South Coast Air Basin											
Toxic Air Contaminants - Annual Average Concentrations and Health Risk											
TAC*	Conc./Risk	1990	1991	1992	1993	1994	1995	1996	1997	1998	1999
Acetaldehyde	Annual Avg	2.46	3	2.46	2.67	2.3	0.97	2.08	1.77	1.54	1.63
	Health Risk 	12	15	12	13	11	5	10	9	8	8
Benzene	Annual Avg	3.42	2.91	2.61	2.17	2.4	1.89	1.45	1.34	1.25	1.2
	Health Risk 	317	269	242	201	222	175	134	124	116	111
"1,3-Butadiene"	Annual Avg	0.53	0.45	0.5	0.57	0.5	0.46	0.39	0.38	0.35	0.33
	Health Risk 	200	170	187	212	187	173	146	142	133	123
Carbon Tetrachloride	Annual Avg	0.14	0.13		0.11		0.1	0.08		0.11	
	Health Risk 	36	35		28		27	21		30	
Chromium (Hexavalent)	Annual Avg			0.39	0.29	0.29	0.46	0.18	0.17	0.15	
	Health Risk 			59	43	43	69	27	25	22	
para-Dichlorobenzene	Annual Avg		0.17	0.19	0.17	0.13	0.17	0.11	0.13		
	Health Risk 		11	13	12	8	11	7	9		
Formaldehyde	Annual Avg	2.92	3.08	2.22	3.22	3.14	3.57	5.06	4.47	3.79	4.06
	Health Risk 	22	23	16	24	23	26	37	33	28	30
Methylene Chloride	Annual Avg	1.86	1.51	0.9	1.23	1.1	1.28	0.95	1.14	0.85	0.92
	Health Risk 	7	5	3	4	4	5	3	4	3	3
Perchloroethylene	Annual Avg	0.58	0.55	0.41	0.45	0.39	0.36	0.32	0.27	0.26	
	Health Risk 	23	22	17	18	16	15	13	11	10	
Diesel Particulate Matter**	Annual Avg	3.6					2.7				2.4
	Health Risk 	1080					810				720
Average Basin Risk***	Without Diesel PM	616	550	548	554	514	505	398	356	350	275
	With Diesel PM	1696					1315				995

*   Concentrations for Chromium (Hexavalent) are expressed as ng/m3 and concentrations for Diesel PM are expressed as ug/m3. Concentrations for all other TACs are expressed as parts per billion.											
"**  Diesel PM concentration estimates are based on receptor modeling techniques, and estimates are available only for selected years. Estimated concentration for 1999 reflects the year 2000."											
*** Health Risk represents the number of excess cancer cases per million people based on a lifetime (70-year) exposure to the annual average concentration. It reflects only those compounds listed in this table											
and only those with data for that year. There may be other significant compounds for which we do not monitor or have health risk information. Additional information about interpreting the toxic air contaminant air											
"quality trends can be found in Chapter 1, Interpreting the Emission and Air Quality Statistics."