Principal Research Results

Influences of Domestic and Foreign Anthropogenic Emissions on
Atmospheric Fine Particulate Matter (PM2.5) in Greater Tokyo
Background
The Ministry of the Environment of Japan has recognized health impacts of suspended fine particles below 2.5 μm in
diameter in the ambient air (hereinafter, PM2.5) in a report issued in April 2008. In Japan, about one-third of PM2.5 in mass basis is
occupied by sulfate and nitrate respectively formed by SOX and NOX emitted from automobile and large-point sources like factories
and power plants. PM2.5 is a trans-boundary air pollutant due to long retention time in the atmosphere. In order to consider mitigation
strategies of PM2.5 pollution, it is important to know how much PM2.5 pollution in Japan is mitigated by reducing SOX and NOX
emissions from domestic sources and what is the sensitivity of growing foreign emissions on PM2.5 in Japan. To contribute to thoseissues, CRIEPI has developed an air quality model for East Asia1) to analyze atmospheric concentrations of PM2.5 in Japan2).

Objectives
The purpose of this study is to assess influences of domestic and foreign emissions on PM2.5 in Greater Tokyo by analyzing
quantitative relationships between anthropogenic emissions and ambient concentrations of sulfate and nitrate in PM2.5 by simulatingPM2.5 concentrations by the air quality model for East Asia.

Principal Results
Changes in PM2.5 concentrations were estimated by changing SOX and NOX emissions by +20 % (which is equivalent to thegrowth rate in three years) in each of 12 source regions (Figs. 1 and 2). Below are the findings on sulfate and nitrate in PM2.5 inGreater Tokyo.
(1) Concentrations of sulfate and nitrate varied most for the change in local emissions in Greater Tokyo and were relatively sensitive
to emissions from domestic sources and sources in North Central China and Korean Peninsula. Changes in concentrations ofnitrate to nearby emissions were larger than those of sulfate, because of faster formation (Fig. 3).
(2) For sulfate, concentrations were largely altered by local emissions in summertime when the monthly concentrations were thehighest in the simulated year. The sensitivity of concentrations to foreign emissions was larger than domestic emissions in springtime. For nitrate to increases in local emissions, the increasing ratio of concentrations was larger than that of emissions in summertime (excess response) due to activated chemical formation and particulation of nitric acid, the precursor to nitrate. On the otherhand in wintertime, the concentration decreased with increasing local emissions due to consumption of ozone, which was needed
for the formation of nitric acid, by freshly emitted NOX (Fig. 4). Those characteristic behaviors were caused by the complexity ofnitrate formation and unproportional changes in nitrate concentrations to NOX emissions (non-linearity).
From the above findings, it is concluded that sulfate and nitrate in PM2.5 in Greater Tokyo are much influenced by localemissions. However, the influence of foreign emissions is also not negligible. It is importantly noted that non-linearity making thecomplexity in nitrate behavior should be taken into account when considering nitrate reduction.

Future Developments
Similar analysis will be carried out for ozone, another most concerned pollutant, in order to contribute to better quality of theatmospheric environment.
Main Researcher: Hiroshi HAYAMI, Ph. D.,
Senior Research Scientist, Chemical Environment Sector, Environmental Sciences Laboratory
Reference
H. Hayami, 2008, “Sensitivity of secondary particulate matter in Greater Tokyo to foreign and domestic emissions of air pollutants”,
CRIEPI Report V07020 (in Japanese)＊1：Numerical models which compute temporal changes in concentrations of various materials in the atmosphere by considering processes likeadvection/diffusion, chemical reaction and deposition from inputs of meteorological conditions and emissions.
＊ 2：H. Hayami, 2007, “Sensitivity of secondary particulate matter in Greater Tokyo to foreign and domestic emissions of air pollutants”, Journalof Japan Society for Atmospheric Environment, 42, 234-252 (in Japanese)46

2. Environment

2.0Volcanoes

Monthly emissions [Mt/mo]

1.8

Ships

1.6

Others (Taiwan, etc.)

1.4

SW China

1.2

NW China

1.0South Central China
Middle Central China

0.8

North Central China

0.6

NE China

0.4

Korean Peninsula

0.2Japan w/o G.Tokyo
Greater Tokyo

0.0
SO2

Fig.1 Source regions

NOX

Fig.2 Monthly emissions from each source region

2*The SO2 concentration in Greater Tokyo
increases by up to 20% with respect to +20%
increases in local emissions, because SO2 is a
primary pollutant. However, sulfate and nitrateincrease by only up to 5% with respect to +20%
local emissions, because they are secondary
pollutants and long-lived in the atmosphere.
Over 1% increases of sulfate and nitrateconcentrations to +20% emissions in North
Central China suggest that influences fromdistant sources are not negligible.

15%

sulfatesulfatenitratenitrate

5%

SO2SO
2VOL

OCNOTHSWC

NWC

NECSCC

MCC

NCC

KOR

VolcanoesShipsOthers

SW China

NW China

NE China

S C. China

M C. China

Korean P.

Jpn w/o GT

G.TokyoN C. China

JPN0%
TKY

Annual-mean change ratioof concentration

20%

Fig.3 Change ratio in concentration to +20% emissions of SOX and NOX in each source region

20%

8Foreign
Domestic
G.TokyoChange ratio of conc.

15%

610%

45%

20%

0550%

nitrate

40%*The monthly sulfate concentration in
Greater Tokyo is the highest in July

430%

320%

210%

10%

0conc. [μg m-3 ]sulfate

and the lowest in January. The change
ratio in concentration to +20%
emissions varies with season, eg. 8%
increase in concentration brought by+20% foreign emissions in April. The
nitrate concentration in Greater
Tokyo shows extreme responses tolocal emissions; excess changes(>20%) to +20% local emissions insummertime and negative changes inwintertime.

-1-10%
4

5678

910 11 12

123A
avg.

Month (FY2000)

Fig.4 Change ratio of sulfate and nitrate concentrations along with their mean concentrations

47