Size resolved chemical composition of nanoparticles from reactions of sulfuric acid with ammonia and dimethylamine

Figures & data

Figure 1. Schematic of the flow tube reactor.

Figure 2. Size distributions of particles measured by SMPS from the reactions of (a) 2.5 × 10¹⁰ cm⁻³ H₂SO₄ with 8.9 × 10¹⁰ cm⁻³ DMA, and (b) 2.5 × 10¹⁰ cm⁻³ H₂SO₄ with 1.3 × 10¹² cm⁻³ NH₃ under dry conditions and at 60% RH.

Figure 3. Typical desorption profiles of ions formed by heating H₂SO₄-DMA (a, c) and H₂SO₄-NH₃ (b, d) particles collected on the Pt filament. The top panels show ions collected in the negative ion mode. The lower panels show ions collected in the positive ion mode. The dashed lines show the evolution of the filament temperature.

Figure 4. Size resolved acid:base ratio of newly formed particles in the H₂SO₄-DMA system under dry conditions and at 60% RH. The concentrations of H₂SO₄ and DMA introduced into the flow tube reactor were 2.5 × 10¹⁰ and 8.9 × 10¹⁰ cm⁻³, respectively, for both the dry conditions and at 60% RH. The error bars represent standard deviations of at least three repeated measurements. The horizontal black line represents the acid:base ratio of fully neutralized H₂SO₄-DMA particles.

Figure 5. Ratios of SO₅⁻:SO₃⁻ and HSO₄⁻:SO₃⁻ as a function of particle size for newly formed particles in the H₂SO₄-DMA system under dry conditions. The concentrations of H₂SO₄ and DMA introduced into the flow tube reactor were 2.5 × 10¹⁰ and 8.9 × 10¹⁰ cm⁻³, respectively. The error bars represent standard deviations of at least three repeated measurements. The horizontal black line represents a SO₅⁻:SO₃⁻ ratio of 0.44.

Figure 6. Size resolved acid:base ratio of newly formed particles formed in the H₂SO₄-NH₃ system under dry conditions and at 60% RH. The concentrations of H₂SO₄ and NH₃ introduced into the flow tube reactor were 2.5 × 10¹⁰ and 1.3 × 10¹² cm⁻³, respectively, for both the dry conditions and 60% RH. The error bars represent standard deviations of at least three repeated measurements. The horizontal black line represents the acid:base ratio of fully neutralized H₂SO₄-DMA particles.

Table 1. Thermodynamic modeling of H₂SO₄-NH₃ and H₂SO₄-DMA particles.

	Model settings					Model results
	Acid:Base^a	Base	pKa1, H2SO4	pKa2, H2SO4	pKa, base	pH	[HSO4^−] + [SO4^2−]/[BH^+]^b	[SO4^2−]/[HSO4^−]	[BH^+]/CB^c
Base Case	1:2	NH3	−3	2	9.25	4.00	0.50	99	1
		DMA	−3	2	10.73	4.58	0.50	335	1
Sensitivity Case I	1:2	NH3	0.5	5.5	5.75	5.36	0.70	0.73	0.71
		DMA	0.5	5.5	7.23	6.23	0.55	5.4	0.91
Sensitivity Case II	2:1	NH3	0.5	5.5	5.75	0.78	1.3	≪1	1.0
		DMA	0.5	5.5	7.23	0.79	1.3	≪1	1.0

^aRatio of acid:base in particle phase; ^bBH ⁺ represents the protonated form of the corresponding base B; ^cC_B represents total bulk concentration of the base in particles.