Birch Pollen Concentrations Research Articles

Spatio-temporal monitoring and modelling of birch pollen levels in Belgium

In Belgium, ~ 10% of the people is estimated to suffer from allergies due to pollen emitted by the birch family trees. Timely information on forthcoming pollen exposure episodes using a forecasting system can allow patients to take preventive measures. To date, the only available information on pollen concentrations in Belgium comes from five stations that monitor daily airborne birch pollen concentrations, but real-time and detailed spatial information is lacking. Pollen transport models can both quantify and forecast the spatial and temporal distribution of airborne birch pollen concentrations if accurate and updated maps of birch pollen emission sources are available and if the large inter-seasonal variability of birch pollen is considered. Here we show that the SILAM model driven by ECMWF ERA5 meteorological data is able to determine airborne birch pollen levels using updated maps of areal fractions of birch trees, as compared to the pollen observations of the monitoring stations in Belgium. Forest inventory data of the Flemish and Walloon regions were used to update the default MACCIII birch map. Spaceborne MODIS vegetation activity combined with an updated birch fraction map and updated start and end dates of the birch pollen season were integrated into SILAM. The correlation (R2) between SILAM modelled and observed time series of daily birch pollen levels of 50 birch pollen seasons increased up to ~ 50%. The slopes of the linear correlation increased on average with ~ 60%. Finally, SILAM is able to capture the threshold of 80 pollen grains m−3 exposure from the observations.

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.

Pollen forecasts in complex topography: two case studies from the Alps using the numerical pollen forecast model COSMO-ART

Pollen concentrations on Alpine mountain tops are poorly known due to few observations and few modeling studies. We present two case studies from the Alps that provide insights into the spatial and temporal distribution of birch pollen. The numerical pollen dispersion model COSMO-ART (COnsortium for Small-scale MOdelling-Aerosols and Reactive Trace gases) was used to simulate the birch pollen transport during the 2017 pollen season. The model configuration included 1.1-km horizontal grid spacing and 80 vertical levels. The simulations were compared with daily pollen concentrations from two mountain tops in the Alps (Weissfluhjoch near Davos, Switzerland, at 2692 m and Schneefernerhaus, Germany, at 2650 m a.s.l.). In addition, the Swiss pollen stations at Davos (1587 m a.s.l.) and Buchs (446 m a.s.l.) were used. COSMO-ART simulations agreed well with the observations at Davos and Weissfluhjoch. At the Environmental Research Station Schneefernerhaus, the pollen concentrations were generally overestimated. We analyzed the pollen transport episode of 9 April 2017 at Weissfluhjoch in more detail using vertical cross sections of the COSMO-ART simulations. The results suggest that pollen can be lifted up to 3000 m in the morning hours and are subsequently transported by large-scale winds leading to higher birch pollen concentrations at Weissfluhjoch than at Davos. This suggests that the actual situation regarding sources, topography and wind determines the pollen distribution and not only altitude. Still, pollen levels at Weissfluhjoch are more than one order of magnitude lower than typical pollen levels at lowland Swiss stations such as Buchs.

Relationships between aeroallergen levels and hospital admissions for asthma in the Brussels-Capital Region: a daily time series analysis

BackgroundOutdoor pollen grain and fungal spore concentrations have been associated with severe asthma exacerbations at the population level. The specific impact of each taxon and the concomitant effect of air pollution on these symptoms have, however, still to be better characterized. This study aimed to investigate the short-term associations between ambient concentrations of various aeroallergens and hospitalizations related to asthma in the Brussels-Capital Region (Belgium), an area recording especially high rates of admissions.MethodsBased on administrative records of asthma hospitalizations and regular monitoring of 11 tree/herbaceous pollen taxa and 2 fungal spore taxa, daily time series analyses covering the 2008–2013 period were performed. Effects up to 6 days after exposure were captured by combining quasi-Poisson regression with distributed lag models, adjusting for seasonal and long-term trends, day of the week, public holidays, mean temperature and relative humidity. Effect modification by age and air pollution (PM, NO2, O3) was tested.ResultsA significant increase in asthma hospitalizations was observed for an interquartile range increase in grass (5.9%, 95% CI: 0.0, 12.0), birch (3.2%, 95% CI: 1.1, 5.3) and hornbeam (0.7%, 95% CI: 0.2, 1.3) pollen concentrations. For several taxa including grasses, an age modification effect was notable, the hospitalization risk tending to be higher in individuals younger than 60 years. Air pollutants impacted the relationships too: the risk appeared to be stronger for grass and birch pollen concentrations in case of high PM10 and O3 concentrations respectively.ConclusionsThese findings suggest that airborne grass, birch and hornbeam pollen are associated with severe asthma exacerbations in the Brussels region. These compounds appear to act in synergy with air pollution and to more specifically affect young and intermediate age groups. Most of these life-threatening events could theoretically be prevented with improved disease diagnosis/management and targeted communication actions.

Hourly pattern of allergenic alder and birch pollen concentrations in the air: Spatial differentiation and the effect of meteorological conditions

In temperate climate widespread alder and birch are an important source of strong aeroallergens. The diurnal pattern of airborne pollen concentrations depends on the rhythm of pollen release from anthers as well as weather conditions, convection air currents, long-distance transport, pollen trap location and local vegetation. The aim of the study was to present a diurnal pattern of Alnus (alder) and Betula (birch) pollen concentrations in the air in a horizontal and vertical gradient and examine the weather parameters that had the greatest impact on the pattern. The study was conducted in Rzeszów City, southeast Poland over three years. Pollen grains were collected using a Hirst volumetric spore trap at three sampling points: two at 12 m the agl, and one at 1.5 m agl. Data were analysed using circular statistics and a nonlinear function. For alder, three models of hourly patterns were elaborated and the most common presented early morning minimum and early afternoon maximum. For birch, the most common model has one peak at night and a marked decrease in concentrations in early morning, although a second model has peak during early afternoon. A model with 3 peaks is much less common. These models are characteristic for warm temperate climate regions, where alders and birches are common. The diurnal patterns did not depend on the localization of traps or proximity of the pollen source, although these factors influenced the hourly concentrations, with higher values observed at roof level. Significant relationships between the hourly pollen counts and meteorological parameters were observed only for alder. Three incidents of increasing birch pollen concentrations were observed during the first two hours of precipitation and linked to a convection effect. Unstable weather conditions caused by air convection might strongly modify the circadian pattern and cause the nightly peaks concentrations. The general results are that people suffering from allergies may be exposed to high birch and alder pollen concentrations at almost all times during the day with the exception of the morning hours, as well as during the first hours of convective precipitation. Precise information on pollen concentrations aids in allergy prevention, so cities should provide aerobiological monitoring at least at “roof level” and “nose level”.

Birch, grass, and mugwort pollen concentrations and intradiurnal patterns at two different urban sites in Berlin, Germany

Birch, grass, and mugwort pollen concentrations and intradiurnal patterns at two different urban sites in Berlin, Germany

Birch, grass, and mugwort pollen concentrations and intradiurnal patterns at two different urban sites in Berlin, Germany

Purpose The study investigated the seasonal courses and intradiurnal patterns of birch (Betula), grass (Poaceae), and mugwort (Artemisia) pollen at two sites in the city of Berlin in 2014 and 2015.

Variations and trends of Betula pollen seasons in Moscow (Russia) in relation to meteorological parameters

This study investigates possible links of meteorological data and the start date, end date, duration, date of peak, peak value and Seasonal Pollen Index (SPI) of birch pollen seasons recorded in Moscow, Russia, during 1993–2015. Pollen data were collected by a volumetric spore trap. Correlation analysis was used to study relationships between various parameters of pollen seasons. Simple linear regression analysis was conducted to investigate trends over time; multiple stepwise regression analysis was used to describe SPI fluctuations as a function of seasonal or monthly climatic parameters. Air temperatures increased significantly during the study period, but no effect on the timing of the birch pollen season was found. Only the severity of the season showed significant changes that can be considered as a consequence of global warming. Rainfall in May and June of the year preceding flowering, total rainfall in the 40-day pre-season period and average temperature during the pollination were shown to be the most important parameters affecting birch pollen concentrations.

Statistical modelling of non-stationary processes of atmospheric pollution from natural sources: example of birch pollen

A statistical model for predicting daily mean pollen concentrations during the flowering season is constructed and its parameterization and application to birch pollen in Riga (Latvia) are discussed. The model involves several steps of transformations of both meteorological data and pollen observations, aiming at a normally distributed homogeneous stationary dataset with linearized dependencies between the transformed meteorological predictors and pollen concentrations. The data transformation includes normalization of daily mean birch pollen concentrations, a switch of the independent axis from time to heat sum, a projection of governing parameters to pollen concentrations, and a reduction of non-stationarity via removal of the mean pollen season curve. These transformations resulted in a substantial improvement of statistical features of the data and, consequently, a higher efficiency of statistical procedures and better scores of the model. The transformed datasets are used for the model construction via multi-linear regression. For the application in Riga, the model coefficients were calculated using 9 years of birch pollen observations. The model was evaluated using years withheld from the training dataset. The evaluation showed robust model performance with the overall Model Accuracy exceeding 80% and Odds Ratio=30.

Seasonal variation of birch and grass pollen loads and allergen release at two sites in the German Alps

Less vegetated mountainous areas may provide better conditions for allergy sufferers. However, atmospheric transport can result in medically relevant pollen loads in such regions. The majority of investigations has focused on the pollen load, expressed as daily averages of pollen per cubic meter of air (pollen grains/m³); however, the severity of allergic symptoms is also determined by the actual allergen content of this pollen, its pollen potency, which may differ between high and low altitudes. We analysed airborne birch and grass pollen concentrations along with allergen content (birch: Bet v 1, grass: Phl p 5) at two different altitudes (734 and 2650 m a.s.l.) in the Zugspitze region (2009–2010). Back-trajectories were calculated for the high altitude site and for specific days with abrupt increases in pollen potency. We observed several days with medically relevant pollen concentrations at the highest site. In addition, a few days with pollen were not associated with allergens and vice versa. The calculated seasonal mean allergen release per pollen grain was 1.8–3.3 pg Bet v 1 and 5.7 pg Phl p 5 in the valley and 1.1–3.7 pg Bet v 1 and 0.7–1.5 pg Phl p 5 at the high altitude site. Back-trajectories revealed that high pollen potency at the higher site was generally associated with south-westerly to south-easterly (birch), or northerly (grass) wind directions. By investigating days with sudden increases in pollen potency, however, it was difficult to draw definitive conclusions on long- or short-range transport. Our findings suggest that people allergic to pollen might suffer less at higher altitudes and further indicate that a risk assessment relying on the actual concentration of airborne pollen does not necessarily reflect the actual allergy exposure of individuals.

The threat of allergenic airborne trees pollen to pollinosis sufferers in a rural area (Western Pomerania, Poland)

The aim of the study was to investigate the concentration of <em>Alnus</em> L., <em>Corylus</em> L. and <em>Betula</em> L. pollen in the village of Gudowo (Western Pomerania, Poland) in the years 2012–2014 in order to estimate the threat of allergenic tree pollen in this rural region. Measurements were performed using the volumetric method (VPPS Lanzoni 2000 pollen sampler). The duration of the pollen season was determined by the 98% method, taking days on which, respectively, 1% and 99% of the annual total pollen grains appeared as the beginning and end of the season. Pollen grains from hazel occurred in the air as the first ones, before pollen grains from alder and birch. The earliest beginning of the hazel pollen season was recorded in 2012, whereas alder and birch pollen seasons started the earliest in 2014. Daily maximum pollen concentrations of the investigated taxa were recorded in 2014. Birch pollen allergens posed the largest threat to pollinosis sufferers. In the years 2012–2014, pollen concentrations equal or higher than threshold values, at which people with pollinosis show allergic symptoms, were recorded most frequently for birch, hazel, and alder (25, 19, and 14 days, respectively). The highest hourly alder pollen concentration was recorded at 16:00 and in the case of hazel at 15:00. The diurnal distribution of birch pollen concentrations does not show any distinct peaks.

A relationship between birch pollen counts and meteorological factors in Sapporo

Occurrence of airborne pollen in Sapporo has been studied for 19 years during the period between 1995 and 2013. There are wide year-to-year variations in the quantities of birch pollens. A simple linear regression with the least squares method was used for studying correlations between the annual quantities of birch pollens and the meteorological factors. A significant positive correlation was found between the hours of sunlight in June of the preceding year and the annual birch pollen concentrations with the correlation coefficient, R = 0.667. Also, we found the significant positive correlation between the hours of sunlight in March and the annual birch pollen concentrations with the correlation coefficient, R = 0.684. These results suggest that the atmospheric birch pollen counts can be predicted from meteorological factors.

Effects of Airborne Birch Pollen Levels on Clinical Symptoms of Seasonal Allergic Rhinoconjunctivitis

Background: Most panel studies focusing on rhinitis and conjunctivitis symptoms and birch pollen have been performed on a linear basis and have not included air pollution and meteorological variables as potential confounders. The objective of this panel study was to assess the relationship between symptoms of seasonal allergic rhinoconjunctivitis and daily airborne birch pollen concentrations, checking with adequate statistical tools the shapes of concentration-response curves and controlling for confounders. Methods: The severity of rhinitis, conjunctivitis, and bronchial symptoms was recorded daily in March and April 2010 (3,311 person-days) in 61 seasonal allergic rhinoconjunctivitis patients sensitized to birch. Data were analyzed with generalized additive and generalized estimating equation models to quantify the effects of birch pollens. Results: The relationship between birch pollen and the percentage of patients with nasal, ocular and bronchial symptoms was linear until birch daily average concentrations of, respectively, 110, 70, and 70 grains/m³; it reached a plateau thereafter. For an increase of 10 grains/m³, the OR (95% CI) for nasal, ocular, and bronchial symptoms were, respectively, 1.07 (1.03-1.12), 1.17 (1.08-1.27), and 1.12 (1.03-1.21). At the beginning of the season, no nasal or ocular symptoms were observed below a threshold of 30 grains/m³. Conclusions: Adequate modeling regression shows that the clinical response to natural exposure to birch pollen in sensitized patients varies during Betula pollen season, with a threshold at the beginning of the season, while over the whole season the relationship is linear for nasal, ocular, and bronchial symptoms up to a saturation point, followed by a plateau.

Birch pollen grains in the air of Szczecin in 2000-2004

Betula pollen is a common cause of pollinosis in northern and central Europe. The aim of the study was to characterize the birch pollen seasons in Szczecin in 2000 - 2004 and diurnal periodicity of pollen in the air. Measurements were performed using the volumetric method. The analysed meteorological parameters were the maximum temperature, relative humidity, rainfall and wind speed. The beginning and end of a season were established by the 95% method. During five studied years the highest concentration of birch pollen in the air was noted in 2003, with the pollen season starting in the middle of April and lasting till the 11<sup>th</sup> of May. The highest pollen count of 5736 grains per 1m<sup>3</sup> was observed in the end of April. Two peaks of the of birch pollen grains per 1m<sup>3</sup> were observed daily. The highest concentration was noted between 2-4 p.m. A positive and statistically significant correlation was found between the birch pollen concentration and air temperature and wind speed. A negative correlation was found in case of the relative humidity. Besides the individual rhythm of pollination, the meteorological conditions are the most important factors influencing the birch pollen concentration in the air.

Allergy symptoms in relation to alder and birch pollen concentrations in Finland

In order to study allergic people responding to daily changes in pollen concentrations, we compared personal diary data on allergic symptoms and the use of allergy medicines to daily pollen counts during the two unequal alder and birch pollen seasons of 2009 and 2010. Almost 90% of the 61 subjects with physician-diagnosed birch pollinosis developed conjunctival, nasal or other symptoms during the peak birch pollination. Most subjects (95%) also reported symptoms during the alder pollination. Despite a delay between the most severe symptoms and the pollen peaks and the increased risk of allergy symptoms between the alder and birch pollen peaks at much lower pollen concentrations, the number of subjects with allergy symptoms correlated with the daily pollen concentrations in both years (r 09 = 0.35, r 10 = 0.36, p < 0.01). The positive correlation was even stronger (r 09 = 0.69, r 10 = 0.74, p < 0.001) in relation to the cumulative sum of daily concentrations. The use of allergy medicines precisely followed the abundance of allergy symptoms in both years (r 09 = 0.96, r 10 = 0.70, p < 0.001). We conclude that there is a fair correlation between the daily allergy symptoms and the particular pollen concentrations, but the risk of developing symptoms at low, moderate and high concentrations is affected by the progression of the pollen season.

A mechanistic modeling system for estimating large scale emissions and transport of pollen and co-allergens.

Allergic airway diseases represent a complex health problem which can be exacerbated by the synergistic action of pollen particles and air pollutants such as ozone. Understanding human exposures to aeroallergens requires accurate estimates of the spatial distribution of airborne pollen levels as well as of various air pollutants at different times. However, currently there are no established methods for estimating allergenic pollen emissions and concentrations over large geographic areas such as the United States. A mechanistic modeling system for describing pollen emissions and transport over extensive domains has been developed by adapting components of existing regional scale air quality models and vegetation databases. First, components of the Biogenic Emissions Inventory System (BEIS) were adapted to predict pollen emission patterns. Subsequently, the transport module of the Community Multiscale Air Quality (CMAQ) modeling system was modified to incorporate description of pollen transport. The combined model, CMAQ-pollen, allows for simultaneous prediction of multiple air pollutants and pollen levels in a single model simulation, and uses consistent assumptions related to the transport of multiple chemicals and pollen species. Application case studies for evaluating the combined modeling system included the simulation of birch and ragweed pollen levels for the year 2002, during their corresponding peak pollination periods (April for birch and September for ragweed). The model simulations were driven by previously evaluated meteorological model outputs and emissions inventories for the eastern United States for the simulation period. A semi-quantitative evaluation of CMAQ-pollen was performed using tree and ragweed pollen counts in Newark, NJ for the same time periods. The peak birch pollen concentrations were predicted to occur within two days of the peak measurements, while the temporal patterns closely followed the measured profiles of overall tree pollen. For the case of ragweed pollen, the model was able to capture the patterns observed during September 2002, but did not predict an early peak; this can be associated with a wider species pollination window and inadequate spatial information in current land cover databases. An additional sensitivity simulation was performed to comparatively evaluate the dispersion patterns predicted by CMAQ-pollen with those predicted by the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, which is used extensively in aerobiological studies. The CMAQ estimated concentration plumes matched the equivalent pollen scenario modeled with HYSPLIT. The novel pollen modeling approach presented here allows simultaneous estimation of multiple airborne allergens and other air pollutants, and is being developed as a central component of an integrated population exposure modeling system, the Modeling Environment for Total Risk studies (MENTOR) for multiple, co-occurring contaminants that include aeroallergens and irritants.

ANALYSIS OF CHANGES IN FLOWERING PHASES AND AIRBORNE POLLEN DISPERSION OF THE GENUS BETULA (BIRCH)

The scientists evaluate the climate change by various methods. The long‐term phonological observation is a quite significant indicator of this phenomenon. Moreover, the forecasting of plants flowering period or changing of amount of pollen production is important for guarantying of social health. The aim of the research ‐ to analyze the interdependence of flowering changes and pollen concentration under the climate change according to the long‐term phenological data and evaluation of aeropalynological situation in Lithuania. For this purpose one based upon the data of birch flowering (1970–1999) and birch flowering and pollen concentration in air (2004–2008). The interpretation of data with statistic methods showed that the start of birch flowering varies in different years (8–32 days) and the regional differences increase (approximately 3 days during 30 years). One phenological station does not reflect the real aerobiological situation in the observation site. Tight analysis of pollen and phenological data basing upon the flowering data allows gathering knowledge about possible change of the pollen seasons in future. Santrauka Klimato kaita mokslininkai vertina ivairiais metodais. Labai reikšmingas šio reiškinio indikatorius ‐ daugiamečiu fenologiniu stebejimu duomenys. Augalu žydejimo laiko ar žiedadulkiu produkcijos kiekio pokyčio prognozavimas yra svarbus visuomenes sveikatai užtikrinti. Tyrimo tikslas ‐ pagal ilgamečius fenologinius duomenis ir ivertinus aeropalinologine situacija Lietuvoje išanalizuoti žydejimo pokyčiu ir žiedadulkiu koncentracijos tarpusavio priklausomuma vykstant klimato kaitai. Šiam tikslui remtasi beržo žydejimo (1970–1999 m.) ir beržo žydejimo bei žiedadulkiu koncentracijos ore (2004–2008 m.) duomenimis. Duomenis interpretuojant statistiniais metodais nustatyta, kad beržo žydejimo pradžia ivairiais metais varijuoja (8–32 dienos), ir dideja regioniniai skirtumai (apytiksliai 3 dienos per 30 metu). Viena fenologine stotis neatspindi realios aerobiologines situacijos stebejimo vietoje. Glaudi žiedadulkiu ir fenologiniu duomenu analize, remiantis žydejimo duomenimis, leidžia daryti prielaidas apie galima žiedadulkiu sezonu kaita ateityje. Резюме Для оценки изменения климата ученые используют различные методы. Значительным показателем этого явления являются многолетние фенологические наблюдения. Кроме того, прогнозирование времени цветения или изменения продукции пыльцы растений является важным этапом в управлении здравоохранением. Целью нашего исследования было на основании многолетних фенологических наблюдений и оценки аеропалинологической ситуации в Литве проанализировать взаимосвязь между изменением цветения и концентрацией пыльцы в воздухе в связи с изменением климата. Для этой цели были использованы данные цветения березы за период 1970– 1999 гг., цветения березы и данные концентраций пыльцы в воздухе, охватывающие период 2004–2008 гг. Благодаря применению статистических методов для интепретаций данныx, было установлено, что началo цветения березы колеблется из года в год (8–32 дня), увеличиваются региональные различия (около 3 дней за 30 лет). Показано, что одна фенологическая станция не отражает реальную аеропалинологическую ситуацию. Сравнительный фенологический и пыльцевой анализ, проведенный на основании данных цветения, свидетельствуeт о возможныx измененияx в пыльцeвыx сезонаx в будущем.

Analysis of Airborne Betula Pollen in Finland; a 31-Year Perspective

In this 31-year retrospective study, we examined the influence of meteorology on airborne Betula spp. (birch) pollen concentrations in Turku, Finland. The seasonal incidence of airborne birch pollen in Turku occurred over a brief period each year during spring (April 30 – May 31). Mean peak concentrations were restricted to May (May 5 to 13). Statistically significant increases in the annual accumulated birch pollen sum and daily maximum values were observed over the study period. Birch pollen counts collected in April were retrospectively shown to increase over the duration of the study. Increases in April temperature values were also significantly associated with the earlier onset of the birch pollen season. Furthermore, the number of days where daily birch pollen concentrations exceeded 10 and 1,000 grains/m3 also increased throughout the study period. These data demonstrate that increases in temperature, especially during months preceding the onset of the birch pollen season, favor preseason phenological development and pollen dispersal. Birch pollen derived from other geographical locations may also contribute to the aerospora of Turku, Finland. To date, the public health burden associated with personal exposure to elevated birch pollen loads remains unclear and is the focus of future epidemiological research.

Relationship between birch pollen counts and meteorological factors for 8 years in Sapporo

Occurrence of airborne pollen in Sapporo was studied for the 8 years between 1995 and 2002. Observations on pollen seasons of cedar, birch, grass, and mugwort are presented. There are wide year-to-year variations in quantities of birch pollens. Simple linear regression by the least squares method was used for studying correlations between annual quantities of birch pollen and the meteorological factors. A highly significant (P = 0.00004) positive correlation was found between precipitation in February of the preceding year and annual birch pollen concentrations with the coefficient of determination, R2 = 0.950. These results suggest that atmospheric birch pollen counts can be predicted from the meteorological factor in the preceding year.

Similarity in seasonal appearance between atmospheric birch-pollen grains and allergen in paucimicronic, size-fractionated ambient aerosol.

Specific allergen from various pollen types has been found to be carried through the outdoor air, not only by intact pollen grains, but also by much smaller, paucimicronic particles. There is no complete agreement on whether, for birch (Betula), the seasonal appearance of atmospheric pollen allergen follows the fluctuation pattern of the pollen season. Assessment of birch-pollen allergen in size-fractionated ambient aerosol was performed by descending elution of allergen from impaction strips of a five-stage cascade impactor, and compared with atmospheric birch-pollen concentrations as measured with a volumetric pollen trap. An overall similarity in the courses of the seasonal presence was found for both birch pollen and allergen in particles of all paucimicronic size fractions, although some airborne allergen was detected before and after the birch-pollen season. Transfer of pollen allergen to both natural and pollutant environmental dust particles is thought to be the probable explanation of secondary allergen carriage by paucimicronic particles. Until simple techniques for direct and rapid assessment of atmospheric pollen allergen become available, the pollen count gives sufficiently reliable information about the seasonal course of airborne pollen allergen.