AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The First Global Picture of Observation-Based Estimate on Continental Boundary Layer New Particle Formation
TUOMO NIEMINEN, Veli-Matti Kerminen, Tuukka Petäjä, Markku Kulmala, University of Eastern Finland
Abstract Number: 167 Working Group: Aerosols, Clouds, and Climate
Abstract Formation of secondary aerosol particles is a major source of atmospheric aerosols. Regional events of new particle formation (NPF) have been observed worldwide, but reports of the seasonality of the NPF related parameters are rather scarce.
We present a global picture on the relevance of NPF. We gathered observations of the annual cycle of NPF events from sites with at least one year of particle size distribution measurements available. The data of sub-micron aerosol number size distribution is analyzed to reveal the characteristic features (event frequencies, particle formation rates and growth rates) of the NPF events at different sites. A common size range of 10-25 nm was used for nucleation mode particles. Altogether we identified 35 measurement sites worldwide where aerosol size distributions have been measured for at least one year. These sites range from arctic and remote areas to heavily polluted megacities.
Regional NPF events were observed at all the sites throughout the year. Globally averaged NPF frequencies range from 12% of days during December-February to 31% of days in March-May. The smallest NPF frequencies occurred in polar areas (NPF occurring in less than 20% of days), and the highest in the African savannah area (over 60% of days).
The particle formation rates did not, on average, show large seasonal variation, but there exist large differences between different environments. The highest formation rates occur inside cities and other anthropogenically heavily influenced areas. In these areas the SO2 concentrations are typically high leading to high concentrations of sulphuric acid, which is one of the key precursor species in atmospheric NPF. On the other hand, the highest particle growth rates do not occur in these same areas of high formation rates, pointing to the decoupling of the mechanisms leading to the initial particle formation and the later growth of the particles.