Kinetic Investigation of Secondary Organic Aerosol Formation of Products from Isoprene and Alpha-Pinene Oxidation
PETER METTKE, Laurent Poulain, Andreas Tilgner, Anke Mutzel, Martin Brüggemann, Hartmut Herrmann, Leibniz Institute for Tropospheric Research
Abstract Number: 284
Working Group: Aerosol Chemistry
Abstract
Isoprene and monoterpene oxidation have been shown to contribute significantly to the formation of secondary organic aerosol (SOA) in recent decades. However, the involved SOA formation pathways are not clearly understood leading to large discrepancies in observed and predicted formation rates and spatial distributions of SOA by atmospheric chemistry models.
Isoprene hydroxy hydroperoxides (ISOPOOH) are the main first-generation products of isoprene OH oxidation in rural areas. Further oxidation leads to the formation of highly oxidized ISOPOOH oxidation products, that have been identified as important SOA precursors previously. Similarly, oxidation products of α-pinene have been shown to make up large fractions of SOA. Nonetheless, kinetic investigations of the corresponding SOA formation processes are largely missing, leaving huge uncertainties in evaluating their impact on atmospheric chemistry, and thus, its implications for climatic processes.
Within the present work, the two most abundant isomers of isoprene-derived hydroxy hydroperoxides (ISOPOOH) have been synthesized using a novel synthetic procedure. The products were characterized using nuclear magnetic resonance (NMR) spectroscopy and online MS techniques, namely PTR‑ToFMS, AMS and CI‑APi-ToFMS. Moreover, to elucidate gas-particle interactions, the partitioning behaviour of 1,2‑ISOPOOH was investigated in more detail for various seed particles. For acidic seed particles an uptake of 1,2-ISOPOOH with a specific uptake coefficient of γ=(9±4)×10-3 was observed.
Furthermore, the OH oxidation of 1,2‑ISOPOOH as well as α-pinene under low-NOx conditions was studied. The formation of numerous highly oxygenated organic molecules was observed. Subsequently, the uptake coefficients of the individual compounds were determined for two different seed particle compositions for both precursor compounds and analysed using a resistance model which considers limitations by gas- or particle-phase processes. Finally, overall trends for specific uptake coefficients depending on molecular properties, such as vapor pressure, molecular mass or their respective O/C ratio were investigated.