Pollen emission from olive trees and concentrations of airborne pollen in an urban area of North Sardinia

In this study the seasonal and daily variations in olive airborne pollen concentrations were measured in the atmosphere of Sassari (Italy) and the olive pollen emission was monitored in the countryside during the flowering period in 1995 and 1996, in order to detect the patterns of change in the atmosphere. The intensity and the timing of pollination was also studied in relation to phenological stages occurrence. In addition, the influence of the main meteorological parameters on pollen emission and airborne pollen dispersal in the city was assessed. Airborne pollen reached its highest concentration a few days before the peak of pollen emission in 1995 but several days after it in 1996 (6 days). Analysis of hourly concentrations shows that the maximum emission and dispersion recorded during the observation period occurred in the middle of the day. Significant regressions were found between hourly temperature and air humidity values and hourly pollen concentrations recorded in the olive grove for almost every day studied, indicating a negative correlation between humidity and pollen concentration and a positive correlation between pollen concentration and temperature. On the other hand, no significant correlation was observed between the meteorological parameters and pollen concentration recorded in the urban area.     

Modelling the pollen season start in <Emphasis Type="Italic">Corylus avellana</Emphasis> and <Emphasis Type="Italic">Alnus glutinosa</Emphasis>

Hazel (Corylus avellana L.) and black alder (Alnus glutinosa (L.) Gaertn.) are important sources of airborne pollen and represent an allergen threat during the flowering period. Researches on airborne pollen concentrations in both species are useful in allergology, as well as for fruit production for hazel. The aims of the present study were: (1) to investigate the relationships between environmental conditions and the airborne pollen concentration of hazel and black alder during the flowering period by correlation and multiple regression analysis and (2) to predict the pollen season start (PSS) by using a sequential model, in order to obtain a helpful tool in allergology and hazel cultivation. In this study, the applied method defines the pollen season as the period in which 90 % of the total season’s catch occurred, using a data set of 18 years (1996–2014). The relationships between daily meteorological parameters (temperature, humidity, rainfall and wind speed) during the 14-day period that precedes the PSS and the PSS of hazel and black alder (day of the year) were investigated. The results showed that mean temperature and the number of rainy days before the PSS are the main factors influencing PSS for both taxa. Moreover, the chilling and heat needed to break dormancy were estimated in order to predict the PSS of both species. Different years and different thresholds of temperature and chill days were used to calibrate and validate the model.     

Flowering phenology,pollen flow and fruit production in the andean shrub Befaria resinosa

Summary In the eastern Andes of Colombia, the shrub Befaria resinosa (Ericaceae) has peaks of flowering that are separated by extended periods of low flower production. The effect that these fluctuations in flower production have on pollen flow was investigated by using fluorescent dye as a pollen analog. Dye applied to open flowers was dispersed over long distances more often during low flower production than during high flower production. Whether enhanced pollen dispersal during flowering lows is of benefit to individual plants is not clear. The proportion of flowers that set fruit is positively correlated with flower abundance, negating the possibility that increased pollen dispersal results in a higher rate of fruit production due to outbreeding effects. It is also difficult to attribute the pattern of fruit production to changes in pollinator visitation rates, which are negatively correlated with flower abundance in the case of hummingbirds and not correlated at all with flower abundance in the case of insects. An opportunistic, large-bodied hummingbird (Colibri coruscans) visits B. resinosa during high flowering and may be a particularly effective pollinator, accounting for some of the increase in the proportion of flowers setting fruit. Rainfall is positively correlated with flower production and may be an important factor in shaping flowering phenology, but it is not significantly correlated with the proportion of flowers setting fruits. The possibility that low-level flowering may counteract inbreeding that results from peak flowering is discussed.     

Factors affecting pollination ecology of Quercus anemophilous species in north-west Spain

Pollination ecology of Quercus is influenced by meteorological, biotic and genetic factors. This study was undertaken to ascertain the effect induced by these factors on pollen production, release and dispersion. Aerobiological data have been used in recent years as phenological information, because the presence of pollen in the air is the result of flowering across a wide area. The onset of the Quercus pollen season and the atmospheric pollen concentrations during the pollination period in two localities of north-west Spain (Ourense and Santiago) were determined from 1993 to 2001. There were important variations in total annual pollen as a result of meteorological conditions, lenticular galls produced by Neuropterus on catkins and biennial genetic rhythms of pollen production. In order to determine the beginning of flowering, a thermal time model has been used. Chill requirements were around 800 chilling hours (CH) and heat requirements were 953 growth degree days (GDD in °C) in Santiago and 586 GDD in Ourense. Pollen in the air show positive correlation (99% significance) with daily thermal oscillation, maximum and minimum temperatures, and hours of sunshine. Regression analysis with previous days' pollen concentrations explained the high percentage of pollen concentration variability, as meteorological variables do not, on their own, explain pollen production and release.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 283–297.     

An integrated use of aerobiological and phenological data to analyse flowering in olive groves

Aerobiological and phenological investigation has been linked to analyse the flowering phenomena of olive (Olea europaea L.), a tree of economic importance, in Umbria, central Italy.

Olive tree flowering was analysed by phenological observations in olive groves. Aerobiological monitoring was carried out with pollen traps that captured the pollen grains in the atmosphere by remote distances. This combined study of flowering was useful in overcoming the principal limit of phenological observations caused by their geographical narrowness.

Eleven phenological stations in Perugia province were used and periodic observations were carried out during the flowering season. Two aerobiological stations located near the cities of Perugia and Spoleto were utilized to trap olive pollen grains in the atmosphere.

Graphic and statistical analyses were used in order to study flowering dynamics, and to compare the methodological approaches.

The phenological areas, according to their characteristics, were divided in two clusters each one related to a different pollen monitoring station. Statistical analyses showed the presence of a three ‐ four‐day period during which pollen released in the groves is persistent in the narrowness and resulted in a high correlation with the pollen monitored by the pollen traps. On the other hand, the phenological data considered along with the daily pollen concentrations permit the pollen peaks to be attributed to particular olive areas or olive cultivars. This demonstrates that both methodologies can be used effectively as integrated research tools in this kind of study.     

Use of <Emphasis Type="Italic">Quercus ilex</Emphasis> subsp. <Emphasis Type="Italic">ballota</Emphasis> phenological and pollen-production data for interpreting <Emphasis Type="Italic">Quercus</Emphasis> pollen curves

Although aerobiological data are often used in phenological research as an indicator of flowering, airborne pollen concentrations are influenced by a number of factors that could affect pollen curves. This paper reports on a study of various aspects of reproductive biology in Q. ilex subsp. ballota, together with environmental factors influencing pollen release and transport, with a view of achieving reliable interpretation of Quercus pollen curves in Ourense (NW Spain). Aerobiological data were recorded from 2002 to 2004 at two sites in the province of Ourense. From 1st February to the end of the flowering period, phenological observations were carried out on 19 trees from the Q. ilex subsp. ballota population found in the Ourense area. Pollen production was calculated for the same trees. The chilling and heating requirements for triggering development were also calculated. The mean flowering period lasted 11-15 days. Reduced pollen output per catkin and, especially, a reduced number of catkins per tree in 2003 and 2004, prompted a marked decline in overall pollen production. Major differences observed in Q. ilex subsp. ballota pollen curves were attributed to the considerable influence both of weather conditions during pollination and pollen production. In years with high pollen production and weather conditions favouring pollen release, Q. ilex subsp. ballota contributed almost 10% to the total Quercus pollen curve. Around 20% of the pollen trapped was captured before or after flowering periods.     

Airborne olive pollen in Vigo (Northwest Spain): a survey to forecast the onset and daily concentrations of the pollen season

Temperature is one of the main factors affecting the start of flowering in tree species that flower at the beginning of spring. Knowledge of the chilling and heat needs required by plants to overcome the period of dormancy enables us to determine the onset of pollination, which is of great importance to allergy sufferers. This study attempted to obtain behaviour models with a view to determining both the onset of the olive pollen season and daily pollen concentrations during the pollination period in Vigo. Monitoring was carried out using a Lanzoni VPPS 2000 pollen trap, from 1995 to 2002 inclusive.

Olea pollen is mainly detected during the spring, principally in May. Given the geographical location, the very limited presence of this tree in the study area and the low Olea pollen concentrations detected in northern Spain as a whole, the values recorded here in the atmosphere of Vigo are particularly striking. A strong correlation was observed between total quantity olive pollen collected over the season and rainfall recorded during the second fortnight in February. According to the proposed model, an average of 680 Chilling Hours (CH) are necessary to overcome the chill period and break the state of bud dormancy, and 481 Growth Degree Days (GDD) °C are needed to induce flowering. Models for predicting daily mean pollen concentrations combine temperature and the previous days' pollen concentrations as predictor variables to provide a high level of prediction.     

The North Atlantic Oscillation synchronises fruit production in western European forests

Weather and its lagged effects have been associated with interannual variability and synchrony of fruit production for several tree species. Such relationships are used often in hypotheses relating interannual variability in fruit production with tree resources or favourable pollinating conditions and with synchrony in fruit production among sites through the Moran effect (the synchronisation of biological processes among populations driven by meteorological variability) or the local availability of pollen. Climatic teleconnections, such as the North Atlantic Oscillation (NAO), representing weather packages, however, have rarely been correlated with fruit production, despite often being better predictors of ecological processes than is local weather. The aim of this study was to test the utility of seasonal NAO indices for predicting interannual variability and synchrony in fruit production using data from 76 forests of Abies alba, Fagus sylvatica, Picea abies, Pseudotsuga menziesii, Quercus petraea, and Q. robur distributed across central Europe. Interannual variability in fruit production for all species was significantly correlated with seasonal NAO indices, which were more prominently important predictors than local meteorological variables. The relationships identified by these analyses indicated that proximal causes were mostly responsible for the interannual variability in fruit production, supporting the premise that local tree resources and favourable pollinating conditions are needed to produce large fruit crops. Synchrony in fruit production between forests was mainly associated with weather and geographical distance among sites. Also, fruit production for a given year was less variable among sites during warm and dry springs (negative spring NAO phases). Our results identify the Moran effect as the most likely mechanism for synchronisation of fruit production at large geographical scales and the possibility that pollen availability plays a role in synchronising fruit production at local scales. Our results highlight the influence of the NAO on the patterns of fruit production across western Europe.     

Annual variation in floral phenology and pollen production in a 25‐year‐old plantation of Tectona grandis

Teak is a timber tree that is widely distributed in the tropics. Several studies on pollination and reproductive biology have been conducted, but generally information on flowering phenology and annual variation in total pollen production per tree is lacking. The reproductive phenology as well as flower‐ and pollen grain production of individuals in a population is important to theoreticians, field biologists and plant breeders, as they determine the distribution of genotypes within populations and influences the degree of differentiation among populations. This study reports flowering phenology and variation in total flower, fruit‐ and pollen production per tree in teak in a 25‐year‐old plantation across three consecutive years (2006–2008). The results show that the date of onset and end of flowering was highly variable across years. The longest flowering period of 93 days was observed in 2006. There was an asynchrony in the number of open flowers due to differences in time of anthesis among individuals (± 2 days) and inflorescences within individuals (± 6 h). The production of pollen grains per tree in 2007 was 33%, i.e. 16% more compared to 2006 and 2008. The fruit production per tree was 42% and 27% higher in 2007 compared to 2006 and 2008. Concentration of pollen grains (both on jelly‐coated microscopic slides and stigmas) were highest between noon and 2 pm. At this time, the stigmatic pollen load ranged between 4–8 pollen grains per stigma, which is sufficient for fruit development. The study concludes that the asynchronization of the flower opening might give rise to a high amount of self‐pollination in the stand, ultimately leading to poor fruit setting. Also, the large production of flowers and pollen per tree induced geitonogamy and decreased female fitness, as T. grandis is preferentially an out‐crossing species.     

Differences between airborne pollen and flowering phenology of urban trees with reference to production, dispersal and interannual climate variability

Annual totals of daily arboreal pollen concentrations were analysed in Mar del Plata (Argentina) during 1993 and 1994. Flowering patterns were associated with timing and intensity of pollen appearing in the air. Seasonal climatic parameters before the start of flowering and current weather conditions during dispersion were considered.Flowering showed a regular pattern between years and it could be defined by cumulated pollen percentages. Arboreal pollen counts were higher in the first year and is probably due to 1) better climatic conditions connected with pollen productivity and 2) lower precipitation after pollen emission. Betula and Q. ilex showed an opposite behaviour that appears to be caused by a biennial fluctuating rhythm of pollen production.     

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.     

FLORAL BIOLOGY,HUMMINGBIRD POLLINATION AND FRUIT PRODUCTION OF TRUMPET CREEPER (CAMPSIS RADICANS,BIGNONIACEAE)

Trumpet creeper is self-incompatible and bears long, tubular, orange flowers from June to September. Flowering peaks rapidly, then declines and continues at low levels for several weeks. The initial burst of flowering may attract pollinators that return even during subsequent reduced flowering. Most flowers open before noon and nectar production totals 110 μl of 26% sucrose equivalents per flower, an exceptionally high production for a temperate zone plant. Production ceases within 20–30 hr of flower opening, but corollas persist for several days and may serve to attract pollinators. Effective pollination reduces the period of stigma receptivity and speeds closing of stigma lobes. Only 1–9% of flowers produced mature fruits at four sites in Illinois and Missouri. Roughly 400 pollen grains had to be deposited on a receptive stigma to cause fruit development beyond an initial period of high abortion. At two sites, 17% and 89% of stigmas received over 400 pollen grains. Assuming 50% of deposited grains were from the same plant, fruit production at one site was clearly pollinator limited, that at the second site may have been. Ruby-throated Hummingbirds (Archilochus colubris) deposited ten times as much pollen per stigma per visit as honeybees (Apis mellifera) and bumblebees (Bombus spp.). Fruit set was highest where rubythroat visitation was most frequent. Trumpet creeper appears primarily adapted for hummingbird pollination, but can also be adequately pollinated by honeybees and bumblebees. This is one of the first attempts to relate pollen-depositing capabilities of pollinators of any plant to pollen requirements for fruit production. Several characteristics suggest that trumpet creeper may be adapted to pollination at low densities (often called traplining) in its presumed original, woodland, habitat.     

Factors affecting fruit and seed production of Paeonia ostii “Feng Dan”, an economically important oil tree

Many factors may affect reproduction of animal-pollinated species. In this study, the effects of pollen limitation, attractive traits (flower number, plant height and flower width) and flowering phenological traits (flowering onset, duration and synchrony) on female reproduction, as well as the patterns of variation in fruit and seed production within plants, were investigated in Paeonia ostii “Feng Dan” over two flowering seasons (2018 and 2019). Fruit set was very high (90%), and pollen supplementation did not increase fruit and seed production in either year, indicating no pollen limitation. Fruit set, ovule number per fruit and mean individual seed weight per fruit were not affected by any of the six attractive and phenological traits in either year, whereas seed number per fruit was related to the three attractive traits in one or both years. Seed number per plant was positively affected by the three attractive traits and best explained by flower number in both years, but the effect of each of the three phenological traits on seed number per plant differed between years. Within plants, the fruit set, ovule number, seed set and seed number per fruit declined from early- to late-opening flowers, presumably because of resource preemption, but the mean individual seed weight did not vary across the flowering sequence. Our study shows that attractive traits of Paeonia ostii “Feng Dan” are more important than flowering phenological traits in the prediction of total seed production per plant.     

WITHIN- AND AMONG-TREE VARIATION IN FLOWER AND FRUIT PRODUCTION IN TWO SPECIES OF CARYA (JUGLANDACEAE)

The patterns of variability in the production of staminate inflorescences, pistillate flowers, and fruits for Carya ovata (Mill.) K. Koch and C. tomentosa (Poir.) Nutt. at Hutcheson Memorial Forest (Somerset County, New Jersey) were examined over a four-year period. We sought to determine 1) the patterns of variability in flowering and fruiting (within-trees, among-trees, and between-years), 2) if variable flowering might account for observed nut-bearing patterns, and 3) what were the relative contributions of intrinsic (genetic) and/or extrinsic (environmental) factors in determining flower production and fruit set. In general, our fine-scale analysis of shoots within canopies did not reveal a distinct mast fruiting pattern. While the number of male and female flowers varied significantly (among trees and between years), fruit set was not markedly affected. Variability of flowering and fruiting among shoots within trees was low. Both flowering and fruiting were observed to have a strong genetic and/or microenvironmental basis; however, flowering appeared more plastic and thus more sensitive to yearly environmental vagaries than did fruiting. Favorable environmental conditions at the time of flower differentiation may result in increased flower production; but, this does not necessarily result in increased fruit set. Many pistillate flowers abscise around the time of pollination and fertilization, apparently adjusting fruit set to available shoot resources. Approximately 50% of the pistillate flowers of both species fail to set fruit. Overall, individual trees exhibit their own flowering and fruiting schedules, suggesting the need to account for this level of variability in future studies of mast fruiting.     

Pollen limitation and seed set associated with year-to-year variation in flowering of Gmelina arborea in a natural tropical forest

The year-to-year variations in flowering, pollen and fruit production in ten Gmelina arborea individuals in a natural forest were observed over a period of five years, 2009?2013, and pollinator visits were observed closely over two years, 2011 and 2012. A pollen supplementation experiment was also undertaken in two years (2011 and 2012) of contrasting flowering levels. Considerable year-to-year variations were observed in flower, pollen and fruit production. The observed variation represented a normal sequence of good-year and poor-year cycling which is most parsimoniously attributed to resource allocation. The average level of pollen production per individual tree in good flowering years oscillated between 6.6 and 9.62 × 10⁸, which in the poor flowering years was between 1.92 and 3.07 × 10⁸. The magnitude of pollen limitation across years was highly significant (p < 0.0001). Fruit set through supplemental pollination was 73% and 96% greater than that of the open-pollinated branches in the year 2011 and 2012, respectively. Pollen limitation, irrespective of the arrival of outcross pollen, can reduce annual seed set in predominantly bee-pollinated trees. However, various other factors may cause flower abortion in addition to pollen limitation. The results of this study would be very valuable to the seed orchard managers and the silviculturists to manage the seed production areas (SPAs) of G. arborea. The study ultimately recommends supplemental pollination in seed orchards of G. arborea for better genetic gain and good seed yield.     

Air and surface soil samples – two different pairs of shoes? Comparing the pollen spectrum on different days of the pollen season

The pollen spectra of air and surface soil samples from a rooftop (at 14 m) and from ground level (at 1.6 m) in the suburbs of Vienna (Austria) were compared. Two soil samples and two air samples were taken on four different days to account for possible differences: in winter when no pollination occurred (reference day), in spring during the main flowering of Betula (birch day), in spring/summer during the main flowering of Poaceae (grass day), and in autumn during the main flowering of Ambrosia (ragweed day). Thirty-five different pollen types were used to describe the pollen spectra. Frequencies of certain pollen types reflect a seasonal impact on both the surface soil and air samples and show a similarity between air and soil samples on most of the days. However, the seasonal impact is higher in the air samples and shows a high consistency for ground and rooftop level. Kendall’s tau correlation coefficients further substantiate the similarities of the samples especially for the pollen season days. Exceptions include the winter day when pollination was low and the air samples recorded nearly no pollen at all, and the ragweed day when Ambrosia pollen was abundant in three of four samples but not in the ground surface soil sample. Thus, (1) air and surface pollen samples record similar signals during the pollen season but not during the ragweed and winter season and (2) air and surface pollen samples show the impact of local vegetation also in pollen traps located at different heights.     

Numerical analysis of surface and fossil pollen spectra from northern Fennoscandia

Aim Determination of the main directions of variance in an extensive data base of annual pollen deposition, and the relationship between pollen data from modified Tauber traps and palaeoecological data. Location Northern Finland and Norway. Methods Pollen analysis of annual samples from pollen traps and contiguous high‐resolution samples from a peat sequence. Numerical analysis (principal components analysis) of the resulting data. Results The main direction of variation in the trap data is due to the vegetation region in which each trap is located. A secondary direction of variation is due to the annual variability of pollen production of some of the tree taxa, especially Betula and Pinus. This annual variability is more conspicuous in ‘absolute’ data than it is in percentage data which, at this annual resolution, becomes more random. There are systematic differences, with respect to peat‐forming taxa, between pollen data from traps and pollen data from a peat profile collected over the same period of time. Main conclusions Annual variability in pollen production is rarely visible in fossil pollen samples because these cannot be sampled at precisely a 12‐month resolution. At near‐annual resolution sampling, it results in erratic percentage values which do not reflect changes in vegetation. Profiles sampled at near annual resolution are better analysed in terms of pollen accumulation rates with the realization that even these do not record changes in plant abundance but changes in pollen abundance. However, at the coarser temporal resolution common in most fossil samples it does not mask the origin of the pollen in terms of its vegetation region. Climate change may not be recognizable from pollen assemblages until the change has persisted in the same direction sufficiently long enough to alter the flowering (pollen production) pattern of the dominant trees.     

Pollen and nectar as a reward in the basal epidendroid Psilochilus modestus (Orchidaceae: Triphoreae): A study of floral morphology, reproductive biology and pollination strategy

Psilochilus modestus Barb. Rodr. is a basal epidendroid orchid occurring in both the semi-deciduous and Atlantic rain forests of the state of São Paulo, southeastern Brazil. This species presents a perfect flowering synchrony within populations, since all the mature buds of each plant open simultaneously in the morning hours of the same day. These flowers are available only for 1 day and are pollinated by several species of small solitary and social native bees. These bees exploit both pollen and nectar as a reward. The bees collecting pollen promote a higher fruit set and perform mainly self-pollination while those collecting nectar, which are less numerous, are responsible for an increase in cross-pollinations. P. modestus is self-compatible but pollinator dependent. Natural fruit set (open pollination) is low when compared with the numbers obtained under manual self- and cross-pollination. Low fruit set in natural conditions is related to deficient pollen transfer, and pollinator inefficiency seems to be the main factor. Some factors, such as the small amount of nectar produced, the low number of flowers per inflorescence and their availability for 1 day only added to the perfect flowering synchrony seem to be responsible for the increase of cross-pollinations. The offering of both pollen and nectar as a reward can represent a transitional condition in basal Epidendroideae. Based on floral morphology, reward production and pollinator behavior, the relationship of P. modestus with the basal and most derived groups within Orchidaceae is discussed.     

Olea Europaea Pollen in the Atmosphere of Málaga (S. Spain) and its Relationship with Meteorological Parameters

The atmosphere of Málaga was sampled from 1992 to 1995 for the pollen of Olea europaea L., one of the most common airborne allergens in the Mediterranean area. A Burkard seven-day-recording trap showed that the pollen of this species is principally detected during spring with the highest concentrations occurring in May. During the main pollination period, the 24 hour intradiurnal variation pattern showed a high degree of homogeneity with no noteworthy peaks. The correlations between the pollen concentrations recorded and the different meteorological parameters show that temperature, sunshine hours and wind direction are those most closely correlated with variations in the daily pollen count.     

Pollen concentrations inside private cars during the Poaceae and Artemisia spp. pollen season – a case study

A growing number of studies are researching indoor air concentrations of pollen in buildings, but to our knowledge no studies have dealt with the precise concentration of pollen inside private cars. The aim of this study was to assess the risk of exposure to pollen in private cars throughout the Poaceae and Artemisia spp. pollen season.

The study was conducted in the town of Lappeenranta and along Highway 6 in south‐east Finland between July 14 and August 17, 2003. The pollen concentrations were measured inside two moving and parked cars using rotorod‐type samplers. Surface and ambient Burkard samples were also collected.

Both Poaceae and Artemisia spp. pollen were recorded only on one day and in low concentrations (<10 pollen grains per cubic meter, pg/m³) inside moving and parked cars, whereas the concentrations of Betula spp. (0–15 vs. 0–12?pg/m³) and Pinus (0–41 vs. 0–80?pg/m³) ranged from low to moderate, respectively. The number of pollen grains on the inside surfaces of cars ranged from zero to 72?pg/cm² during the measurement periods.

The concentrations of Poaceae and Artemisia spp. pollen in the indoor air of the car during the flowering period were low, therefore, likely to cause reactions only in the most sensitive people. By contrast, even after the main flowering period the concentrations of Betula spp. pollen were on a level high enough to cause reactions in individuals with allergies.