Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere

4 pages 359-363 in the print version, additional 7 pages online.Peer reviewe

Enrichment of 13C in diacids and related compounds during photochemical processing of aqueous aerosols: New proxy for organic aerosols aging

To investigate the applicability of compound specific stable carbon isotope ratios (delta C-13) of organics in assessment of their photochemical aging in the atmosphere, batch UV irradiation experiments were conducted on two ambient (anthropogenic and biogenic) aerosol samples in aqueous phase for 0.5-120 h. The irradiated samples were analyzed for delta C-13 of diacids, glyoxylic acid (omega C-2) and glyoxal. delta C-13 of diacids and related compounds became larger with irradiation time (i.e., aging), except for few cases. In general, delta C-13 of C-2-C-4 diacids showed an increasing trend with decreasing chain length. Based on delta C-13 of diacids and related compounds and their relations to their concentrations, we found that C-2 and C-3 are enriched with C-13 during the photochemical decomposition and production from their higher homologues and oxoacids. Photochemical breakdown of higher (>= C-3) to lower diacids is also important in the enrichment of C-13 in C3-C9 diacids whereas their production from primary precursors causes depletion of C-13. In case of omega C-2 and glyoxal, their photochemical production and further oxidation to highly oxygenated compounds both cause the enrichment of C-13. This study reveals that delta C-13 of diacids and related compounds can be used as a proxy to trace the aging of organic aerosols during long-range atmospheric transport

Ion-induced nucleation of pure biogenic particles

Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere, and that ions have a relatively minor role. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution