No description available.

No description available.

A laboratory model of an instrument concept to measure the absorption of solar radiation by atmospheric aerosols was designed, built and tested. The concept was based on the photophonic phenomenon discovered by Bell and an acoustic resonator developed by Helmholtz. The design consisted of two chambers: an aerosol chamber and a reference chamber combined into a double Helmholtz resonator configuration. The radiation from the visible light source was amplitude modulated by a mechanical chopper. The modulated light beam was passed through the chambers and pressure variations resulted from energy absorbed by the aerosol in the chamber. The pressure signal was sensed by microphones, then the electrical signal amplified and processed by a differential amplifier. The testing showed the instrument had sufficient sensitivity and low enough system noise to measure an absorption coefficient of about 10⁻⁶/meter. Methods of signal improvement and noise reduction were discussed and tested. The results showed the instrument could measure absorption coefficients within the range expected by the earth's atmospheric aerosols. The instrument design was not optimized for maximum signal or minimum noise, but the justifiable conclusion was reached that the concept showed the promise of leading to a useful instrument in the measurement of atmospheric aerosol absorption and an improvement over the present instruments. / Master of Science

No description available.

No description available.

No description available.

published_or_final_version / Urban Planning and Environmental Management / Doctoral / Doctor of Philosophy

A particle counting instrument, the Coherent Optical Particle Spectrometer (COPS) has been developed for measuring particles in aerosol systems. It optically counts and sizes single particles one at a time as they pass through an optically defined inspection region so particle size distributions can be directly measured. COPS uses the coherent nature of light available in a laser beam to measure the phase shift in the scattered light, which is fundamentally different from previous intensity based techniques. The Van-Cittert-Zernike theorem shows that scattered light from small particles will be coherent if viewed upon at the focal point of a gathering lens. Optical homodyne detection can then be used to measure the extent of the phase shift due to the particle. Scattering mechanisms can relate the phase shift to particle diameter so particle size can be determined. An optical inspection region is given by the resolution limited blur spot diameter and depth of focus of the gathering lens. Particles scattering outside this zone will not contribute to measured phase signals. Calculations show that COPS can count in concentrations of 10('9) particles per cubic centimeter with 5% coincidence error. Mie scattering calculations, coupled with homodyne theory, predict a minimum detectable particle diameter ranging from 0.03 to 0.3 micrometers, depending on optical configuration. Theory shows that small, strongly absorbing particles impart a much larger phase shift than refractive particles so a lower detection limit is predicted for particles such as soot and silicon. Particles above one micrometer show classic resonance typical of Mie calculations. An experimental COPS system verified the predicted results from the model. Resolution of particle size ranged from 25 to 60 percent of particle diameter. Preliminary experiments showed that COPS has in situ sampling possibilities and will work for liquid systems as well. Coherent detection of scattered light shows promise for in situ measurement of submicrometer aerosols in high particle laden streams with maximum sensitivity for strongly absorbing particles.

An incoherent CO₂ laser radar, or lidar, system using a tunable CO₂ TEA laser has been developed, along with analytical techniques to permit the determination of atmospheric transmittance and aerosol backscatter from multi-angle lidar returns. This work has been motivated by the need for a more complete knowledge of the optical properties of the atmosphere in the 9 to 11 μm spectral region. Results of preliminary observations are discussed. CO₂ lidar systems have been used before to measure backscatter and transmittance. Here, a new analytic method is developed, applicable to the 8-12 μm window region in conditions of high visibility, when the aerosol component of extinction is negligible compared to the molecular component. In such cases the backscatter sensed by the system is due to the atmospheric aerosol while atmospheric transmittance is determined by molecular species such as carbon dioxide and water vapor. It is not possible to assume a functional relationship between backscatter and extinction, as required by many previous analytic techniques. Therefore, a new solution technique based on a weighted, non-linear least squares fit applied to multi-zenith angle lidar returns has been developed. It is shown how constraints may be applied to rule out solutions which are unlikely on a priori grounds. An error analysis and a discussion of proper weighting techniques are presented. A CO₂ lidar system capable of acquiring multi-angle returns was developed, which included a gain-switching amplifier to compress the dynamic range of the return signal. The entire system is operated under computer control and data acquisition and storage are fully automated. A laser pulse energy monitor allows sequential returns to be averaged to reduce signal fluctuations. Preliminary observations with the system have demonstrated the capability of acquiring and averaging hundreds of returns on a routine basis. The return signal was observed to have fluctuations of 20 to 50% from shot to shot, due to atmospheric fluctuations. This result indicates signal averaging will be necessary to reduce signal fluctuations to levels where the multi-angle solution method may be applied.

Understanding the composition of atmospheric organic particulate matter (OPM) is essential for predicting its effects on climate, air quality, and health. However, the polar oxygenated fraction (PO-OPM), which includes a significant mass contribution from carboxylic acids, is difficult to speciate and quantitatively determine by current analytical methods such as gas chromatography-mass spectrometry (GC-MS). The method of chemical derivatization and two-dimensional GC with time of flight MS (GC×GC/TOF-MS) was examined in this study for its efficacy in: 1) quantifying a high percentage of the total organic carbon (TOC) mass of a sample containing PO-OPM; 2) quantitatively determining PO-OPM components including carboxylic acids at atmospherically relevant concentrations; and 3) tentatively identifying PO-OPM components. Two derivatization reagent systems were used in this study: BF₃/butanol for the butylation of carboxylic acids, aldehydes, and acidic ketones, and BSTFA for the trimethylsilylation (TMS) of carboxylic acids and alcohols. Three α-pinene ozonolysis OPM filter samples and a set of background filter samples were collected by collaborators in a University of California, Riverside environmental chamber. Derivatization/GC×GC TOF-MS was used to tentatively identify some previously unidentified α-pinene ozonolysis products, and also to show the characteristics of all oxidation products determined. Derivatization efficiencies as measured were 40-70% for most butyl derivatives, and 50-58% for most trimethylsilyl derivatives. A thermal optical method was used to measure the TOC on each filter, and a value of the quantifiable TOC mass using a gas chromatograph was calculated for each sample using GC×GC separation and the mass-sensitive response of a flame ionization detector (FID). The TOC quantified using TMS and GC×GC-FID (TMS/TOCGC×GC FID) accounted for 15-23% of the TOC measured by the thermal-optical method. Using TMS and GC×GC/TOF-MS, 8.85% of the thermal optical TOC was measured and 48.2% of the TMS/TOCGC×GC-FID was semi-quantified using a surrogate standard. The carboxylic acids tentatively identified using TMS and GC×GC/TOF-MS accounted for 8.28% of the TOC measured by thermal optical means. GC×GC TOF-MS chromatograms of derivatized analytes showed reduced peak tailing due in part to the lesser interactions of the derivatized analytes with the stationary phase of the chromatography column as compared to the chromatograms of underivatized samples. The improved peak shape made possible the greater separation, quantification, and identification of high polarity analytes. Limits of detection using derivatization and GC×GC/TOF-MS were μL injected for a series of C2-C6 di-acids, cis-pinonic acid, and dodecanoic acid using both butylation and TMS. Derivatization with GC×GC/TOF-MS was therefore effective for determining polar oxygenated compounds at low concentrations, for determining specific oxidation products not previously identified in OPM, and also for characterizing the probable functional groups and structures of α-pinene ozonolysis products.