New particle formation and growth in the marine atmosphere.

Atmospheric aerosols are considered as an important factor influencing the evolution of the climate. Their effect can be either direct by absorbing or reflecting solar radiation or indirect by interacting with clouds, and represents the highest uncertainty among all climate forcing agents. The cause of this uncertainty lies in (1) the lack of basic understanding of atmospheric new particle formation (NPF) and growth mechanisms to climate-relevant sizes - cloud condensation nuclei (CCN; seeds upon which cloud droplets may form) - and thus (2) improper incorporation of these microphysical processes in climate models. Therefore, the research proposed here is motivated by the need to identify the sources, transformations and sinks of newly formed particles that serve as CCN in the remote marine atmosphere a region relatively little influenced by anthropogenic activities. This study will be undertaken in the framework of the Atmospheric Tomography (ATom) airborne research experiment and involves at the National Oceanic and Atmospheric Administration (NOAA), Boulder, USA. The ATom flights will comprise repeated, global-scale measurements of atmospheric composition in the remote marine atmosphere. Based on these measurements the research will focus on aerosol modeling using tools such as (a) GISS-TOMAS, which is a combination of the TwO Moment Aerosol Sectional (TOMAS) aerosol microphysics model with the Goddard Institute for Space Studies General Circulation Model (GISS), and (b) Lagrangian trajectory model used to diagnose the influence of convective transport on in situ observations from aircraft. Input data for these model simulations will mostly be dry particle size distributions between ~ 4 to 1000 nm in diameter, spanning newly formed, CCN-active and larger particles collected during direct airborne measurement with Nucleation-Mode Aerosol Size Spectrometer (N-MASS) and optical particle counter - the Ultra-High Sensitivity Aerosol Size Spectrometer (UHSAS). This research will improve knowledge of the processes of new particle formation and growth to CCN- active size and will help constrain global simulations in critical and grossly under-sampled regions of the troposphere. Further, it is foreseen that this study will contribute to substantially strengthen the links and networking between the University of Vienna and leading US research institutes on atmospheric research.