San Diego 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	1.33	1.5	1.22	1.41	1.48	0.64	1.03	1	0.86	1.03
	Health Risk 	7	7	6	7	7	3	5	5	4	5
Benzene	Annual Avg	2.25	1.7	1.48	1.16	1.39	0.98	0.76	0.76	0.76	0.87
	Health Risk 	208	158	137	107	129	90	71	70	70	81
"1,3-Butadiene"	Annual Avg	0.33	0.26	0.26	0.31	0.31	0.24	0.21	0.2	0.2	0.23
	Health Risk 	125	97	97	117	115	91	78	75	74	85
Carbon Tetrachloride	Annual Avg	0.13	0.13		0.1		0.1	0.08			
	Health Risk 	35	34		27		26	20			
Chromium (Hexavalent)	Annual Avg			0.24	0.19	0.16	0.18	0.11	0.11	0.1	
	Health Risk 			37	28	23	27	16	16	15	
para-Dichlorobenzene	Annual Avg		0.1	0.11	0.13	0.15	0.12	0.11	0.13		
	Health Risk 		7	8	8	10	8	7	8		
Formaldehyde	Annual Avg	1.64	1.53	1.26	1.76	2.25	2.13	2.62	2.62	2.27	2.66
	Health Risk 	12	11	9	13	17	16	19	19	17	20
Methylene Chloride	Annual Avg	0.59	0.83	1.34	1.13	0.73	0.63	0.59	0.57		0.53
	Health Risk 	2	3	5	4	3	2	2	2		2
Perchloroethylene	Annual Avg	0.28	0.27	0.26	0.2	0.21	0.25	0.15	0.13		
	Health Risk 	11	11	11	8	8	10	6	5		
Diesel Particulate Matter**	Annual Avg	2.9					1.9				1.4
	Health Risk 	870					570				420
Average Basin Risk***	Without Diesel PM	400	327	308	319	312	273	224	200	180	192
	With Diesel PM	1270					843				612

*   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."