Differences in atmospheric trees pollen seasons in winter, spring and summer in two European geographic areas, Spain and Italy

The global climate change reported over recent years may prompt changes in the atmospheric pollen season (APS). The aim of this study is to evaluate the possible impact provoked by meteorological conditions variations at different seasons of the year or different geographical areas on APS. Alnus, Betula and Castanea atmospheric pollen seasons and trends during the last 17 years at Ourense and Vigo (Galicia—NW Spain) and Perugia (Italy) were analysed. Possible incidence of the meteorological trends observed in the different cities on the atmospheric pollen seasons and the chill and heat requirements were evaluated. Pollen data from Ourense, Vigo and Perugia (1995–2011) were used. Pollen sampling was performed using LANZONI VPPS 2000 volumetric traps (Hirst in Ann Appl Biol 36:257–265, 1952), placed on top of different buildings at a similar height from the ground. Several methods, dates and threshold temperatures for determining the chill and heat requirements needed to trigger flowering were tested. Different temporary order in the pollination sequence was observed between the three pollen types studied in the three sites. Alnus flowers few days in advance in Ourense respecting to Vigo and 1 month earlier than Perugia. The Betula flowering start date in Ourense and Vigo is almost simultaneous, taking place only 5 days in advance with respect to Perugia. Finally, scarce differences in the APS onset of Castanea were detected between the three cities. The variations observed among the two areas (Umbria, Italy and Galicia, Spain) in the onset of pollen season in the winter or spring flowering trees could be explained by differences in the thermal requirements needed for flowering as consequence of the climatic conditions recorded during the previous period to flowering. The length of the chilling and heat period as well as the thermal requirements obtained showed differences between geographical areas. The chill requirements accumulated were higher in Perugia than Ourense and Vigo. By contrary, the lowest heat accumulation was achieved in Perugia. The observed trends in the APS characteristics and the weather-related parameters were not homogeneous both in the pollen types and sites. The pollen index of Betula and Castanea pollen in Ourense shows a significant trend to increase.     

Trends in grass pollen season in southern Spain

The main characteristics of Poaceae pollen season at 8 sites in Andalusia were studied. Special attention was paid in the trends of grass pollen-season start and peak dates. Moreover, we analyse the intensity of the grass pollen season over the study period as well as potential temporal and spatial patterns in these data. Statistical analysis was performed to determine the possible influence of weather-related parameters on variations in the grass pollen season. Main results show an advance in the start and peak of grass pollen season and an increase in the annual Pollen Index and in the severity of the season (days > 25 pollen grains/m³). The future consequences of these changes in grass phenology could be related with changes in land use and also in pollinosis symptoms due to the higher concentrations recorded but also to the variations on pollen season dates.     

Pinus pollen season trend in South Spain

In Andalusia (southern Spain), Pinus species are found in mountainous areas and nature reserves, though some species are also grown as ornamentals in cities. Annual airborne pollen trends are regarded as an indicator of variations in climate prompted by overall climate change. Airborne pollen concentration also provides a useful tool for analyzing alterations in the distribution of vegetation in response to environmental factors and to changes in land use. The present study analyzed the Pinus pollen season over 22 years (1993–2014) in 4 Andalusian cities (Córdoba, Granada, Jaén, and Málaga), and examined correlations between airborne pollen concentrations and meteorological parameters (temperature and rainfall). Pinus pollen season lasted from March to June, starting first in Málaga and later in eastern Andalusia. Differences between the pollen curves for each city were attributable to differing proportions of pine species in each province. Temperatures during the months prior to flowering tended to fall, prompting delayed onset of the pollen season in most cities. No significant results were observed for rainfall patterns in most cities. Total pollen concentrations increased at most sites, suggesting that the recorded decline in pine-nut output was not influenced by flowering rates, but to the impact of a local pest.     

Effect of meteorological parameters on Poaceae pollen in the atmosphere of Tetouan (NW Morocco)

Poaceae pollen is one of the most prevalent aeroallergens causing allergenic reactions. The aim of this study was to characterise the grass pollen season in Tetouan during the years 2008–2010, to analyse the effect of some meteorological parameters on the incidence of the airborne Poaceae pollen, and to establish forecasting variables for daily pollen concentrations. Aerobiological sampling was undertaken over three seasons using the volumetric method. The pollen season started in April and showed the highest pollen index in May and June, when the maximum temperature ranged from 23 to 27 °C, respectively. The annual pollen score recorded varied from year to year between 2,588 and 5,404. The main pollen season lasted 114–173 days, with peak days occurring mainly in May; the highest concentration reached 308 pollen grains/m³. Air temperature was the most important meteorological parameter and correlated positively to daily pollen concentration increase. An increase in relative humidity and precipitation was usually related to a decrease in airborne pollen content. External validation of the models performed using data from 2011 showed that Poaceae pollen concentration can be highly predicted (64.2–78.6 %) from the maximum temperature, its mean concentration for the same day in other years, and its concentration recorded on the previous day. Sensitive patients suffering allergy to Poaceae pollen are at moderate to highest risk of manifesting allergic symptoms to grass pollen over 33–42 days. The results obtained provide new information on the quantitative contribution of the Poaceae pollen to the airborne pollen of Tetouan and on its temporal distribution. Airborne pollen can be surveyed and forecast in order to warn the atopic population.     

Comparison of airborne herb pollen types in Córdoba (Southwestern Spain) and Poznan (Western Poland)

This study sought to compare airborne pollen counts for a number of common herbaceous species (Plantago, Chenopodiaceae–Amaranthaceae, Rumex, and Urticaceae) in two cities with differing weather conditions, Córdoba (Southwestern Spain) and Poznan (Western Poland). Pollen seasons for these species were studied from 1995 to 2005. Aerobiological sampling was performed using a Hirst type 7-day spore trap, in accordance with the procedure developed by the European Aerobiology Network. A Spearman correlation test was used to test for correlations between meteorological parameters and daily airborne pollen counts. The Spearman correlation test and the Wilcoxon signed ranks test were also used to compare mean daily pollen counts for the two study sites. In Córdoba, the pollen season generally started around two months earlier than in Poznan, and also lasted longer. These findings were attributed to the presence of a larger number of species in Córdoba, with overlapping pollen seasons, and also to more favorable weather conditions. Trends in pollen season start dates were fairly stable over the study period, with a slight tendency to delayed onset in Córdoba and a modest advance in start date in Poznan. The pollen season end date also remained reasonably stable over the study, with only a slight tendency for the season to end earlier in Córdoba and later in Poznan. A clear trend towards declining annual pollen counts was recorded over the study period for all pollen types in both cities.     

Annual variations of air-borne pollen in the Coastal Plain of Israel

A survey of airborne pollen was conducted during 1984 in the coastal plain of Israel. The flora of that area is continuously changing due to urbanization and agriculture, thus affecting the airborne pollen spectrum.

Significant pollen counts were monitored throughout the year, with a seasonal peak during spring. Meteorological parameters, such as wind velocity, wind direction and temperature affected pollen content of the air. Under certain conditions, even pollen of insect-pollinated plant species was found in the air.

The most conspicuous among the airborne pollen were olive, cypress and pine trees as well as pollen grains from the Poaceae, Amaranthaccae, Chenopodiaceae, Asteraceae, Brassicaceae and Urticaccae.

Results indicate that most of the airborne pollen grains were of local origin and from cultivated trees. Thus, it is possible to reduce airborne pollen contaminants around human habitations by selection of the proper non-allergenic ornamental plants.     

Alternative statistical methods for interpreting airborne Alder (<Emphasis Type="Italic">Alnus glutimosa</Emphasis> (L.) Gaertner) pollen concentrations

This paper reports on the behaviour of Alnus glutinosa (alder) pollen grains in the atmosphere of Ponferrada (León, NW Spain) from 1995 to 2006. The study, which sought to determine the effects of various weather-related parameters on Alnus pollen counts, was performed using a volumetric method. The main pollination period for this taxon is January-February. Alder pollen is one of the eight major airborne pollen allergens found in the study area. An analysis was made of the correlation between pollen counts and major weather-related parameters over each period. In general, the strongest positive correlation was with temperature, particularly maximum temperature. During each period, peak pollen counts occurred when the maximum temperature fell within the range 9 degrees C-14 degrees C. Finally, multivariate analysis showed that the parameter exerting the greatest influence was temperature, a finding confirmed by Spearman correlation tests. Principal components analysis suggested that periods with high pollen counts were characterised by high maximum temperature, low rainfall and an absolute humidity of around 6 g m(-3). Use of this type of analysis in conjunction with other methods is essential for obtaining an accurate record of pollen-count variations over a given period.     

Study of Poaceae phenology in a Mediterranean climate. Which species contribute most to airborne pollen counts?

The present study sought to determine which of the common Poaceae species in the study area contribute most to the Poaceae pollen season curve, and to determine the phenological behaviour of the species studied. The different floral phenophases in thirty-three Poaceae species common in and around the city of Córdoba (SW Iberian Peninsula) were checked periodically over the period 2004–2006. Results showed that longer phenological ranges were recorded in the coolest and wettest year, and shorter ranges in the warmest and driest year. Moreover, ranges varied as a function of altitude: populations in lower-lying areas flowered earlier than those at higher altitudes. The results, taken in conjunction with the findings of preliminary research into potential pollen production, showed that probably only four of the Poaceae species studied—Dactylis glomerata, Lolium rigidum, Trisetaria panicea and Vulpia geniculata—were major contributors to the Poaceae airborne pollen curve.     

Spatial and temporal variations in the Annual Pollen Index recorded by sites belonging to the Portuguese Aerobiology Network

This study presents the findings of a 10-year survey carried out by the Portuguese Aerobiology Network (RPA) at seven pollen-monitoring stations: five mainland stations (Oporto, Coimbra, Lisbon, Évora and Portimão) and two insular stations [Funchal (Madeira archipelago) and Ponta Delgada (Azores archipelago)]. The main aim of the study was to examine spatial and temporal variations in the Annual Pollen Index (API) with particular focus on the most frequently recorded pollen types. Pollen monitoring (2003–2012) was carried out using Hirst-type volumetric spore traps, following the minimum recommendations proposed by the European Aerobiology Society Working Group on Quality Control. Daily pollen data were examined for similarities using the Kruskal–Wallis nonparametric test and multivariate regression trees. Simple linear regression analysis was used to describe trends in API. The airborne pollen spectrum at RPA stations is dominated by important allergenic pollen types such as Poaceae, Olea and Urticaceae. Statistically significant differences were witnessed in the API recorded at the seven stations. Mean API is higher in the southern mainland cities, e.g. Évora, Lisbon and Portimão, and lower in insular and littoral cities. There were also a number of significant trends in API during the 10-year study. This report identifies spatial and temporal variations in the amount of airborne pollen recorded annually in the Portuguese territory. There were also a number of significant changes in API, but no general increases in the amount of airborne pollen.     

Annual Records of Airborne Pollen of Poaceae in Five Areas in Lagos,Nigeria

Poaceae pollen grains are known to be highly allergenic and they are potential causes of allergic respiratory diseases. In order to investigate the incidence of airborne Poaceae, and contribute to current trends in the development of aeropalynology/allergy studies in Nigeria, five highly populated locations in Central Lagos State, Surulere, Ebute-Metta, University of Lagos, Bariga and Gbagada, were sampled. Gravimetric aerosamples were collected monthly from January 2013 to December 2014. The lowest count in 2013 was recorded in the Ebute-Metta area (179), while the highest in 2013 was recorded in Gbagada (564). In 2014, the Surulere area (282) had the lowest count while Bariga (671) had the highest. The locations have similar monthly pollen distribution pattern but different peak months. Generally, Poaceae pollen counts were lowest in the months of June and July. These are therefore the safest months for Poaceae pollen hypersensitive individuals in the study areas. Relative humidity was the most important meteorological parameter with significant correlations in Ebute-Metta and Bariga locations. Results from this work will form the basis for a forecast service required to inform and educate the general public and allergy sufferers about Poaceae pollen distribution in Lagos State.     

<Emphasis Type="Italic">Betula</Emphasis> pollen: One of the most important aeroallergens in Ourense,Spain. Aerobiological studies from 1993 to 2000

This study presents the results obtained for airborne Betula pollen between 1992 and 2000 in Ourense, Spain, sampled by volumetric spore-trap (LANZONI VPPS2000). Annual and year-on-year variations were analyzed, and a statistical study of the correlation between daily counts and several meteorological parameters was performed. Birch pollen is present in the atmosphere during March and April in Ourense. Significant differences were observed among the different years. Values obtained for the correlation coefficient between Betula pollen counts and the various meteorological parameters studied indicate, for Ourense, a positive correlation between pollen count and both temperature and sunlight. A negative correlation was recorded for relative humidity. Temperature is thus the determining factor for flowering onset and intensity. Regression equations included values for the days prior to pollen concentration measurement in order to optimize results.     

Regional and seasonal variation of airborne pollen and spores among the cities of South China

The composition and relative abundance of airborne pollen in urban areas of south China are strongly influenced by geographical location, vegetation, climate, and sampling device. This paper summarizes the latest reports on air pollen for 12 major cities in southern China from 1986 to 2017. The most significant taxa across all sites are Pinaceae, Poaceae, Cupressaceae, and Platanus, making up over 50% of the total airborne pollen in urban environments throughout the years. Clear shifting has been observed from long pollen seasons in the tropics to shorter periods in the south middle and north subtropical regions. There is also a discernible shift in the initiation and length of the pollen season towards higher latitudes. Both reflect the strong influence of solar radiation incidence on pollen production during spring and summer months in the southern urban areas. In this study, the comparison between airborne pollen and meteorological data indicates that the airborne pollen concentration was positively related to temperature but negatively related to precipitation and relative humidity. This study reveals that the consistent wind speed over the year had a very little but positive effect on pollen and spore concentration. The active sampler (volumetric method) in Guangzhou and Zhanjiang collected more spore and pollen species than the passive sampler (gravity method) in other cities. Understanding the future potential impacts of climate change on the phenological cycles and range of allergenic species is a critical step in the advancement of aerobiology studies in south China.     

Long-term trends in airborne fungal-spore concentrations: a comparison with pollen

We examined the long-term trends in airborne fungal-spore concentrations in Thessaloniki, Greece, over the period 1987–2005. We estimated trends in the spore levels for the 14 taxa that contribute at least 0.1 % to the total airborne spore concentration. We also tested for trends towards earlier, longer or more highly peaked spore seasons. There was decreasing concentration of spores for 11 of the 14 taxa, especially for Agrocybe, Botrytis, Cladosporium, and Nigrospora, where this trend was significant. Using ANCOVA, there was a highly significant negative trend overall (p < 0.001). Regarding the spore-season related attributes, there were very few significant trends. However, the main spore season tended to start later (for 12 of the 14 taxa) and become shorter (for 10 of the 14 taxa); later onset was more pronounced during the most recent part of the study period. Fungi seem to display a delayed and slower response to climate change than plants and in a direction opposite to that of pollen.     

Comparison of two pollen counting methods of slides from a hirst type volumetric trap

Two of the most frequently used methods of pollen counting on slides from Hirst type traps are evaluated in this paper: the transverse traverse method and the longitudinal traverse method. The study was carried out during June–July 1996 and 1997 on slides from a trap at Worcester, UK. Three pollen types were selected for this purpose: Poaceae, Urticaceae and Quercus. The statistical results show that the daily concentrations followed similar trends (p < 0.01, R-values between 0.78–0.96) with both methods during the two years, although the counts were slightly higher using the longitudinal traverses method. Significant differences were observed, however, when the distribution of the concentrations during 24 hour sampling periods was considered. For more detailed analysis, the daily counts obtained with both methods were correlated with the total number of pollen grains for the taxon over the whole slide, in two different situations: high and low concentrations of pollen in the atmosphere. In the case of high concentrations, the counts for all three taxa with both methods are significantly correlated with the total pollen count. In the samples with low concentrations, the Poaceae and Urticaceae counts with both methods are significantly correlated with the total counts, but none of Quercus counts are. Consideration of the results indicates that both methods give a reasonable approximation to the count derived from the slide as a whole. More studies need be done to explore the comparability of counting methods in order to work towards a Universal Methodology in Aeropalynology. This revised version was published online in June 2006 with corrections to the Cover Date.     

Airborne pollen of Brisbane,Australia: A five-year record, 1994 - 1999

The seasonal incidence of pollen in the atmosphere of Brisbane has been established from a near-continuous, volumetric trapping program over the five-year period, July 1994-June 1999. Grass pollen accounts for 71.6% of the average annual pollen load with highest densities (up to 150 grains/m 3 ) recorded in summer and autumn. Significant contributions were also made by taxa of the Cupressaceae (8.7%) and Urticaceae (1.8%) during spring and of the Pinaceae (4.5%) during winter. Pollen seasons of the Casuarinaceae (6.5%) and Myrtaceae (3.2%) are more extended, the former peaking in late winter and the latter in late spring. The onset and duration of the Poaceae and Urticaceae seasons varied from year to year, being later when precipitation levels were low in the late spring-early summer months. Total pollen numbers and grass pollen densities are substantially less than those recorded from southern Australia. Nevertheless, respiratory disease in Brisbane affects up to 10% of the population, and airborne pollen of Poaceae, Urticaceae, Cupressaceae, Pinaceae, and Myrtaceae have been implicated in the release of allergens.     

Trends in pollen season characteristics of Alnus,Poaceae and Artemisia allergenic taxa in Bratislava,central Europe

Over the period 2002–2019, air temperature and precipitation significantly increased regionally for Bratislava, which could lead to phenological changes in some plant species. This study aimed to analyse the changes in the intensity, timing, and duration of pollen seasons of three allergological important plant taxa (Alnus, Poaceae, Artemisia) in the study area over 18 years. The pollen sampling was performed using a Hirst-type sampler. Mann–Kendall tau test was used to determine trends in pollen season characteristics, while Spearman’s correlation analysis was used to identify the relationships between the characteristics of pollen seasons and both air temperature and precipitation trends. The notable changes in the pollen-season-related features were observed for all analysed taxa. The Alnus pollen season now reaches the peak earlier and its intensity is rising in line with the summer-autumn temperature increasing trend, while unexpectedly intensity and duration of the Artemisia pollen season are declining in line with the increased precipitation and/or temperature trends. On the other hand, the intensity of the Poaceae pollen season is also declining, however, without statistically significant correlations with recorded increases in meteorological parameters considered. This phenomenon is probably related to both the reduction of the area of grasslands due to urbanization and the implementation of effective maintenance of urban green areas (e.g., timely mowing preventing the repeatedly flowering of grasses).

     

The patterns of Corylus and Alnus pollen seasons and pollination periods in two Polish cities located in different climatic regions

This study compares phenological observations of Corylus (hazel) and Alnus (alder) flowering with airborne pollen counts of these taxa recorded using volumetric spore traps (2009–2011). The work was carried out in the Polish cities of Szczecin and Rzeszów that are located in different climatic regions. Correlations between pollen concentrations and meteorological data were investigated using Spearman’s rank correlation analysis. The timings of hazel and alder pollination and the occurrence of airborne pollen varied greatly and were significantly influenced by meteorological conditions (p < 0.05). The flowering synchronization of hazel and alder pollination in Szczecin and Rzeszów varied over the study period. Hazel and alder trees flowered notably earlier in stands located in places that were exposed to sunlight (insolated) and sheltered from the wind. On the other hand, a delay in the timing of pollination was observed in quite sunny but very windy sites. In Rzeszów, maximum hazel pollen concentrations did not coincide with the period of full pollination (defined as between 25 % hazel and alder and 75 % of flowers open). Conversely, in Szczecin, the highest hazel pollen concentrations were recorded during phenophases of the full pollination period. The period when the highest alder pollen concentrations were recorded varied between sites, with Rzeszów recording the highest concentrations at the beginning of pollination and Szczecin recording alder pollen throughout the full pollination period. Substantial amounts of hazel and alder pollen grains were recorded in the air of Rzeszów (but not Szczecin) before the onset of the respective pollen seasons.     

Fluctuations and trends in airborne concentrations of some abundant pollen types,monitored at Vienna,Leiden, and Brussels

The annual sums of daily airborne pollen concentrations fluctuate from year to year. It has been suggested that for some taxa there is a regular or alternating pattern in these fluctuations. On the other hand, environmental changes may lead to decreasing or increasing trends in airborne pollen concentrations. These two phenomena can only be studied reliably on the basis of long-term volumetric observations of abundantly occurring pollen types. For this study two arboreal (Betula and Quercus) and two herbaceous (Poaceae and Urtica) types were chosen.

For some of these pollen types a weak but significant trend is observed. For the arboreal types (Quercus and Betula) there appears to be a rather constant biennial fluctuating rhythm.     

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.     

Trend of herbaceous pollen diffusion and allergic sensitisation in Genoa, Italy

In order to investigate the relationship betweenallergenic load and allergic sensitisation prevalenceon a long period, we analysed the annual data ofherbaceous pollen airborne diffusion in Genoa(NW-Italy) for 17 years (1981–1997), with particularregard to the most important allergenic species:Poaceae, Parietaria, Artemisia, Ambrosia. Weevaluated the relative trend and compared it with theprevalence data of patients sensitisation to thesepollens in the same period.The analysis of annual pollen amount revealed asignificant rising trend (r = 0.73, p < 0.05) of Parietaria pollen (average 14.324 grains/m³/year),whereas Poaceae (2048/year) and Artemisia(170/year) pollen count did not show any significantchange. Ambrosia (average 70/year) has been rising since 1989 (r = 0.87, p < 0.05) and reached themaximum pollen count in the last three years.The prevalence of pollen sensitisation resulted to bevery high (about 75%) in our atopic patients withrespiratory symptoms and did not change significantlyin the years: Parietaria pollen allergy waspresent in about 70% of patients with at least oneSPT positive to pollens (and 55% of atopicsubjects), and this frequency, much higher than theone found in North Italy, showed low year-to-year variability.Among pollinotics patients, Poaceae cutaneoussensitisation was found at a quite stable rate in theabove mentioned period (about 51%), as well as thatto Artemisia pollen (8%). Ambrosia skinprick test positivity is very rare (about 0.5%),without any evident increase.The present study shows that, for some of theherbaceous species, we cannot demonstrate astraightforward relationship between the trend ofairborne pollen and the frequency of sensitisation inexposed people. However, in the case of Parietaria, the high level of pollen amount in theair is clearly related with the high rate of cutaneous positivity in patients, but it seems tosuggest a ``plateau' that is not modified by anyfurther increase in airborne pollen (perhaps forgenetic limiting factors). On the other hand, Ambrosia pollen count, even if increasing in Genoa'satmosphere, could still be too low, and it would takesome more time to cause allergic sensitisation in exposed people.This kind of study, pointing out the influence ofairborne allergen exposure on hypersensitivitymechanisms, should be extended in time and world-wideto obtain general conclusions.