Many scientific papers have been written concerning gas sensors for different sensor applications using several sensing principles. This review focuses on sensors and sensor systems for gaseous ammonia. Apart from its natural origin, there are many sources of ammonia, like the chemical industry or intensive life-stock. The survey that we present here treats different application areas for ammonia sensors or measurement systems and different techniques available for making selective ammonia sensing devices. When very low concentrations are to be measured, e.g. less than 2 ppb for environmental monitoring and 50 ppb for diagnostic breath analysis, solid-state ammonia sensors are not sensitive enough. In addition, they lack the required selectivity to other gasses that are often available in much higher concentrations. Optical methods that make use of lasers are often expensive and large. Indirect measurement principles have been described in literature that seems very suited as ammonia sensing devices. Such systems are suited for miniaturization and integration to make them suitable for measuring in the small gas volumes that are normally available in medical applications like diagnostic breath analysis equipment.

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Ammonia sensors and their applications - a review

The first part of this two-part review focused on the fundamental and diagnostics aspects of laser-induced plasmas, only touching briefly upon concepts such as sensitivity and detection limits and largely omitting any discussion of the vast panorama of the practical applications of the technique. Clearly a true LIBS community has emerged, which promises to quicken the pace of LIBS developments, applications, and implementations. With this second part, a more applied flavor is taken, and its intended goal is summarizing the current state-of-the-art of analytical LIBS, providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools. More specifically, we discuss instrumental and analytical approaches (e.g., double- and multi-pulse LIBS to improve the sensitivity), calibration-free approaches, hyphenated approaches in which techniques such as Raman and fluorescence are coupled with LIBS to increase sensitivity and information power, resonantly enhanced LIBS approaches, signal processing and optimization (e.g., signal-to-noise analysis), and finally applications. An attempt is made to provide an updated view of the role played by LIBS in the various fields, with emphasis on applications considered to be unique. We finally try to assess where LIBS is going as an analytical field, where in our opinion it should go, and what should still be done for consolidating the technique as a mature method of chemical analysis.

https://journals.sagepub.com/doi/pdf/10.1366/11-06574

Laser-induced breakdown spectroscopy (LIBS), part II: review of instrumental and methodological approaches to material analysis and applications to different fields.

Oxy-fuel combustion of solid fuels

Atmospheric aerosol particles of biological origin are a very diverse group of biological materials and structures, including microorganisms, dispersal units, fragments and excretions of biological organisms. In recent years, the impact of biological aerosol particles on atmospheric processes has been studied with increasing intensity, and a wealth of new information and insights has been gained. This review outlines the current knowledge on major categories of primary biological aerosol particles (PBAP): bacteria and archaea, fungal spores and fragments, pollen, viruses, algae and cyanobacteria, biological crusts and lichens and others like plant or animal fragments and detritus. We give an overview of sampling methods and physical, chemical and biological techniques for PBAP analysis (cultivation, microscopy, DNA/RNA analysis, chemical tracers, optical and mass spectrometry, etc.). Moreover, we address and summarise the current understanding and open questions concerning the influence of PBAP on the atmosphere and climate, i.e. their optical properties and their ability to act as ice nuclei (IN) or cloud condensation nuclei (CCN). We suggest that the following research activities should be pursued in future studies of atmospheric biological aerosol particles: (1) develop efficient and reliable analytical techniques for the identification and quantification of PBAP; (2) apply advanced and standardised techniques to determine the abundance and diversity of PBAP and their seasonal variation at regional and global scales (atmospheric biogeography); (3) determine the emission rates, optical properties, IN and CCN activity of PBAP in field measurements and laboratory experiments; (4) use field and laboratory data to constrain numerical models of atmospheric transport, transformation and climate effects of PBAP. Keywords: primary biological atmospheric aerosol; climate; cloud condensation nuclei; biology; atmospheric ice nuclei (Published: 22 February 2012) Citation: Tellus B 2012, 64 , 15598, DOI: 10.3402/tellusb.v64i0.15598

https://www.tandfonline.com/doi/pdf/10.3402/tellusb.v64i0.15598

Primary biological aerosol particles in the atmosphere: a review

Particulate matter (PM) emissions from stationary combustion sources burning coal, fuel oil, biomass, and waste, and PM from internal combustion (IC) engines burning gasoline and diesel, are a significant source of primary particles smaller than 2.5 μm (PM2.5) in urban areas. Combustion-generated particles are generally smaller than geologically produced dust and have unique chemical composition and morphology. The fundamental processes affecting formation of combustion PM and the emission characteristics of important applications are reviewed. Particles containing transition metals, ultrafine particles, and soot are emphasized because these types of particles have been studied extensively, and their emissions are controlled by the fuel composition and the oxidant-tem-perature-mixing history from the flame to the stack. There is a need for better integration of the combustion, air pollution control, atmospheric chemistry, and inhalation health research communities. Epidemiology has demonstrated t...

https://www.tandfonline.com/doi/pdf/10.1080/10473289.2000.10464197

Combustion aerosols: factors governing their size and composition and implications to human health.

A numerical model and experiments over PMMA are used to evaluate the main assumptions used in the theoretical description of a diffusion flame established in a natural boundary layer. Flow characteristics (2-D Boundary Layer) and surface thermal balance are identified as the critical assumptions to be evaluated. Comparison of experiments, numerical results, and theoretical model serve to validate the assumptions leading to the definition of a mass transfer number but establish the need to model all three-dimensional features of the flow.

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Diffusion Flames Upwardly Propagating over PMMA: Theory, Experiment and Numerical Modeling

This paper describes a technique developed to make in situ, time-resolved measurements of the effective thermal conductivity of ash deposits formed under conditions that closely replicate those found in the convective pass of a commercial boiler. Since ash deposit thermal conductivity is thought to be strongly dependent on deposit microstructure, the technique is designed to minimize the disturbance of the natural deposit microstructure. Traditional techniques for measuring deposit thermal conductivity generally do not preserve the sample microstructure. Experiments are described that demonstrate the technique, quantify experimental uncertainty, and determine the thermal conductivity of highly porous, unsintered deposits. The average measured conductivity of loose, unsintered deposits is 0.14 {+-} 0.03 W/(m K), approximately midway between rational theoretical limits for deposit thermal conductivity.

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Experimental measurements of the thermal conductivity of ash deposits: Part 1. Measurement technique

A trace species detection System for engine health monitoring, the system including a laser (32) for generating a laser beam (34), and optics for focusing the laser beam into an exhaust plume of an engine for thereby creating a spark in the exhaust plume. The System further includes spectral analysis instrumentation (40) for detecting light emissions from the spark, and statistical processing instrumentation (100) for analyzing data from the spectral analysis instrumentation (40) for thereby identifying and quantifying specific particles within a volume of the spark. The invention also provides a method of monitoring the health of an engine, the method including generating a laser beam, focusing the laser beam into an exhaust plume of the engine for thereby creating a spark in the exhaust plume, detecting light emissions from the spark, and analyzing data from the detection for thereby identifying and quantifying specific particles within a volume of the spark.

LIBS system and method for engine exhaust monitoring

Ash deposits reduce heat transfer rates to furnace walls, superheater tubes, and other heat transfer surfaces in coal-fired power plants. The effective thermal conductivity of a porous ash deposit is one important parameter for determining the magnitude of this reduction. In this paper, we report in situ , time-resolved measurements of the effective thermal conductivity of ash deposits formed under conditions that closely replicate those found in the convective pass of a commercial boiler. Experiments were conducted using an Illinois #6 coal and a blend of Illinois #6 coal and wheat straw to determine the thermal conductivity of highly porous, unsintered deposits and to examine the influence of the initial stages of sintering on these deposits. For deposits formed while firing both fuels the measured thermal conductivity of loose, unsintered deposits is 0.15 W/(m K), almost a factor of three greater than that of air under these conditions. The initial stages of deposit sintering and densification are accompanied by a substantial increase in deposit thermal conductivity. Subsequent sintering continues to densify the deposit but has little effect on deposit thermal conductivity. These trends correspond to anticipated effects of sintering on the development of a layered deposit structure and on particle contact efficiency. Measured values of thermal conductivity are also observed to lie between rational theoretical bounds based on deposit porosity and structure.

in situ measurements of the thermal conductivity of ash deposits

A LIBS measurement system is described herein that provides an orifice, aperture or opening in a substantially V-shaped chute or sleeve that allows access to the material to be analyzed from the underside of the chute. The laser beam is aimed through the hole and return light (signal) is collected through the hole by a photodetector assembly. A diverter device, which is located at an output end of the chute, diverts certain particles away from the chute upon receipt of an actuation signal.

Steven G. Buckley

Papers

Diffusion Flames Upwardly Propagating over PMMA: Theory, Experiment and Numerical Modeling

Experimental measurements of the thermal conductivity of ash deposits: Part 1. Measurement technique

LIBS system and method for engine exhaust monitoring

in situ measurements of the thermal conductivity of ash deposits

Rapid material analysis using LIBS spectroscopy