National Air Quality Trends Index for Criteria Pollutants: 1975-97

1975=1.0; 1998=1.0 for PM-10

KEY: CO=carbon monoxide; NO₂=nitrogen dioxide; PM-10=particulate matter 10 microns in diameter or smaller.

NOTES: Numbers of monitoring sites that provide raw date vary by pollutant and year. For 1975-77: CO (141 sites), lead (43 sites), NO₂ (40 sites), ozone (149 sites). For 1978-87: CO (208 sites), lead (160 sites), NO₂ (93 sites); ozone (320 sites). For 1988-97: CO (368 sites); lead (195 sites); NO₂ (224 sites), ozone (660 sites).

SOURCE: U.S. Environmental Protectien Agency, Office of Air and Radiation, Air Quality and Planning and Standards, National Air Quality and Emissions Trends Report, 1997, 454/R-98-016, December 1998, available at www.epa.gov/oar/aqtrnd971, table A-9.

第2-1図　CPsの年次変化

出典：EPA

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