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.

This article reports what are to the authors' knowledge the first gas-phase laser-induced breakdown spectroscopy (LIBS) measurements using a fiber-optically delivered spark. A silver- and polymer-coated hollow fiber delivered high-energy nanosecond 1064 nm Nd:YAG laser pulses, which were focused to generate high-energy-density plasmas in ultra-lean methane–air mixtures. Emissions from these plasmas were collected and spectroscopically analyzed to quantify relative fuel-to-air ratio. These measurements were compared with others made using traditional LIBS techniques without the fiber-optically delivered spark. Similar results were obtained, but with larger shot-to-shot variability, for the case of the fiber-optically delivered spark.

Fiber-Optic Spark Delivery for Gas-Phase Laser-Induced Breakdown Spectroscopy

An FTIR-based spectroscopic technique is described that exploits silicon's transmissivity in the IR to make nonintrusive measurements of species concentration and temperature profiles in microcombustors. Species concentration is determined from the integrated absorbance (Beer's law), whereas gas temperature is determined by fitting a narrow-band spectral model (EM2C) to CO2 absorption spectra. The technique is demonstrated in a millimeter-scale combustor burning a lean (Φ = 0.86) CH4–air mixture. The results show that accuracies of ±0.25 e-3 mol/L and ±100°C with spatial resolution ∼1 mm are possible. Heat fluxes to the wall are also estimated and thermal losses are found to be very high (∼90%).

In Situ Species and Temperature Measurements in a Millimeter-Scale Combustor

Heat is exchanged between high and low temperature gases in a regenerator type of heat exchanger, wherein the high temperature gas is conducted through a high temperature passage formed in a housing, and the low temperature gas is conducted through a low temperature passage formed in the housing. A porous heat transfer core is rotated such that portions of the core pass sequentially through the high and low temperature passages. The high temperature gas traveling in the high temperature passage is caused to flow through, and heat, a portion of the core disposed in the high temperature passage. The low temperature gas traveling in the low temperature passage is caused to flow through, and be heated by, a heated portion of the core disposed in the low temperature passage. A low pressure zone is established in a chamber situated at each location where the core travels from one of the passages to the other. A pressure in the low pressure zone is lower than pressures-in both of the passages, whereby gases tending to leak from one of the passages to the other are drawn into the low pressure zone and are conducted out of the housing.

Regenerator type heat exchanger

Three-dimensional distribution of signal from single monodisperse aerosol particles in a laser induced plasma: Initial measurements

The authors report results from an experimental study that examines the influence of sintering and microstructure on ash deposit thermal conductivity. The measurements are made using 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. The technique is designed to minimize the disturbance of the natural deposit microstructure. The initial stages of sintering and densification are accompanied by an increase in deposit thermal conductivity. Subsequent sintering continues to densify the deposit, but has little effect on deposit thermal conductivity. SEM analyses indicates that sintering creates a layered deposit structure with a relatively unsintered innermost layer. They hypothesize that this unsintered layer largely determines the overall deposit thermal conductivity. A theoretical model that treats a deposit as a two-layered material predicts the observed trends in thermal conductivity.

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Steven G. Buckley

Papers

Fiber-Optic Spark Delivery for Gas-Phase Laser-Induced Breakdown Spectroscopy

In Situ Species and Temperature Measurements in a Millimeter-Scale Combustor

Regenerator type heat exchanger

Three-dimensional distribution of signal from single monodisperse aerosol particles in a laser induced plasma: Initial measurements

Experimental measurements of the thermal conductivity of ash deposits: Part 2. Effects of sintering and deposit microstructure