Effects of temperature on the formation of secondary organic aerosol from amine precursors

Figures & data

Table 1. Environmental chamber experiments.

Exp. #	Amine	Structure	Temperature gradient	[Amine] ppb	Oxidant	[Precursor] ppb
1.	TMA	(CH3)3N	10°C - 40°C - 10°C	100	OH	1000
2.	TMA	(CH3)3N	40°C - 10°C -40°C	100	OH	1000
3.	TMA	(CH3)3N	10°C - 40°C - 10°C	100	NO3	215
4.	TMA	(CH3)3N	40°C - 10°C -40°C	100	NO3	400
5.	DEA	(CH3CH2)2NH	10°C - 40°C - 10°C	100	OH	1000
6.	DEA	(CH3CH2)2NH	40°C - 10°C -40°C	100	OH	1000
7.	DEA	(CH3CH2)2NH	10°C - 40°C - 10°C	100	NO3	140
8.	DEA	(CH3CH2)2NH	40°C - 10°C -40°C	100	NO3	350
9.	BA	CH3(CH2)3NH2	10°C - 40°C - 10°C	100	OH	1000
10.	BA	CH3(CH2)3NH2	40°C - 10°C -40°C	100	OH	1000
11.	BA	CH3(CH2)3NH2	10°C - 40°C - 10°C	<100	NO3	<345
12.	BA	CH3(CH2)3NH2	40°C - 10°C -40°C	100	NO3	345

Figure 1. Mass concentration profiles (10 min averages) for the trimethylamine ( - circle), diethylamine ( - square), and butylamine (Δ - triangle) oxidation experiments (CHC = cold-hot-cold, HCH = hot-cold-hot).

Table 2. Average density, volatility, and elemental ratio (HR-ToF-AMS) values at 10°C and 40°C for each of the amine oxidation experiments.

	Temp.^a	TMA - OH			TMA - NO3			DEA - OH			DEA - NO3			BA - OH			BA - NO3
Density^b	CHC	1.78	1.45	1.41	^c	—^d	—	1.93	1.59	1.54	1.32	1.27	1.26	1.58	1.41	1.24	1.56	1.48	—
	HCH	1.69	1.47	*	—	—	—	*	1.78	1.46	1.17	1.12	1.14	1.27	1.42	1.33	1.14	1.10	1.11
VFR^b	CHC	0.68	0.89	0.80	^e0.04	—	—	0.49	0.81	0.66	^e0.03	0.05	0.06	0.65	0.80	0.69	^e0.04	0.03	—
	HCH	^e0.77	0.80	*	—	—	—	*	0.56	0.81	^e0.04	0.08	0.04	^e0.27	0.23	0.36	0.30	0.47	0.63
H/C	CHC	1.94	1.80	1.81	2.75	—	—	1.81	1.67	1.79	2.80	2.75	2.70	1.83	1.88	1.89	3.01	2.92	—
	HCH	1.86	2.02	2.00	2.71	—	—	—	2.27	2.19	2.88	2.88	2.85	1.77	1.82	1.81	3.01	3.00	3.00
O/C	CHC	0.67	0.75	0.69	0.06	—	—	0.38	0.34	0.30	0.03	0.04	0.05	0.28	0.20	0.19	0.02	0.05	—
	HCH	0.72	0.55	0.49	0.06	—	—	—	0.13	0.11	0.04	0.03	0.04	0.25	0.28	0.26	0.03	0.03	0.03
N/C	CHC	0.31	0.30	0.28	0.36	—	—	0.14	0.07	0.10	0.35	0.35	0.34	0.09	0.08	0.08	0.55	0.55	—
	HCH	0.30	0.24	0.20	0.35	—	—	—	0.01	0.01	0.48	0.48	0.49	0.04	0.09	0.06	0.52	0.54	0.54
OM/OC	CHC	2.41	2.50	2.40	1.73	—	—	1.82	1.68	1.66	1.68	1.70	1.70	1.64	1.51	1.51	1.92	1.95	—
	HCH	2.47	2.18	2.06	1.71	—	—	—	1.38	1.34	1.85	1.85	1.85	1.53	1.62	1.57	1.90	1.92	1.92

^a Temperature gradient of the experiment. CHC = cold-hot-cold, HCH = hot-cold-hot (cold = 10°C, hot = 40°C).

^b Density is in g/cm³. Volatility is expressed as the particle volume ratio or volume fraction remaining (VFR) after heating in a thermodenuder.

^c There was an artificially large density observed at the start of particle nucleation in the cold start NO₃ experiment. This is possibly due to the evaporation of particles in the line between the APM and in-series SMPS. This instrument is located outside of the enclosure (room temperature). While the line from the chamber to the APM is insulated, the line between the APM and SMPS is not. Therefore, the particle diameter measured by the in-series SMPS would be smaller than expected for the selected APM particle mass, translating to a smaller particle volume bias and larger measured density. The significant bias in the cold start period along with the loss of particles with increasing temperature is consistent with the observation of a volatile salt aerosol.

^d (-) below detection limit of instrument, (*) instrument offline.

^e The thermodenuder was set to 100°C instead of 40°C in these experiments.

Figure 2. Correlation plots of the organic mass spectra (cold [initial] vs. hot, normalized to total mass) from the cold start (a) TMA + OH, (b) TMA + NO₃, (c) DEA + OH, (d) DEA + NO₃, (e) BA + OH, and (f) BA + NO₃ oxidation experiments. The dashed lines indicate the 1:1 ratio.

Figure 3. Time profiles for m/z 122 (unit mass resolution) and fragment ion C₃H₈NO₄⁺ (high resolution) in the cold start (top) and hot start (bottom) trimethylamine with OH oxidation experiments.

Figure 4. Proposed mechanism for the formation of temperature dependent aerosol with ion fragments at m/z 76 and m/z 122 observed by the HR-ToF-AMS (rH = hydrogen rearrangement).