Sacramento Valley 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	1.29			1.37	1.04	0.39	1.03	1.05	0.92	1.23
	Health Risk 	6			7	5	2	5	5	5	6
Benzene	Annual Avg	2.02	1.88	1.35	1	1.02	0.8	0.56	0.55	0.5	0.56
	Health Risk 	187	174	125	93	95	74	51	51	47	52
"1,3-Butadiene"	Annual Avg	0.38	0.33	0.28	0.29	0.22	0.19	0.18	0.16	0.15	0.13
	Health Risk 	142	125	106	108	83	70	66	60	58	48
Carbon Tetrachloride	Annual Avg	0.12	0.12		0.11		0.1	0.08			
	Health Risk 	33	33		29		26	21			
Chromium (Hexavalent)	Annual Avg			0.17	0.14	0.13	0.18	0.11	0.1	0.1	
	Health Risk 			26	21	19	26	16	15	15	
para-Dichlorobenzene	Annual Avg			0.11	0.1	0.2	0.14	0.11	0.14		
	Health Risk 			7	7	14	9	7	10		
Formaldehyde	Annual Avg	1.57			1.77	1.75	1.91	2.76	2.92	2.52	3.61
	Health Risk 	12			13	13	14	20	22	19	27
Methylene Chloride	Annual Avg	0.65	0.56	0.55	0.98	0.66	0.53	0.54	0.52		0.6
	Health Risk 	2	2	2	3	2	2	2	2		2
Perchloroethylene	Annual Avg	0.07	0.07	0.06	0.05	0.17	0.05	0.06	0.05		
	Health Risk 	3	3	3	2	7	2	2	2		
Diesel Particulate Matter**	Annual Avg	2.5					1.6				1.2
	Health Risk 	750					480				360
Average Basin Risk***	Without Diesel PM	385	336	269	282	238	225	190	166	143	134
	With Diesel PM	1135					705				494

*   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."