Estimating the contribution of ion-ion recombination to sub-2 nm cluster concentrations from atmospheric measurements
- ISSN: 16807316
- DOI: 10.5194/acp-13-11391-2013
The significance of ion-ion recombination for atmospheric new particle\nformation is not well quantified. Here we present and evaluate a method\nfor determining the size distribution of recombination products from the\nsize distributions of neutral and charged clusters. Our method takes\ninto account the production of recombination products in the collisions\nbetween oppositely charged ions and the loss due to coagulation.\nFurthermore, unlike previous studies, we also consider the effect of\ncondensational growth on the size distribution of recombination\nproducts. We applied our method to the data measured in Hyytiala,\nFinland, to estimate the contribution of ion-ion recombination to the\nconcentrations of atmospheric clusters in the size range of 0.9-2.1 nm.\nWe observed that the concentration of recombination products was highest\nin the size classes between 1.5 and 1.9 nm. The median concentrations of\nrecombination products were between 6 and 69 cm(-3) in different size\nclasses, which resulted in a small proportion of all neutral clusters,\nvarying between 0.2 and 13 %. When examining the whole size range\nbetween 0.9 and 2.1 nm, the median fraction of recombination products of\nall neutral clusters was only 1.5 %. We also investigated how the\nresults change if the effect of condensational growth is neglected. It\nseems that with that assumption the fragmentation of newly formed\nrecombination products has to be taken into account, or else the\nconcentration of recombination products is overestimated. Overall, we\nconcluded that our method provides reasonable results, which are\nconsistent with the earlier estimates on the contribution of\nrecombination products to atmospheric cluster population in Hyytiala.\nStill, in order to determine the size distribution of recombination\nproducts more accurately in the future, more precise measurements of the\nsize distribution of atmospheric clusters would be needed.