An Overview of Atmospheric Mass Spectrometric Observation of the Chemical Composition of Aerosol and Condensing Gas Species

Description

Collaboators: Dept. of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA University of Helsinki, Finland University of Washington, Seattle, WA, USA Fundamental, understanding and modeling of the atmospheric aerosol life cycle is required to evaluate anthropogenic aerosol impacts, and thus climate sensitivity, in current, past and future climate. Over the last decade or so, the application and deployment of continuous mass spectrometry has determined the chemical composition of sub-micron aerosol, resolving inorganic and organic chemical budgets associated with primary emission, secondary condensation and new particle formation, all of which are critical for evaluation of direct and indirect (cloud) effects. The major (new) result is that roughly half of the aerosol is composed of secondary organic, carbon-containing species, that are highly oxidized and significantly hygroscopic CCN active. What has been lacking for ambient observation is the capability to extract detailed source apportionment of this complex organic. Most recently, the development and application of chemical ionization time-of-flight mass spectrometry (ToF-CIMS) has provided molecular signatures that have the potential to distinguish anthropogenic and biogenic sources – and their oxidation processes – of aerosol components, both in the gas (condensing) and aerosol phases. This includes laboratory and ambient observations, connecting new particle and accumulation (CCN) growth. For example, molecular clusters, inorganic and organic, have been resolved in nucleation and growth of nanoparticles, distinguishing for the first time the relative role of sulfuric acid and extremely low volatility organic compounds (ELVOC) in determining the aerosol number (e.g. CCN) budget. An overview of atmospheric aerosol mass spectrometric observations will be presented. The challenge is to connect the fundamental chemical and physical processes to evaluation of the aerosol lifecycle now and in the pre-industrial atmosphere, which determines aerosol radiative forcing as reported by the IPCC. Looking to the future, where North American and European emissions of inorganic and organic precursors are decreasing while Asian emissions increase, first principle process understanding is required to quantitatively predict aerosol number and mass loading and their radiative impact.