A multipollutant evaluation of APEX using microenvironmental ozone, carbon monoxide, and particulate matter (PM_2.5) concentrations measured in Los Angeles by the exposure classification project

Figures & data

Figure 1. Microenvironmental measurements were made in three study areas, downtown Los Angeles, Alhambra, and Long Beach.

Note: Triangles indicate locations of nearby air monitoring stations of the South Coast Air Quality Management District (SCAQMD).

Table 1. APEX microenvironment parameters

Microenvironment	Parameter	Conditions	Distribution
Indoors—residence	AER	Temp < 68; A/C: central	LogN(0.577, 1.897, 0.1, 10)
		Temp 68–76; A/C: central	LogN(1.084, 2.336, 0.1, 10)
		Temp 77–85; A/C: central	LogN(0.861, 2.415, 0.1, 10)
		Temp > 85; A/C: central	LogN(0.861, 2.344, 0.1, 10)
		Temp < 68; A/C: room	LogN(0.672, 1.863, 0.1, 10)
		Temp 68–76; A/C: room	LogN(1.674, 2.223, 0.1, 10)
		Temp > 76; A/C: room	LogN(0.949, 1.644, 0.1, 10)
		Temp < 50; A/C: none	LogN(0.543, 3.087, 0.1, 10)
		Temp 50–67; A/C: none	LogN(0.747, 2.085, 0.1, 10)
		Temp 68–76; A/C: none	LogN(1.372, 2.283, 0.1, 10)
		Temp > 76; A/C: none	LogN(0.988, 1.967, 0.1, 10)
Indoors–school	AER	All	Discrete (range 0.1 to 3.0)
Indoors–restaurant, bar, night club, café	AER	All	LogN(3.712, 1.855, 1.46, 9.07)
Indoors-other	AER	All	LogN(1.109, 3.015, 0.07, 13.8)
Indoors-All	O3 Decay rate	All	LogN(2.51, 1.53, 0.95, 8.05)
	PM25 Decay rate	All	Uniform(0.1,1.1)
	CO Decay rate	All	No decay
	O3 Proximity	All	Normal(1.0, 0.07, 0.9, 1.1)
All MEs	PM25 Proximity	All	Normal(1.0, 0.07, 0.9, 1.1)
All MEs	CO Proximity	All	Normal(1.0, 0.15, 0.8, 1.2)
Outdoors-near road	O3 Proximity	All	Normal(0.755, 0.203, 0.422, 1.0)
Outdoors-other	O3 Proximity	All	Normal(1.0, 0.07, 0.9, 1.1)
In-vehicle	O3 Proximity	Local roads (6%)	Normal(0.755, 0.203, 0.422, 1.0)
		Urban roads (65%)	Normal(0.754, 0.243, 0.355, 1.0)
		Interstates (29%)	Normal(0.364, 0.165, 0.093, 1.0)
	O3 Penetration	All	Normal(0.300, 0.232, 0.1, 1.0)

Notes: Temp is daily average temperature in degrees Fahrenheit. A/C indicates the type of air conditioning. LogN is lognormal(geometric mean, geometric standard deviation, minimum, maximum). Normal is Gaussian(mean, standard deviation, minimum, maximum). When a sampled value is below the minimum or above the maximum, it is resampled by APEX (Gaussian and lognormal distributions).

Table 2. Mapping of 40 ECP microenvironments to condensed set of 24 APEX microenvironments

APEX microenvironment	ECP microenvironment
Indoors
01: indoors–residence	11: indoors–apartment
02: indoors–community center or auditorium	12: indoors–community center or auditorium
03: indoors–restaurant	13: indoors–food court
	17: indoors–restaurant–fast food
04: indoors–hotel/motel	14: indoors–hotel
05: indoors–office building, bank, post office	15: indoors–office/office building
	16: indoors–public building (post office, etc.)
06: indoors–bar, night club, café	18: indoors–restaurant–café or other
07: indoors–school	19: indoors–school
08: indoors–shopping mall/non-grocery store	20: indoors–shopping mall or enclosed courtyard
	24: indoors–non-food store (department, pharmacy, etc.)
09: indoors–grocery store/convenience store	21: indoors–food store (bakery, supermarket, etc.)
10: indoors–metro-subway-train station	22: indoors–subway station or train station
11: indoors–hospital/medical care facility	23: indoors–hospital
Outdoors-other
12: outdoors–residential	35: outdoors–neighborhood background or residential grounds
13: outdoors–general non-residential	32: outdoors–community or retirement center
	34: outdoors–mall, market, patio, or plaza
	41: outdoors–public building
14: outdoors–park or golf course	36: outdoors–park or golf course
15: outdoors–restaurant or café	42: outdoors–restaurant/picnic
16: outdoors–school grounds	43: outdoors–school grounds
Outdoors-near road
17: outdoors–metro-subway-train stop	31: outdoors–bus stop
	46: outdoors–metro station platform
	47: outdoors–bus transit center
18: outdoors–within 10 yards of street	33: outdoors–freeway edge or gradient, pedestrian overpass
	40: outdoors–pedestrian walk
	45: outdoors–street–residential
19: outdoors–garage (covered or below ground)	37: outdoors–parking garage or covered parking
	38: outdoors–parking garage–below ground
20: outdoors–parking lot (open), street parking	39: parking lot (open), street parking, window shopping
21: outdoors–service station	44: outdoors–service station
In-Vehicle
22: vehicle–car	51: vehicle–auto–commercial strip, surface street
	52: vehicle–auto–freeway
	53: vehicle–auto–garage–underground
	54: vehicle–auto–refueling
	55: vehicle–auto–residential street
	56: vehicle–auto–restaurant drive-through
	57: vehicle–auto–urban canyon or urban streets
23: vehicle–bus	58: vehicle–bus
24: vehicle–train or subway	59: vehicle–train

Table 3. Comparisons of APEX estimated ratios of indoor microenvironmental O₃ concentration to simultaneous nearby outdoor microenvironmental O₃ concentration obtained from ECP measurements

Indoor microenvironment		Outdoor microenvironment	Indoor-to-Outdoor O3 ratio
			ECP measurements				APEX
	Description		N^a	Min	Med	Max	Min	Med	Max
1	Residence	Other	3	0.11	0.24	1.41	0.01	0.23	2.71
		Near-road	1	–	1.02	–	–	–	–
2	Community Center or auditorium	Other	4	0.07	0.18	0.28	0.03	0.30	0.86
		Near-road	7	0.07	0.13	0.46	–	–	–
3	Restaurant	Other	11	0.07	0.30	1.00	0.16	0.59	1.79
		Near-road	10	0.16	0.48	14.3	–	–	–
4	Hotel/motel	Other	1	–	0.54	–	0.01	0.30	1.85
		Near-road	3	0.56	0.65	0.77	–	–	–
5	Office building, bank, post office	Other	6	0.16	0.58	1.94	0.01	0.29	2.04
		Near-road	11	0.14	0.42	1.38	–	–	–
7	School	Other	5	0.34	0.37	0.65	0.01	0.22	1.98
		Near-road	2	0.37	0.63	0.89	–	–	–
8	Shopping mall, non-grocery store	Other	5	0.10	0.31	0.40	0.01	0.29	1.43
		Near-road	4	0.10	0.25	0.42	–	–	–
9	Grocery store, convenience store	Other	3	0.14	0.16	0.90	0.01	0.30	1.79
		Near-road	6	0.14	0.29	0.66	–	–	–
All	All indoors^b	Other	25	0.07	0.30	1.94	0.01	0.38	2.71
		Near-road	29	0.09	0.37	14.3	–	–	–

Notes: The “all indoors ME” value for a particular test group may combine (average) pollutant values from two or more indoor MEs that were measured at about the same time. So the “all” N value may be less than the sum of the N values for individual MEs.

^a N is the number of ratios of measured values. The APEX statistics are based on >1000 simulated values.

^b The values in the “all indoors” rows (e.g. the 29 and 0.09 in the last row) are not expected to be consistent with the numbers above.

Table 4. Comparisons of APEX estimated ratios of indoor microenvironmental CO concentration to simultaneous nearby outdoor microenvironmental CO concentration obtained from ECP measurements

Indoor microenvironment		Outdoor ME	Indoor-to-Outdoor CO ratio
			ECP measurements				APEX
	Description		N^a	Min	Med	Max	Min	Med	Max
1	Residence	Other	2	0.71	0.85	1.00	0.07	1.00	336
		Near-road	0	–	–	–	–	–	–
2	Community Center or auditorium	Other	3	0.48	1.28	2.00	0.39	1.04	380
		Near-road	7	0.73	1.13	2.88	–	–	–
3	Restaurant	Other	12	0.63	1.62	19.0	0.48	1.00	95
		Near-road	10	0.64	1.06	7.00	–	–	–
4	Hotel/motel	Other	1	–	0.39	–	0.16	1.00	315
		Near-road	3	0.88	0.93	1.20	–	–	–
5	Office building, bank, post office	Other	7	0.78	1.00	1.60	0.05	1.05	485
		Near-road	11	0.50	1.00	1.80	–	–	–
7	School	Other	5	0.09	0.69	2.00	0.10	1.08	416
		Near-road	2	1.00	2.00	3.00	–	–	–
8	Shopping mall, non-grocery store	Other	5	0.55	1.33	1.80	0.06	1.03	371
		Near-road	5	0.69	1.00	1.92	–	–	–
9	Grocery store, convenience store	Other	3	1.26	1.80	17.6	0.08	1.02	507
		Near-road	7	0.52	1.00	1.93	–	–	–
All	All indoors^b	Other	25	0.55	1.10	19.0	0.05	1.01	507
		Near-road	29	0.64	1.00	3.33	–	–	–

Notes: The “all indoors ME” value for a particular test group may combine (average) pollutant values from two or more indoor MEs that were measured at about the same time. So the “all” N value may be less than the sum of the N values for individual MEs.

^a N is the number of ratios of measured values. The APEX statistics are based on >1000 simulated values.

^b The values in the “all indoors” rows are not expected to be consistent with the numbers above.

Table 5. Comparisons of APEX estimated ratios of indoor microenvironmental PM2.5 concentration to simultaneous nearby outdoor microenvironmental PM2.5 concentration obtained from ECP measurements

Indoor microenvironment		Outdoor ME	Indoor-to-Outdoor PM2.5 ratio
			ECP measurements				APEX
	Description		N^a	Min	Med	Max	Min	Med	Max
1	Residence	Other	3	0.29	0.33	0.89	0.04	0.60	7.37
		Near-road	1	–	0.37	–	–	–	–
2	Community Center or auditorium	Other	4	0.16	0.37	0.61	0.07	0.69	4.57
		Near-road	8	0.13	0.36	0.67	–	–	–
3	Restaurant	Other	12	0.30	0.98	34.25	0.39	0.87	6.97
		Near-road	10	0.33	1.00	15.36	–	–	–
4	Hotel/motel	Other	1	–	0.80	–	0.04	0.68	4.71
		Near-road	3	0.16	0.70	1.78	–	–	–
5	Office building, bank, post office	Other	7	0.10	0.28	0.50	0.04	0.68	7.34
		Near-road	11	0.13	0.24	0.78	–	–	–
7	School	Other	5	0.13	0.41	0.53	0.04	0.58	7.41
		Near-road	2	0.10	3.01	5.91	–	–	–
8	Shopping mall, non-grocery store	Other	5	0.08	0.55	2.00	0.03	0.68	6.59
		Near-road	5	0.10	0.34	0.57	–	–	–
9	Grocery store, convenience store	Other	3	0.51	0.56	1.31	0.04	0.69	6.84
		Near-road	7	0.48	2.11	12.43	–	–	–
All	All indoors^b	Other	26	0.08	0.55	24.14	0.03	0.76	7.41
		Near-road	30	0.10	0.52	15.36	–	–	–

Notes: The “all indoors ME” value for a particular test group may combine (average) pollutant values from two or more indoor MEs that were measured at about the same time. So the “all” N value may be less than the sum of the N values for individual MEs.

^a N is the number of ratios of measured values. The APEX statistics are based on >1000 simulated values.

^b The values in the “all indoors” rows are not expected to be consistent with the numbers above.

Table 6. Comparison of APEX estimated ratios of microenvironmental O₃ concentrations to simultaneous fixed-site O₃ concentrations obtained from ECP measurements

Microenvironment		Microenvironment-to-monitor O3 ratios
		ECP measurements			APEX estimates
Code	Description	N^a	Min	Med	Max	Min	Med	Max
Indoors
1	Residence	3	0.08	0.26	1.55	0.01	0.23	2.74
2	Community Center or auditorium	6	0.12	0.19	0.57	0.02	0.29	0.90
3	Restaurant	15	0.05	0.26	10.00	0.16	0.58	1.81
4	Hotel/motel	2	0.24	0.28	0.33	0.01	0.30	1.80
5	Office building, bank, post office	8	0.15	0.55	1.65	0.01	0.29	1.88
7	School	8	0.13	0.31	0.84	0.01	0.22	1.85
8	Shopping mall, non-grocery store	5	0.07	0.20	0.37	0.01	0.29	1.41
9	Grocery store, convenience store	7	0.14	0.33	0.51	0.01	0.30	1.91
10	Metro–subway–train	2	0.86	0.90	0.93	0.03	0.27	0.92
All	All indoors	56	0.05	0.29	10.00	0.01	0.36	2.74
Outdoors-Other
12	Residential grounds	4	0.85	0.97	1.10	0.90	1.00	1.10
13	General–non-residential	16	0.36	0.91	2.06	0.90	1.00	1.10
14	Park or golf course	17	0.47	0.98	1.53	0.90	1.00	1.10
15	Restaurant or café	15	0.55	1.00	3.40	0.90	1.00	1.10
16	School grounds	11	0.50	1.02	2.82	0.90	1.00	1.10
All	All outdoors—other	63	0.36	0.98	3.40	0.90	1.00	1.10
Outdoors-Near road
17	Metro–subway–train stop	15	0.33	0.81	1.12	0.42	0.73	1.00
18	Within 10 yards of street	28	0.14	0.73	6.40	0.42	0.74	1.00
19	Parking garage	10	0.18	0.58	1.14	0.42	0.72	1.00
20	Parking lot (open), street parking	36	0.20	0.92	6.10	0.42	0.74	1.00
21	Service station	7	0.55	0.98	2.03	0.42	0.73	1.00
All	All outdoors-near road	96	0.14	0.84	6.40	0.42	0.74	1.00
Vehicle
22	Car	57	0.11	0.46	1.90	0.09	0.63	1.00
All	All vehicle	57	0.11	0.46	1.90	0.09	0.63	1.00

^a Number of ratios.

Table 7. Comparisons of descriptive statistics for ratios of microenvironmental O3 concentrations to simultaneous fixed-site O3 concentrations obtained from ECP measurements and APEX estimates—grouped microenvironments

Statistic	Microenvironment-to-monitor O3 ratio
	Indoors		Outdoors-Other		Outdoors-Near road		Vehicle
	ECP	APEX	ECP	APEX	ECP	APEX	ECP	APEX
Number of values	56	>1000	63	>1000	96	>1000	57	>1000
Mean	0.58	0.39	1.09	1.00	1.05	0.73	0.57	0.62
SD	1.33	0.24	0.50	0.05	0.99	0.15	0.39	0.22
Minimum	0.05	0.01	0.36	0.90	0.14	0.42	0.11	0.09
5th pct	0.08	0.07	0.50	0.92	0.26	0.48	0.13	0.24
10th pct	0.12	0.10	0.60	0.93	0.34	0.52	0.20	0.32
25th pct	0.19	0.19	0.83	0.96	0.62	0.62	0.32	0.46
50th pct	0.29	0.36	0.98	1.00	0.84	0.74	0.46	0.63
75th pct	0.56	0.56	1.30	1.04	1.10	0.85	0.64	0.80
90th pct	0.97	0.69	1.59	1.07	1.86	0.93	1.17	0.91
95th pct	1.56	0.76	1.99	1.08	2.67	0.96	1.47	0.95
Maximum	10.00	2.74	3.40	1.10	6.40	1.00	1.90	1.00

Figure 2. Microenvironment-to-monitor O₃ ratios.

Table 8. Comparison of ratios of microenvironmental CO concentrations to simultaneous fixed-site CO concentrations obtained from ECP measurements and APEX estimates

Microenvironment		Microenvironment-to-monitor CO ratios
		ECP measurements			APEX estimates
Code	Description	N^a	Min	Med	Max	Min	Med	Max
Indoors
1	Residence	2	0.92	1.09	1.25	0.07	1.01	389
2	Community Center or auditorium	5	0.67	1.08	1.38	0.36	1.08	339
3	Restaurant	16	0.63	2.50	35.7	0.39	1.02	97
4	Hotel/motel	6	0.71	1.50	2.18	0.16	0.98	329
5	Office building, bank, post office	9	0.33	1.00	2.33	0.06	1.07	511
6	Bar, night club, cafe	8	0.44	1.24	4.78	0.53	1.00	53
7	School	10	0.44	1.06	1.63	0.09	1.10	349
8	Shopping mall, non-grocery store	20	0.57	1.79	5.00	0.06	1.07	419
9	Grocery store, convenience store	9	0.33	1.88	6.29	0.08	1.06	414
10	Metro–subway–train	16	0.29	1.46	24.2	0.33	1.04	72
11	Hospital, medical care facility	6	0.83	1.32	4.75	0.07	1.07	331
All	All indoors	107	0.29	1.36	35.7	0.06	1.04	511
Outdoors-Other
12	Residential grounds	4	0.00	0.28	1.32	0.80	1.00	1.20
13	General–non-residential	15	0.43	1.40	2.50	0.80	1.00	1.20
14	Park or golf course	19	0.20	1.14	12.0	0.80	1.00	1.20
15	Restaurant or café	14	0.22	1.14	5.67	0.80	1.00	1.20
16	School grounds	11	0.25	2.00	18.1	0.80	1.00	1.20
All	All outdoors-other	63	0.00	1.33	18.1	0.80	1.00	1.20
Outdoors-Near road
17	Metro–subway–train stop	23	0.35	1.27	4.75	0.80	1.00	1.20
18	Within 10 yards of street	28	0.29	2.10	5.60	0.80	1.00	1.20
19	Parking garage	10	0.00	1.52	37.4	0.80	1.00	1.20
20	Parking lot (open), street parking	36	0.25	1.40	6.00	0.80	1.00	1.20
21	Service station	6	0.86	1.60	4.00	0.80	1.00	1.20
All	All outdoors-near road	103	0.00	1.60	37.4	0.80	1.00	1.20
Vehicle
22	Car	57	0.17	1.91	6.67	0.80	1.00	1.20
23	Bus	1	–	2.18	–	0.80	1.00	1.20
24	Train	6	0.71	0.94	5.18	0.80	1.00	1.20
All	All vehicle	64	0.17	1.79	6.67	0.80	1.00	1.20

^a Number of ratios.

Table 9. Comparisons of descriptive statistics for ratios of microenvironmental CO concentrations to simultaneous fixed-site CO concentrations obtained from ECP measurements and APEX estimates—grouped microenvironments

Statistic	Microenvironment-to-monitor CO ratio
	Indoors		Outdoors-Other		Outdoors-Near road		Vehicle
	ECP	APEX	ECP	APEX	ECP	APEX	ECP	APEX
Number of values	107	>1000	63	>1000	103	>1000	64	>1000
Mean	2.54	3.14	1.90	1.00	2.21	1.00	2.05	1.00
SD	4.29	23.28	2.70	0.10	3.73	0.10	1.38	0.10
Minimum	0.29	0.06	0.00	0.80	0.00	0.80	0.17	0.80
5th pct	0.46	0.74	0.23	0.83	0.37	0.83	0.39	0.83
10th pct	0.63	0.81	0.28	0.86	0.52	0.86	0.60	0.86
25th pct	0.91	0.91	0.57	0.92	0.91	0.92	0.94	0.92
50th pct	1.36	1.04	1.33	1.00	1.60	1.00	1.79	1.00
75th pct	2.70	1.20	2.00	1.08	2.50	1.08	2.93	1.08
90th pct	4.36	1.58	3.43	1.14	3.90	1.14	4.00	1.14
95th pct	7.51	2.13	5.33	1.17	5.35	1.17	4.98	1.17
Maximum	35.7	510	18.13	1.20	37.40	1.20	6.67	1.20

Figure 3. Microenvironment-to-monitor CO ratios.

Table 10. Comparison of ratios of microenvironmental PM2.5 concentrations to simultaneous fixed-site PM2.5 concentrations obtained from ECP measurements and APEX estimates

Microenvironment		Microenvironment-to-monitor PM2.5 ratios
		ECP measurements			APEX estimates
Code	Description	N^a	Min	Med	Max	Min	Med	Max
Indoors
1	Residence	2	0.43	0.51	0.58	0.04	0.60	7.74
2	Community Center or auditorium	5	0.33	0.70	0.84	0.08	0.68	4.81
3	Restaurant	14	0.97	1.93	31.17	0.38	0.87	7.03
4	Hotel/motel	6	0.33	1.08	3.92	0.04	0.68	5.03
5	Office building, bank, post office	9	0.27	0.33	1.12	0.03	0.68	7.89
6	Bar, night club, cafe	7	1.11	1.52	2.92	0.45	0.86	2.33
7	School	10	0.09	0.70	12.36	0.04	0.58	7.96
8	Shopping mall, non-grocery store	17	0.13	0.91	2.22	0.03	0.68	6.90
9	Grocery store, convenience store	9	0.83	2.33	6.00	0.04	0.68	7.16
10	Metro–subway–train	14	0.70	1.58	4.40	0.08	0.62	2.81
11	Hospital, medical care facility	6	0.44	0.84	1.34	0.04	0.67	7.34
All	All indoors	99	0.09	1.19	31.17	0.03	0.73	7.96
Outdoors-Other
12	Residential grounds	3	1.14	1.28	1.61	0.90	1.00	1.10
13	General–non-residential	15	0.55	1.32	2.04	0.90	1.00	1.10
14	Park or golf course	18	0.46	1.80	8.00	0.90	1.00	1.10
15	Restaurant or café	12	0.96	1.95	18.00	0.90	1.00	1.10
16	School grounds	9	0.58	2.10	4.23	0.90	1.00	1.10
All	All outdoors-other	57	0.46	1.50	18.00	0.90	1.00	1.10
Outdoors-Near road
17	Metro–subway–train stop	22	0.41	1.61	5.40	0.90	1.00	1.10
18	Within 10 yards of street	24	0.41	1.71	4.60	0.90	1.00	1.10
19	Parking garage	10	0.80	1.11	4.00	0.90	1.00	1.10
20	Parking lot (open), street parking	30	0.34	1.68	6.67	0.90	1.00	1.10
21	Service station	6	0.73	1.21	1.60	0.90	1.00	1.10
All	All outdoors-near road	92	0.34	1.61	6.67	0.90	1.00	1.10
Vehicle
22	Car	45	0.46	1.96	13.10	0.90	1.00	1.10
23	Bus	1	–	1.62	–	0.90	1.00	1.10
24	Train	6	0.70	1.17	1.40	0.90	1.00	1.10
All	All vehicle	52	0.46	1.64	13.10	0.90	1.00	1.10

^a Number of ratios.

Table 11. Comparisons of descriptive statistics for ratios of microenvironmental PM2.5 concentrations to simultaneous fixed-site PM2.5 concentrations obtained from ECP measurements and APEX estimates—grouped microenvironments

Statistic	Microenvironment-to-monitor PM2.5 ratio
	Indoors		Outdoors-Other		Outdoors-Near road		Vehicle
	ECP	APEX	ECP	APEX	ECP	APEX	ECP	APEX
Number of values	99	>1000	57	>1000	92	>1000	52	>1000
Mean	2.23	0.73	2.16	1.00	1.98	1.00	2.61	1.00
SD	4.27	0.50	2.47	0.05	1.23	0.05	2.66	0.05
Minimum	0.09	0.03	0.46	0.90	0.35	0.90	0.46	0.90
5th pct	0.28	0.24	0.58	0.92	0.72	0.92	0.58	0.92
10th pct	0.34	0.33	0.75	0.93	0.88	0.93	0.73	0.93
25th pct	0.77	0.51	1.17	0.96	1.12	0.96	1.26	0.96
50th pct	1.19	0.73	1.50	1.00	1.61	1.00	1.64	1.00
75th pct	1.91	0.88	2.23	1.04	2.41	1.04	2.79	1.04
90th pct	3.82	1.01	3.64	1.07	3.67	1.07	6.10	1.07
95th pct	9.62	1.12	4.76	1.08	4.28	1.08	10.7	1.08
Maximum	31.2	7.96	18.0	1.10	6.67	1.10	13.1	1.10

Figure 4. Microenvironment-to-monitor PM_2.5 ratios.

Table 12. Comparison of distributions of indoor/outdoor ratios: ECP measurements and APEX predictions

	O3		CO		PM2.5
Statistic	ECP	APEX	ECP	APEX	ECP	APEX
Number of values	25	>1000	25	>1000	26	>1000
Minimum	0.07	0.01	0.55	0.05	0.08	0.03
10th pctile	0.10	0.10	0.67	0.89	0.17	0.34
25th pctile	0.16	0.20	0.87	1.00	0.29	0.54
Median	0.30	0.38	1.10	1.01	0.55	0.76
75th pctile	0.43	0.57	1.60	1.16	0.88	0.90
90th pctile	0.92	0.70	2.00	1.56	12.9	1.00
Maximum	1.94	2.71	19.0	507	24.1	7.41

Figure 5. Comparison of distributions of indoor/outdoor ratios: ECP measurements and APEX predictions.