Laboratory characterization of an aerosol chemical speciation monitor with PM_2.5 measurement capability

Figures & data

Figure 1. Schematic of the experimental setup for (a) large particle size (>650 nm d_va) lens transmission and particle bounce measurement, (b) and (c) small particle size side (<650 nm d_va) lens transmission efficiency curve measurement without CPMA and with CPMA, respectively, and (d) schematic of an ACSM/AMS equipped with the new PM_2.5 inlet, IPL, and capture vaporizer.

Figure 2. Calculated size-dependent particle loss for the old and new designs of the ACSM inlet.

Figure 3. (a) Average PM_2.5 lens transmission efficiency (E_L) measured using NH₄NO₃, NaNO₃, and PSL particles for different lens assemblies compared with that of PM₁ lens from Liu et al. (2007) (error bars are one standard deviation and 50% cutoff sizes are indicated by arrows). The transmission cutoff of the PM_2.5 EPA Federal Reference Method (FRM) WINS (Well impactor ninety-six) separator, converted to vacuum aerodynamic diameter using an average ambient particle density of 1.6 g/cm³ (Hu et al. 2012), is shown for reference. (b) Velocity calibration of the IPL compared with those of the standard lens (PM₁) and the high pressure lens (HPL). From top to bottom, the traces are HPL, IPL, and standard PM₁ lens. Blue solid points are NH₄NO₃ results, while red solid points are NaNO₃ results. The fit coefficients are given in Table 1.

Table 1. Summary of velocity calibration fitting parameters for standard PM₁, IPL, and HPL lenses. The formula used for fitting is , which is from Williams et al. (2013).

Lens/parameter name	Standard PM1	IPL	HPL
Vg	556.50	382.01	398.00
D*	18.20	93.33	92.80
B	0.73	0.54	0.91
Vl	48.56	15.59	78.50

Figure 4. Schematic diagram of particles impacting the standard vaporizer (a and b) and capture vaporizer (c), showing (a) flash vaporization, (b) bounce off the surface, and (c) trapped and delayed vaporization. Shading represents idealized vapor plume. Black arrow indicates attachment point of the thermocouple.

Figure 5. Collection efficiency due to particle bounce, E_B, plotted as a function of particle size on the standard vaporizer and capture vaporizer for NaNO₃ particles. (Dashed lines are guides for the eye).

Figure 6. (a) Q-AMS measured sulfate loading vs. CPMA and CPC calculated sulfate loading for standard and capture vaporizers. (b) Q-AMS measured NH₄ loading vs. CPMA and CPC calculated NH₄ loading for standard and capture vaporizers. (c) Chemical composition-dependent collection efficiency (CDCE) for capture vaporizer compared with that for standard vaporizer.

Figure 7. (a) Δχ² contour plot used for to determine RIE's from mixed NH₄NO₃ (AN)/(NH₄)₂SO₄ (AS) particles. A Δχ² value of 2.3 denotes the range of RIE values for 1 sigma uncertainties. (b) Measured AS/(AS + AN) mass fraction vs. input mass fraction in the atomizer solution. (c) Measured NH₄ vs. NH₄ predicted from measured NO₃ and SO₄. The fitting equation is NH_4meas = b × NH_4predict + a.

Figure 8. Mapping of the capture vaporizer surface using the m/z 46 to m/z 30 + m/z 46 ratio and the total m/z 30 + m/z 46 signal. The edges of the capture vaporizer are indicated with short-dashed vertical lines, and the edges of the opening to the internal cavity are indicated with long-dashed vertical lines. The black trace is a typical ambient aerosol beam width profile (Salcedo et al. 2007) produced by a PM₁ lens in an AMS, and projected on the dimension of the capture vaporizer at the ACSM chamber length.

Figure 9. Fragmentation patterns observed in the CV (solid) and the SV (shaded) for NH₄ (left four bar pairs [yellow]), NO₃ (middle bar pair [blue]), and SO₄ (right four bar pairs [red]). The NH₄ measurements are shown for both NH₄NO₃ and (NH₄)₂SO₄.

Table 2(a). Modified fragmentation table entries for sulfate for the CV. The frag_NO₃ is unchanged, although the m/z 46/30 ratio has changed.

m/z	frag_sulfate	frag_H2SO4	frag_SO3
18	frag_SO3[18]		0.938*frag_SO3[64], 0.938*frag_SO3[48]
32	frag_SO3[32], frag_H2SO4[32]	0.034*frag_H2SO4[81], 0.034*frag_H2SO4[98]	0.105*frag_SO3[48], 0.105*frag_SO3[64]

(b). Corresponding standard frag table for the SV.

m/z	frag_sulfate	frag_H2SO4	frag_SO3
18	frag_SO3[18]		0.67*frag_SO3[64], 0.67*frag_SO3[48]
32	frag_SO3[32], frag_H2SO4[32]	0.068*frag_H2SO4[81], 0.068*frag_H2SO4[98]	0.21*frag_SO3[48], 0.21*frag_SO3[64]

Figure 10. Normalized species concentrations measured at different CV temperatures for mixed NH₄NO₃ and (NH₄)₂SO₄ particles and for organic (α-pinene ozonolysis SOA) particles.

Figure 11. pToF profiles for selected SO₄-related ions (m/z 48 and 64), selected NH₄-related ions (m/z 15, 16, and 17), selected NO₃-related ions (m/z 30 and 46), and selected organic-related ions (m/z 43, 44, and 45) for (a) NH₄NO₃ with SV, (b) NH₄NO₃ with CV, (c) (NH₄)₂SO₄ with SV, (d) (NH₄)₂SO₄ with CV, (e) glutaric acid with SV, and (f) glutaric acid with CV (× x: x is the scaling factor).

Liu, P. S. K., Deng, R., Smith, K. A., Williams, L. R., Jayne, J. T., Canagaratna, M. R., Moore, K., Onasch, T. B., Worsnop, D. R., and Deshler, T. (2007). Transmission Efficiency of an Aerodynamic Focusing Lens System: Comparison of Model Calculations and Laboratory Measurements for the Aerodyne Aerosol Mass Spectrometer. Aerosol Sci. Technol., 41:721–733.

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