Special Issue

New Trend of Researches on Atmospheric Environmental Protection

Control Techniques and Measurement of Hazardous Air Pollutants

Reviews

Researches for Atmospheric Environment Protection in National Institute for Resources and Environment

Ikuo TAMORI (ex-,Atmospheric Environmental Protection Department,NIRE)
Takashi IBUSUKI (Atmospheric Environmental Protection Department,NIRE)

Abstract
History of atmospheric environmental issues as well as pollutants is reviewed. Researches for protection of atmospheric environment including emission control technologies being conducted by National Institute for Resources and Environment (NIRE) are summarized from the viewpoint of "ECO-TECHNOLOGY" which has been proposed by NIRE as the basic concept (Connecting the researches for the resources and energy with those for the environment tightly, namely combining the researches for ecology and technology).

Key Words : Atmospheric environmental issues, Researches of NIRE, Ecotechnology

(Language:Japanese)

Reviews

Nonthermal Plasma Chemical Decomposition of Hazardous Air Pollutants

Shigeru FUTAMURA and Aihua ZHANG (Excited State Chemistry Div.,Atmospheric Environmental Protection Dept.,NIRE)

Abstract
Nonthermal plasma chemical processing of hazardous air pollutants (HAPs) has been reviewed from the viewpoint of organic reaction chemistry mainly based on the authors' data on the decomposition of HAPs and their molecular probes. Nonthermal plasma affords pertinent reaction media to efficiently decompose up to 1,000 ppm of HAPs such as trichloroethylene, tetrachloroethylene, and 1,1,1-trichloroethane. The structure-reactivity relationship for HAPs, effects of background gases and water on their decomposition efficiencies, and distributions of organic byproducts suggest that their decomposition homolytically proceeds via their excited states. Radical-induced HAP decomposition also occurs when in situ radical concentrations are high.

Active oxygen species are much less responsible for the initial steps of HAP decomposition, but the decomposition of nonchlorinated HAPs is accelerated by oxenoid species generated from water. Almost all the carbons of the reacted HAPs can be recovered as CO and CO₂ in air due to the promoted autoxidation. Water acts as an efficient oxidant in CO oxidation.

Plasma chemical processing is one of the most promising technologies for HAP decomposition since less than 1,000 ppm of HAPs can be almost completely decomposed with suppressed formation of organic byproducts at 1 to 3 s of residence time. One of the largest challenges for this technology could be suppression of inorganic byproducts such as nitrogen oxides, which requires improved reactor geometry and control of input power and residence time.

Key Words : Nonthermal plasma, HAPs, Byproducts, Mechanism

(Language:Japanese)

Reviews

Development of Catalytic System for Diesel NOx Removal

Akira OBUCHI and Satoshi KUSHIYAMA (Environmental Technology Div., Atmospheric Environmental Protection Dept., NIRE)

Abstract
Atmospheric pollution by nitrogen oxides (NOx) is becoming serious, especially in urban areas in Japan. Diesel_powered vehicles are among the main emission sources of NOx. This research aims at the development of a practical NOx removal system for diesel engines by combining advanced catalytic techniques to decompose or reduce NOx with hydrocarbons.

To sum up the results obtained so far, first we have confirmed that the selective catalytic reduction with organic compounds is the most promising process for the diesel NOx removal. Second, we have developed and/or confirmed several most promising candidates as the catalysts for this process, which include Pt supported catalysts, Co/Al₂O₃ and Au/Al₂O₃ + Mn₂O₃. Third, since the single use of either of these catalysts cannot cover the whole temperature range of the diesel exhaust, nor solve problems of byproducts such as N₂O and aldehydes, combination or hybridization of catalysts having different functions were proved to be necessary. A double-layered catalyst comprising Pt catalysts convered with H-ZSM-5 showed the best performance.

We could not accomplish durability and economical evaluations for the above promising catalysts, which are indispensable for the practical application. We expect that we can reach the goal by appropriate multi_layering of catalysts described as above, and will continue studies along this line.

Key Words : Nitrogen oxides, Diesel engine exhaust, Selective reduction, Catalyst, Double-layered catalyst, Organic

(Language:Japanese)

Reviews

Control of Adsorption by Microwave Irradiation

Satoru KOBAYASHI (Environmental Technology Div., Atmospheric Environmental Protection Dept., NIRE)

Abstract
The process of gas adsorption is currently controlled by temperature and/or pressure swing methods. The control by pressure swing can not be applied to the system in which adsorption force is very strong. On the other hand, the control by temperature swing has a problem that overall adsorption rate is strongly influenced by heat transfer. In this study, a possibility was examined of the application of microwave irradiation for the control of adsorption in order to solve the problems mentioned above. Microwave irradiation provides a rapid heating of adsorbents with high conductivity such as activated carbons. It can be also expected that some adsorbates with large dielectric losses are easily desorbed by the excitation on microwave irradiation, while not for the adsorbates with small dielectric losses.

Key Words : microwave, adsorption, desorption, gas

(Language:Japanese)

Reviews

Emission Control of Volatile Chlorinated Hydrocarbons Using Cyclodextrins

Isamu Uemasu and Satoshi Kushiyama(Environmental Technology Div., Atmospheric Environmental Protection Dept., NIRE)

Abstract
The emission control of volatile chlorinated hydrocarbons at industry is mandatory, and thus in this study, examination was made of the use of cyclodextrins (CDs) as absorbents so as to establish a novel and effective method for capturing the organic compounds. Branched CDs, very soluble in water, were found considerably effective. The solubility of various volatile chlorinated hydrocarbons such as trichloroethylene in aqueous solutions of branched CDs was determined. The amounts of chlorinated hydrocarbons captured by CDs were closely correlated with molecular size and shape.

Partition coefficients of a linear partition model were calculated from solubility data. Absorption experiments were conducted using apparatus in which chlorinated hydrocarbon gas diluted with nitrogen came into contact with aqueous solutions of branched CDs. The efficiency of capture or removal was correlated with the partition coefficients. Higher concentrations of CDs and greater flow rate of fresh absorption solution enhanced the removal of chlorinated hydrocarbon gas.

Key Words : Emission control, Volatile chlorinated hydrocarbons, Branched cyclodextrins

(Language:Japanese)

Reviews

Problems in Measuring Particulate Matter Generated by Combustion

Masaaki SHIRAHASE (Air Quality Measurement Div.,Atmospheric Environmental Protection Dept.,NIRE)
Nobuyuki KOGURE (Air Quality Measurement Div.,Atmospheric Environmental Protection Dept.,NIRE)
Akira OBUCHI (Environmental Technology Div., Atmospheric Environmental Protection Dept., NIRE)
Akihiko OHI (Air Quality Measurement Div.,Atmospheric Environmental Protection Dept.,NIRE)

Abstract
Effective control techniques for particulate matter emitted from many emission sources should be established, since the attainment rate of environmental quality standard for suspended particulate matter remains inadequate. Particulate matter generated by combustion, emitted from stationary smoke and dust facilities such as boiler and incinerator, and automobiles, is a significant source of suspended particulate matter. This report presents measuring methods for particulate matter from stationary sources and automobiles. We pointed out the possibility that the properties of particulate matter measured at stationary sources and automobiles are different on the basis of each sampling condition. The necessity of measuring the condensed dust is also discussed in the case of particulate matter from stationary sources.

The problem of hazardous air pollutants is becoming increasingly serious in Japan. Diesel exhaust particulate is one source of hazardous air pollutants containing many polycyclic aromatic hydrocarbons to be possibly carcinogenic. The methods for analyzing polycyclic aromatic hydrocarbons and problems are discussed.

Key Words : Particulate matter, Condensed dust, Source inventory, Diesel exhaust particulate, Polycyclic aromatic hydrocarbons

(Language:Japanese)

Reviews

Measurement Techniques of Hazardous Organic Vapor Pollutants in the Atmosphere

Toshiyuki TANAKA (Air Quality Measurement Div.,Atmospheric Environmental Protection Dept.,NIRE)

Abstract
Measurement techniques relevant to the field study for hazardous organic vapor pollutants such as benzene in air are described. Atmospheric organic vapor pollutants are sampled by using porous polymer beads in tubes at room temperature or canisters evacuated and are analyzed by GC-FID or GC-MS. The outline of reported measurement techniques and some examples of field studies in urban areas are reviewed.

Key Words : volatile organic compound, hazardous air pollutant, gas chromatograph, Tenax, canister

(Language:Japanese)