Abstract
A continuous emission monitoring system (CEMS) is a well-known tool used to analyze the concentrations of air pollutants from stationary sources. In a CEMS, the presence of a high moisture level in a sample causes a loss of analytes due to artifact formation or absorption. This issue brings about a bias in the measurement data. Thus, moisture removal is an important pretreatment step. Condensation and permeation methods have been widely employed to remove moisture from the CEMS for gaseous compounds. In terms of particulate matter, dilution methods have been applied to reduce the moisture level in the gas stream. Therefore, condensation, permeation, and dilution methods are critically reviewed in this work. The removal efficiencies and recovery rates of analytes are discussed, as well as the advantages and disadvantages of each technique. Furthermore, the suitable applications of each technique are determined. Condensation methods have not been well documented so far, while permeation and dilution methods have been continuously studied. Many types of permeation materials have been developed. The limitations of each method have been overcome over the years. However, the most reliable technique has not yet been discovered.
Highlights
The continuous emission monitoring system (CEMS) has been applied to monitor the air pollutants emitted from stationary sources
The CEMS is usually applied to detect the emissions of air pollutants such as carbon monoxide (CO), carbon dioxide (CO2), sulfur oxides (SOx), nitrogen oxides (NOx), hydrogen chloride (HCl), hydrogen fluoride (HF), ammonia (NH3), water vapor (H2O), particulate matter, etc
It was found that the number of particles increased by approximately 50%, and the PM10 concentration increased by as much as 46% when the experiment was conducted at 75% relative humidity [20]
Summary
The continuous emission monitoring system (CEMS) has been applied to monitor the air pollutants emitted from stationary sources. Size distributions of particles can be continuously determined using a fast-mobility particle sizer and an electric low-pressure impactor [5,6,14,15,16] Among these methods, light-scattering meters, opacity meters, Beta attenuation meters, and electrification devices have been widely applied for CEMS [17,18]. The United States Environmental Protection Agency (U.S EPA) stated that moisture is one of the significant bias sources for extractive CEMS [22]. Moisture causes effects such as the absorption of water-soluble gases or artifact formation. Moisture removal is an important issue for extractive CEMS
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