Nanoparticle Chemical Composition During New Particle Formation

Figures & data

TABLE 1 Molecular apportionment of the atomic composition measured by NAMS

Start	Total integrated atomic signals (sum of all charge states) for C, O, N, S, Si
Step 1.	Remove particles having >90% N, S, or Si and classify as unrealistic or uninterpretable compositions. Remove particles having >90% O and classify as particulate water. Only the remaining particles move forward to Step 2.
Step 2.	Apportion all S plus stoichiometric amount of O (= 4S) to SO4 ^−2. (If insufficient O remains from Step 1, classify remaining S as residual S.)
Step 3.	Apportion N (up to 2Snonresidual from step 1) to NH4 ^+.
Step 4.	Apportion all Si plus stoichiometric O (= 2Si) to SiO2. (If insufficient O remains from Step 2, classify remaining Si as residual Si.)
Step 5.	Apportion remaining N from Step 3 plus stoichiometric O (= 3N/2) as NH4NO3. (If insufficient O remains from Step 4, classify remaining N as residual N.)
Step 6.	Apportion remaining O from Step 5 plus all C to carbonaceous matter; calculate O/C atomic ratio from these values.
Step 7.	Report mole fractions of SO4 ^−2, NO3 ^−, NH4 ^+, SiO2, carbonaceous matter, residual elements from Steps 2–6. Calculate mass fractions from the mole fractions.

TABLE 2 Particle growth rates from 10 to 25 nm mobility diameter during the analyzed NPF events

Event date	Particle growth rate (nm/h)
20 October	3
21 October	6
28 October	3
4 November	4
5 November	2
8 November	2
11 November	2

FIG. 1 SMPS-measured contour plot of the particle size distribution for 4–9 November 2007. The dotted lines indicate the range of mobility diameters for particles analyzed by NAMS.

FIG. 2 Average mass spectrum of particles analyzed by NAMS during the NPF event on 8 November 2007 (11:00 a.m.–3:30 p.m. local time). The pie chart gives the atomic mole fractions during this period.

TABLE 2 Average on- and off-event atomic mole fractions on NPF event days. Molar N/S, NO₃ ⁻/SO₄ ⁻², C/N_cation, and O/C ratios indicate changes in average particle composition during events. The final column provides the number of particles analyzed in each data set. Median values exclude 4 November, where particle composition was not measured off-event ^a

Event date	Type	C (%)	N (%)	O (%)	S (%)	N/S	NO3 ^−/SO4 ^−2	C/Ncation	O/C	No. of particles
20 October	On-event	18 ± 1	20 ± 1	54 ± 4	7.3 ± 0.5	2.8 ± 0.3	0.75 ± 0.08	1.3 ± 0.1	0.84 ± 0.08	2717
	Off-event (a.m./p.m.)	25 ± 2	16 ± 1	52 ± 4	7.1 ± 0.5	2.2 ± 0.2	0.51 ± 0.05	2.1 ± 0.2	0.70 ± 0.07	198
21 October	On-event	14 ± 1	24 ± 2	54 ± 4	7.0 ± 0.5	3.5 ± 0.4	1.0 ± 0.1	0.88 ± 0.09	0.85 ± 0.09	1944
	Off-event (a.m./p.m.)	22 ± 2	20 ± 1	52 ± 4	6.4 ± 0.4	3.1 ± 0.3	0.81 ± 0.08	1.6 ± 0.2	0.66 ± 0.07	198
28 October	On-event	15 ± 1	23 ± 2	55 ± 4	7.3 ± 0.5	3.2 ± 0.3	0.90 ± 0.09	0.91 ± 0.09	0.88 ± 0.09	3997
	Off-event (p.m. only)	22 ± 2	18 ± 1	53 ± 4	6.5 ± 0.5	2.8 ± 0.3	0.80 ± 0.08	1.7 ± 0.2	0.85 ± 0.09	1617
4 November	On-event	14 ± 1	24 ± 2	56 ± 4	5.8 ± 0.4	4.2 ± 0.4	1.5 ± 0.2	0.90 ± 0.09	1.0 ± 0.1	338
5 November	On-event	12 ± 1	27 ± 2	55 ± 4	6.7 ± 0.5	4.0 ± 0.4	1.3 ± 0.1	0.70 ± 0.07	0.89 ± 0.09	615
	Off-event (a.m./p.m.)	15 ± 1	26 ± 2	55 ± 4	4.5 ± 0.3	5.7 ± 0.6	1.8 ± 0.2	0.99 ± 0.10	0.86 ± 0.09	78
8 November	On-event	13 ± 1	24 ± 2	57 ± 4	6.5 ± 0.5	3.7 ± 0.4	1.2 ± 0.1	0.81 ± 0.08	1.1 ± 0.1	497
	Off-event (a.m./p.m.)	16 ± 1	23 ± 2	55 ± 4	6.6 ± 0.5	3.5 ± 0.4	1.2 ± 0.1	1.1 ± 0.1	0.93 ± 0.09	183
11 November	On-event	15 ± 1	24 ± 2	55 ± 4	6.1 ± 0.4	3.9 ± 0.4	1.4 ± 0.1	0.98 ± 0.10	0.95 ± 0.10	1034
	Off-event (a.m./p.m.)	17 ± 1	22 ± 2	55 ± 4	6.1 ± 0.4	3.6 ± 0.4	1.2 ± 0.1	1.2 ± 0.1	0.91 ± 0.09	617
Median	On-event	15 ± 1	24 ± 2	55 ± 4	6.8 ± 0.5	3.6 ± 0.4	1.1 ± 0.1	0.90 ± 0.09	0.89 ± 0.09
	Off-event	20 ± 1	21 ± 1	54 ± 4	6.5 ± 0.5	3.3 ± 0.3	0.99 ± 0.10	1.4 ± 0.1	0.86 ± 0.09
^a Typically, on- and off-event time periods each consist of 4–5 h of measurements during the event day (10 h total per event). The off-event time periods are typically split evenly between before (a.m.) and after (p.m.) the event.

FIG. 3 (a) Comparison of the percent change in atomic mole fraction on- versus off-event. (b) Comparison of the change in the molar ratios N/S, NO₃ ⁻/SO₄ ⁻², C/N_cation, and O/C ratios on- versus off-event. The dotted line separates atomic ratios determined directly by NAMS (to the left) from molecular ratios inferred from the apportionment scheme (to the right). For both (a) and (b), median values for event days analyzed by NAMS are given by the bar. Whiskers indicate the range of values for individual days. The event on 4 November is excluded from these plots, as particle composition was not measured off-event on this day. In (a), the dotted lines represent the uncertainty in atomic mole fraction measured by NAMS.