What is pollen: botanical background and behaviour on surfaces

The botanical definition of pollen

Pollen are the male reproductive cells of seed plants packed in microspores produced in the stamens of flowering plants. The pollen grain contains the genetic information of the father plant and has as its biological function the reaching of a female flower for fertilisation. Pollen of wind-pollinating plants are specially optimised for air transport: they are light aerodynamic and produced in enormous quantities. More on the basic mechanism of ozone water on organic compounds: ozonewater.

Sporopollenin: the most resistant organic substance in nature

The outer layer of the pollen grain consists of sporopollenin a biopolymer that offers extreme resistance to chemical and biological degradation. That resistance explains why pollen fossils millions of years old are still recognisable in geological layers. Sporopollenin also contains proteins and lipids that determine the adhesiveness of the pollen grain and that react to ozone oxidation. Those organic components are the point of attack for the effectiveness of ozone water in pollen removal. More on the ozone water machine: ozone water machine.

Mass production: why there are so many pollen

Wind-pollinating plants produce pollen grains in astronomical quantities. A single birch tree produces during its flowering period of two to three weeks an estimated five billion pollen grains. With wind pollination the chance that an individual pollen grain reaches a flower of the same species is extremely small making enormous numbers necessary for successful reproduction. That mass production is the direct cause of the rapidly increasing pollen layer on outdoor surfaces during pollen season.

Distance and dispersal: how far do pollen travel

Pollen grains of wind pollinators are so light that they are transported by air streams over enormous distances. Birch pollen can under favourable meteorological conditions be found more than five hundred kilometres from the source tree. That long dispersal means pollen grains are present in the air even in areas without direct proximity of flowering plants. Pollen concentration in the air peaks in dry and windy weather; after rain concentration is temporarily strongly reduced as raindrops wash pollen grains from the air.

Electric charge: why pollen adhere to surfaces

Pollen grains build up an electrostatic charge during their transport through the air through friction with air molecules. That charge attracts pollen grains to surfaces with an opposite charge. Car paint glass plastic and metal all have specific electrostatic charges that attract pollen grains as soon as they come into the direct vicinity of those surfaces. The adhesiveness of the protein-rich outer layer reinforces adhesion after the pollen grain has reached the surface via electric attraction. More on removing pollen from car surfaces: removing pollen car.

Pollen season: succession per plant species

Pollen season is not one continuous period but consists of successive flowering seasons of different plant species. In the Netherlands Belgium and Germany hazel and alder start early in the year. Birches follow in spring as the most massive pollen producer in Western Europe. Grasses form the largest pollen producer during late spring and early summer. Some weeds such as mugwort continue flowering into early autumn. That succession of flowering species makes pollen season a lengthy phenomenon that can run from January to September in mild years.

Pollen grain size and visibility

Most wind-dispersed pollen grains are ten to twenty-five micrometres in size corresponding to a hundredth to a twenty-fourth of a millimetre. That size makes individual pollen grains invisible to the naked eye but the collective accumulation of millions of pollen grains on a surface is visible as a yellow or green haze. On white or light-coloured plastic that haze is most contrastingly visible. On dark surfaces the pollen layer is less conspicuous but equally present. More on removing pollen from windows: removing pollen windows.

Pollen and humidity: the effect of rain

Rain has a twofold effect on pollen. On one hand rain washes pollen grains from the air and temporarily strongly reduces air concentration of pollen which is noticeable after a rainy period as a day with a low pollen count. On the other hand the organic components in the outer layer of pollen grains partially dissolve in rainwater on surfaces. After evaporation of the rainwater those dissolved pollen residues remain as stains on the surface that are harder to remove than dry pollen grains. Those dried pollen residues after rain require longer contact time from ozone water for complete removal. More on removing pollen indoors: removing pollen home.

The organic composition as the basis for ozone water

The proteins lipids and carbohydrates in the outer layer of the pollen grain are organic compounds that react to the oxidation mechanism of dissolved ozone. The ozone oxidises the carbon compounds in the outer layer chemically attacks the adhesive structure and breaks down the adhesion of the pollen grain to the surface. After the oxidation reaction the ozone decomposes to oxygen and water without leaving active chemical residues on the surface. The two-cloth method is the practical application of this principle: two-cloth method. Cleaning without chemicals: cleaning without chemicals.

Pollen grains and insect pollination: a different type of pollen

Not all pollen are wind-dispersed pollen grains. Insect-pollinating plants such as roses apple trees and rapeseed produce larger stickier and heavier pollen grains that are transferred by insects from flower to flower. Those pollen grains are rarely the cause of pollen accumulation on outdoor surfaces: they are too heavy for wind dispersal and remain in the immediate vicinity of the plant. The pollen grains that settle on surfaces during pollen season and cause cleaning problems come almost exclusively from wind pollinators: birches grasses alders and some weeds.

Pollen concentration: daily and seasonal pattern

Pollen concentration in the air follows a daily pattern. Concentration rises in the morning as temperature increases and wind speed rises reaches a peak in the afternoon and falls in the evening when it becomes cooler and calmer. That daily cycle is the reason pollen concentration is typically lower early in the morning than in the afternoon: cleaning outdoor surfaces early in the morning gives a cleaner starting point for the day than cleaning in the afternoon when the pollen shower is at its highest. More on removing pollen from the car: removing pollen car.

Pollen grains and temperature: the effect of heat

High temperatures accelerate the drying of pollen grains on surfaces. A pollen grain landing on a metal or glass surface at high temperatures dries faster than at low temperatures. Dried pollen grains are harder to remove than fresh ones because the adhesive structure is hardened by the heat. Cleaning surfaces that receive a lot of pollen early in the day before daytime temperature rises high gives the most effective result. Ozone water also reacts with dried pollen grains but requires longer contact time than with fresh pollen.

Pollen and climate change: longer seasons

Climatological studies show that pollen season in large parts of Europe has become longer than a few decades ago. Earlier spring and higher average temperatures lead to flowering plants starting earlier and the flowering period of some species being extended. Higher carbon dioxide concentrations in the atmosphere promote plant growth and pollen production in some species. These developments mean the cleaning-relevant period of pollen season for users of outdoor surfaces may become longer over the years. More on the workplace approach: removing pollen workplace.

Pollen grains on textiles versus hard surfaces

The behaviour of pollen grains differs significantly between textile and hard surfaces. On hard surfaces such as glass metal and plastic pollen grains remain on the outermost surface layer and are accessible for the oxidation reaction of ozone water. On textile surfaces pollen grains penetrate into the spaces between fibres and can be several fibre layers deep. That depth makes ozone water less effective on textiles than on hard surfaces: the ozone water less well reaches deeper pollen grains. That fundamental consideration explains why removing pollen from clothing has washing at 40 degrees as the most effective method and not exclusively the two-cloth method. More on removing pollen from clothing: removing pollen clothing.

Pollen grains and porous versus dense surfaces

On porous surfaces such as untreated wood stone and some types of plastic with an open cell structure pollen grains can partially penetrate into the material. That penetration depends on the porosity of the material and humidity: in wet conditions penetration is greater than in dry conditions as moisture expands the material and enlarges the pores. On dense closed surfaces such as polished metal glass and high-gloss plastic pollen grains remain on the outside and are most accessible for ozone treatment. That surface characteristic is one of the explanations for the fact that car paint windows and smooth plastic garden furniture are the most effectively ozone-water-cleanable pollen locations.

Costs and affordability

Understanding what pollen are and how they work helps in choosing the most effective cleaning method per surface type and degree of contamination. Questions? get in touch. Full overview: knowledge guide.

Testimonials

💬 "Only when I understood how pollen are composed and why they adhere so strongly did I also understand why ozone water is more effective than a dry cloth. The chemical basis makes sense when you know that pollen contain organic compounds that react to oxidation." — Ozone water installation user

Further reading

Full overview: ozone water knowledge guide. Removing pollen general: removing pollen. Pollen allergy cleaning: pollen allergy cleaning. Pollen home: removing pollen home.