Abstract
Abstract. Thermodenuding particles can provide insights into aerosol composition and may be a way to create particles in laboratory chambers that better mimic the atmosphere. The relative volatility of secondary organic aerosol (SOA) was investigated by evaporating organics from the particles using a thermodenuder (TD) at temperatures between ∼60 and 100 °C. Volatility was influenced by the parent hydrocarbon, oxidation chemistry and relative humidity (RH). For SOA generated from ozonolysis, limonene had lower volatility than α-pinene, and OH scavengers had no influence on volatility. For photooxidation, α-pinene SOA was slightly more volatile than limonene SOA. Increasing RH also modestly increased volatility, while toluene SOA was unaffected by heating to 98 °C. For both α-pinene and limonene, the concentration of NOx and the HC / NOx ratio had no discernible effect on SOA volatility. Refractive indices for the original and denuded particles were retrieved from polar nephelometer measurements using parallel and perpendicular polarized 532 nm light. Retrievals were performed with a genetic algorithm method using Mie–Lorenz scattering theory and measured particle size distributions. Retrieved refractive indices for the SOA before thermodenuding varied between 1.35 and 1.61 depending on several factors, including parent hydrocarbon, oxidation chemistry, and SOA generation temperature. For high NOx SOA, as particles shrink, their refractive index returns to the value of the corresponding size particles before heating (limonene) or slightly higher (α-pinene). For low NOx however, the resulting refractive index is 0.05 ± 0.02 lower than the corresponding size undenuded particles. Additionally, for α-pinene SOA from ozonolysis with OH radical scavenger, resulting refractive indices were higher by about 0.03 after heating. Consistent with no change in size, refractive indices of toluene SOA were unaffected by heating. Finally, refractive index data available to date are reviewed, leading to the suggestion that the most representative values for mr at λ =532 nm for biogenic and anthropogenic SOA are 1.44 and 1.55, respectively.
Highlights
Retrievals were pertermine such as stihnegloepsticcaatltepraaralbmeEedtoae,rrsatshryemleSmvayentstryttoefamrcatdoiratainvde transfer specific absorption using Mie–Lorenz thSeocriye. nAdcdeitsionally, reliable formed with a genetic algorithm method using Mie–Lorenz phase function and polarization information is essential for scattering theory and measured particle size distributions. the interpretation of satellite and aircraft measurements to Retrieved refractive indices for the secondary organic aerosol (SOA) before thermode- infer aerosol optical depth, size and single scatter albedo nuding varied between 1.35 and 1.61 depending on several factors, including parent hydrocarbon, oxidation chemistry, (MOisrhgcahneicnkcoo,m20p0o7u)n.dsOcocnestaitunteS20c–i7e0n%ceof aerosol mass and SOA generation temperature
For high NOx SOA, as in the lower troposphere depending on space and time, of particles shrink, their refractive index returns to the value which roughly 70–90 % is contributed by secondary organic of the corresponding size particles before heating aerosols (SOAs) (Hallquist et al, 2009)
We investigate volatility and related mr’s for SOA generated from α-pinene, limonene and toluene using several different oxidation chemistries. αPinene and limonene are representative biogenic hydrocarbons, accounting for approximately 25 % and 16 % of global monoterpene emissions, respectively, and toluene is typically the most abundant aromatic compound emitted globally (Kanakidou et al, 2005)
Summary
Experiments were performed in a 24 m3 Teflon chamber constructed on the roof of the Math Sciences Building at UCLA. The chamber is described in detail by Chung et al (2008). Air is supplied to the chamber by two 33-gallon oil-free portable air compressors (Craftsman) after passing through a series of packed bed scrubbers filled with Purafil Triple Blend (Purafil Inc.), activated charcoal, and HEPA capsule filters (Gelman). The scrubbed air had < 5 particles cm−3, Atmos.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
