Multispecies remote sensing measurements of vehicle emissions on Sherman Way in Van Nuys, California

Figures & data

Table 1. Summary of emissions, measurement specifics, and observed driving mode

	g/kg Emissions ^a
	CO	HC ^b	NO ^c /NO2/NOx ^d	NH3
Median	2.6	0.8	0.16/0.05/0.39	0.21
Mean ^e	19.4 ± 1.3	2.4 ± 0.3	2.6 ± 0.1/0.09 ± 0.01/4.1 ± 0.1	0.59 ± 0.02
Mean percentile ^f	83	68	79/56/79	73
Percent of total emissions from top 1%	32%	33%	16%/40%/16%	12%
Attempts/Plates/Matched	14691/13009/12963
Mean model year	2001.5
Speed/Acceleration/VSP	51.7 kph/0.5 kph/sec/6.2 kw/tonne
Notes: ^aAssumes a fuel carbon fraction of 0.85. ^bGrams of HC using the FID correction noted in the text. ^cGrams of NO. ^dGrams of NO2. ^eStandard errors of the means calculated from the daily measurement means. ^fPercentile in which the mean emission rate is found when the emission data are rank-ordered.

Figure 1. The measured Sherman Way fleet fraction versus model year for 1990 and newer models. The 1989 and older vehicles make up 3.5% of the total fleet. The 2001 recession is not detectable in this data set, whereas the 2008 downturn is quite striking in its magnitude and has rapidly aged the vehicle fleet.

Figure 2. Amount of overlap among remote sensing measurements responsible for highest 50% of observed CO, HC, and NO. Values shown are the percentage of measurements found within each segment of the 12,929 total measurements constituting the figure. Total area outside of circles, but contained within the drawn rectangle, is 92% of all measurements. All areas within the rectangle shown in this figure are drawn to scale.

Table 2. On-road remote sensing emissions compared with reported historical values collected at the Van Nuys Airport tunnel

Study Year	Mass CO/NOx ^a	Mass HC/NOx ^a	g CO/kg ^b	g HC/kg ^b	g NOx/kg ^b	g NH3/kg ^b	Model Year (Age)
1987	13.3	1.7	NA	NA	NA	NA	NA
1993	NA	NA	170 ^c	14 ^c	NA	0.5 ^c,d	1986.4 (7.6)
1995	11.2	0.8	120	9	11	NA	1983.9 (11.5)
2010^e	6.5 ± 0.4	0.5 ± 0.04	21.3 ± 2.5	1.7 ± 0.2	3.3 ± 0.4	NA	NA
This study^f	4.7 ± 0.3	0.6 ± 0.1	19.4 ± 1.3	2.4 ± 0.3	4.1 ± 0.1	0.59 ± 0.02	2001.5 (9.4)
Notes: ^aAssumes all NOx is NO2. ^bAssumes a fuel carbon fraction of 0.85. ^cLiterature g/L values assumed a gasoline density of 0.75 kg/L. ^dOnly 76% of fleet estimated to have catalyst. ^eMeans of all measurement results and only nonmethane HC values are reported. The errors are the propagated 1-sigma errors reported for the tunnel measurements. ^fStandard errors of the means calculated from the daily means.

Figure 3. Mean g NH₃/kg emission versus vehicle age for the Sherman Way data (filled triangles) compared with three California sites measured in March of 2008. Vehicle age has been defined as the difference between the fractional measurement year and the vehicle model year. The error bars plotted are standard errors of the mean calculated using the daily model year means and all of the emission values have been calculated assuming a fuel carbon fraction of 0.85.

Table 3. Emission comparison for the weekday and weekend data

			Mean g/kg Emissions ^a
	Vehicles (hr)	Mean Model Year	CO	HC ^b	NO ^c /NO2/NOx ^d	NH3
Weekday ^e	6757 (15)	2001.7	18.0 ± 1.4	2.4 ± 0.5	2.60 ± 0.08/0.12 ± 0.02/4.1 ± 0.1	0.58 ± 0.03
Weekend ^f	6206 (13.8)	2001.3	21.0	2.5	2.6/0.06/4.0	0.61
Notes: ^aAssumes a fuel carbon fraction of 0.85. ^bGrams of HC using the FID correction noted in the text. ^cGrams of NO. ^dGrams of NO2. ^eStandard error of the means calculated using the daily means. ^fInsufficient number of days to calculate standard errors of the mean.