Air Quality in Selected U.S. Cities, 1990–2000

(number of days with AQI values greater than 100)¹

Metropolitan statistical area	1990	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Atlanta, Ga.	42	23	20	36	15	35	25	31	50	61	26
Baltimore, Md.	29	50	23	48	41	36	28	30	51	40	16
Boston, Mass.-N.H.	7	13	9	6	10	8	2	8	7	5	1
Chicago, Ill.	4	25	6	3	8	23	7	9	10	14	0
Cleveland/Lorain/Elyria, Ohio	10	23	11	17	24	27	18	13	22	21	5
Dallas, Tex.	24	2	12	14	27	36	12	20	28	23	20
Denver, Colo.	9	6	11	6	2	3	0	0	7	3	2
Detroit, Mich.	11	27	7	5	11	14	13	11	17	15	3
El Paso, Tex.	19	7	10	7	11	8	7	4	6	6	3
Houston, Tex.	51	36	32	27	38	65	26	47	38	50	42
Kansas City, Mo.-Kans.	2	11	1	4	10	23	10	17	15	5	10
Los Angeles/Long Beach, Calif.	173	168	175	134	139	113	94	60	56	27	48
Miami, Fla.	1	1	3	6	1	2	1	3	8	5	0
Minneapolis/St. Paul, Minn.-Wis.	4	2	1	0	2	5	0	0	1	0	0
New York, N.Y.	36	49	10	19	21	19	15	23	17	24	12
Philadelphia, Pa.-N.J.	39	49	27	62	37	38	38	38	37	32	18
Phoenix/Mesa, Ariz.	12	11	11	15	10	22	15	12	14	10	10
Pittsburgh, Pa.	19	21	9	13	19	25	11	21	39	23	4
St. Louis, Mo.-Ill.	23	24	14	9	32	36	20	15	23	29	14
San Diego, Calif.	96	67	66	59	46	48	31	14	33	16	14
San Francisco, Calif.	0	0	0	0	0	2	0	0	0	0	0
Seattle/Bellevue/Everett, Wash.	9	4	3	0	3	0	6	1	3	1	1
Washington, DC-Md.-Va.-W.Va.	25	48	14	52	22	32	18	30	47	39	11

1. AQI—Air Quality Index. AQI measures how polluted air is by measuring five major pollutants: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen oxide. Based on the amount of each pollutant in the air, the AQI assigns a numerical value to air quality as follows: 0 to 50 (good); 51 to 100 (moderate); 101 to 150 (unhealthy for sensitive groups); 151 to 200 (unhealthy); 201 to 300 (very unhealthy); 301 to 500 (hazardous).

Source: U.S. Environmental Protection Agency, Office of Air Quality Planning & Standards.

U.S. Emissions of Greenhouse Gases, 1990–2000

Environment

The Toxic 100: Top Corporate Air Polluters in the United States