Atmospheric Ions: Chemical Composition, Diurnal Variation, and Insights into New Particle Formation
Abstract
Ions in the atmosphere are mainly produced by cosmic radiation (CR) and radioactive decay of radon. To a first approximation, when an ion collides with a neutral molecule, the charge will be transferred if energetically favorable. Typical lifetimes of ions are on the order of several minutes, giving the ions time to reach a pseudo steady state with most of the negative charges on the strongest acids (e.g. sulfuric, nitric, malonic acid), and the positive charges on the strongest bases (e.g. ammonia, amines, pyridines, quinolines), although these species may only be present in trace amounts. This feature makes the analysis of the ambient ions particularly interesting, as sulfuric acid, amines and organic acids are often mentioned as precursors for new atmospheric new particle formation. In this study, a recently developed high-resolution mass spectrometer (APi-TOF) has been deployed in spring at the SMEAR II station in Hyytiälä, Finland. The chemical composition and temporal behavior of both ambient negative and positive ions were measured with higher sensitivity and mass resolution than in previous studies. Several new molecules and clusters were identified, utilizing the high mass accuracy and the time behavior of the ion peaks. The negative ion spectrum is dominated by highly oxygenated species, both inorganic and organic, consistent with by photo-chemical production, leading to strong diurnal cycles. At high H2SO4 concentrations, HSO4- and its clusters with one and two neutral H2SO4 molecules dominate the negative ion spectrum. These periods occur simultaneously with new particle formation events in Hyytiälä, suggesting that the sulfuric acid clusters play an important role in the initial formation of new particles. At the highest H2SO4 concentrations, larger H2SO4 clusters contain ammonia and amine molecules. Other peaks, likely organic acids containing sulfate and/or nitrate species, are also observed with distinct diurnal cycles. New results from both ambient observations and laboratory experiments will be discussed in relation to understanding chemical composition of cluster formation and new particle formation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.A23G..03W
- Keywords:
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- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: composition and chemistry;
- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE / Instruments and techniques