Principal Research Results

Air Quality Impact Assessment for the Cogeneration Systems in Urban Area

Background
More than 3,850 cogeneration systems have been introduced as energy-saving equipment for both commercial and industrial
uses since the 1980s in Japan. The heat produced when energy is generated can be used for hot water supply and air conditioning, so
cogeneration systems are located near sites where the heat is required. Almost all of the cogeneration systems operate by internal combustion, such as gas turbines, gas engines and diesel engines that burn fossil fuel, thus exhaust gases from cogeneration systems contain nitrogen oxides (NOx). The impacts of these emissions on air quality, by taking into account building downwash, must therefore
be considered because many cogeneration systems have stacks that are lower than the height of a nearby building in urban areas.

Objectives
To estimate annual emissions of NOx discharged from cogeneration systems based on the results of a questionnaire survey
and evaluate the air quality impact of cogeneration systems using an atmospheric dispersion model.

Principal Results
1. Estimation of annual NOx emissions discharged from cogeneration systems
A questionnaire survey and an interview of consumers within the Tokyo metropolitan area were conducted. Questionnaires
were sent to commercial and industrial consumers with total power generation capacities of 1,000 kW or more. In the survey, exhaustheights, discharge concentrations of NOx, operation hours, and so forth were determined. On the basis of the results of the survey, it
was determined that in many cases discharged NOx concentration levels are approximately 50% of those indicated in the regulations
issued by local governments. Moreover, the amount of NOx discharged from all cogeneration systems installed within the Tokyo metropolitan area was estimated to be approximately 1,100 tons/year.
2. Simulation of air quality impact of the cogeneration systems
A Gaussian plume model was applied to compute spatial distributions of concentrations of NOx released from cogeneration
systems in urban areas of Tokyo. Calculated concentrations of NOx in the center of Tokyo (the area inside of the JR Yamanote Line),
where many cogeneration systems are introduced, were higher than those of surrounding areas and the annual mean concentrations
within that area were 0.6 to 2.5 ppb in most calculation points and the average concentration was 1.6 ppb, which are equivalent to approximately 3.1% of ambient air concentrations. Moreover, there were also areas within the calculation domain that showed concentrations higher than 10 ppb.

Future Developments
An air quality impact assessment on the assumption that more cogeneration systems are installed based on the diffusion scenario in urban areas will be conducted.
Main Researcher: Ayumu Sato,
Research Scientist, Atmospheric Environment Sector, Environmental Science Research Laboratory
Reference
A. Sato and Y. Ichikawa, 2003, Atmospheric dispersion of nitrogen oxides released from cogeneration systems in urban area., Komae
Research Laboratory Rep.No.T02007 (in Japanese).
A. Sato and Y. Ichikawa, 2004, Estimation of annual emissions of NOx discharged from cogeneration systemsin the Tokyo metropolitan area., Komae Research Laboratory Rep.No.T03009 (in Japanese).

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B. Creation of integrated energy service

Cogeneration systems installed within
the Tokyo metropolitan area
〜1,000kW

1,000kW〜

Questionnaire Survey(This Study)
Survey Results
YesNOxconcentrations

SurveyResults

SurveyResults

Survey Results
No

Operatinghours

Amounts ofexhaust gas

Regulations issued by
local governments

NOx
concentrations
Regulation
valuesx0.5(GT,GE)
x1.0(DE)

SurveyResults

Control subjects
Yes

Amounts of
exhaust gas

Operatinghours

Control subjects
NoNOx
concentrations
Catalog
Values(GT)

Fuelconsumption
Past results
Emissionfactors

Interview
results(GE)

Amounts of
exhaust gas

Operatinghours

Fuel
consumption

Clean AirAct (DE)

Past results
Emissionfactors

Annual NOx emissions
GT＝Gas Turbine
GE＝Gas Engine
DE＝Diesel Engine

Geographic information system

Map of NOx emissions

Fig.1 Flow diagram for estimation of NOx emissionsNOx concentrations, amounts of exhaust gas and operation hours using in estimation
were established based on the questionnaire survey results.

Fig.2 Map of NOx emissions from cogeneration
systems

Table1 Annual NOx emissions(tons/year,2002)
GTGE

DE

Total

Commercial 139

266

90495

Industrial

204

131

271

606

Total

343

397

361

1,101

Fig.3 Contour plots of ground-level annual mean
concentrations of nitrogen oxides

At the areas along the JR Yamanote Line, such as Shinjuku,Osaki, Hamamatsucho, and Tokyo, the concentrations
showed higher values than those of the surrounding areas.

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