The neutralization of acidic aerosols by ammonia has been studied through experiments which combine ambient air with laboratory generated sulfuric acid aerosol. Results indicated that acidic aerosol mixed with organic free air and ammonia was neutralized on a time scale < 1 min, consistent with expectations. However, in the presence of ambient organic gases and ammonia, the rate of aerosol neutralization is significantly reduced. This reduction in ammonia uptake was concurrent with an increase in the amount of particle phase organics. A steady state in the NH4+/SO42- in the presence of organic gases was established on time scales of 10 min to several hours, corresponding to NH3 uptake coefficients in the range of 4 x 10(-3)-2 x 10(-4). The degree to which neutralization was slowed was dependent upon the initial ammonia concentration and the organic mass added to the aerosols. These results suggest that inorganic equilibrium thermodynamic models may overestimate the rate of ammonia uptake and that ambient particles may remain acidic for longer than previously expected.
Dielectric waveguide with deep subwavelength mode confinement based on coupled semiconductor nanowires is proposed. Through the coupling between two adjacent nanowires with high refractive indexes, light can be efficiently confined in the nano-gap between the nanowires with a low refractive index. Numerical simulations indicate that the effective mode area of such a waveguide can be as small as lambda(2)(0)/200, which is one order of magnitude smaller than that of a single nanowire, and such a mode confinement is comparable to that of hybrid plasmonic waveguide. It is also shown that from the view of real applications, possible existing low refractive index oxidization layers of nanowires, low refractive index substrate and small deviation of nanowire dimensions do not have significant influence on the property of the waveguide. As the propagation length is theoretically infinite for dielectric waveguides, such a coupled nanowire waveguide with deep subwavelength mode confinement may have important applications in future integrated photonic circuits.