations and Quercus woodlands have been estimated as: 40km (Plasencia), 66km (Don Benito), 62km (Zafra) from the context of this study. Daily mean Quercus pollen concentration can exceed 1,700Pm(-3), levels reached not less than 24 days in a single year. High Quercus pollen concentration were mostly associated with moderate wind speed events (6-10ms(-1)), whereas that a high wind speed (16-20ms(-1)) seems to be associated with low concentrations.

Regional forecast model for the Olea pollen season in Extremadura (SW Spain)

The olive tree (Olea europaea) is a predominantly Mediterranean anemophilous species. The pollen allergens from this tree are an important cause of allergic problems. Olea pollen may be relevant in relation to climate change, due to the fact that its flowering phenology is related to meteorological parameters. This study aims to investigate airborne Olea pollen data from a city on the SW Iberian Peninsula, to analyse the trends in these data and their relationships with meteorological parameters using time series analysis. Aerobiological sampling was conducted from 1994 to 2013 in Badajoz (SW Spain) using a 7-day Hirst-type volumetric sampler. The main Olea pollen season lasted an average of 34 days, from May 4th to June 7th. The model proposed to forecast airborne pollen concentrations, described by one equation. This expression is composed of two terms: the first term represents the resilience of the pollen concentration trend in the air according to the average concentration of the previous 10 days; the second term was obtained from considering the actual pollen concentration value, which is calculated based on the most representative meteorological variables multiplied by a fitting coefficient. Due to the allergenic characteristics of this pollen type, it should be necessary to forecast its short-term prevalence using a long record of data in a city with a Mediterranean climate. The model obtained provides a suitable level of confidence to forecast Olea airborne pollen concentration.

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.

A series of abnormal climatic conditions caused the most severe outbreak of first-generation adults of the meadow moth (Loxostege sticticalis L.) in China

The meadow moth, Loxostege sticticalis L., is a destructive migratory pest in the northern temperate zone. The outbreak mechanism of first-generation adults in China remains unclear. In 2008, the density of first-generation larvae was very low or even negligible in most sites in China. However, a great number of first-generation adults appeared unexpectedly in late July, and their offspring caused the most severe infestation on record. The present study aims to determine where the large influx of immigrant adults originated from and how this unprecedented population was established. Source areas were explored by trajectory analysis, and climatic patterns related to the population increase were investigated. Results showed that the outbreak population mainly immigrated from Northeast Mongolia and the Chita State of Russia, and the buildup of such a large population could be attributed to an exceptional northward migration of overwintered adults from North China to East Mongolia in the spring of 2007 and unusually favourable climatic conditions in the next two growth seasons. These results indicated that the population dynamics of meadow moth in Northeast Asia would be difficult to predict when only considering local climatic factors and population size within one country. International joint monitoring and information sharing related to this pest between China, Mongolia and Russia should be implemented.

Modeling olive pollen intensity in the Mediterranean region through analysis of emission sources

Aerobiological monitoring of Olea europaea L. is of great interest in the Mediterranean basin because olive pollen is one of the most represented pollen types of the airborne spectrum for the Mediterranean region, and olive pollen is considered one of the major cause of pollinosis in this region. The main aim of this study was to develop an airborne-pollen map based on the Pollen Index across a 4-year period (2008-2011), to provide a continuous geographic map for pollen intensity that will have practical applications from the agronomical and allergological points of view. For this purpose, the main predictor variable was an index based on the distribution and abundance of potential sources of pollen emission, including intrinsic information about the general atmospheric patterns of pollen dispersal. In addition, meteorological variables were included in the modeling, together with spatial interpolation, to allow the definition of a spatial model of the Pollen Index from the main olive cultivation areas in the Mediterranean region. The results show marked differences with respect to the dispersal patterns associated to the altitudinal gradient. The findings indicate that areas located at an altitude above 300ma.s.l. receive greater amounts of olive pollen from shorter-distance pollen sources (maximum influence, 27km) with respect to areas lower than 300ma.s.l. (maximum influence, 59km).

Effect of land uses and wind direction on the contribution of local sources to airborne pollen

The interpretation of airborne pollen levels in cities based on the contribution of the surrounding flora and vegetation is a useful tool to estimate airborne allergen concentrations and, consequently, to determine the allergy risk for local residents. This study examined the pollen spectrum in a city in central Spain (Guadalajara) and analysed the vegetation landscape and land uses within a radius of 20km in an attempt to identify and locate the origin of airborne pollen and to determine the effect of meteorological variables on pollen emission and dispersal. The results showed that local wind direction was largely responsible for changes in the concentrations of different airborne pollen types. The land uses contributing most to airborne pollen counts were urban green spaces, though only 0.1% of the total surface area studied, and broadleaved forest which covered 5% of the study area. These two types of land use together accounted for 70% of the airborne pollen. Crops, scrubland and pastureland, though covering 80% of the total surface area, contributed only 18.6% to the total pollen count, and this contribution mainly consisted of pollen from Olea and herbaceous plants, including Poaceae, Urticaceae and Chenopodiaceae-Amaranthaceae. Pollen from ornamental species were mainly associated with easterly (Platanus), southerly (Cupressaceae) and westerly (Cupressaceae and Platanus) winds from the areas where the city's largest parks and gardens are located. Quercus pollen was mostly transported by winds blowing in from holm-oak stands on the eastern edge of the city. The highest Populus pollen counts were associated with easterly and westerly winds blowing in from areas containing rivers and streams. The airborne pollen counts generally rose with increasing temperature, solar radiation and hours of sunlight, all of which favour pollen release. In contrast, pollen counts declined with increased relative humidity and rainfall, which hinder airborne pollen transport.

Is long range transport of pollen in the NW Mediterranean basin influenced by Northern Hemisphere teleconnection patterns?

Climatic oscillations triggered by the atmospheric modes of the Northern Hemisphere teleconnection patterns have an important influence on the atmospheric circulation at synoptic scale in Western Mediterranean Basin. Simultaneously, this climate variability could affect a variety of ecological processes. This work provides a first assessment of the effect of North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Western Mediterranean Oscillation (WeMO) on the atmospheric long-range pollen transport episodes in the North-Eastern Iberian Peninsula for the period 1994-2011. Alnus, Ambrosia, Betula, Corylus and Fagus have been selected as allergenic pollen taxa with potential long-range transport associated to the Northern Hemisphere teleconnection patterns in the Western Mediterranean Basin. The results showed an increase of long range pollen transport episodes of: (1) Alnus, Corylus and Fagus from Western and Central Europe during the negative phase of annual NAO and AO; (2) Ambrosia, Betula and Fagus from Europe during the negative phase of winter WeMO; (3) Corylus and Fagus from Mediterranean area during the positive phase of the annual AO; and (4) Ambrosia from France and Northern Europe during the positive phase of winter WeMO. Conversely, the positive phase of annual NAO and AO are linked with the regional transport of Alnus, Betula and Corylus from Western Iberian Peninsula. The positive phase of annual WeMO was also positively correlated with regional transport of Corylus from this area.

Spatiotemporal analysis of olive flowering using geostatistical techniques

Analysis of flowering patterns in the olive (Olea europaea L.) are of considerable agricultural and ecological interest, and also provide valuable information for allergy-sufferers, enabling identification of the major sources of airborne pollen at any given moment by interpreting the aerobiological data recorded in pollen traps. The present spatiotemporal analysis of olive flowering in central Spain combined geostatistical techniques with the application of a Geographic Information Systems, and compared results for flowering intensity with airborne pollen records. The results were used to obtain continuous phenological maps which determined the pattern of the succession of the olive flowering. The results show also that, although the highest airborne olive-pollen counts were recorded during the greatest flowering intensity of the groves closest to the pollen trap, the counts recorded at the start of the pollen season were not linked to local olive groves, which had not yet begin to flower. To detect the remote sources of olive pollen several episodes of pollen recorded before the local flowering season were analysed using a HYSPLIT trajectory model and the findings showed that western, southern and southwestern winds transported pollen grains into the study area from earlier-flowering groves located outside the territory.