The ozonolysis of two sesquiterpenes, α-humulene and β-caryophyllene, will be studied in a 570 L reactor. Gaseous products will be analyzed by FTIR. Particulate products will be sampled on filters and analyzed by liquid chromatography coupled to mass spectrometry. The reaction of water vapor with the Criegee biradicals will be investigated. Experiments in presence of HCHO and HCOOH will be performed in order to clarify the reaction mechanism. The role of different OH scavengers will be also studied.
Size distributions of aerosols will be obtained by SMPS. The temperature dependence of the aerosol yield will be assessed between 275 and 305 K. The total concentration of organic peroxides will be measured by iodometry. New methods will be explored for the detection of individual (hydro)peroxides.
The formation of oligomers and polymers will be investigated in presence and in absence of added acidity. Special extraction procedures will be designed, since polymers can be easily hydrolyzed when using H2O.
The hygroscopicity of the aerosols formed from terpenes will be determined. The CCN (Cloud Condensation Nuclei) activity of aerosols is estimated based on their hygroscopic growth. We will estimate the CCN activity of aerosols directly by using a CCN counter.
Given the very large number of reactions involved in the oxidation mechanism of large biogenic organic compounds, predictive tools must be developed in order to estimate the kinetic parameters of any reaction based on experimental data. We will rely on (i) quantum calculations of energy profiles by Density Functional Theory, Complete Active Space, Coupled Clusters, and by extrapolations of Gaussian methods, and (ii) advanced theoretical methods for the rates and products, based on Transition State Theory, RRKM, and Master Equation analysis.
Structure-Activity Relationships (SARs) will be derived from systematic studies based on these methods and on the available laboratory data, in particular for the following reaction classes:
These SARs should strongly enhance the reliability of the reaction parameters incorporated in models, when no experimental data is available.
The Leuven team will develop, on theoretical basis, complete degradation mechanisms for a number of key terpenes:
These mechanisms will be used to derive template mechanisms for other terpenes, as well as for other unsaturated organic compounds. Our study will focus on the formation of low-volatility species like (di-)carboxylic acids and multi-hydroxy substituted carbonyls.
These mechanisms will be introduced in a chemical box model at IASB-BIRA, following methods employed previously (Capouet et al., 2004). The non-explicit parts of the mechanisms will be parameterized, when necessary. The model and the mechanisms will be tested against laboratory data from IBOOT and from previous studies.
In a first step, the gas-particle partitioning of the terpenes oxidation products will be estimated using the absorptive model of Pankow (2004) and following the kinetic approach of Kamens et al. (1999). The vapor pressure prediction method developed for α-pinene products (Capouet and Müller, 2006) will be extended to the sesquiterpenes. Next, organic aerosols will be represented as a combination of a primarily organic phase (governed by the Pankow model) and a primarily aqueous phase (governed by Henry’s law) (Griffin et al., 2005). Since inorganic aerosols are believed to favor heterogeneous reactions enhancing the aerosol yield from terpenes, the model will be coupled to an inorganic aerosol model (e.g. SCAPE2).
The aerosol model will be coupled to the gas-phase oxidation model, and confronted to laboratory results obtained within IBOOT or in other studies in various conditions, including results from the BIOSOL project of the Belgian SPSD. The extent to which the model can reproduce the observed SOA yield in absence of parameterized heterogeneous reaction (polymer/oligomer formation) will be assessed. The possible role of such reactions will be explored, with a focus on the well-documented cases of glyoxal and other compounds.
Following on our recent work on the reactions of acetone, acetic acid, propionaldehyde, etc., we will conduct a detailed study on the impact of oxygenated compounds (e.g. acetone, acetic acid, hydroxyacetone, glycolaldehyde, acetaldehyde, glyoxal, nopinone) on the oxidant budget in the upper troposphere and lower stratosphere (UT/LS). The temperature and pressure dependence of the reaction of these compounds with OH and HO2 will be determined.
A reduced terpene degradation mechanism will be developed, based on the explicit mechanism described above. This reduced mechanism will be tested against the explicit mechanism using the box model in low- as well as in high-NOx conditions. A simplified representation of the gas-particle partitioning will be introduced in a global chemistry-transport model. The influence of inorganic (sulfate) aerosols on Secondary Organic Aerosols will be parameterized. The global model predictions for Organic Aerosols (OA) will be validated by comparison with field studies, like those obtained within the BIOSOL project. The impact of terpenes on the budget of oxidants will be assessed, as well as a possible range for the global production of aerosol from terpenes.
The follow-up committee of IBOOT is composed of potential users of IBOOT research results. The members of this committee are
The follow-up committee members will check the project advancement in relation to their area of expertise, and will provide suggestions for possible adjustments in the work plan.