Detailed characterization and profiles of crankcase and diesel particulate matter exhaust emissions using speciated organics

Abstract

A monitoring campaign was conducted in August-September 2005 to compare different experimental approaches quantifying school bus self-pollution. As part of this monitoring campaign, a detailed characterization of PM2.5 diesel engine emissions from the tailpipe and crankcase emissions from the road draft tubes was performed. To distinguish between tailpipe and crankcase vent emissions, a deuterated alkane, n-hexatriacontane-d74 (n-C36D74) was added to the engine oil to serve as an intentional quantitative tracer for lubricating oil PM emissions. This paper focuses on the detailed chemical speciation of crankcase and tailpipe PM emissions from two school buses used in this study. We found that organic carbon emission rates were generally higher from the crankcase than from the tailpipe for these two school buses, while elemental carbon contributed significantly only in the tailpipe emissions. The n-C36D74 that was added to the engine oil was emitted at higher rates from the crankcase than the tailpipe. Tracers of engine oil (hopanes and steranes) were present in much higher proportion in crankcase emissions. Particle-associated PAH emission rates were generally very low (< 1 microg/km), but more PAH species were present in crankcase than in tailpipe emissions. The speciation of samples collected in the bus cabins was consistent with most of the bus self-pollution originating from crankcase emissions.

Figure 1

Average crankcase (CK) and tailpipe (TP) fine PM, organic (OC) and elemental (EC) carbon emission rates for Bus 1 (B1) and Bus 2 (B2). Error bars are standard deviations between the runs (only one valid OC/EC measurement for TPB1)

Figure 2

OC and EC fraction emission rates for crankcase (CK) and tailpipe (TP) samples. See text for definitions of EC and OC fractions.

Figure 3

Total hopane and sterane emissions as a percentage of total carbon (TC) for crankcase (CK) and tailpipe (TP) samples. Error bars are standard deviations between the runs

Figure 4

Comparison of individual hopanes (4a) and steranes species (4b) in the lube oil (in μg/g) and crankcase emissions (in μg/km) for Buses 1 and 2. The abbreviations are: hop13=18α(H)-22,29,30-Trisnorneohopane; hop15=17α(H)-22,29,30-Trisnorhopane; hop17=17α(H),21ß(H)-29-Norhopane; hop19=17α(H),21ß(H)-Hopane; hop21=22S-17α(H),21ß(H)-30-Homohopane; hop22=22R-17α(H),21ß(H)-30-Homohopane; hop23=17ß(H),21ß(H)-Hopane; hop24=22S-17α(H),21ß(H)-30,31-Bishomohopane; hop25= 22R-17α(H),21ß(H)-30,31-Bishomohopane; hop26=22S-17α(H),21ß(H)-30,31,32-Trishomohopane; hop27=22R-17α(H),21ß(H)-30,31,32-Trishomohopane; ster42=20S-5α(H),14α(H),17α(H)-cholestane; ster43=20R-5α(H),14ß(H),17ß(H)-cholestane; ster44=20S-5α(H),14ß(H),17ß(H)-cholestane; ster45_40=20R-5α(H),14α(H),17α(H)-cholestane & 20S-13ß(H),17α(H)-diastigmastane; ster46=20S-5α(H),14α(H),17α(H)-ergostane; ster47=20R-5α(H),14ß(H),17ß(H)-ergostane; ster48_41=20S-5α(H),14ß(H),17ß(H)-ergostane & 20R-13α(H),17ß(H)-diastigmastane; ster49=20R-5α(H),14α(H),17α(H)-ergostane; ster50=20S-5α(H),14α(H),17α(H)-stigmastane; ster51=20R-5α(H),14ß(H),17ß(H)-stigmastane; ster52=20S-5α(H),14ß(H),17ß(H)-stigmastane; ster53=20R-5α(H),14α(H),17α(H)-stigmastane

Figure 4

Comparison of individual hopanes (4a) and steranes species (4b) in the lube oil (in μg/g) and crankcase emissions (in μg/km) for Buses 1 and 2. The abbreviations are: hop13=18α(H)-22,29,30-Trisnorneohopane; hop15=17α(H)-22,29,30-Trisnorhopane; hop17=17α(H),21ß(H)-29-Norhopane; hop19=17α(H),21ß(H)-Hopane; hop21=22S-17α(H),21ß(H)-30-Homohopane; hop22=22R-17α(H),21ß(H)-30-Homohopane; hop23=17ß(H),21ß(H)-Hopane; hop24=22S-17α(H),21ß(H)-30,31-Bishomohopane; hop25= 22R-17α(H),21ß(H)-30,31-Bishomohopane; hop26=22S-17α(H),21ß(H)-30,31,32-Trishomohopane; hop27=22R-17α(H),21ß(H)-30,31,32-Trishomohopane; ster42=20S-5α(H),14α(H),17α(H)-cholestane; ster43=20R-5α(H),14ß(H),17ß(H)-cholestane; ster44=20S-5α(H),14ß(H),17ß(H)-cholestane; ster45_40=20R-5α(H),14α(H),17α(H)-cholestane & 20S-13ß(H),17α(H)-diastigmastane; ster46=20S-5α(H),14α(H),17α(H)-ergostane; ster47=20R-5α(H),14ß(H),17ß(H)-ergostane; ster48_41=20S-5α(H),14ß(H),17ß(H)-ergostane & 20R-13α(H),17ß(H)-diastigmastane; ster49=20R-5α(H),14α(H),17α(H)-ergostane; ster50=20S-5α(H),14α(H),17α(H)-stigmastane; ster51=20R-5α(H),14ß(H),17ß(H)-stigmastane; ster52=20S-5α(H),14ß(H),17ß(H)-stigmastane; ster53=20R-5α(H),14α(H),17α(H)-stigmastane

Figure 5

N-alkanes and n-alkylcyclohexanes emissions as a percentage of total carbon (TC) for crankcase (CK) and tailpipe (TP) samples

Figure 6

Distribution of n-alkanes (6a) and n-alkylcyclohexanes (6b), in the fuel and lube oil obtained from both school buses. nCx = n-alkane with x carbon numbers (i.e. nC14 = n-tetradecane); Cx-Cyhx = Cx: n-alkyl with x carbon numbers, Cyhx: cyclohexane (i.e. C7-Cyhx=n-heptylcyclohexane).

Figure 6

Distribution of n-alkanes (6a) and n-alkylcyclohexanes (6b), in the fuel and lube oil obtained from both school buses. nCx = n-alkane with x carbon numbers (i.e. nC14 = n-tetradecane); Cx-Cyhx = Cx: n-alkyl with x carbon numbers, Cyhx: cyclohexane (i.e. C7-Cyhx=n-heptylcyclohexane).

Figure 7

Comparison of crankcase (CK) and tailpipe (TP) emissions of selected PAH and oxy-PAH from Buses 1 and 2 (B1 and B2) expressed as the percentage of total carbon with the average lube oil PAH concentrations. The abbreviations are: BcPh= benzo(c)phenanthrene; BaA= Benz(a)anthracene; Chr/Tphe= chrysene/triphenylene; 7-MeBaA= 7-methylbenz(a)anthracene; BaA-7,12-dione =Benz(a)anthracene-7,12-dione; B(b+j+k)F =Benzo(b+j+k)fluoranthene; BeP= benzo(e)pyrene; BaP=benzo(a)pyrene; Per= Perylene; 7-MeBaP= 7-methylbenzo(a)pyrene; B(ghi)Per =Benzo(ghi)perylene; In[123-cd]P=Indeno[123-cd]pyrene; DB(ah+ac)A = Dibenzo(ah+ac)anthracene; Coronene