Application of a FIGAERO ToF CIMS for on-line characterization of real-world fresh and aged particle emissions from buses

Figures & data

Figure 1. Representation of the experimental setup displaying the bus accelerating passed the inlets to the instruments (three times) to which gas phase and particle measurements are made. The middle panel displays these three passages of the bus as observed in elevated CO₂ and NO₂ concentrations. The top panels display the subsequent CIMS desorption profile for sulfuric acid (top right) and the corresponding high resolution peak fitting (top left).

Table 1. Summary of top 20 EF_FRESH and EF_AGED of PM contributing species in RME_HEV, CNG, and diesel emissions. EF_TOTAL (in mg kg⁻¹) and EF_CIMS observed are also calculated.

	RMEHEV			CNG			Diesel
Species	EFFRESH	EFAGED	Species	EFFRESH	EFAGED	Species	EFFRESH	EFAGED
	mg kg^−1	mg kg^−1		mg kg^−1	mg kg^−1		mg kg^−1	mg kg^−1
HNO3^a	1.200	35.000	HNO3^a	2.300	23.000	H2SO4^a	3.400	2.600
C18H34O2^b	0.420	0.265	H2SO4^a	1.200	0.020	HNO3^a	2.500	32.000
H2SO4^a	0.300	0.290	C7H8O^b^,^c	0.900	3.200	C7H8O^b^,Table Footnotec	2.300	16.700
HNCO^c	0.120	0.120	C6H5NO3^a	0.800	2.100	C7H4O7^b	1.400	2.300
C6H5O2^c	0.089	0.076	C7H4O7^b	0.500	1.700	C6H5O^c	1.400	8.200
C14H28O2^b	0.086	0.065	C6H5O^c	0.300	2.600	C7H7NO3^c	0.800	1.900
C6H5NO3^a	0.068	0.475	C3H6O3^a	0.018	55.000	C3H6O3^a	0.040	50.000
C7H7NO3^c	0.051	0.343	C2H4O3^a	0.002	32.000	C2H4O3^a	0.020	10.000
H6S2O6^b	0.030	2.000	C6H5O2^c	0.100	2.300	C6H5NO3^a	0.400	1.800
C18H36O2^b	0.025	0.016	C7H7NO3^c	0.100	0.800	HNCO^c	0.120	0.120
C16H32O2^b	0.021	0.030	C9H14O6^b	0.100	1.200	C2H6O2^a	0.100	9.300
C5H8O4^b	0.020	0.700	C2H6O2^a	0.080	2.500	C6H5O2^c	0.100	2.800
C4H6O4^a	0.020	3.400	C5H8O4^b	0.040	1.200	C9H14O6^b	0.100	0.800
C16H30O2^b	0.018	0.010	C4H8SO5^d	0.040	1.640	C4H6O5^a	0.054	82.000
C18H30O2^b	0.017	0.010	H6S2O6^b	0.003	2.000	C3H4O4^a	0.050	67.000
C3H6O3^a	0.015	40.000	C4H6O5^a	0.002	126.000	C5H8O4^b	0.050	2.300
C2H4O3^a	0.015	20.000	C4H6O4^a	0.002	3.400	C2H5N3O2	0.004	0.004
C18H32O3^b	0.013	0.012	C7H12O5^b	0.001	1.200	H6S2O6^b	0.003	2.000
C18H28O2^b	0.013	0.005	C7H10O5^b	0.001	1.300	C4H6O4^a	0.002	5.400
C18H34O3^b	0.013	0.003	C3H4O4^a	0.000	45.300	C2H2O3^a	0.001	1.000
EFTOTAL	34.1	1322.0	EFTOTAL	14.2	2140.0	EFTOTAL	355.4	2467.0
EFCIMS	2.7	297.4	EFCIMS	6.5	323.6	EFCIMS	12.9	312.9
% CIMS	7.8	22.5	% CIMS	45.7	15.1	% CIMS	3.6	12.7

^a Directly calibrated.

^b Indirect calibration via fit to C8 carboxylic acid.

^cRelative calibration to similar functional group direct calibration.

^d Relative glycolic acid sulfate calibration.

Figure 2. Average mass spectra for a bus desorption file focusing on the theoretical deprotonated mass for stearic acid (C₁₈H₃₆O₂). Plot A shows the theoretical mass peak at m/z = 283.26 and calibrated signal peak significant shifted to lower m/z (peak to the left) obtained by using standard mass calibrants. Plot B is the same plot but using PFPA as a mass calibrant and there is a perfect fit between theoretical and calibrated positions.

Figure 3. Illustrating of the CIMS results from measuring lubrication oil after being nebulized and passed through the Go:PAM reactor. The bottom panel shows the average Go:PAM background MS during desorption with no addition of lubrication oil and the top panel represents the % increase of signal for each mass during calibration. The top right table illustrates the species which increased the most relative to the background.

Figure 4. Peak fitting for lactic acid sulfate (LAS) (C₃H₅SO₆) and its subsequent desorption profile displayed with H₂SO₄ standard and nonstandard (with double desorption) profiles and urea sulfate ion. The C₁₀H₁₈O₄ desorption profile is displayed as a guideline for what a “standard” desorption by the FIGAERO produces.

Figure 5. Urea oxidation products and further byproducts of isocyanic acid and salt formation. Spectral fits for key species are highlighted to illustrate the accuracy of identification.

Figure 6. Contribution of FAs to the EF_FRESH and EF_AGED for RME_HEV buses. The top right panel illustrates the factor change of EF between EF_FRESH and EF_AGED as a function of O:C ratio of the FAs.

Figure 7. Mass composition measured by CIMS for the fuel types in fresh and aged emissions sorted into six source types: SCR technology, C₆ oxidation products, OSs, FAs, and acids which may come from multiple sources (FRESH – oxidation of lubrication oil during combustion and AGED – oxidation of lubrication oil, oxidation of fuel combustion species. Here the inorganic acids H₂SO₄ and HNO₃ were omitted.