Two statistical approaches to forecasting the start and duration of the pollen season of Ambrosia in the area of Lyon (France)

The aim of the present study was to forecast the start and duration of the pollen season of Ambrosia from meteorological data, in order to provide early information to allergists and allergic people. We used the airborne pollen data from Lyon (France), sampled using a Hirst trap from 1987 to 1999, and the meteorological data for the same period: air temperature (minimal, maximal, and average), rainfall, relative humidity, sunshine duration and soil temperature. Two forecasting models were used, one summing the temperatures and the other making use of a multiple regression on 10-day or monthly meteorological parameters. The start of the pollen season was predicted with both methods, results being more accurate with the regression (the errors between the predicted and the observed SDP ranging from 0 to 3 days). The duration of the pollen season was predicted by a regression model, errors ranging from 0 to 7 days. The models were later tested with satisfactory results from 2 additional years (2000 and 2001). Such forecasting models are helpful for allergic people, who have to begin their anti-allergic treatment before the start of the pollen season and not when the symptoms have appeared, since a preventive treatment is more efficient than a curative one. The regression allows predictions to be made 3-5 weeks in advance and so it is of particular interest. The forecasts will be broadcast on the Internet.     

Predicting the grass pollen count from meteorological data with regard to estimating the severity of hayfever symptoms in Melbourne (Australia)

In Melbourne, Australia, grass pollen is the predominant cause of hayfever in late spring and summer. The grass pollen season has been monitored in Melbourne, using a Burkard spore trap, for 13 years (1975–1981, 1985 and 1991–1997). Total counts for grass pollen were highly variable from one season to the next (approximately 1000 to >8000 grains/m³). The daily grass pollen counts also showed a high variability (0 to approximately 400 grains/m³). In this study, the grass pollen counts of the 13 years (12 grass pollen seasons, extending from October to January) have been compared with meteorological data in order to identify the conditions that can determine the daily amounts of grass pollen in the air. It was found that the seasonal total of grass pollen was directly correlated with the rainfall sum of the preceding 12 months (1 September–31 August): seasonal total of grass pollen (counts/m³)=18.161 × rainfall sum of the preceding 12 months (mm) −8541.5 (r _s=0.74,P<0.005,n=12). The daily amounts of grass pollen in the air were positively correlated with the corresponding daily average ambient temperatures (P<0.001). The daily amount of grass pollen which was to be expected with a certain daily average temperature was linked to the seasonal total of grass pollen: in years with high total grass pollen counts, a lower daily average temperature was required for a high daily pollen count than in years with low total grass pollen counts. As the concentration of airborne grass pollen determines the severity of hayfever in sensitive patients, an estimation of daily grass pollen counts can provide an indication of potential pollinosis symptoms. We compared daily grass pollen counts with the reported symptomatic responses of hayfever sufferers in November 1985 and found that hayfever symptoms were significantly correlated to the grass pollen counts (P<0.001 for nasal,P<0.005 for eye symptoms). Thus, a combination of meteorological information (i.e. rainfall and temperature) allows for an estimation of the potential daily pollinosis symptoms during the grass pollen season. Here we propose a symptom estimation chart, allowing a quick prediction of eye and nasal symptoms that are likely to occur as a result of variations in meteorological conditions, thus enabling both physicians and patients to take appropriate avoidance measures or therapy.     

Dynamics and behaviour of airborne Quercus pollen in central Iberian Peninsula

Quercus pollen is one of the most abundant pollen types in the atmosphere of central Iberian Peninsula (Spain), as a consequence of the extensive representation of well-preserved forests and shrub communities dominated by species of the genus Quercus in this area. This paper analysed key features of the Quercus pollination season in the central Iberian Peninsula and the influence of weather-related variables on airborne Quercus pollen concentration through statistical techniques of correlation analysis and the use of a decision tree model for predicting pollen concentrations. Quercus species are very common in Spain and Portugal, dominating a number of ecosystems including Mediterranean forests. This gives rise to very high airborne Quercus pollen concentrations, particularly in spring. Sampling was carried out over a 6-year period using a Hirst volumetric sampler, and the sampling procedure established by the Spanish Aerobiology Network. Results show that between 92 and 98.5 % of total annual airborne Quercus pollen was recorded in the April–June period. Annual pollen index were high in all study years, averaging 12,344 grains, but it should be highlighted that pollen production was highly variable between years. Correlations between mean daily Quercus pollen concentration and weather-related variables showed that in the pre-peak period, a significant positive correlation was observed with the mean daily temperature and the hours of sunshine and a negative correlation was observed with the humidity and the rainfall. In the post-peak period, a significant negative correlation was found with the mean daily temperature and the hours of sunshine. The predictions obtained in the decision tree model showed a moderate significant correlation (r = 0.42) with the daily Quercus pollen concentration predicted and the one observed. Temperature is the most influential variable in the release of Quercus pollen.     

Threat of allergenic airborne grass pollen in Szczecin,NW Poland: the dynamics of pollen seasons,effect of meteorological variables and air pollution

The dynamics of Poaceae pollen season, in particularly that of the Secale genus, in Szczecin (western Poland) 2004–2008 was analysed to establish a relationship between the meteorological variables, air pollution and the pollen count of the taxa studied. Consecutive phases during the pollen season were defined for each taxon (1, 2.5, 5, 25, 50, 75, 95, 97.5, 99% of annual total), and duration of the season was determined using the 98% method. On the basis of this analysis, the temporary differences in the dynamics of the seasons were most evident for Secale in 2005 and 2006 with the longest main pollen season (90% total pollen). The pollen season of Poaceae started the earliest in 2007, when thermal conditions were the most favourable. Correlation analysis with meteorological factors demonstrated that the relative humidity, mean and maximum air temperature, and rainfall were the factors influencing the average daily pollen concentrations in the atmosphere; also, the presence of air pollutants such as ozone, PM₁₀ and SO₂ was statistically related to the pollen count in the air. However, multiple regression models explained little part of the total variance. Atmospheric pollution induces aggravation of symptoms of grass pollen allergy.     

Fifteen years' record of airborne allergenic pollen and meteorological parameters in Thessaloniki,Greece

A pollen calendar has been constructed for the area of Thessaloniki and relationships between pollen transport and meteorological parameters have been assessed. Daily airborne pollen records were collected over a 15-year period (1987-2001), using a Burkard continuous volumetric pollen trap, located in the centre of the city. Sixteen allergenic pollen types were identified. Simultaneously, daily records of five main meteorological parameters (mean air temperature, relative humidity, rainfall, sunshine, wind speed) were made, and then correlated with fluctuations of the airborne pollen concentrations. For the first time in Greece, a pollen calendar has been constructed for 16 pollen types, from which it appears that 24.9% of the total pollen recorded belong to Cupressaceae, 20.8% to Quercus spp., 13.6% to Urticaceae, 9.1% to Oleaceae, 8.9% to Pinaceae, 6.3% to Poaceae, 5.4% to Platanaceae, 3.0% to Corylus spp., 2.5% to Chenopodiaceae and 1.4% to Populus spp. The percentages of Betula spp., Asteraceae (Artemisia spp. and Ambrosia spp.), Salix spp., Ulmaceae and Alnus spp. were each lower than 1%. A positive correlation between pollen transport and both mean temperature and sunshine was observed, whereas usually no correlation was found between pollen and relative humidity or rainfall. Finally, wind speed was generally found to have a significant positive correlation with the concentrations of 8 pollen types. For the first time in the area of Thessaloniki, and more generally in Greece, 15-year allergenic pollen records have been collected and meteorological parameters have been recorded. The airborne pollen concentration is strongly influenced by mean air temperature and sunshine duration. The highest concentrations of pollen grains are observed during spring (May).     

An aerobiological study of Urticaceae pollen in the city of Granada (S. Spain): Correlation with meteorological parameters

An aerobiological study was made of Urticaceae pollen in the city of Granada, relating the mean values of the daily counts to meteorological parameters. Sampling was carried out with a Burkard seven‐day‐recording spore trap from October 1992 to September 1997. This pollen type has an extremely long main pollen season (MPS), with maximum counts in (January) February, March and April, causing numerous cases of human pollinosis throughout the entire Mediterranean region, including Granada. A highly constant intradiurnal variation pattern was obtained showing that the maximum peaks usually occur between 12.00 and 20.00. According to Spearman's correlation coefficient, during the pre‐peak period the parameters which have the greatest effect on the levels of this type of pollen are daily and accumulated temperature and sunshine, accumulated rainfall, and wind direction from the third quadrant; during the post‐peak period these same variables presented significantly negative coefficients. Daily rainfall and relative humidity presented negative coefficients during the entire MPS. The maximum daily temperature was the variable which provided the closest match with the theoretical predictive pattern presented here.     

A 2-year aeropalynological survey of allergenic pollen in the atmosphere of Kastamonu, Turkey

Knowledge of airborne pollen concentrations and the weather conditions influencing them is important for air quality forecasters, allergists and allergy sufferers. For this reason, a 7-day recording volumetric spore trap of the Hirst design was used for pollen monitoring between January 2006 and December 2007 in Kastamonu, Turkey. A total of 293,427 pollen grains belonging to 51 taxa were recorded during the study period. In the 2?years of study, the period March–August was identified as the main pollination season for Kastamonu. The highest monthly pollen counts were observed in May in both years. Six taxa made up 86.5% of the total amount of pollen recorded in the atmosphere of Kastamonu. These were as follows: Pinaceae (42.9%), Cupressaceae (20.6%), Poaceae (9.7%), Quercus (5.5%) Betula (5.3%) and Carpinus (2.6%). Four of these are considered to be highly allergenic (Betula, Carpinus, Cupressaceae and Poaceae). There were also a greater percentage of highly allergenic taxa found within the city, including Betula pendula that is not part of the local flora. This shows that through urban planting, the public and municipalities can unconsciously create a high risk for allergy sufferers. Daily average pollen counts from the six most frequently recorded pollen types were entered into Spearman’s correlation analysis with meteorological data. Mean daily temperature, relative humidity, daily rainfall and wind speed were found to significantly (p?<?0.05) affect atmospheric pollen concentrations, but the relationships between pollen concentrations and meteorological variables can vary and so there is a need for more local studies of this nature.     

A predictive study of cupressaceae pollen season onset, severity, maximum value and maximum value date

In this paper Cupressaceae pollen season onset, severity, maximum value and maximum value date, have been studied for 15 consecutive years (1982–1996). The data set was obtained using a Hirst spore-trap (Burkard Manufacturing). In order to determine the influence of the previous months’ meteorological variables on Cupressaceae season’s parameters, the sums of maximum, average and minimum temperatures, and total rainfall for the months of October, November and December were used as independent variables in predictive formulae built by multiple regression analyses. The variance explained percentage by regression analyses varied between 60 and 87%. Total rainfall in the months prior to anthesis and temperature (particularly minimum temperature) are important factors to consider in forecasting models of Cupressaceae pollen season parameters, but meteorological conditions at the time of pollen production are also important and can modify the pre-established potential of pollination.     

Aerobiology of Urticaceae pollen in Trieste (NE Italy)

The aerobiological behaviour of Urticaceae in Trieste and the correlations with the meteorological parameters were examined. Airborne pollen was collected from 1990 to 1999 using a Hirst type spore trap (Burkard) and the data interpretation was performed according to the standard method adopted by the Italian Aeroallergen Network. The main pollen season of Urticaceae in Trieste goes from mid-April to mid-September. The highest values occur in May and June. Although different seasonal patterns are found every year, the main peak occurs on average at the beginning of May, followed by other decreasing peaks until September. Thecumulative counts vary greatly over the years, with a mean value of 18.315 p/m³. The maximum annual total pollen grains was registered in 1996 and the minimum in 1991. Spearman's correlation was used to establish the relationship between the daily pollen counts and the daily meteorological data both considering their original quantitative values and transformed values according to their day by day changes. Daily pollen concentrations present usually positive correlation with temperature, negative with rainfall and wind speed and no correlation with humidity. Better results were obtained with transformed values.     

Variations and trends of birch pollen seasons during 15 years (1996–2010) in relation to weather conditions in Poznań (western Poland)

Birch (Betula) pollen seasons were examined in relation to meteorological conditions in Poznań (1996–2010). Birch pollen grains were collected using a volumetric spore trap. An alternate biennial cycle of birch pollen season intensity was noticed in Poznań. The main factors influencing birch pollen season intensity were average daily minimum temperatures during the second fortnight of May and the month of June one year before pollination as well as the intensity of the pollen season of the previous year. Most of the pollen grains are recorded during the first week of the season; the number of pollen grains recorded at this time is positively correlated with mean maximum temperature and negatively correlated with daily rainfall. The significant effect of rainfall in reducing the season pollen index was noticed only during weak pollen seasons (season pollen index <?mean). In addition, mean daily maximum temperature during the first two weeks of the birch pollen season markedly influences its duration. No significant trends in duration and intensity of the pollen season were recorded, however, a slight tendency towards early pollination was observed (?0.4 days/year, p?=?0.310).     

Airborne birch pollen in Neuchâtel (Switzerland): onset, peak and daily patterns

An accurate forecast of the starting point of thebirch pollen season in Neuchâtel can be made byadding the positive daily average air temperature fromFebruary 1st onward until the figure 270 is reached.At this point, the birch trees are ready to bloom.After that, the daily average temperature has toexceed 10 °C to allow pollen release.Today, the birch pollen season starts some 19 daysearlier in the year than in the 1980's, a consequenceof a recent climate change.The daily patterns of airborne birch pollen isirregular. Moreover, pollen concentrations frequentlyexceed the threshold of the appearance of allergicsymptoms, except during rainfall. Therefore, the onlybehavioral recommendation that can be given to peopleallergic to birch pollen is to shorten as much aspossible the contact with outdoor air during the mainbirch pollen season.     

Variations in mugwort (Artemisia spp.) airborne pollen concentrations at three sites in central Croatia, in period from 2002 to 2003

In spite of the low atmospheric pollen levels, Artemisia sensitisation and allergy has been reported widely. The aim of the study was to determine the length of pollen season, intradiurnal, daily and monthly pollen variation, and the effect of some meteorological parameters on atmospheric pollen concentrations in Central Croatia. Seven-day Hirst volumetric pollen and spore traps were used for pollen sampling. The Artemisia pollen season lasted from the end of July until the end of September with the highest concentrations in August. The percentage of the total pollen count ranged from 0.52% to 0.92%. The intradiurnal peak occurred between 10 a.m. and 12 a.m. Statistical analysis showed a significant correlations between higher air temperature and high pollen concentration as well as high precipitation and low pollen concentration. Results of this study are expected to help in preventing the symptoms of allergic reaction in individuals with Artemisia pollen hypersensitivity.     

Localisation of allergens in ryegrass pollen and in airborne micronic particles

Summary In Melbourne, Australia, grass pollen allergens, especially from ryegrass, are a major cause of allergic hayfever and asthma. This review outlines recent developments in our understanding of how grass pollen allergens find their way into the atmosphere and how they are transported in particulate form. Much of this work has relied on antibody technology in immunological and immunocytochemical investigations. The localisation of allergens in situ has proved difficult due to their water-soluble character. Recently, allergens have been localised in developing ryegrass pollen by dryfixation, rapid-freeze and freeze-substitution techniques. This involved anthers being substituted in a mixture of aldehydes, organic solvents, and 2,2-dimethoxypropane. Incubation in dimethylsulfoxide prior to embedding in LR Gold resin provided good infiltration with freeze-substituted material. Immunogold-labelled sections show that the major allergens, Lol p 1 and Lol p 5, are synthesised in the pollen cytoplasm from the early bicellular stage, soon after the first starch granules are formed. From the early tricellular stage, Lol p 5 moves into the starch granules where it remains until maturity. Lol p 1 is localised in the cytoplasm of mature pollen grains. The incidence of airborne grass pollen, as measured in pollen traps, correlates with hayfever symptoms. Forecasting models which rely on rainfall and temperature data have been produced for the grass pollen (daily and seasonal) counts in Melbourne. Research over the past six years has shed light on the causes of grass-pollen-induced asthma. Micronic particles in the atmosphere may be starch granules originating from pollen grains osmotically ruptured by rainwater. Ultrastructural and immunological characterisation of micronic particles collected from outdoor air filters confirm the presence of airborne starch granules. These are loaded with grass pollen allergens, occur in the atmosphere especially after rainfall, and correlate significantly with instances of allergic asthma. Diesel particles might also play a role in the transmission of grass pollen allergens and thus become an extra asthma trigger. A variation in the mode of release of micronic particles occurs in other species, such as birch, where such particles are derived from burst birch pollen tubes. These particles are positive for Bet v 1 and are starch granules which are released into the atmosphere after light rain as a result of pollen germination on, e.g., leaves. After subsequent rupture of pollen tubes their contents are released when conditions become drier.Abbreviations DECP diesel exhaust carbon particles - DMP 2,2-dimethoxypropane - GPC grass pollen count - IgE immunoglobulin E - IgG immunoglobulin G - OGPS onset of the grass pollen season     

Poaceae pollen concentrations in the atmosphere of three inland Croatian sites (2003-2004)

The aim of the study was to determine the length of Poaceae pollen season, intradiurnal, daily and monthly pollen variation, and the effect of some meteorological parameters on atmospheric pollen concentration, at three monitoring sites in inland Croatia during the 2003-2004 period. Seven-day Hirst volumetric pollen and spore traps were used for pollen sampling. At all three monitoring sites considerably higher precipitation and lower average temperature in 2004 led to a marked decrease in the grass pollen concentration in the air at all three monitoring sites. The highest grass pollen concentrations were recorded in Ivani? Grad (typical rural area), considerably lower in Samobor (effect of forest vegetation), and lowest in Zagreb (urban area). The highest atmospheric Poaceae pollen concentrations in inland Croatia were generally recorded in May and June. The highest intradiurnal concentrations were recorded between 8.00 and 12.00 a.m. Results of this aeropalynologic study are expected to help in preventing the symptoms of allergic reaction in individuals with Poaceae pollen hypersensitivity.     

Poaceae pollen in the atmosphere of Zagreb (Croatia), 2002 – 2005

Pollen of grasses (Poaceae) is one of the most important airborne allergen sources worldwide. The aim of the study was to determine diurnal, day‐to‐day, weekly, monthly and annual pollen variation, and the effect of selected meteorological parameters on atmospheric pollen concentrations in Zagreb. A preliminary study was carried out during four seasons (2002 – 2005), using a 7‐day VPPS 2000 Hirst volumetric pollen trap. Total annual grass pollen concentrations in Zagreb were constant (2 673 – 3 074 p.g.m^?3), with a relative drop in 2004 (1 196 p.g.m^?3). The beginning of the grass pollen season is usually observed when the average daily temperature exceeds 13.5°C (max. daily temp. 19.5°C), without precipitation. In all four study years the absolute peak of concentrations occurs in the second half of May. The length of pollen season during the study period was 157 – 173 days. A high variability was observed in the maximal concentration and in the number of days when grass pollen concentration exceeded the threshold value of 30 p.g.m^?3 (9 – 40 days). Statistically significant correlations were found between airborne grass pollen concentrations and air temperature, level of precipitation and relative humidity.     

Poaceae pollen in the atmosphere of Tetouan (NW Morocco): effect of meteorological parameters and forecast of daily pollen concentration

The Poaceae pollen season has been characterized in Tetouan during a 7-year period, and the effect of weather conditions on daily concentrations was examined. The forecast models were produced using a stepwise multiple regression analyses. Firstly, three models were constructed to predict daily Poaceae pollen concentrations during the main pollen season, as well as the pre-peak and post-peak periods with data from 2008 to 2012 and tested on data from 2013 and 2014. Secondly, the regression models using leave-one-out cross-validation were produced with data obtained during 2008–2014 taking into account meteorological parameters and mean pollen concentrations of the same day in other years. The duration of the season ranged from 70 days in 2009 to 158 days in 2012. The highest amount of Poaceae pollen was detected in spring and the first fortnight of July. The annual sum of airborne Poaceae pollen concentrations varied between 2100 and 6251. The peak of anthesis was recorded in May in six of the other years studied. The regression models accounted for 36.3–85.7% of variance in daily Poaceae pollen concentrations. The models fitted best when the mean pollen concentration of the same day in other years was added to meteorological variables, and explained 78.4–85.7% of variance of the daily pollen changes. When the year 2014 was used for validating the models, the lowest root-mean-square errors values were found between the observed and estimated data (around 13). The reasonable predictor variables were the mean pollen concentration of the same day in other years, mean temperature, precipitations, and maximum relative humidity.     

Poaceae pollen in the air depending on the thermal conditions

The relationship between the meteorological elements, especially the thermal conditions and the Poaceae pollen appearance in the air, were analysed as a basis to construct a useful model predicting the grass season start. Poaceae pollen concentrations were monitored in 1991–2012 in Kraków using the volumetric method. Cumulative temperature and effective cumulative temperature significantly influenced the season start in this period. The strongest correlation was seen as the sum of mean daily temperature amplitudes from April 1 to April 14, with mean daily temperature >15 °C and effective cumulative temperature >3 °C during that period. The proposed model, based on multiple regression, explained 57 % of variation of the Poaceae season starts in 1991–2010. When cumulative mean daily temperature increased by 10 °C, the season start was accelerated by 1 day. The input of the interaction between these two independent variables into the factor regression model caused the increase in goodness of model fitting. In 2011 the season started 5 days earlier in comparison with the predicted value, while in 2012 the season start was observed 2 days later compared to the predicted day. Depending on the value of mean daily temperature from March 18th to the 31st and the sum of mean daily temperature amplitudes from April 1st to the 14th, the grass pollen seasons were divided into five groups referring to the time of season start occurrence, whereby the early and moderate season starts were the most frequent in the studied period and they were especially related to mean daily temperature in the second half of March.     

Risk of pollen allergy in Nerja (southern Spain): a pollen calendar

An aeropalynological study was carried out in the atmosphere of the city of Nerja (southern Spain) during a period of 4 years (2000–2003), using a Hirst type volumetric pollen trap. An annual pollen index of 59,750 grains, on average, was obtained with 80–85% of the total pollen recorded from February to May, with Pinus, Olea, Urticaceae, Cupressaceae, Quercus and Poaceae being the principal pollen producers in abundance order. A total of 29 pollen types that reached a 10-day mean equal to or greater than 1 grain of pollen per m³ of air is reflected in a pollen calendar. The results were compared with those obtained for nearby localities and a correlation analysis was made between the daily fluctuations of the main pollen types and total pollen, and meteorological parameters (temperature, rainfall and hours of sun). The daily, monthly and annual values reached by the most important pollen types from an allergenic point of view (Olea, Urticaceae and Poaceae) confirms Nerja as a high-risk locality for the residents and the numerous tourists who visit the area.     

Aerobiology of Fagaceae pollen in Trieste (NE Italy)

The aerobiological behaviour of Fagaceae in Trieste and the correlations with the meteorological parameters were examined. Airborne pollen grains of Castanea, Fagus and Quercus were collected from 1990 to 2003 using a Hirst type spore trap. The main pollen season (MPS) takes place in April and May for Quercus and Fagus, in June and July for Castanea. The highest values occur in year 1993 for Quercus, in 1998 for Castanea and in 1992 for Fagus. The Fagaceae content of the air is mainly due to Quercus and Castanea pollen, Fagus usually having a scarce pollen shedding in Trieste. The highest counts of Fagaceae pollen grains are found from late April to mid May and are mainly due to the pollen shedding of oaks. The cumulative counts vary over the years, with a mean value of 2.719 pollen grains, a lowest total of 1.341 in 2002 and a highest total of 4.704 in 1993. No positive nor negative long-term trends in pollen shedding are found. No cyclic variations were observed. Spearman’s correlation was used to establish the relationship between the daily pollen counts and the daily meteorological data. Daily pollen concentrations present sometimes positive correlation with temperature, negative with rainfall and wind speed, and no correlation with humidity. Fagus and Quercus start dates result positively correlated between themselves. Significant correlations are found between the start of MPS and the mean and maximum temperature in March for Fagus and Quercus, and May for Castanea.     

Airborne pollen in Nuuk, Greenland, and the importance of meteorological parameters

To describe the season of airborne pollen ofbirch and grass in the city of Nuuk, Greenland,pollen concentrations were measured dailythroughout the pollen seasons in 1997 to 1999.The study was part of a large epidemiologicalcross-sectional study of allergy and riskfactors for allergy in Greenlander Inuit livingin Greenland and Denmark.For the three years the mean birch pollenseason started around 8 June, lasted in average16 days and the mean annual total pollen countwas 46. The highest daily concentration of 23birch pollen pr. m³ was measured in 1999.The mean grass pollen season began around 22July, it lasted 53 days and the mean annualtotal pollen count was 81. The highest grasspollen number registered for one day reached 12in 1998. Several other types of pollen werealso measured, generally in smallconcentrations, but for Cyperaceae and Alderthe mean annual total pollen count were 43 and19 respectively. Though the measuredconcentrations are small, it is concluded thatairborne pollen occur in the arctic climate ofNuuk in potentially clinically relevantamounts.For the three years large variations wereobserved for the start, duration and amountsfor both birch and grass. Models forestimation of the starting date based onGrowing Degree Hours (GDHs) predicted the startof the birch and grass pollen with greataccuracy – within one day. Analysis of themeteorological conditions show that themeasured pollen in general originated from thearea around Nuuk, but there are indicationsthat pollen might have been long-transportedfrom Canada.