Exhaust Emissions from In-Use General Aviation Aircraft (2016)

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62 Exhaust Emissions from In-Use General Aviation Aircraft Figure D-2. Determination of the emission ratio for NOx (green) vs Total C (blue). The time traces in the left plot have been plotted against one another on the right hand plot (blue circles). The red line shows the best fit, with the resulting slope (m), intercept (b) and coefficient of correlation (R2) shown on the plot. The corresponding EI is also shown (EI NOx). Figure D-1. Time series for many measured species for aircraft N6453H.

Method for Calculating Emission Ratios 63 Figure D-3. Example plume analysis showing updated methods that include periods of manually defined “background” signal. Panel A shows 4 time traces for species of interest, including NOx (green). In Panels B and C, emission ratios for NOx are determined via three methods (see text). Periods of manually defined background have been added to the data in Panels B and C, as indicated by the extended baseline in Panel B, and the locus of points (cyan  signs) in the lower left of Panel C. µ 12 8 4 0 P M m as s (v ia M A A P ) [ g/ m -3 ] 16 14 12 10 T H C a s C 1 F ID [p pm ] 19:01:00 6/3/15 19:01:15 19:01:30 19:01:45 19:02:00 Time [UTC] 600 550 500 450 400 To ta l C [p pm ] 2500 2000 1500 1000 500 0 N O x [p pb ]100x10 3 80 60 40 20 0 C O [p pb ] FID CO CO2 A. 2500 2000 1500 1000 500 0 ∇ N O x 19:01:00 6/3/15 19:02:00 Time 200 150 100 50 0 ∇ T ot al C ar bo n Area Ratio: = 7.532 B. 2500 2000 1500 1000 500 0 N O x [p pb ] 600550500450400 TotalCarbon [ppmv] m = 4.35 = -1.36e+03 R 2 = 0.111 EI NOx= 14.367 g/kg BG curvefit: m = 6.5985 b = -2626.5 R 2 = 0.48554 b C.

64 Emission ratios are the first step in calculating emission indices from time series data. Emission indices are in units of grams of compound per kilogram of fuel (e.g., g X/kg fuel). Raw data gives the emission ratio: the concentration enhancement of the compound of interest over the con- centration enhancement of carbon dioxide (DCX/DCCO2). Emission indices are calculated know- ing the carbon content of the fuel and performing a unit conversion. This standard procedure assumes that the major carbon-containing combustion product is CO2, with negligible amounts of other carbon-containing compounds (e.g., CO and methane). This is not true for the piston engines that the research team measured, with carbon monoxide (CO) constituting a significant portion of the exhaust. For this reason, the concentration enhancement of total carbon (DCTotC) is used in lieu of CO2 in the emission ratio. This ensures proper accounting when CO is not negligible. The equation below is a simplified conversion from the emission ratio versus the total carbon (DCX/DCTotC) to the emission index (EIX) (Timko et al. 2010, Herndon et al. 2010). MWX is the molar mass of the compound of interest; FCO2 is the fuel carbon content, expressed in grams of CO2 per kilogram of fuel, and is 3160 for Jet A and 3067 for AVGAS 100 LL; and 44 is the molar mass of CO2 in g/mol. All unit conversions are rolled in. 44 Eq. E-12EI gX kg Fuel C C MW F X x TotC X CO ( )    = ∆ ∆ A similar method is used for the particulate mass measurements (Timko et al. 2010), sub- stituting grams of compound with number of particles or other measures as necessary. Slightly different equations are required for EIm,X, the particulate mass emission index, than for EIn,X, the particulate number emission index, due to differences in the units of the measurements. In the equations below, DMx is the concentration enhancement of a particle of type X in the exhaust relative to ambient, in µg m-3. DNx is a particle count: the concentration enhancement of particle type X relative to ambient, in units of # cm-3. DCCO2 is the corresponding enhancement in CO2, in ppm. The particulate inlet had its own CO2 monitor, and this measure is used to ensure that the timing of the particle inlet matches up with the gas-phase measurements of DCTotC. The tem- perature (T, Kelvin) and pressure (P, Torr) are those that define the condition for the particulate measurement flow calibration and correspond to 293.15 K and 760 Torr, respectively for the MAAP instrument (Multi Angle Absorption Photometer). For example, 0.06236 is the ideal gas constant in units of m3 Torr K-1 mol-1. i i0.06236 44 Eq. E-2, 2EI gX kg Fuel M C T P F m X x TotC CO ( )    = ∆ ∆ i i i # 0.06236 44 10 Eq. E-3, 12 2EI X kg Fuel N C T P F n X x TotC CO ( )    = ∆ ∆ Method for Calculating Emission Indices A P P E N D I X E