<p><strong>Abstract.</strong> Primary biological aerosol particles (PBAPs) are ubiquitous in the atmosphere and constitute ∼<span class="thinspace"></span>30<span class="thinspace"></span>% of atmospheric aerosol particle mass in sizes<span class="thinspace"></span> &amp;gt;<span class="thinspace"></span>1<span class="thinspace"></span>µm. PBAP components, such as bacteria, fungi and pollen, may affect the climate by acting as cloud-active particles, thus having an effect on cloud and

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... ion formation processes. In this study, size-segregated aerosol samples (&amp;lt;<span class="thinspace"></span>1.0, 1&amp;ndash;2.5, 2.5&amp;ndash;10 and &amp;gt;<span class="thinspace"></span>10<span class="thinspace"></span>µm) were collected in boreal forest (Hyytiälä, Finland) during a 9-month period covering all seasons and analysed for free amino acids (FAAs), DNA concentration and microorganism (bacteria, <i>Pseudomonas</i> and fungi). Measurements were performed using tandem mass spectrometry, spectrophotometry and qPCR, respectively. Meteorological parameters and statistical analysis were used to study their atmospheric implication for results. Distinct annual patterns of PBAP components were observed, late spring and autumn being seasons of dominant occurrence. Elevated abundances of FAAs and bacteria were observed during the local pollen season, whereas fungi were observed at the highest level during autumn. Meteorological parameters such as air and soil temperature, radiation and rainfall were observed to possess a close relationship with PBAP abundances on an annual scale.</p>