Thomas Rosenørn

Cloud condensation nuclei activation of monoterpene and sesquiterpene secondary organic aerosol

[1] The ability of biogenic secondary organic aerosol (SOA) to contribute to the concentration of cloud condensation nuclei (CCN) in the atmosphere is examined. Aerosol is generated by the ozonolysis reaction of monoterpenes (α-pinene, β-pinene, 3-carene, and limonene) and sesquiterpenes (β-caryophyllene, α-humulene, and o-cedrene) in a 10 m 3 temperature-controlled Teflon smog chamber. In some cases, a self-seeding technique is used, which enables high particle concentrations with the desired diameters without compromising particle composition and purity. The monoterpene SOA is excellent CCN material, and it activates similarly (average activation diameter equals 48 ± 8 nm at 1% supersaturation for the species used in this work) to highly water-soluble organic species. Its effective solubility in water was estimated to be in the range of 0.07- 0.40 g solute/g H 2 O. CCN measurements for sesquiterpene SOA (average activation diameter equals 120 ± 20 nm at 1% supersaturation for the species used in this work) show that it is less CCN active than monoterpene SOA. The initial terpene mixing ratio (between 3 and 100 ppb) does not affect the CCN activation for freshly generated SOA.

Cloud Droplet Activation of Amino Acid Aerosol Particles.

In this work we investigated the ability of a series of amino acids to act as cloud condensation nuclei using a static thermal gradient diffusion type cloud condensation nucleus counter. Particles of pure dry l-glycine, glycyl-glycine, l-serine, l-methionine, l-glutamic acid, l-aspartic acid, and l-tyrosine were studied as well as internally mixed dry particles containing ammonium sulfate and one or two of the following amino acids: l-methionine, l-aspartic acid, or l-tyrosine. The amino acids ranged in water solubility from high (>100 g/L), intermediate (10-100 g/L), low (3-10 g/L), to very low (<3 g/L). With the exception of l-methionine and l-tyrosine, all the studied pure amino acid particles activated as though they were fully soluble, although Kohler theory modified to account for limited solubility suggests that the activation of the intermediate and low solubility amino acids l-serine, l-glutamic acid, and l-aspartic acid should be limited by solubility. Activation of mixed particles containing at least 60% dry mass of l-tyrosine was limited by solubility, but the activation of the other investigated mixed particles behaved as if fully soluble. In general, the results show that particles containing amino acids at atmospherically relevant mixture ratios are good cloud condensation nuclei.

Micro- and Nanostructural Characteristics of Particles Before and After an Exhaust Gas Recirculation System Scrubber

This work provides insight into the morphology and mixing state of submicron particles in diesel exhaust from a ship engine with an exhaust gas recirculation scrubber. Particles from this low-speed ship engine on test bed were collected using a microinertial impactor with transmission electron microscopy (TEM) grids on two stages. Micro- and nanostructural characteristics of single particles were studied by TEM. Image analysis was carried out on overview and high-resolution images, revealing influence of the exhaust gas treatment (scrubber) on the particle morphology and mixing state. Soot agglomerates were found to be collapsed after scrubber, reflected by their change in fractal dimension (Df ) from 1.88 to 2.13. Soot was predominantly found internally mixed with other components, with a higher degree of internal mixing observed after scrubber. Soot nanostructural characteristics on the near atomic scale such as layer distance, lamella length, and tortuosity were not observed to be influenced by the scrubber. We also found that particles in the size range between 30 and 50 nm, which were abundant in the exhaust before and after scrubber, were not graphitic soot. Furthermore, we found indications that these particles are composed of other crystalline material (salts). Copyright 2013 American Association for Aerosol Research

Knudsen cell construction, validation and studies of the uptake of oxygenated fuel additives on soot

Intention, Goal, Scope, BackgroundThe properties of atmospheric particles are important to public health, radiative forcing of the atmosphere and to elucidating the chemical reactivity of atmospheric particles. We have constructed a Knudsen cell to study the uptake of organic compounds on soot. This article describes the construction and validation of the instrument, and our results on commercial soot concerning the uptake coefficient of ethanol, acetone, 1-butanol and diethoxymethane.ObjectivesFirst, a technical description of the instrument is presented. Next, its performance is validated by measuring the uptake of NO2 on hexane soot. Finally, the uptake coefficients of four oxygenated hydrocarbons on commercial soot are presented. The objective is to contribute to the understanding of the formation of particles in motor vehicle exhaust.MethodsA Knudsen cell is used to measure the uptake of specific gas-surface systems. A quadrupole mass spectrometer is used to determine the decay rate of a pulse of reagent gas in the reaction chamber.Results and DiscussionThe BET surface area of the commercial soot was 12.6 m2/g. The uptake coefficient (γ) has been determined for ethanol (γ0,BET=7.7+-4.8×10−8), 1-butanol (γ0,BET= 1.4±0.54×10−7), acetone (γ0,BET=1-5±0.15×10−7) and diethoxymethane (γ0,BET=2.6±0.61×10−7). These results are characteristic of the specific soot sample used. The ordering of the uptake coefficients, ethanol < 1-butanol ∼ acetone < diethoxymethane, can be ascribed to a combination of physical (size and mass) and chemical effects. In addition, the initial uptake coefficient for NO2 on fresh hexane soot was determined to be γ0,BET= 1.7±1.1×10−4.ConclusionsIn conclusion, we demonstrate that this instrument is able to measure uptake coefficients that are in agreement with accepted literature values. New data is presented concerning four light oxygenated hydrocarbons.Recommendations and OutlookA large amount of detailed information concerning individual heterogeneous reactions is necessary in order to model the composition of motor vehicle emissions. We look forward to increasing the size of this database. Results for a series of alcohols and alkanes will be presented in a forthcoming publication.