The effects of thermodenuder treatment on the cloud condensation nuclei (CCN) activity and elemental composition of organic particles grown by alpha-pinene ozonolysis were investigated. The secondary organic material (SOM) was produced in a continuous-flow chamber, with steady-state organic particle mass concentrations M(org) ranging from 1.4 to 37 mu g m(-3). Particles exiting in the outflow were heated to temperatures T of up to 100 degrees C in a thermodenuder. The oxygen-to-carbon (O:C) and hydrogen-to-carbon (H:C) ratios were measured by on-line mass spectrometry. The observed elemental ratios were fit by a linear function, given by (H:C) = -0.8 (O:C) + 1.8 for 0.38 < O:C < 0.50. This fit included the dependence on both M(org) and T, meaning that the single variable of post-thermodenuder M(org) was sufficient as an accurate predictor for O:C(M(org)(T)) and H:C(M(org)(T)). This result suggests that equilibrium partitioning theory largely governed the initial volatilization in the thermodenuder. By comparison, the CCN activity had a different dependence on thermodenuder treatment. At 25 degrees C, the CCN activity was independent of M(org), having an effective hygroscopicity parameter kappa(org) of 0.103 +/- 0.002. At 100 degrees C, however, kappa(org) varied from 0.105 for M(org) = 1.4 mu g m(-3) to 0.079 for M(org) = 37 mu g m(-3), indicating that for high mass concentration the CCN activity decreased with heat treatment. The interpretation is that the oligomer fraction of the SOM increased at elevated T, both because of particle-phase reactions that produced oligomers under those conditions and because of the relative enrichment of lower-volatility oligomers in the SOM accompanying the evaporation of higher-volatility monomers from the SOM. Oligomers have high effective molecular weights and thereby significantly influence CCN activity. The production rates of different types of oligomers depend on the types and concentrations of functional groups present in the SOM, which in turn are strongly influenced by M(org). We conclude with a hypothesis, which is supported by a detailed molecular kinetic model, that the changes in kappa(org) at high T were more significant at high compared to low M(org) because particle-phase SOM at high M(org) contained a mix of functional groups favorable to oligomerization, such as carbonyl groups.
Using strong couplings of different Fabry-Perot (FP) resonators in metal-insulator-metal waveguides, a compact plasmonic wavelength demultiplexer is numerically demonstrated with high wavelength resolution. In the demultiplexer, it is found that new right-angle resonators emerge with bandwidth narrower than that of the isolated FP resonators. These narrowband right-angle resonators interfere with the broadband FP resonators, resulting in Fano-line shapes in the transmission spectra. Consequently, these sharp and asymmetric Fano-line shapes considerably increase the resolution of wavelength demultiplexing, which is significantly narrower than the full width of the isolated FP resonator. (C) 2011 Optical Society of America
This paper presents the results of laboratory studies on the condensational uptake of gaseous organic compounds in the exhaust of a light-duty gasoline engine onto preexisting sulfate and nitrate seed particles. Significant condensation of the gaseous organic compounds in the exhaust occurs onto these inorganic particles on a time scale of 25 min. The amount of condensed organic mass (COM) is proportional to the seed particle mass, suggesting that the uptake is due to dissolution determined by the equilibrium partitioning between gas phase and particles, not adsorption. The amount of dissolution in unit seed mass, S, decreases as a power function with increased dilution of the exhaust, ranging from 0.23 g g(-1) at a dilution ratio of 81, to 0.025 g g(-1) at a dilution ratio of 2230. It increases nonlinearly with increasing concentration of the total hydrocarbons in the gas phase (THC), rising from 0.12 g g(-1) to 0.26 g g(-1) for a CTHC increase of 1 to 18 mu g m(-3), suggesting that more organics are partitioned into the particles at higher gas phase concentrations. In terms of gas-particle partitioning, the condensational uptake of THC gases in gasoline engine exhaust can account for up to 30% of the total gas + particle THC. The organic mass spectrum of COM has the largest fragment at m/z 44, with mass ratios of mass fragments 43/44 and 57/44 at 0.59 and 2.91, much lower than those reported for gasoline engine primary organic aerosols. The mass fragment 44/total organic mass ratio of 0.097 indicates that COM contains large oxygenated components. By incorporating the present findings, regional air quality modelling results suggest that the condensational uptake of THC onto sulfate particles alone can be comparable to the primary particle mass under moderately polluted ambient conditions. These findings are important for modelling and regulating the air quality impacts of gasoline vehicular emissions.
We report the observation of a series of perylene bisimide derivatives containing two or three perylene moieties. Dramatically different assembling behavior can be observed under ambient conditions on highly oriented pyrolitic graphite (HOPG) surface with scanning tunneling microscopy (STM). The dihedral angles between the perylene moieties are suggested to be sensitively dependent on the linker units. The linear linker units could make the perylene moieties with spatial configuration be observed on the surface. The length of linear connecting parts would also influence the dihedral angles. The fundamental processes occurring at solid-liquid interfaces have been found, because of the extended observation time or elevated temperatures. All these results would help to comprehend the conformational polymorphism of carrier transport in the organic thin films.