Hans Moosmuller | University of Nevada, Reno (original) (raw)
Papers by Hans Moosmuller
Aerosol Science and Technology, Jul 18, 2022
Environmental Science & Technology, Jan 18, 2001
The measurement of diesel vehicle exhaust particulate mass is currently accomplished using filter... more The measurement of diesel vehicle exhaust particulate mass is currently accomplished using filter collection methods according to the Code of Federal Regulations (CFR). Such filter methods limit time resolution to a minimum of several minutes, making it impossible to study emissions during transient operating conditions. Extensive testing of five different measurement methods has demonstrated that fast response measurements of diesel exhaust particulate mass concentrations, consistent with CFR filter measurements, are feasible using existing technology. The measurement principles of choice are the real time weighing of exhaust samples as implemented in the tapered element oscillating microbalance (TEOM) and the measurement of light scattering from exhaust particles as implemented in the DustTrak nephelometer. Each of these two instruments has distinctive strengths. The TEOM excels in the area of constant calibration, independent of vehicle. For the DustTrak, this calibration varies by vehicle. On the other hand, the DustTrak has an excellent signal-to-noise ratio, freedom from interference due to other exhaust sample properties, good time resolution, and simplicity. The strengths of the two measurement methods are complimentary, so an obvious suggestion is to integrate them. The nephelometer would obtain a fast response signal, with near real time calibration provided by the microbalance.
Journal of The Optical Society of America B-optical Physics, 1984
We recently reported the first known study of stimulated Rayleigh-Brillouin gain spectra of pure ... more We recently reported the first known study of stimulated Rayleigh-Brillouin gain spectra of pure gases1 This was done by crossing two single-frequency laser beams in the gas samples of interest. As in Raman-gain techniques, the detected background light in stimulated Rayleigh-Brillouin gain spectroscopy is greatly reduced since the desired signal is emitted only along the probe beam. Thus, the stimulated Rayleigh-Brillouin gain spectroscopy reported is potentially a sensitive spectroscopic technique for probing the low-frequency excitations and fluctuations in systems with weak scatterers or with high background light.
1049674Final reportWilder, CharlenePDFResearch PaperDRI-03-10FTA-NV-26-7003-2006-01NTIS-PB2007109... more 1049674Final reportWilder, CharlenePDFResearch PaperDRI-03-10FTA-NV-26-7003-2006-01NTIS-PB2007109059FTA 26-7003FTA 26-7001-01FTA 26-7003-02DriversExhaust gasesAir qualityAir pollutionLas Vegas (Nevada)United States. Federal Transit AdministrationWatson, John G. (John George), 1949-Barber, Peter W.Chang, M. C. OliverChow, Judith C.Etyemezian, Vicken R.Green, Mark C.Keislar, Robert E.Kuhns, Hampden D.Mazzoleni, ClaudioMoosmuller, HansNicolic, DjordjeWhitaker, Charles E.University of Nevada System. Desert Research InstituteUnited States. Federal Transit AdministrationNTL-ENERGY AND ENVIRONMENT-Air QualityNTL-ENERGY AND ENVIRONMENT-ENERGY AND ENVIRONMENTBTS Data DirectoryThe Southern Nevada Air Quality Study (SNAQS) created cross-plume and in-plume measurement systems to quantify emissions distributions and source profiles from transportation emissions, specifically gasoline and diesel powered vehicles. The cross-plume system measures backscattered ultraviolet radiation to estimate particulate emissions and infrared and ultraviolet absorption to measure gas concentrations in exhaust plumes. The in-plume system draws a portion of air from the plume and directs it to continuous monitors and filter samples that are analyzed in the laboratory. Both systems were applied to on-road measurements in Las Vegas, Nevada. Results from both methods found that most of the particulate and gas pollutant emissions came from a small fraction of the vehicles. High carbon monoxide emitters were not always high particulate matter and oxide of nitrogen emitters, implying that smog checks must measure all of these pollutants to be effective. Receptor models were applied to ambient particulate samples taken in Las Vegas using source profiles obtained with the in-plume system. Gasoline engine exhaust was the largest contributor to the carbon component at all sites, and diesel exhaust was only a large contributor at commercial sites near major highways. Residential wood combustion was also an important contributor in residential areas, but not in the commercial areas. /Abstract from report summary page
Journal of Quantitative Spectroscopy & Radiative Transfer, Apr 1, 2022
Journal of Quantitative Spectroscopy & Radiative Transfer, Nov 1, 2018
The aerosol single scattering albedo (SSA) is the dominant intensive particle parameter determini... more The aerosol single scattering albedo (SSA) is the dominant intensive particle parameter determining the aerosols radiative forcing in the earth's atmosphere . We use Mie theory to examine the behavior of SSA as a function of size parameter x and complex refractive index m for homogeneous spherical particles. Previously, we investigated the limiting cases of the small particle limit (x << 1) and the large particle limit (x >> 1), where SSA is proportional to x 3 and independent of the size parameter x, respectively . In between these cases lies the transition (or peak) region, where SSA transitions from the small to the large particle regime and, for sufficiently small imaginary parts of the refractive index, shows one or more peaks. Here, we investigate the behavior of SSA in the transition region including conditions on the complex refractive index for peak formation, peak location, and general properties of SSA as function of size parameter.
Solar Energy, Oct 1, 2017
Field experiments have revealed that deposition of dust particles plays a significant role in opt... more Field experiments have revealed that deposition of dust particles plays a significant role in optical degradation of photovoltaic (PV) cell performance. Such experiments have been performed as a function of tilt angle of the cells, exposure time, and other environmental factors. However, very little is known about cell degradation as function of intensive particle parameters such as size and complex refractive index. This paper shows that, for normally incident solar radiation, deposited aerosols degrade PV cell performance due to particle absorption and due to scattering into the backward hemisphere. The fraction power lost (FL), together with the optical depth of the deposited particles, determines the fraction of power lost from the incident light beam. We have performed scattering calculations simulating the interaction of light with particles on substrates that analyzed FL as function of particle size and particle complex refractive index. We have found that for small particles and a relatively large imaginary part of their refractive index, absorption losses dominate while for large particles and a relatively small imaginary part of the refractive index, backscattering losses dominate. Per optical depth, fine particles result in higher optical losses than coarse ones due to their larger absorption and hemispheric backscattering. Overall, our work quantifies optical losses caused by deposited aerosols toward the goals of estimating PV cell performance for energy forecasting, informing PV cell designers about potential efficiency losses caused by particle deposition, and optimizing cleaning schedules.
Solar Energy, Apr 1, 2018
Deposition of particles on photovoltaic (PV) modules has the potential to increase costs of solar... more Deposition of particles on photovoltaic (PV) modules has the potential to increase costs of solar energy production and maintenance and to affect grid-connected energy forecasting. Particles deposited on PV modules can reduce the optical transmission to the PV semiconductor significantly (>50%) due to absorption and scattering. Although there are many previous studies of PV module efficiency losses with respect to exposure time, angle tilt of the PV module, and other environmental factors, there has been little study of PV module efficiency losses with respect to the optical characteristics of the deposited particles (e.g., refractive index, optical depth). Here, we deposited two types of dust onto glass slides, optically absorbing dust and optically non-absorbing dust. We systematically increased the mass per unit area deposited onto the glass slides and measured the optical depth and total transmission (i.e., direct plus diffuse light) using a spectrophotometer with an integrating sphere detector system. Our experimental measurements were compared with a two-stream radiative transfer model, and with Monte Carlo radiative transfer calculations, yielding good agreement for both absorbing and nonabsorbing dust. Our results indicate that total transmission decreases approximately linearly as a function of dust mass deposited per unit area, with the slope being highly sensitive to the absorptivity of the dust. The obtained results and models used in this study can be used in conjunction with deposition models to predict the degradation of the optical transmission of PV modules with respect to mass per unit area dust loading.
Optics Communications, 2021
Black objects are sometimes associated with black carbon, while shiny, highly reflecting surfaces... more Black objects are sometimes associated with black carbon, while shiny, highly reflecting surfaces are typically associated with metals. Here, we discuss several objects in everyday life that upon use take on a black color that is unlikely to be due to black carbon. We propose that this black color is caused by the formation of metallic nanoparticles from abrasion processes. We support this hypothesis using Mie theory and the fact that spherical metal particles are only shiny or bright if the imaginary part of their refractive index and its product with the particle size-parameter are both larger than three. While this is commonly true for bulk metals, the second condition is generally not fulfilled for metallic nanoparticles, and hence, such particles become highly absorbing, i.e., black. For the black grime accumulated on bicycle drivetrains and climbing ropes, we detected metal nanoparticles with electron microscopy, which likely originated from mechanical abrasion processes during use.
Aerosol Science and Technology, Aug 1, 2011
In the past two decades, several experimental and simulation studies have proposed simple empiric... more In the past two decades, several experimental and simulation studies have proposed simple empirical relations between projected two-dimensional (2-D) and three-dimensional (3-D) structural properties of fractal-like aggregates in the cluster-dilute regime. These empirical relations have found extensive use in inferring the 3-D structural properties of aggregates from their projected (i.e., 2-D) properties-measurable from aggregate electron microscopy images. This study probes the limitations and nongeneralizability of these simple and straightforward empirical relationships and proposes replacing them with new empirical formulas. A straightforward empirical relationship for directly determining the 3-D fractal dimension (D f ) of an aggregate from the knowledge of its 2-D aspect ratio is also identified. These new relationships were derived by comparing the ratios of several 2-D and 3-D structural properties of a statistically significant number of simulated aggregates with point-contacting monomers as a function of their 3-D D f ranging from 1.0 to 3.0 in increments of 0.1.
Journal of the Air & Waste Management Association, Dec 1, 2009
Although emissions of air pollutants from some military tactical equipment are not subject to the... more Although emissions of air pollutants from some military tactical equipment are not subject to the emissions standards, local communities near military bases must conform to the National Ambient Air Quality Standards. Military diesel generators are widely used in training. A portable in-plume system was used to measure fuel-based emission factors (EFs) for particulate matter (PM), carbon monoxide (CO), nitrogen oxides (NO x ), and hydrocarbons (HCs) for 30-, 60-, and 100-kW generators at five load levels and for cold starts. It was found that EFs depend on multiple parameters including engine size, engine load, unit age, and total running hours. The average CO EF of generators tested was 5% lower, and the average NO x EF was 63% lower than AP-42 estimates; average PM EF was 80% less than the AP-42 estimates. A 2002 model-year 60-kW engine produced 25% less PM than a 1995 engine of the same family with similar running hours. CO EFs decrease with increasing engine load, NO x EFs increase up to mid-loads and decrease slightly at high loads, PM EFs increase with loads for 30-and 60-kW engines. CO and PM have higher EFs and NO x has a lower EF during cold starts than during hot-stabilized operation. PM chemical source profiles were also examined. Diesel generators account for approximately 19% of all nonroad equipment fuel used by the U.S. Marine Corps. More stringent emission standards have been adopted for air pollutants such as NO x and PM from nonroad diesel engines. This study used a portable in-plume system to characterize gaseous and particulate fuel-based EFs from military generators. Real-world EFs can be quantified by in-plume measurements and provide more realistic measures for emissions inventories, source modeling, and receptor modeling than certification measurements. These data are essential to state and local air quality planners charged with maintaining regional air quality and protecting human health.
![Research paper thumbnail of Erratum to “Small and large particle limits of single scattering albedo for homogeneous, spherical particles” [J. Quant. Spectrosc. Radiat. Transfer 204 (2018) 250–255]](https://attachments.academia-assets.com/120846116/thumbnails/1.jpg)
](Journal of Quantitative Spectroscopy & Radiative Transfer, Feb 1, 2020
Fig. 1 in our publication [1] , one clearly notices that for vanishing size parameter x , the sol... more Fig. 1 in our publication [1] , one clearly notices that for vanishing size parameter x , the solid lines showing Mie theory results and the dashed lines showing Rayleigh theory results do not converge as expected. This is due to a numerical error. A corrected version of Fig. 1 is shown below; here it is obvious that Mie and Rayleigh theory results converge for vanishing size parameter x. 1. corrected: Single scattering albedo SSA as function of size parameter x for a refractive index m = 1.5 + i κ with Mie and Rayleigh calculations shown as solid and dashed lines, respectively. Vertical dashed lines indicate approximate boundaries between Rayleigh, peak, and geometric regimes.
Environmental Science & Technology, Apr 5, 2001
The measurement of elemental carbon (EC) and organic carbon (OC) mass for particles emitted by di... more The measurement of elemental carbon (EC) and organic carbon (OC) mass for particles emitted by diesel vehicles is currently accomplished using particle collection on filters, followed by analysis using the thermal/optical reflectance carbon analysis method (TOR) or one of its variations. Such filter methods limit time resolution to a minimum of several minutes, making it impossible to study emissions during transient operating conditions. Testing of five different measurement methods has demonstrated that fast response measurement of diesel exhaust particulate EC and OC concentrations, consistent with TOR filter measurements, is feasible using existing technology. EC mass concentrations are best measured through determination of particulate light absorption with a photoacoustic instrument or determination of light extinction with a smoke meter. The photoacoustic instrument has the better dynamic range and sensitivity, whereas the smoke meter is a simpler instrument. Fast response OC measurements cannot be made with any single instrument tested. However, a combination of real time weighing as implemented in the tapered element oscillating microbalance with the photoacoustic instrument has been shown to be capable of determining OC concentrations with good time response. The addition of a nephelometer to the OC measurement could potentially improve time resolution, freedom from interferences, and sensitivity.
Atmosphere, May 18, 2023
Following Lorenz's work using analogue pairs for establishing 10-to-14-day predictability limits ... more Following Lorenz's work using analogue pairs for establishing 10-to-14-day predictability limits for synoptic weather regimes, predictability limits for the Rex block, the long-wave wintertime ridge over the eastern Pacific Ocean and the western United States, have been estimated. This was accomplished by using mid-latitude geopotential height reanalysis data over a period of 38 years, 1979-2016, and associated 90-day winters (DJF). The metric used to define analogue pairs is the RMS difference assessed for the hemispheric 850, 500, and 200 hPa geopotential height fields. The resultant set of analogue pairs was used to estimate predictability with respect to both a single latitude circle (40 • N) that passes through the Rex Block and for a multi-latitude swath (20-80 • N). Our methods showed a range of results, by choice of Fourier component wavenumbers 2 through 8. These results indicate system predictability for low wavenumber components to exceed the 10-14-day limit imposed by Lorenz' results. The results to 21 days, the maximum predictability limit value allowed by our method, do not preclude the possibility of a greater range of system predictability past 21 days. The unique aspect of this work is determination of predictability limits as a function of geopotential wave structure found through Fourier decomposition.
Physical Review Letters, Mar 19, 2010
In the preceding Comment, Sander et al. claim that the very low fractal dimensions (D f ) we obse... more In the preceding Comment, Sander et al. claim that the very low fractal dimensions (D f ) we observed is caused by sampling and process effects. To substantiate their claim, they used a detailed stochastic particle model to simulate soot particle formation in a premixed flame-similar to the one used for our experimental work-and to study the soot agglomerate properties. The authors also claim to have previously validated their model over a number of different flame conditions without providing any information on what model predictions were validated or referencing any publication on their model validation. We are of the opinion that the study conducted by Sander et al. is fraught with fundamental errors, thereby making their claims unacceptable with respect to our findings. (i) In the publication describing Celnik et al.'s soot formation model , the effects of fuel-to-air equivalence ratio (') on soot formation inside of a premixed flame are not accounted for. Our observations of low D f agglomerates were limited to ' ranging between 2.0 and 3.5 in a premixed flame, with D f decreasing from 1.51 to 1.2 with increasing '. The comments by Sander et al. do not include any information about the ' used in their premixed flame model. (ii) Second, we observe D f 1:2 agglomerates only around ' 3:5, which corresponds to decreased Brownian motion of monomers in the premixed flame due to a decrease in flame temperature. One also finds significant amount of organic carbon coating on the agglomerates at high ' (i.e., 3) [3]. These two phenomena affect the agglomerate morphology, but are not accounted for in the Celnik et al. model. Just because Sander et al. observe low D f for a subset population of agglomerates generated under unspecified conditions, does not invalidate our experimental observation and hypothesis. In other words, while Sander et al.'s modeling results and our experimental findings have both resulted in observation of low D f soot agglomerates, this does not mean that the causes of low D f for our experimental study are necessarily the same as for their modeling study.
Physical review, Jun 1, 1985
Steady-state stimulated Rayleigh-Brillouin gain spectroscopy and its application are reported. Th... more Steady-state stimulated Rayleigh-Brillouin gain spectroscopy and its application are reported. The stimulated gain, which is derived in terms of the spectral function of density fluctuations, is shown to approach, in the hmit of zero density, the gain derived from the individual-particle picture of Rayleigh scattering. Using a pulsed pump laser, experimental gain spectra of pure SF6, pure Ar, and a SF6-and He-gas mixture are obtained and explained. Other associated coherent Rayleigh- Brillouin spectroscopies and the possibility of using a cw pump laser for higher spectral resolution are discussed.
DRI drafted the quality assurance plan to help the field scientists to identify precision, accura... more DRI drafted the quality assurance plan to help the field scientists to identify precision, accuracy and validity targets relevant to their measurements. They also identified the necessary procedures and activities to reach these targets and recommended special activities in critical areas such as carbonyl measurements.
A compact airborne down-looking lidar system has been developed at the U. S. Environmental Protec... more A compact airborne down-looking lidar system has been developed at the U. S. Environmental Protection Agency's Environmental Monitoring Systems Laboratory in Las Vegas.1,2This differential absorption lidar (DIAL) is designed to simultaneously measure range-resolved concentrations of ozone (O3) and sulfur dioxide (SO2) in the lower troposphere, together with an indication of the aerosol distribution. The five laser wavelengths (i.e., λI= 277 nm, λ2= 292 nm, λ3= 313 nm, λ4= 319 nm, λ5= 359 nm) are generated via Raman conversion of a focused KrF excimer laser.3
Aerosol Science and Technology, Jul 18, 2022
Environmental Science & Technology, Jan 18, 2001
The measurement of diesel vehicle exhaust particulate mass is currently accomplished using filter... more The measurement of diesel vehicle exhaust particulate mass is currently accomplished using filter collection methods according to the Code of Federal Regulations (CFR). Such filter methods limit time resolution to a minimum of several minutes, making it impossible to study emissions during transient operating conditions. Extensive testing of five different measurement methods has demonstrated that fast response measurements of diesel exhaust particulate mass concentrations, consistent with CFR filter measurements, are feasible using existing technology. The measurement principles of choice are the real time weighing of exhaust samples as implemented in the tapered element oscillating microbalance (TEOM) and the measurement of light scattering from exhaust particles as implemented in the DustTrak nephelometer. Each of these two instruments has distinctive strengths. The TEOM excels in the area of constant calibration, independent of vehicle. For the DustTrak, this calibration varies by vehicle. On the other hand, the DustTrak has an excellent signal-to-noise ratio, freedom from interference due to other exhaust sample properties, good time resolution, and simplicity. The strengths of the two measurement methods are complimentary, so an obvious suggestion is to integrate them. The nephelometer would obtain a fast response signal, with near real time calibration provided by the microbalance.
Journal of The Optical Society of America B-optical Physics, 1984
We recently reported the first known study of stimulated Rayleigh-Brillouin gain spectra of pure ... more We recently reported the first known study of stimulated Rayleigh-Brillouin gain spectra of pure gases1 This was done by crossing two single-frequency laser beams in the gas samples of interest. As in Raman-gain techniques, the detected background light in stimulated Rayleigh-Brillouin gain spectroscopy is greatly reduced since the desired signal is emitted only along the probe beam. Thus, the stimulated Rayleigh-Brillouin gain spectroscopy reported is potentially a sensitive spectroscopic technique for probing the low-frequency excitations and fluctuations in systems with weak scatterers or with high background light.
1049674Final reportWilder, CharlenePDFResearch PaperDRI-03-10FTA-NV-26-7003-2006-01NTIS-PB2007109... more 1049674Final reportWilder, CharlenePDFResearch PaperDRI-03-10FTA-NV-26-7003-2006-01NTIS-PB2007109059FTA 26-7003FTA 26-7001-01FTA 26-7003-02DriversExhaust gasesAir qualityAir pollutionLas Vegas (Nevada)United States. Federal Transit AdministrationWatson, John G. (John George), 1949-Barber, Peter W.Chang, M. C. OliverChow, Judith C.Etyemezian, Vicken R.Green, Mark C.Keislar, Robert E.Kuhns, Hampden D.Mazzoleni, ClaudioMoosmuller, HansNicolic, DjordjeWhitaker, Charles E.University of Nevada System. Desert Research InstituteUnited States. Federal Transit AdministrationNTL-ENERGY AND ENVIRONMENT-Air QualityNTL-ENERGY AND ENVIRONMENT-ENERGY AND ENVIRONMENTBTS Data DirectoryThe Southern Nevada Air Quality Study (SNAQS) created cross-plume and in-plume measurement systems to quantify emissions distributions and source profiles from transportation emissions, specifically gasoline and diesel powered vehicles. The cross-plume system measures backscattered ultraviolet radiation to estimate particulate emissions and infrared and ultraviolet absorption to measure gas concentrations in exhaust plumes. The in-plume system draws a portion of air from the plume and directs it to continuous monitors and filter samples that are analyzed in the laboratory. Both systems were applied to on-road measurements in Las Vegas, Nevada. Results from both methods found that most of the particulate and gas pollutant emissions came from a small fraction of the vehicles. High carbon monoxide emitters were not always high particulate matter and oxide of nitrogen emitters, implying that smog checks must measure all of these pollutants to be effective. Receptor models were applied to ambient particulate samples taken in Las Vegas using source profiles obtained with the in-plume system. Gasoline engine exhaust was the largest contributor to the carbon component at all sites, and diesel exhaust was only a large contributor at commercial sites near major highways. Residential wood combustion was also an important contributor in residential areas, but not in the commercial areas. /Abstract from report summary page
Journal of Quantitative Spectroscopy & Radiative Transfer, Apr 1, 2022
Journal of Quantitative Spectroscopy & Radiative Transfer, Nov 1, 2018
The aerosol single scattering albedo (SSA) is the dominant intensive particle parameter determini... more The aerosol single scattering albedo (SSA) is the dominant intensive particle parameter determining the aerosols radiative forcing in the earth's atmosphere . We use Mie theory to examine the behavior of SSA as a function of size parameter x and complex refractive index m for homogeneous spherical particles. Previously, we investigated the limiting cases of the small particle limit (x << 1) and the large particle limit (x >> 1), where SSA is proportional to x 3 and independent of the size parameter x, respectively . In between these cases lies the transition (or peak) region, where SSA transitions from the small to the large particle regime and, for sufficiently small imaginary parts of the refractive index, shows one or more peaks. Here, we investigate the behavior of SSA in the transition region including conditions on the complex refractive index for peak formation, peak location, and general properties of SSA as function of size parameter.
Solar Energy, Oct 1, 2017
Field experiments have revealed that deposition of dust particles plays a significant role in opt... more Field experiments have revealed that deposition of dust particles plays a significant role in optical degradation of photovoltaic (PV) cell performance. Such experiments have been performed as a function of tilt angle of the cells, exposure time, and other environmental factors. However, very little is known about cell degradation as function of intensive particle parameters such as size and complex refractive index. This paper shows that, for normally incident solar radiation, deposited aerosols degrade PV cell performance due to particle absorption and due to scattering into the backward hemisphere. The fraction power lost (FL), together with the optical depth of the deposited particles, determines the fraction of power lost from the incident light beam. We have performed scattering calculations simulating the interaction of light with particles on substrates that analyzed FL as function of particle size and particle complex refractive index. We have found that for small particles and a relatively large imaginary part of their refractive index, absorption losses dominate while for large particles and a relatively small imaginary part of the refractive index, backscattering losses dominate. Per optical depth, fine particles result in higher optical losses than coarse ones due to their larger absorption and hemispheric backscattering. Overall, our work quantifies optical losses caused by deposited aerosols toward the goals of estimating PV cell performance for energy forecasting, informing PV cell designers about potential efficiency losses caused by particle deposition, and optimizing cleaning schedules.
Solar Energy, Apr 1, 2018
Deposition of particles on photovoltaic (PV) modules has the potential to increase costs of solar... more Deposition of particles on photovoltaic (PV) modules has the potential to increase costs of solar energy production and maintenance and to affect grid-connected energy forecasting. Particles deposited on PV modules can reduce the optical transmission to the PV semiconductor significantly (>50%) due to absorption and scattering. Although there are many previous studies of PV module efficiency losses with respect to exposure time, angle tilt of the PV module, and other environmental factors, there has been little study of PV module efficiency losses with respect to the optical characteristics of the deposited particles (e.g., refractive index, optical depth). Here, we deposited two types of dust onto glass slides, optically absorbing dust and optically non-absorbing dust. We systematically increased the mass per unit area deposited onto the glass slides and measured the optical depth and total transmission (i.e., direct plus diffuse light) using a spectrophotometer with an integrating sphere detector system. Our experimental measurements were compared with a two-stream radiative transfer model, and with Monte Carlo radiative transfer calculations, yielding good agreement for both absorbing and nonabsorbing dust. Our results indicate that total transmission decreases approximately linearly as a function of dust mass deposited per unit area, with the slope being highly sensitive to the absorptivity of the dust. The obtained results and models used in this study can be used in conjunction with deposition models to predict the degradation of the optical transmission of PV modules with respect to mass per unit area dust loading.
Optics Communications, 2021
Black objects are sometimes associated with black carbon, while shiny, highly reflecting surfaces... more Black objects are sometimes associated with black carbon, while shiny, highly reflecting surfaces are typically associated with metals. Here, we discuss several objects in everyday life that upon use take on a black color that is unlikely to be due to black carbon. We propose that this black color is caused by the formation of metallic nanoparticles from abrasion processes. We support this hypothesis using Mie theory and the fact that spherical metal particles are only shiny or bright if the imaginary part of their refractive index and its product with the particle size-parameter are both larger than three. While this is commonly true for bulk metals, the second condition is generally not fulfilled for metallic nanoparticles, and hence, such particles become highly absorbing, i.e., black. For the black grime accumulated on bicycle drivetrains and climbing ropes, we detected metal nanoparticles with electron microscopy, which likely originated from mechanical abrasion processes during use.
Aerosol Science and Technology, Aug 1, 2011
In the past two decades, several experimental and simulation studies have proposed simple empiric... more In the past two decades, several experimental and simulation studies have proposed simple empirical relations between projected two-dimensional (2-D) and three-dimensional (3-D) structural properties of fractal-like aggregates in the cluster-dilute regime. These empirical relations have found extensive use in inferring the 3-D structural properties of aggregates from their projected (i.e., 2-D) properties-measurable from aggregate electron microscopy images. This study probes the limitations and nongeneralizability of these simple and straightforward empirical relationships and proposes replacing them with new empirical formulas. A straightforward empirical relationship for directly determining the 3-D fractal dimension (D f ) of an aggregate from the knowledge of its 2-D aspect ratio is also identified. These new relationships were derived by comparing the ratios of several 2-D and 3-D structural properties of a statistically significant number of simulated aggregates with point-contacting monomers as a function of their 3-D D f ranging from 1.0 to 3.0 in increments of 0.1.
Journal of the Air & Waste Management Association, Dec 1, 2009
Although emissions of air pollutants from some military tactical equipment are not subject to the... more Although emissions of air pollutants from some military tactical equipment are not subject to the emissions standards, local communities near military bases must conform to the National Ambient Air Quality Standards. Military diesel generators are widely used in training. A portable in-plume system was used to measure fuel-based emission factors (EFs) for particulate matter (PM), carbon monoxide (CO), nitrogen oxides (NO x ), and hydrocarbons (HCs) for 30-, 60-, and 100-kW generators at five load levels and for cold starts. It was found that EFs depend on multiple parameters including engine size, engine load, unit age, and total running hours. The average CO EF of generators tested was 5% lower, and the average NO x EF was 63% lower than AP-42 estimates; average PM EF was 80% less than the AP-42 estimates. A 2002 model-year 60-kW engine produced 25% less PM than a 1995 engine of the same family with similar running hours. CO EFs decrease with increasing engine load, NO x EFs increase up to mid-loads and decrease slightly at high loads, PM EFs increase with loads for 30-and 60-kW engines. CO and PM have higher EFs and NO x has a lower EF during cold starts than during hot-stabilized operation. PM chemical source profiles were also examined. Diesel generators account for approximately 19% of all nonroad equipment fuel used by the U.S. Marine Corps. More stringent emission standards have been adopted for air pollutants such as NO x and PM from nonroad diesel engines. This study used a portable in-plume system to characterize gaseous and particulate fuel-based EFs from military generators. Real-world EFs can be quantified by in-plume measurements and provide more realistic measures for emissions inventories, source modeling, and receptor modeling than certification measurements. These data are essential to state and local air quality planners charged with maintaining regional air quality and protecting human health.
Journal of Quantitative Spectroscopy & Radiative Transfer, Feb 1, 2020
Fig. 1 in our publication [1] , one clearly notices that for vanishing size parameter x , the sol... more Fig. 1 in our publication [1] , one clearly notices that for vanishing size parameter x , the solid lines showing Mie theory results and the dashed lines showing Rayleigh theory results do not converge as expected. This is due to a numerical error. A corrected version of Fig. 1 is shown below; here it is obvious that Mie and Rayleigh theory results converge for vanishing size parameter x. 1. corrected: Single scattering albedo SSA as function of size parameter x for a refractive index m = 1.5 + i κ with Mie and Rayleigh calculations shown as solid and dashed lines, respectively. Vertical dashed lines indicate approximate boundaries between Rayleigh, peak, and geometric regimes.
Environmental Science & Technology, Apr 5, 2001
The measurement of elemental carbon (EC) and organic carbon (OC) mass for particles emitted by di... more The measurement of elemental carbon (EC) and organic carbon (OC) mass for particles emitted by diesel vehicles is currently accomplished using particle collection on filters, followed by analysis using the thermal/optical reflectance carbon analysis method (TOR) or one of its variations. Such filter methods limit time resolution to a minimum of several minutes, making it impossible to study emissions during transient operating conditions. Testing of five different measurement methods has demonstrated that fast response measurement of diesel exhaust particulate EC and OC concentrations, consistent with TOR filter measurements, is feasible using existing technology. EC mass concentrations are best measured through determination of particulate light absorption with a photoacoustic instrument or determination of light extinction with a smoke meter. The photoacoustic instrument has the better dynamic range and sensitivity, whereas the smoke meter is a simpler instrument. Fast response OC measurements cannot be made with any single instrument tested. However, a combination of real time weighing as implemented in the tapered element oscillating microbalance with the photoacoustic instrument has been shown to be capable of determining OC concentrations with good time response. The addition of a nephelometer to the OC measurement could potentially improve time resolution, freedom from interferences, and sensitivity.
Atmosphere, May 18, 2023
Following Lorenz's work using analogue pairs for establishing 10-to-14-day predictability limits ... more Following Lorenz's work using analogue pairs for establishing 10-to-14-day predictability limits for synoptic weather regimes, predictability limits for the Rex block, the long-wave wintertime ridge over the eastern Pacific Ocean and the western United States, have been estimated. This was accomplished by using mid-latitude geopotential height reanalysis data over a period of 38 years, 1979-2016, and associated 90-day winters (DJF). The metric used to define analogue pairs is the RMS difference assessed for the hemispheric 850, 500, and 200 hPa geopotential height fields. The resultant set of analogue pairs was used to estimate predictability with respect to both a single latitude circle (40 • N) that passes through the Rex Block and for a multi-latitude swath (20-80 • N). Our methods showed a range of results, by choice of Fourier component wavenumbers 2 through 8. These results indicate system predictability for low wavenumber components to exceed the 10-14-day limit imposed by Lorenz' results. The results to 21 days, the maximum predictability limit value allowed by our method, do not preclude the possibility of a greater range of system predictability past 21 days. The unique aspect of this work is determination of predictability limits as a function of geopotential wave structure found through Fourier decomposition.
Physical Review Letters, Mar 19, 2010
In the preceding Comment, Sander et al. claim that the very low fractal dimensions (D f ) we obse... more In the preceding Comment, Sander et al. claim that the very low fractal dimensions (D f ) we observed is caused by sampling and process effects. To substantiate their claim, they used a detailed stochastic particle model to simulate soot particle formation in a premixed flame-similar to the one used for our experimental work-and to study the soot agglomerate properties. The authors also claim to have previously validated their model over a number of different flame conditions without providing any information on what model predictions were validated or referencing any publication on their model validation. We are of the opinion that the study conducted by Sander et al. is fraught with fundamental errors, thereby making their claims unacceptable with respect to our findings. (i) In the publication describing Celnik et al.'s soot formation model , the effects of fuel-to-air equivalence ratio (') on soot formation inside of a premixed flame are not accounted for. Our observations of low D f agglomerates were limited to ' ranging between 2.0 and 3.5 in a premixed flame, with D f decreasing from 1.51 to 1.2 with increasing '. The comments by Sander et al. do not include any information about the ' used in their premixed flame model. (ii) Second, we observe D f 1:2 agglomerates only around ' 3:5, which corresponds to decreased Brownian motion of monomers in the premixed flame due to a decrease in flame temperature. One also finds significant amount of organic carbon coating on the agglomerates at high ' (i.e., 3) [3]. These two phenomena affect the agglomerate morphology, but are not accounted for in the Celnik et al. model. Just because Sander et al. observe low D f for a subset population of agglomerates generated under unspecified conditions, does not invalidate our experimental observation and hypothesis. In other words, while Sander et al.'s modeling results and our experimental findings have both resulted in observation of low D f soot agglomerates, this does not mean that the causes of low D f for our experimental study are necessarily the same as for their modeling study.
Physical review, Jun 1, 1985
Steady-state stimulated Rayleigh-Brillouin gain spectroscopy and its application are reported. Th... more Steady-state stimulated Rayleigh-Brillouin gain spectroscopy and its application are reported. The stimulated gain, which is derived in terms of the spectral function of density fluctuations, is shown to approach, in the hmit of zero density, the gain derived from the individual-particle picture of Rayleigh scattering. Using a pulsed pump laser, experimental gain spectra of pure SF6, pure Ar, and a SF6-and He-gas mixture are obtained and explained. Other associated coherent Rayleigh- Brillouin spectroscopies and the possibility of using a cw pump laser for higher spectral resolution are discussed.
DRI drafted the quality assurance plan to help the field scientists to identify precision, accura... more DRI drafted the quality assurance plan to help the field scientists to identify precision, accuracy and validity targets relevant to their measurements. They also identified the necessary procedures and activities to reach these targets and recommended special activities in critical areas such as carbonyl measurements.
A compact airborne down-looking lidar system has been developed at the U. S. Environmental Protec... more A compact airborne down-looking lidar system has been developed at the U. S. Environmental Protection Agency's Environmental Monitoring Systems Laboratory in Las Vegas.1,2This differential absorption lidar (DIAL) is designed to simultaneously measure range-resolved concentrations of ozone (O3) and sulfur dioxide (SO2) in the lower troposphere, together with an indication of the aerosol distribution. The five laser wavelengths (i.e., λI= 277 nm, λ2= 292 nm, λ3= 313 nm, λ4= 319 nm, λ5= 359 nm) are generated via Raman conversion of a focused KrF excimer laser.3