The response of localized surface plasmon resonance (LSPR) spectra of gold and silver nanoparticles, and gold nanoshells to organic vapors was investigated. The surface area of nanomaterials was sufficiently high for quantitative... more
The response of localized surface plasmon resonance (LSPR) spectra of gold and silver nanoparticles, and gold nanoshells to organic vapors was investigated. The surface area of nanomaterials was sufficiently high for quantitative adsorption of volatile organic compounds (VOCs). Surface adsorption and condensation of VOCs caused the environmental refractive index to increase from n = 1.00 in pure air to as high as n = 1.29 in near saturated toluene vapor. The extinction and wavelength shift of the LSPR spectra were very sensitive to changes in the surface refractive index of the nanoparticles. Responses of the LSPR band were measured with a real-time UV–vis spectrometer equipped with a CCD array detector. The response of silver nanoparticles to organic vapors was most sensitive in changes in extinction, while gold nanoshells exhibited red-shifts in wavelength (∼250 nm/RIU) when exposed to organic vapors. The LSPR spectral shifts primarily were determined by the volatility and refractive indices of the organic species. The T 90 response time of the VOC–LSPR spectrum was less than 3 s and the response was completely reversible and reproducible.
The single hygroscopicity parameters increase with particle size. The functional groups of aerosols exhibited strong size dependence. The hygroscopicity of organic species is low for Taipei aerosols. a b s t r a c t The hygroscopicity,... more
The single hygroscopicity parameters increase with particle size. The functional groups of aerosols exhibited strong size dependence. The hygroscopicity of organic species is low for Taipei aerosols. a b s t r a c t The hygroscopicity, functional groups and phase transitions of urban aerosol particles in Taipei City were studied using a cloud condensation nuclei counter (CCNc) with a scanning mobility particle sizer (SMPS) and an attenuated total reflectance with infrared (ATR-IR) detection technique. With the assumption of larger particles being activated first, the derived single hygroscopicity parameter (k) exhibited an increasing trend with particle size, i.e., from 0.022 ± 0.01 at 87 ± 10 nm to 0.13 ± 0.03 at 240 ± 20 nm. The collected size-selected particles were characterized using ATR-IR for the functional groups of alkyl, carbonyl, ammonium, sulfate and nitrate, which showed various size dependence patterns, linked to different formation mechanisms. The hygroscopic response based on the ratio (x W_solute) for sample film of absorption by the enhanced water-stretching peak to that by the selected solute showed a better consistency with pure ammonium sulfate for sub-micron size particles. Based on the derived ammonium sulfate volume fraction from IR analysis, the k received from CCNc measurements was concluded mainly contributed by ammonium sulfate for sub-micrometer particles. The increasing trend of sodium nitrate absorbance at aerosol diameter !1 mm was due to a reaction of nitric acid with sea salt particles. The micrometer sized particles were apparent not only in a significantly higher x W_solute than pure sodium nitrate but also had a deliquescence RH of 69 ± 1%, similar to that of sodium nitrate-sodium chloride mixtures. Overall, the organic species in this study exhibited a low hygroscopicity with less than 0.036 of contribution for the overall k, and the major hygroscopic material of urban aerosols consisted primarily of ammonium sulfate in the sub-micrometer particles and sodium nitrate with sea salt in the coarse particles.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with... more
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of... more
The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of particles produced by reaction of isoprene with hydroxyl radicals and of α-pinene with ozone in the Harvard Environmental Chamber (HEC). The infrared spectra showed that the isoprene-derived film had strong hydroxyl absorptions whereas the α-pinene-derived film had strong carbonyl absorptions. The organic films were exposed to dry and humid flows of ozone, as well as to ultraviolet irradiation, to mimic reactive aging processes that can occur in the troposphere. Both the isoprene-and α-pinene-derived films were nonreactive with respect to ozone exposure, for both dry and humid conditions, indicating that the secondary organic material consisted mostly of saturated organic species. Both films, however, were susceptible to aging by ultraviolet radiation possibly due to the presence of organic hydroperoxides, and all functional groups other than carbonyls decreased upon irradiation. In regard to hygroscopicity, as a benchmark the ratio x W_CO for oxalic acid of the intensity of the water-bending peak to that of carbonyl absorption (arising from carboxylic acids) was recorded from 20% to 80% relative humidity (RH). This quantity was then also measured for the isoprene-and α-pinene-derived organic films. The result of (x W_CO) isoprene > (x W_CO) benchmark across the range of studied RH values shows that species other than carboxylic acids contributed significantly to the hygroscopicity of the isoprene-derived film. The spectra were consistent with alcohols and hydroperoxides as the hygroscopic components. By comparison, the result of (x W_CO) pinene ≈ (x W_CO) benchmark indicates a dominance of carboxylic acids with respect to the hygroscopicity of this film.
The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of... more
The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of particles produced by reaction of isoprene with hydroxyl radicals and of α-pinene with ozone in the Harvard Environmental Chamber (HEC). The infrared spectra showed that the isoprene-derived film had strong hydroxyl absorptions whereas the α-pinene-derived film had strong carbonyl absorptions. The organic films were exposed to dry and humid flows of ozone, as well as to ultraviolet irradiation, to mimic reactive aging processes that can occur in the troposphere. Both the isoprene- and α-pinene-derived films were nonreactive with respect to ozone exposure, for both dry and humid conditions, indicating that the secondary organic material consisted mostly of saturated organic species. Both films, however, were susceptible to aging by ultraviolet radiation possibly due to the presence of organic hydroperoxides, and all functional groups other than carbonyls decreased upon irradiation. In regard to hygroscopicity, as a benchmark the ratio x(W_CO) for oxalic acid of the intensity of the water-bending peak to that of carbonyl absorption (arising from carboxylic acids) was recorded from 20% to 80% relative humidity (RH). This quantity was then also measured for the isoprene- and α-pinene-derived organic films. The result of (x(W_CO))(isoprene) > (x(W_CO))(benchmark) across the range of studied RH values shows that species other than carboxylic acids contributed significantly to the hygroscopicity of the isoprene-derived film. The spectra were consistent with alcohols and hydroperoxides as the hygroscopic components. By comparison, the result of (x(W_CO))(pinene) ≈ (x(W_CO))(benchmark) indicates a dominance of carboxylic acids with respect to the hygroscopicity of this film.
The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of... more
The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of particles produced by reaction of isoprene with hydroxyl radicals and of α-pinene with ozone in the Harvard Environmental Chamber (HEC). The infrared spectra showed that the isoprene-derived film had strong hydroxyl absorptions whereas the α-pinene-derived film had strong carbonyl absorptions. The organic films were exposed to dry and humid flows of ozone, as well as to ultraviolet irradiation, to mimic reactive aging processes that can occur in the troposphere. Both the isoprene- and α-pinene-derived films were nonreactive with respect to ozone exposure, for both dry and humid conditions, indicating that the secondary organic material consisted mostly of saturated organic species. Both films, however, were susceptible to aging by ultraviolet radiation possibly due to the presence of organic hydroperoxides, and all functional groups other than carbonyls decreased upon irradiation. In regard to hygroscopicity, as a benchmark the ratio x(W_CO) for oxalic acid of the intensity of the water-bending peak to that of carbonyl absorption (arising from carboxylic acids) was recorded from 20% to 80% relative humidity (RH). This quantity was then also measured for the isoprene- and α-pinene-derived organic films. The result of (x(W_CO))(isoprene) > (x(W_CO))(benchmark) across the range of studied RH values shows that species other than carboxylic acids contributed significantly to the hygroscopicity of the isoprene-derived film. The spectra were consistent with alcohols and hydroperoxides as the hygroscopic components. By comparison, the result of (x(W_CO))(pinene) ≈ (x(W_CO))(benchmark) indicates a dominance of carboxylic acids with respect to the hygroscopicity of this film.
The first results I obtained in our laboratory by applying non-reactive cathodic sputtering to certain types of insulating materials such as wide-gap semiconductors were fairly promising. Using r.f. diode equipment we have obtained... more
The first results I obtained in our laboratory by applying non-reactive cathodic sputtering to certain types of insulating materials such as wide-gap semiconductors were fairly promising. Using r.f. diode equipment we have obtained CdS and CdSe photoresistors which respond one order of magnitude faster to low level light excitation than resistors obtained by thermal evaporation, i.e. by sublimation in the case of II-VI elements. This cathodic sputtering technique applied to CdSe is now being used in, amongst other applications, the manufacture of sub-assemblies for fast telecopying.
