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Studies focusing on virga are rare, even though it is a commonly occurring phenomenon. In this study, we investigated aerosol backscatter profiles from a ceilometer located on The University of Texas at El Paso (UTEP) campus from 2015–2021 to identify virga events. Ceilometer data effectively captured virga events from regular precipitation based on the backscattering intensities. To characterize the virga phenomena, a systematic method was developed using ceilometer profiles, soundings, surface rain gauges, and radar data from the nearest National Weather Service (NWS) site. A total of 50 virga events were identified during the study period. These events appeared only during a specific time of the year, revealing a seasonal occurrence pattern. We identified and classified these virga events and investigated their impact on the surface measurements recorded by the on-campus Continuous Ambient Air Monitoring Station (CAMS). Virga events were classified as columnar and non-columnar events based on their aerosol profiles. We observed that during some of the columnar virga events, surface particulate matter (PM) levels displayed a sudden upward trend indicating aerosol loading in the surface layer after precipitation evaporation. In total, 20 of the virga events showed a columnar structure out of the 50 identified in this study. More detailed analysis of selected events shows that virga affects regional air quality. A significant result of this study is that analysis of sudden changes in local air quality needs to consider the possible effects of virga on the surface layer.

The Paso Del Norte (PdN) region comprises the city of El Paso, TX, Ciudad Juarez, Mexico, and some neighboring cities in the state of New Mexico. Developing a regional weather model for this specific region has always been challenging due to its complex terrain. To obtain more accurate weather and pollution forecasting for the PdN region, the results of the downscaled WRF (Weather Research and Forecast) model were intercompared with meteorological satellite data, with ground and radiosonde dataset. In addition, it is critical to analyze the distributions of ozone concentrations to better understand atmospheric aerosol concentrations and predict them both more accurately. Hence, in this study the ozone results of CAMx (Comprehensive Air Quality Model with Extensions) were extensively intercompared with ozonesonde data. The radiosonde/ozonesonde data were obtained throughout a campaign conducted during the summer of 2017 in the PdN region. Different meteorological variables such as temperature, pressure, relative humidity, wind speed, and ozone concentrations were used for comparison at several locations in the PdN region. The TCEQ (Texas Commission of Environment Quality) data from different CAMS (Continuous Ambient Monitoring Stations) were used for ground data intercomparison with the WRF results. The meteorological satellite sounding data were retrieved using an in-house satellite antenna receiver. The results of this research paper will not only provide better pollution forecasting capability for the PdN region but also for other regions with similar topography and terrain.

An ozone abatement strategy for the South Coast Air Basin (SoCAB) has been proposed by the South Coast Air Quality Management District (SCAQMD) and the California Air Resources Board (ARB). The proposed emissions reduction strategy is focused on the reduction of nitrogen oxide (NOx) emissions by the year 2030. Two high PM2.5 concentration episodes with high ammonium nitrate compositions occurring during September and November 2008 were simulated with the Community Multi-scale Air Quality model (CMAQ). All simulations were made with same meteorological files provided by the SCAQMD to allow them to be more directly compared with their previous modeling studies. Although there was an overall under-prediction bias, the CMAQ simulations were within an overall normalized mean error of 50%; a range that is considered acceptable performance for PM modeling. A range of simulations of these episodes were made to evaluate sensitivity to NOx and ammonia emissions inputs for the future year 2030. It was found that the current ozone control strategy will reduce daily average PM2.5 concentrations. However, the targeted NOx reductions for ozone were not found to be optimal for reducing PM2.5 concentrations. Ammonia emission reductions reduced PM2.5 and this might be considered as part of a PM2.5 control strategy. Implications: The SCAQMD and the ARB have proposed an ozone abatement strategy for the SoCAB that focuses on NOx emission reductions. Their strategy will affect both ozone and PM2.5. Two episodes that occurred during September and November 2008 with high PM2.5 concentrations and high ammonium nitrate composition were selected for simulation with different levels of nitrogen oxide and ammonia emissions for the future year 2030. It was found that the ozone control strategy will reduce maximum daily average PM2.5 concentrations but its effect on PM2.5 concentrations is not optimal.

The light-scattering properties of mineral dust and soot particles in the El Paso-Juarez Airshed were analyzed using data from an acoustic extinctiometer and a laser particle counter in conjunction with a non-spherical scattering model for polydisperse and randomly oriented particles, the T-matrix model. The data selected correspond to days exhibiting a mean relative humidity (RH) less than 20% to avoid effects of possible aerosol hygroscopic growth. The inter-comparison for the selected days of the extinction and scattering coefficients results obtained using the T-matrix and the laser particle counter, with those obtained from an acoustic extinctiometer at a wavelength of 0.87 μm shows good agreement. In addition, the single-scattering albedo for this region is analyzed for the selected days. The methodology developed in this work can be used as a diagnostic tool to characterize mineral dust and soot particles, and the results of this study will provide a better understanding of the aerosol optical properties for the El Paso-Juarez Airshed.

An essential component of a three-dimensional air quality model is its gas-phase mechanism. We present an overview of the necessary atmospheric chemistry and a discussion of the types of mechanisms with some specific examples such as the Master Chemical Mechanism, the Carbon Bond, SAPRC and the Regional Atmospheric Chemistry Mechanism (RACM). The first versions of the Carbon Bond and SAPRC mechanisms were developed through a hierarchy of chemical species approach that relied heavily on chemical environmental chamber data. Now a new approach has been proposed where the first step is to develop a highly detailed explicit mechanism such as the Master Chemical Mechanism and the second step is to test the detailed explicit mechanism against laboratory and field data. Finally, the detailed mechanism is condensed for use in a three-dimensional air quality model. Here it is argued that the development of highly detailed explicit mechanisms is very valuable for research, but we suggest that combining the hierarchy of chemical species and the detailed explicit mechanism approaches would be better than either alone.Implication: Many gas-phase mechanisms are available for urban, regional and global air quality modeling. A "hierarchy of chemical species approach," relying heavily on smog-chamber data was used for the development of the early series of mechanisms. Now the development of large, explicit master mechanisms that may be condensed is a significant, trend. However, a continuing problem with air quality mechanism development is due to the high complexity of atmospheric chemistry and the current availability of laboratory measurements. This problem requires a balance between completeness and speculation so that models maintain their utility for policymakers.

The reduced Rayleigh equation for the scattering of a surface plasmon polariton incident non-normally on a one-dimensional ridge or groove on an otherwise planar metal surface is solved by a purely numerical approach. The solution is used to calculate the transmission, reflection, and out-of-plane scattering coefficients of the surface plasmon polariton. The angular dependence of the out-of-plane scattering is found to have a conical nature.

Proposed emission control strategies for reducing ozone and particulate matter are evaluated better when air quality and health effects models are used together. The Community Multiscale Air Quality (CMAQ) model is the US Environmental Protection Agency’s model for determining public policy and forecasting air quality. CMAQ was used to forecast air quality changes due to several emission control strategies that could be implemented between 2008 and 2030 for the South Coast Air Basin that includes Los Angeles. The Environmental Benefits Mapping and Analysis Program—Community Edition (BenMAP-CE) was used to estimate health and economic impacts of the different emission control strategies based on CMAQ simulations. BenMAP-CE is a computer program based on epidemiologic studies that link human health and air quality. This modeling approach is better for determining optimum public policy than approaches that only examine concentration changes.

We study properties of a p-polarized surface plasmon polariton propagating circumferentially around a portion of a cylindrical interface between a vacuum and a metal, a situation investigated earlier by Berry (J. Phys. A: Math. Gen. 8 (1975) 1952). When the metal is convex toward the vacuum this mode is radiative and consequently is attenuated as it propagates on the cylindrical surface. An approximate analytic solution of the dispersion relation for this wave is obtained by an approach different from the one used by Berry, and plots of the real and imaginary parts of its wave number are presented. When the metal is concave to the vacuum, the resulting dispersion relation possesses a multiplicity of solutions that have the nature of waveguide modes that owe their existence to the curvature of the interface.

Analytic expressions for the dispersion relation and electric field profiles of guided waves supported by an asymmetric graded-index dielectric waveguide are derived. The system studied consists of vacuum in the region , and a dielectric medium in the region whose dielectric permittivity decreases continuously with increasing distance into it from the interface according to . Here is the (real) index of refraction of the medium at , and it is assumed that . It is found that for frequencies below a certain critical value given by , where is the speed of light in vacuum, the dispersion curve consists of a single branch that exists in a narrow spectral range. Its electric field decays exponentially with increasing distance into each medium. For frequencies above this critical value, the dispersion curve possesses several branches. The corresponding electric field decays exponentially with increasing distance into the vacuum, and decays in an oscillatory fashion with increasing distance into the grad...

The objective of this study is to present differences in the variability of observed and ozone-mixing ratios simulated by a three-dimensional atmospheric chemical model using two chemical mechanisms. In this study the Comprehensive Air Quality Model with Extensions is used to make ozone simulations with the Carbon Bond mechanism, versions 4 and 5. The Paso del Norte region is used as a test-bed for these simulations. The shared variance between the simulations and measurements is typical for air quality models ranging from 0.51 to 0.86 for both mechanisms. The smallest mean normalized gross error is about 31 % with CB4 but the normalized bias is over 30 % as well. Boundary conditions, emissions and other factors affect the levels of ozone of the simulated mixing ratios and therefore error and bias but these factors have a much less affect on the simulated ozone variability. The differences in the ozone variability of the measurements and the simulations are very large and different for the two chemical mechanisms. There are many more instances of low ozone mixing ratios in the measurements than in the simulated ozone. One possible explanation is that these differences are due to problems associated with comparing point measurements with grid averages. A more disturbing possibility is that the bias could be due to the procedures used in the development and testing of air quality modeling systems. Air quality mechanisms are evaluated against environmental chamber data where the chemistry occurs at high concentrations and this may lead to a systematic positive bias in ozone simulations.

Soil-derived dust represents one of the major components of the natural atmospheric aerosols. Arid and semiarid areas with unpaved and non-vegetated land cover are particularly vulnerable to windblown dust, which results in high particulate matter pollution. To understand, predict, and mitigate the impact of dust aerosol on air quality and climate, it is necessary to parameterize the emission rate of dust particles from the wind erosion processes accurately. However, windblown dust emission is poorly represented in existing air quality models. In this paper, a windblown dust emission model has been developed based on a parameterization of threshold wind friction velocity depending on the roughness of surface, vegetation type, soil type, soil moisture content, and on the size distribution of aerosols. The proposed dust model incorporates into a region air quality modeling system to simulate a North American dust storm episode occurring near the border of southwestern USA and northwestern region of Mexico on 23 February 2007. It is shown that the implementation of a windblown dust model in an air quality model can significantly improve the model capability for capturing the dust episode. The simulation of the model is in good agreement with the evolution of dust distribution. The modeled dust spatial patterns matched dust cloud patterns appearing on satellite images. Implementation of the windblown dust model successfully captured the time of peak particulate matter (PM) concentrations for both PM10 and PM2.5, as well as the peak value of the PM2.5 concentration. The modeled results clearly demonstrate an improved ability to predict PM events by applying the windblown dust emission scheme.

Few studies have taken a conventional quantitative environmental justice approach to assessing the inequitable implications of climate change at a fine scale, such as across neighborhoods within an urban area. In this paper, we test the “environmental justice hypothesis” for climate change-related variables in the bi-national context of El Paso, Texas and Ciudad Juarez, Chihuahua using a matched set of social indicators from the 2000 US and Mexican censuses and biophysical data related to heat, ozone and flooding. T-test results demonstrated that social marginality and climate change-related hazard exposure were generally higher in Juarez as compared to El Paso. Using spatial regression models, we found patterns of environmental injustice in the sister cities related to these climate change-related hazards. Lower social class neighborhoods generally faced increased risks from extreme heat in both cities, and from floods and peak ozone in El Paso. In El Paso, children also faced significant and disproportionate exposure to peak ozone, while female-headed households were significantly more burdened by flooding and peak ozone in Juarez. Despite the limitations of this cross-sectional study, we can expect injustices to heighten as neighborhoods at-risk now become increasingly exposed under climate change scenarios. In sum, this analysis provides a model for investigating inequities associated with future small area impacts of climate change.

There are significant human impacts associated with climate change. This paper introduces a model for identifying small area risks associated with children’s vulnerability to climate change-related hazard exposures, which is transferable to other regions and adaptable to varied population and exposure scenarios. The cross-national El Paso-Ciudad Juarez (US-Mexico) metropolis serves as the study area for model implementation, which involves mapping social vulnerability, hazard exposure, and cumulative climate change-related risks. This study addresses two limitations of extant fine-scale climate change vulnerability mapping studies. First, rather than focusing on one exposure variable, it assesses the combined risks of multiple exposures (extreme heat, peak ozone, and floods) and, thus, offers a model for mapping neighborhood-level cumulative climate change exposure risks. Second, it provides a model for small area spatial analyses of climate change vulnerability within low-/middle-income countries and in contexts where climate change risks (and appropriate responses) are cross-national in scope.

A methodology to retrieve Single Scattering Albedo (SSA) values employing the ratio of Direct to Diffuse Irradiances (DDR) is used and applied to the El Paso-Juarez Airshed, a challenging region where air masses interact. The TUV model was used to obtain the calculated DDR irradiances, and the experimental irradiances were obtained from a UV-MFRSR instrument located in the city of El Paso, Texas. The wavelengths used were 332 nm and 368 nm. The retrieved SSA values at both 332 nm and 368 nm were higher in a lightly polluted day (0.66–0.81 at 332 nm, and 0.61 to 0.80 at 368 nm) than in a heavier polluted day (0.56–0.70 at 332 nm and 0.53–0.66 at 368 nm). A sensitivity study of the ground albedo and the asymmetry parameter was performed, which indicated that the variation of the asymmetry parameter is a secondary effect in the retrievals of SSA. In addition, the variation of SSA values during the day was also analyzed for the El Paso-Juarez Airshed and linked to the flow of air masses into the region using HYSPLIT trajectories. A presence of absorptive aerosols was observed during the late morning and the middle of the day. This methodology can be applied in any area, and is particularly useful for cities that experience episodes of high PM concentrations.

A light-extinction technique for monitoring aerosols was used in conjunction with a robust inverse reconstruction model to retrieve aerosol size distribution. Results for the columnar aerosol size distribution for the Paso del Norte Airshed for two different pollution scenarios and at two different seasons were presented. These are well correlated with experimental surface aerosol data for this region. It was observed that, for the clean day scenario, the summer case showed a greater columnar concentration of smaller size aerosols than the winter case. Results for the columnar aerosol size distribution in the polluted day scenario demonstrated that the concentration of aerosols were greater in the summer than in the winter. In addition, HYSPLIT backward trajectories were used to identify pollution sources.

We study theoretically the propagation of a wave packet that is a superposition of three s-polarized guided waves with different frequencies in a planar waveguide consisting of a dielectric medium with a graded index of refraction, sandwiched between perfectly conducting walls. The electric field at each point within the waveguide is calculated, and it is shown that each of the constituent modes ceases to propagate at a specific distance along the waveguide that depends on its frequency and on the geometrical and material parameters defining the waveguide. This simple model displays the phenomenon of rainbow trapping of guided waves in an explicit fashion, without the use of a negative index metamaterial.

Surface ozone pollution has been a persistent environmental problem in the US and Europe as well as the developing countries. A key prerequisite to find effective alternatives to meeting an ozone air quality standard is to understand the importance of local anthropogenic emissions, the significance of biogenic emissions, and the contribution of long-range transport. In this study, an air quality modeling system that includes chemistry and transport, CMAQ, an emission processing model, SMOKE, and a mesoscale numerical meteorological model, WRF, has been applied to investigate an ozone event occurring during the period of the 1996 Paso del Norte Ozone Campaign. The results show that the modeling system exhibits the capability to simulate this high ozone occurrence by providing a comparable temporal variation of surface ozone concentration at one station and to capture the spatial evolution of the event. Several sensitivity tests were also conducted to identify the contributions to high surface ozone concentration from eight VOC subspecies, biogenic VOCs, anthropogenic VOCs and long-range transportation of ozone and its precursors. It is found that the reductions of ETH, ISOP, PAR, OLE and FORM help to mitigate the surface ozone concentration, and like anthropogenic VOCs, biogenic VOC plays a nonnegligible role in ozone formation. But for this case, long-range transport of ozone and its precursors appears to produce an insignificant contribution.

By means of a modal method we have calculated the angular dependence of the reflectivity and the efficiencies of several other diffracted orders of a perfectly conducting lamellar reflection grating illuminated by p-polarized light. These dependencies display the signatures of Rayleigh and Wood anomalies, usually associated with diffraction from a metallic grating. The Wood anomalies here are caused by the excitation of the surface electromagnetic waves supported by a periodically corrugated perfectly conducting surface, whose dispersion curves in both the nonradiative and radiative regions of the frequency-wavenumber plane are calculated. © 2016 IOP Publishing Ltd & European Optical Society. This is the authors' accepted and refereed manuscript to the article.

We present an approach to the design of a one-dimensional perfectly conducting randomly rough surface that when illuminated at normal incidence by a laser beam produces a partially coherent scattered beam with a Gaussian dependence of its mean intensity in the mean scattering surface and with a specified spectral degree of coherence in that surface that can have a nearly arbitrary form. The approach is validated by the results of computer simulations.

A novel in situ methodology for the inverse reconstruction of aerosol size distribution from optical depth data is presented and successfully validated against SEM data for the city of El Paso. Additional results using MFRSR optical depth data for La Jornada city are also shown. The retrieval methodology and corresponding codes are applicable to irregularly shaped aerosol particles in any region.

The dispersion relation is derived and solved for s-polarized surface polaritons propagating circumferentially around a portion of a cylindrical interface between vacuum and an isotropic dielectric. In the case that the dielectric is convex toward the vacuum these modes are found to be radiative, and consequently are attenuated as they propagate on the cylindrical surface. When the dielectric is concave toward the vacuum the resulting surface polaritons are nonradiative and propagate unattenuated on the cylinder. Such modes do not exist in the case of a planar interface between a homogeneous isotropic dielectric and vacuum.

This study examined the effects of varying future reductions in emissions of oxides of nitrogen (NOx) and volatile organic compounds (VOC) on the location and magnitude of peak ozone levels within California's South Coast Air Basin (SoCAB or Basin). As ozone formation is currently VOC-limited in the Basin, model simulations with 2030 baseline emissions (-61% for NOx and -32% for VOC from 2008) predict 10-20% higher peak ozone levels (i.e., NOx disbenefit) in the western and central SoCAB compared with the 2008 base simulation. With additional NOx reductions of 50% beyond the 2030 baseline emissions (-81% from 2008), the predicted ozone levels are reduced by about 15% in the eastern SoCAB but remain comparable to 2008 levels in the western and central Basin. The Basin maximum ozone site shifts westward to more populated areas of the Basin and will result potentially in greater population-weighted exposure to ozone with even a relatively small shortfall in the required NOx reductions unless accompanied by additional VOC reductions beyond 2030 baseline levels. Once committed to a NOx-focused control strategy, NOx reductions exceeding 90% from 2008 levels will be necessary to attain the ozone National Ambient Air Quality Standards (NAAQS). The findings from this study and other recent work that the current VOC emission estimates are underestimated by about 50% suggest that greater future VOC reductions will be necessary to reach the projected 2030 baseline emissions. Increasing the base year VOC emissions by a factor of 1.5 result in higher 2008 baseline ozone predictions, lower relative response factors, and about 20% lower projected design values. If correct, these findings have important implications for the total and optimum mix of VOC and NOx emission reductions that will be required to attain the ozone NAAQS in the SoCAB.Results of this study indicate that ozone levels in the western and central SoCAB would remain the same or increase with even a relatively small shortfall in the projected NOx reductions under planned NOx-focused controls. This possibility, therefore, warrants a rigorous analysis of the costs and effects of varying reductions of VOC and NOx on the formation and combined health impacts of ozone and secondary particles. Given the nonlinearity of ozone formation, such analyses should include the implications of gradually increasing global background ozone concentrations and the Basin's topography and meteorology on the practical limits of alternative emission control strategies.

A general purpose partial differential equation solver, PDE2D, which is useful on a wide range of computational physics applications, including 1D, 2D and 3D, time-dependent, steady-state and eigenvalue problems, is described. This program has the advantages of being both accurate and very easy to use. Its wide applicability is illustrated by solving three representative quantum mechanics problems.

The reduced Rayleigh equation for the scattering of a surface plasmon polariton incident normally on a one-dimensional ridge or groove on an otherwise planar metal surface is solved by a purely numerical approach. The solution is used to calculate the reflectivity and transmissivity of the surface plasmon polariton and its conversion into volume electromagnetic waves in the vacuum above the metal surface. The results obtained are compared with those of earlier calculations of these quantities.

We present a reciprocity and unitarity preserving formulation of the scattering of a scalar plane wave from a two-dimensional, randomly rough surface on which the Neumann boundary condition is satisfied. The theory is formulated on the basis of the Rayleigh hypothesis in terms of a single-particle Green's function G(q‖|k‖) for the surface electromagnetic waves that exist at the surface due to its roughness, where k‖ and q‖ are the projections on the mean scattering plane of the wave vectors of the incident and scattered waves, respectively. The specular scattering is expressed in terms of the average of this Green's function over the ensemble of realizations of the surface profile function (G(q‖|k‖)). The Dyson equation satisfied by (G(q‖|k‖)) is presented, and the properties of the solution are discussed, with particular attention to the proper self-energy in terms of which the averaged Green's function is expressed. The diffuse scattering is expressed in terms of the ensemble average of a two-p...

We study the scattering of a scalar plane wave from a two-dimensional, randomly rough surface, on which the Dirichlet boundary condition is satisfied. The scattering amplitude is obtained in the form of the Fourier transform of an exponential, in which the exponent is written as an expansion in powers of the surface profile function. It is shown that the latter expansion can be written in such a way that the corresponding scattering matrix is manifestly reciprocal. Numerical results for the reflectivity, and for the contribution to the mean differential reflection coefficient from the incoherent component of the scattered field, are obtained and compared with the predictions of small-amplitude perturbation theory and the Kirchhoff approximation. As the wavelength of the incident wave is varied continuously the results of the phase-perturbation theory change continuously from those of the small-amplitude perturbation theory to those of the Kirchhoff approximation.

An analytical approach is used to determine the power spectrum of the surface roughness from experimental data for the reflectivity of randomly rough surfaces. A one-dimensional, randomly rough, perfectly conducting surface that is illuminated by s-polarized light whose plane of incidence is perpendicular to the generators of the surface is considered, and the power spectrum is obtained within the framework of phase perturbation theory. Good agreement with numerically generated experimental data is obtained.

We study theoretically the transmission of p- and s-polarized light through a thin, supported, silver or gold film, both of whose surfaces are one-dimensional, periodically corrugated surfaces, as a function of the wavelength of the incident light. The calculations are carried out by the use of reduced Rayleigh equations in the form of a pair of coupled inhomogeneous matrix equations for the amplitudes of the scattered and transmitted Bragg beams. The results show that enhanced transmission occurs for both p- and s-polarized incident light for large-amplitude periodic corrugations of the two surfaces. In p polarization an additional enhancement occurs at the wavelengths of the surface plasmon polaritons supported by the film. Thus, slits that pierce the film are not necessary for enhanced transmission of light through it.

A time-dependent, 3-dimensional mesoscale model, version 5 (MM5), developed by the Penn State University and the National Center for Atmospheric Research, was applied to study the meteorology over complex terrain of the El Paso-Juarez area. MM5 meteorological output data were compared against experimental data from the Texas Natural Resource Conservation Commission on days of reported high ozone concentrations. Model runs were conducted for a 36-, 12-, 4-km grid arrangement. Results indicate that the dispersion of pollutants by wind plays a significant role on days of low peak ozone concentration.