<p><strong>Abstract.</strong> Ice-nucleating particles (INPs) active at modest supercooling (e.g. −8<span class="thinspace"></span>°C; INP<sub>−8</sub>) can transform clouds from liquid to mixed phase, even at very small number concentrations (&lt;<span class="thinspace"></span>10<span class="thinspace"></span>m<sup>−3</sup>). Over the course of 15 months, we found very similar patterns in weekly concentrations of INP<sub>−8</sub> in PM<sub>10</sub> (median<span class="thinspace"></span> = <span class="thinspace"></span>1.7<span class="thinspace"></span>m<sup>−3</sup>, maximum<span class="thinspace"></span> = <span class="thinspace"></span>10.1<span class="thinspace"></span>m<sup>−3</sup>) and weekly amounts of rainfall (median<span class="thinspace"></span> = <span class="thinspace"></span>28<span class="thinspace"></span>mm, maximum<span class="thinspace"></span> = <span class="thinspace"></span>153<span class="thinspace"></span>mm) at Birkenes, southern Norway. Most INP<sub>−8</sub> were probably aerosolised locally by the impact of raindrops on plant, litter and soil surfaces. Major snowfall and heavy rain onto snow-covered ground were not mirrored by enhanced numbers of INP<sub>−8</sub>. Further, transport model calculations for large (&gt; 4<span class="thinspace"></span>m<sup>−3</sup>) and small (&lt;<span class="thinspace"></span>4<span class="thinspace"></span>m<sup>−3</sup>) numbers of INP<sub>−8</sub> revealed that potential source regions likely to provide precipitation to southern Norway were associated with large numbers of INP<sub>−8</sub>. The proportion of land cover and land use type in potential source regions was similar for large and small numbers of INP<sub>−8</sub>. In PM<sub>2. 5</sub> we found consistently about half as many INP<sub>−8</sub> as in PM<sub>10</sub>. From mid-May to mid-September, INP<sub>−8</sub> correlated positively with the fungal spore markers arabitol and mannitol, suggesting that some fraction of INP<sub>−8</sub> during that period may consist of fungal spores. In the future, warmer winters with more rain instead of snow may enhance airborne concentrations of INP<sub>−8</sub> during the cold season in southern Norway and in other regions with a similar climate.</p>