10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Explaining Atmospheric Particle Growth by Organic Vapors of Biogenic and Anthropogenic Origin
CLAUDIA MOHR, Taina Yli-Juuti, Joel A. Thornton, Felipe Lopez-Hilfiker, Anna Lutz, Arto Heitto, Juan Hong, Neil Donahue, Ilona Riipinen, Wei Huang, Cheng Wu, Federico Bianchi, Qiaozhi Zha, Diego Aliaga, Liine Heikkinen, Markku Kulmala, Marcos Andrade, Stockholm University
Abstract Number: 1258 Working Group: Aerosol Chemistry
Abstract The ability of atmospheric aerosols to act as cloud condensation nuclei (CCN) is influenced by both the particles´ size and chemistry. For particles formed in the atmosphere via nucleation of vapors, this means that they must undergo significant growth before they can become active as CCN. The identification of the condensable organic vapors driving particle growth, and their sources, is thus fundamental for simulating changes to aerosol-cloud interactions, which are one of the most uncertain aspects of anthropogenic climate forcing.
We present particle growth studies from a combination of ambient measurements and process modelling at two locations influenced by new particle formation. We used measured concentrations of oxygenated organic vapors in ambient air as input for the particle growth model MABNAG to investigate identity and nature of the condensable organic vapors driving growth of newly formed particles.
Gas phase concentrations of oxidized organic species were measured in the boreal forest at Hyytiälä, Finland, in spring 2014 with a chemical ionization high-resolution time-of-flight mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS), using iodide as reagent ion. Based on derived molecular formulae of the measured compounds, we calculated their saturation concentrations, and grouped them in a 1-D volatility basis set (VBS). The time series of the organic concentrations grouped in the VBS, together with measured gas concentrations of sulfuric acid and ammonia, relative humidity and temperature, were then used to model the change in size and composition of a newly formed particle under the given ambient conditions. Simulated particle growth rates matched the observed particle growth rates measured with a differential mobility particle sizer within uncertainties. These results suggest that the measured distribution of gaseous oxygenated organic compounds is sufficient to explain particle growth to CCN-active sizes at this location. Most of the simulated growth can be assigned to condensation of low- or extremely low-volatile organic compounds, with significant contributions from nitrate containing compounds. A comparison of measured and modelled evaporative behavior of the grown particles indicates a negligible contribution of particle phase reactions, and points to gas-phase reactions and subsequent condensation of reaction products to be the main driver for particle growth under these conditions.
We also present particle growth observations from a distinctively different environment, where direct atmospheric observations of the life cycle and chemistry of aerosol particles from nucleation to cloud droplets are still scarce. We show first results from a comprehensive 6-month field campaign (December 2017 – May 2018) conducted at the GAW station Chacaltaya in the Bolivian Andes, at 5240 m a. s. l.. The influence of the emissions from the nearby city of La Paz, and of air masses from the Amazon during the rainy season, make this a highly interesting site to study atmospheric particle formation and growth processes. To this purpose we deploy several state-of the-art mass spectrometers. For this presentation we focus on results from the FIGAERO-CIMS and investigate the nature and relative importance of anthropogenic and biogenic organic components contributing to particle growth.