Interpretation of Secondary Organic Aerosol Formation from Diesel Exhaust Photooxidation in an Environmental Chamber

Figures & data

FIG. 1 A schematic diagram of the College of Engineering-Center for Environmental Research and Technology, University of California, Riverside (CE-CERT/UC) mezzanine chamber.

TABLE 1 Engine load, initial concentrations, calculated OH concentration, D_f , bulk effective density, and overall dilution ratio

Run		Load	PM volume (μm^3/cm^3)^a	PM number (10^4 cm^−3)^a	Initial NOx (ppm)^a	Initial ethene (ppb)^a	Calculated OH (molec/cm^3)^b	Df (Average ± SD)^c	Bulk ρeff (g/cm^3)^d	Dilution ratio
Ejector dilution, short transfer line
1	4/17/2010	Idle	68	3.9	0.76	N.A.	N.A.	2.52 → 2.81	0.70	114
In-chamber dilution, short transfer line
2	3/20/2010	Idle	195	9.3	1.60	150	1.4 × 10^6	2.97 ± 0.05	1.16	54
3	4/23/2010	Idle	22	2.5	0.24	32	1.6 × 10^6	2.65 → 2.83	0.84	362
4	5/7/2010	Idle	50	3.7	0.54	71	1.6 × 10^6	2.79 → 2.90	0.99	161
Ejector dilution, long transfer line
5	5/16/2009	Medium	94	2.4	0.57	N.A.	N.A.	N.A.	N.A.	409
6	11/13/2009	Medium	103	5.3	0.65	N.A.	N.A.	2.39 ± 0.03	0.49	359
7	11/16/2009	Medium	36	3.1	0.23	N.A.	N.A.	2.39 ± 0.03	0.49	1015
8	11/18/2009	Medium	53	3.7	0.30	N.A.	N.A.	2.35 ± 0.05	0.55	778
9	2/1/2010	Low	113	4.5	0.91	45	1.1 × 10^6	2.44 ± 0.04	0.51	176
Ejector dilution, long transfer line, dark
10	2/25/2010	Idle	94^e	5.2^e	0.30^d	76	N.A.	2.55 → 2.45	0.67	290
11	5/9/2009	Medium	124^e	4.9^e	0.92^d	N.A.	N.A.	2.38 ± 0.03	0.55	254
12	7/6/2010	Medium	74^e	5.0^e	0.45^d	N.A.	N.A.	2.40 → 2.20	0.62	519
Note: N.A., not acquired.
^aValues when black lights were turned on.
^bCalculated based on ethene decay.
^cCalculated by power curve fit on effective density vs. mobility diameter (see text).
^dValues when injection finished.
^eValues 2 h after injection (typical time left in dark for aging experiments).

FIG. 2 Time series of (a) particle volume concentration and mass concentration, (b) volume fraction remaining (100°C), (c) effective density, fractal-like dimension (D_f ), and (d) OA fraction. See text for detail (Results of Run 1) (conc.: concentration).

FIG. 3 Time series of selected ions measured by an AMS (Run 1).

FIG. 4 Aerosol mass spectrums of diesel exhaust particulate before and after UV irradiation (Run 1) (BL: black light).

FIG. 5 Evolution of particle volume, mass concentration, and bulk effective density (*Lights were not turned on for Run 10 but shown for the sake of comparison. Time injection completed is set to −2 h.).

FIG. 6 Effective densities of particles in an environmental chamber and dilution ratio when the injection was completed (dil.: dilution).

FIG. 7 Time series of particle volume and mass concentration before lights are turned on. Comparison of short transfer line (Run 1) and long transfer line (Run 10) experiments at idle (conc.: concentration).

FIG. 8 Evolution of POA fraction calculated by the AMS C₄H₉ ⁺ tracer method (Equation (2), see text).