Advances in the Separation and Detection of Secondary Organic Aerosol Produced by Decamethylcyclopentasiloxane (D 5 ) in Laboratory-Generated and Ambient Aerosol
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Sea spray aerosols contain a large array of organic compounds that contribute to high viscosities at low relative humidity and temperature thereby slowing translational diffusion of water. The Stokes-Einstein equation describes how viscosity is inversely correlated with the translational diffusion coefficient of the diffusing species. However, recent studies indicate the Stokes-Einstein equation breaks down at high viscosities achieved in the particle phase (>10 12 Pa·s), underestimating the predicted water diffusion coefficient by orders of magnitude and revealing the need for directly studying the diffusion of water in single aerosol. A new method is reported for measuring the water diffusion coefficient in single suspended charged sucrose-water microdroplets in the 30-60 micron diameter range. The translational water diffusion coefficient is quantified using H 2 O/D 2 O isotope exchange technique between 26-54% relative humidity (RH) with a recently developed mobile electrodynamic balance apparatus. The results are in good agreement with literature, particularly the Vignes-type parameterization from experiments using isotope exchange and optical tweezers. This mobile electrodynamic balance will allow future studies of atmospherically relevant chemical systems, including field studies.more » « less
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null (Ed.)This study presents a comprehensive investigation on the aerosol synthesis of a semiconducting double perovskite oxide with a nominal composition of KBaTeBiO 6 , which is considered as a potential candidate for CO 2 photoreduction. We demonstrate the rapid synthesis of the multispecies compounds KBaTeBiO 6 with extreme high purity and controllable size through a single-step furnace aerosol reactor (FuAR) process. The formation mechanism of the perovskite in the aerosol route is investigated using thermogravimetric analysis to identify the optimal reference temperature, residence time and other operational parameters in the FuAR synthesis process to obtain the highly pure KBaTeBiO 6 nanoparticles. It is observed that particle formation in the FuAR is based on a mixture of gas-to-particle and liquid-to-particle mechanisms. The phase purity of the perovskite nanoparticles depends on the ratio of the residence time and the reaction time. The particle size is strongly affected by the precursor concentration, residence time and the furnace temperature. Finally, the photocatalytic performance of the synthesized KBaTeBiO 6 nanoparticles is investigated for CO 2 photoreduction under UV-light. The best performing sample exhibits an average CO production rate of 180 μmol g −1 h −1 in the first half hour with a quantum efficiency of 1.19%, demonstrating KBaTeBiO 6 as a promising photocatalyst for CO 2 photoreduction.more » « less
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We examined the reactive uptake of dinitrogen pentoxide (N 2 O 5 ) to authentic biomass-burning aerosol (BBA) using a small chamber reservoir in combination with an entrained aerosol flow tube. BBA was generated from four different fuel types and the reactivity of N 2 O 5 was probed from 30 to 70% relative humidity (RH). The N 2 O 5 reactive uptake coefficient, γ (N 2 O 5 ), depended upon RH, fuel type, and to a lesser degree on aerosol chloride mass fractions. The γ (N 2 O 5 ) ranged from 2.0 (±0.4) ×10 −3 on black needlerush derived BBA at 30% RH to 6.0 (±0.6) ×10 −3 on wiregrass derived BBA at 65% RH. Major N 2 O 5 reaction products were observed including gaseous ClNO 2 and HNO 3 and particulate nitrate, and used to create a reactive nitrogen budget. Black needlerush BBA had the most particulate chloride, and the only measured ClNO 2 yield > 1%. The ClNO 2 yield on black needlerush decayed from an initial value of ∼100% to ∼30% over the course of the burn experiment, suggesting a depletion of BBA chloride over time. Black needlerush was also the only fuel for which the reactive nitrogen budget indicated other N-containing products were generated. Generally, the results suggest limited chloride availability for heterogeneous reaction for BBA in the RH range probed here, including BBA with chloride mass fractions on the higher end of previously reported values (∼17–34%). Though less than fresh sea spray aerosol, ∼50%. We use these measured quantities to discuss the implications for nocturnal aerosol nitrate formation, the chemical fate of N 2 O 5 (g), and the availability of particulate chloride for activation in biomass burning plumes.more » « less
