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Abstract
Abstract. Secondary organic aerosol (SOA) formation has been investigated as a function of temperature and humidity for the ozone-initiated reaction of the two monoterpenes α-pinene (243–313 K) and limonene (253–313 K) using the 84.5 m3 aerosol chamber AIDA. This paper gives an overview of the measurements done and presents parameters specifically useful for aerosol yield calculations. The ozonolysis reaction, selected oxidation products and subsequent aerosol formation were followed using several analytical techniques for both gas and condensed phase characterisation. The effective densities of the SOA were determined by comparing mass and volume size distributions to (1.25±0.10) g cm−3 for α-pinene and (1.3±0.2) g cm−3 for limonene. The detailed aerosol dynamics code COSIMA-SOA proved to be essential for a comprehensive evaluation of the experimental results and for providing parameterisations directly applicable within atmospheric models. The COSIMA-assisted analysis succeeded to reproduce the observed time evolutions of SOA total mass, number and size distributions by adjusting the following properties of two oxidation product proxies: individual yield parameters (αi), partitioning coefficients (Ki), vapour pressures (pi) and effective accommodation coefficients (γi). For these properties temperature dependences were derived and parameterised. Vapour pressures and partitioning coefficients followed classical Clausius – Clapeyron temperature dependences. From this relationship enthalpies of vaporisation were derived for the two more and less volatile product proxies of α-pinene: (59±8) kJ mol−1 and (24±9) kJ mol−1, and limonene: (55±14) kJ mol−1 and (25±12) kJ mol−1. The more volatile proxy components had a notably low enthalpy of vaporisation while the less volatile proxy components gave enthalpies of vaporisation comparable with those of typical products from α-pinene oxidation, e.g. pinonaldehyde and pinonic acid.
Highlights
Biogenic sources dominate the global emissions of volatile organic compounds into the atmosphere
Because significant amounts of newly formed condensable oxidation products were lost directly from the gas phase to the walls of the AIDA chamber, an effect which cannot be corrected for by straightforward procedures, it proved impossible to conduct an analogous analysis within the framework of the K-α approach for comparison
Including pinonaldehyde in our model analysis with the molar yields determined by Tillmann et al (2009) but relying on the vapour pressure parameterisation derived by Hallquist et al (1997) leads to a stronger temperature dependence of the vapour pressure of the remaining effective semivolatile Secondary organic aerosol (SOA) component as reflected by an increase of the evaporation enthalpy to about 34 kJ mol−1
Summary
Biogenic sources dominate the global emissions of volatile organic compounds into the atmosphere. Global transport models predict a substantial chemical production of organic aerosol in the free troposphere (Tsigaridis et al, 2005) and project an even higher fraction of SOA from oxidation of monoterpenes in future scenarios (Tsigaridis and Kanakidou, 2007). This paper presents investigations on the yield of SOA material from the ozonolysis of α-pinene and limonene under simulated tropospheric conditions in the large aerosol chamber AIDA (Saathoff et al, 2003) on time scales of up to 36 h and at temperatures between 243 and 313 K. In order to evaluate the data and parameterise physical aerosol properties a dynamic SOA model was developed and applied (Naumann, 2009)
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