Table 2.

Descriptive statistics for PM_2.5 and species in California counties, 2000–2003.

	All-year					Cooler months (Oct–Mar)
Pollutants	Obsa	Mean (μg/m3)	IQR (μg/m3)	95th percentile	% Below detection	Obsa	Mean (μg/m3)	IQR (μg/m3)
PM2.5cb	1,878	19.28	14.63	46.91	0.00	844	24.60	21.47
EC	1,879	0.966	0.795	2.57	0.05	842	1.319	1.135
OC	1,879	7.129	4.592	15.91	0.00	842	9.192	6.124
NO3	1,817	5.415	5.524	17.46	0.00	831	7.294	7.985
SO4	1,817	1.908	1.530	5.18	0.00	831	1.483	1.233
Al	1,870	0.044	0.051	0.14	5.45	845	0.036	0.042
Br	1,870	0.004	0.004	0.01	1.76	845	0.005	0.004
Ca	1,870	0.080	0.064	0.20	0.05	845	0.081	0.066
Cl	1,870	0.094	0.069	0.41	2.09	845	0.105	0.083
Cu	1,870	0.007	0.007	0.34	1.34	845	0.008	0.008
Fe	1,870	0.124	0.099	0.26	0.00	845	0.138	0.117
K	1,870	0.117	0.081	0.01	0.00	845	0.135	0.112
Mn	1,870	0.003	0.003	0.01	3.21	845	0.003	0.003
Ni	1,870	0.005	0.003	0.01	2.51	845	0.005	0.003
Pb	1,870	0.004	0.004	1.70	2.83	845	0.005	0.005
S	1,870	0.648	0.499	0.43	0.00	845	0.522	0.434
Si	1,870	0.168	0.151	0.04	0.05	845	0.147	0.132
Ti	1,870	0.009	0.008	47.69	0.32	845	0.008	0.008
V	1,870	0.002	0.003	46.91	5.56	845	0.002	0.002
Zn	1,870	0.012	0.011	2.57	1.82	845	0.018	0.014
PM2.5extc	11,494	18.6	15.1	15.9	0.00	5,777	22.40	19.8

^aTotal number of observations (Obs) for analysis across all of the counties.

^bIncludes six counties with species data, 2000–2003.

^cIncludes all nine counties in Table 1, 1999–2003.