Temporal variation in the spectrum and concentration of airborne microalgae and cyanobacteria in the urban environments of inland temperate climate

Despite their non-negligible representation among the airborne bioparticles and known allergenicity, autotrophic microorganisms—microalgae and cyanobacteria—are not commonly reported or studied by aerobiological monitoring stations due to the challenging identification in their desiccated and fragmented state. Using a gravimetric method with open plates at the same time as Hirst-type volumetric bioparticle sampler, we were able to cultivate the autotrophic microorganisms and use it as a reference for correct retrospective identification of the microalgae and cyanobacteria captured by the volumetric trap. Only in this way, reliable data on their presence in the air of a given area can be obtained and analysed with regard to their temporal variation and environmental factors. We gained these data for an inland temperate region over 3 years (2018, 2020–2021), identifying the microalgal genera Bracteacoccus , Desmococcus , Geminella , Chlorella , Klebsormidium , and Stichococcus (Chlorophyta) and cyanobacterium Nostoc in the volumetric trap samples and three more in the cultivated samples. The mean annual concentration recorded over 3 years was 19,182 cells*day/m 3 , with the greatest contribution from the genus Bracteacoccus (57%). Unlike some other bioparticles like pollen grains, autotrophic microorganisms were present in the samples over the course of the whole year, with greatest abundance in February and April. The peak daily concentration reached the highest value (1011 cells/m 3 ) in 2021, while the mean daily concentration during the three analysed years was 56 cells/m 3 . The analysis of intra-diurnal patterns showed their increased presence in daylight hours, with a peak between 2 and 4 p.m. for most genera, which is especially important due to their potential to trigger allergy symptoms. From the environmental factors, wind speed had a most significant positive association with their concentration, while relative air humidity had a negative influence.