How much does new particle formation near the tropical tropopause contribute to stratospheric aerosol number concentration?

<p>Nucleation of ultrafine aerosols near the tropical tropopause, followed by transport throughout the stratosphere by the Brewer-Dobson circulation, is thought to be the primary source of stratospheric aerosol number concentration. &#160;However, depending on how rapidly the aerosols grow by condensation, many of the ultrafine particles generated by new particle formation (NPF) may be lost due to coagulation with accumulation-mode aerosols. &#160;In this study, we use recent high-altitude aircraft measurements of aerosol size distribution, along with microphysical calculations, to investigate this issue. &#160;Initial ultrafine and accumulation-mode size distributions are specified based on the aircraft measurements, and a bin microphysics model is used to simulate the evolution of the aerosol size distributions. &#160;Coagulation and condensation of gases such as sulfuric acid, ammonia, and nitric acid are included. &#160;Preliminary results indicate that for typical conditions, most of the ultrafine aerosols generated by NPF are removed by coagulation, resulting in a relatively small contribution to the total aerosol number concentration. &#160;We have used the model to investigate the sensitivities of total number concentration evolution to aerosol size distributions and condensation rates.</p>