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70 PM Measurement Instruments The particle measurement instruments used during this research are listed in Table H-1 and include a MAAP (Model 5012, Thermo Scientific), a CAPS-based particle extinction monitor (PMex) (Aerodyne Research Inc.), an AVL particle counter (APC, AVL), and an engine exhaust particle sizer (EEPS) (Model 3090, TSI). These instruments provided information about par- ticle absorption and extinction, number density, and mobility-based size distribution. A High- Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS, Aerodyne Research, Inc.) was also used to provide information about the possible presence of any semi-volatile coatings on the soot. A Teflon-coated aluminum cyclone (Model URG-2000-30ED) with a 2.5-micron- diameter cutoff was used to remove large particles. Carbon dioxide concentration measurements were provided by a LI-840A CO2 analyzer (Li-Cor Biosciences) to provide for 1-s time resolution. The MAAP is a filter-based particle light absorption measurement instrument. It uses multi- ple light-emitting diodes (LEDs) centered at a wavelength of 640nm to determine particle light absorption via carefully correcting the influence of light scattering at several scattering angles. The obtained light absorption is linearly proportional to non-volatile soot mass. A mass absorp- tion coefficient of 6.4 m2/g is normally used to determine non-volatile particle mass (nvPMm). Given the lack of alternate instrumentation, the MAAP instrument was used instead of the SAE E-31 recommended instruments (MSS or LII) for the measurement of nvPMm. A P P E N D I X H SP-AMS Instrument Full name or descrip on What is being measured? EsCOM Engine soot and carbon dioxideopcal monitor Carbon dioxide, parcle sizing, exncon Soot parcle aerosol mass spectrometer Parcle size and chemical composion CAPS-PM-SSA Cavity aenuated phase shi spectroscopy of parcle single scaering albedo and total exncon Parcle single scaering albedo, total exncon MAAP Mul-angle absorpon photometer Black carbon mass loading/ non volale parculate maer mass (nvPMm) APC AVL model parcle counter Non volale parculate maernumber concentraon (nvPMn) EEPS Engine exhaust parcle sizer Parcle size distribuon and total parculate maer mass and number (tPMm* and tPMn) CO2 LI-COR Non-dispersive infrared gas analyzer for carbon dioxide Carbon dioxide (parcle inlet) *see the Engine Exhaust Particle Sizer material provided later in this appendix. Table H-1. Particulate matter instrumentation manifest.
PM Measurement Instruments 71 The CAPS technique, similar in nature to cavity ring-down spectroscopy, relies on the use of a sample cell employing high reflectivity mirrors. In this particular application, square-wave modu- lated red light (~635 nm) from an LED is directed through one mirror and into the sample cell. The distortion in the square wave caused by the effective optical path-length within the cavity (~1 km) is measured as a phase shift in the signal as detected by a photodiode located behind the second mirror. The presence of particles in the cell causes a change in the phase shift, which is related to the total extinction (the sum of scattering and absorption), epart, by the following relationship: θ â θ = Ï Îµcot cot 2 0 c f part (Eq. H-1) where q0 is the phase shift measured in the absence of particles, c is the speed of light, and f is the modulation frequency. The CAPS PMex extinction monitor has a detection level of less than 0.3 µg m-3 with a time response of 1 second. Total particle mass and number (tPMm and tPMn), including both volatile and non-volatile particles were measured using a TSI model 3096 engine exhaust particle sizer (EEPS). This instru- ment uses multiple electrometers to measure particle size distributions 10 times a second. The size range is 5.6 to 560 nm with a resolution of 16 channels per decade for 32 channels in total. The instrument consists of a cyclone at the inlet to remove particles >1 µm. The sample flow is mixed with ions generated using a corona discharge to produce a predictable particle charge level vs. particle size. The charged particles then flow between a charged central rod and an outer cylinder consisting of a series of individual electrometers. The electrometers nearer the sample inlet detect the smaller particles, whereas those nearer the outlet detect the larger particles, thereby providing an electrical mobility-based particle size distribution. Non-volatile PM number (nvPMn) was measured using an AVL particle counter (APC), in com- pliance with the AIR6241 recommendations (SAE International). The APC reports particle number concentration as the number of particles per cubic centimeter. To eliminate contributions of vola- tile particles, the device uses a two-stage dilution process coupled with a volatile particle remover (VPR). The sample is first diluted with air heated to 150°C using a chopper diluter. The sample then flows through a VPR consisting of a catalytic stripper at 350°C to convert gaseous hydrocarbons to carbon dioxide. The sample is then cooled to <35°C before entering a TSI 3790E condensation particle counter (CPC), which uses a light-scattering detector to count the non-volatile particles in the flow. At present, AMS is the only available instrument capable of simultaneously providing quan- titative size and chemical mass loading information in real time for non-refractory sub-micron aerosol particles. It uses an aerodynamic lens to focus the particles into a narrow beam that is then introduced into a high vacuum chamber while the air is differentially pumped. Volatile and semi-volatile species in/on the particles as well as non-volatile black carbon composition are vaporized via optical pumping from a high-power continuous-wave Nd:YAG laser at 1064 nm. The vaporized species are then ionized by the impact of energetic electrons (70 eV). The ions formed are analyzed by a time-of-flight mass spectrometer (Tofwerk, Thun, Switzerland). Particle aerodynamic size is determined via particle time-of-flight. The Engine Exhaust Particle Sizer⢠(EEPSâ¢) spectrometer is a fast-response, high-resolution instrument that measures the size distribution and number concentration of engine exhaust particle emissions in the range of 5.6 to 560 nanometers. It offers the fastest time resolution availableâ 10 times per secondâwhich makes it well suited for dynamic and transient tests. The EEPS
72 Exhaust Emissions from In-Use General Aviation Aircraft spectro meter operates at 10 L/min, which greatly reduces particle sampling losses due to dif- fusion. Additionally, it operates at ambient pressure to eliminate any concern about evaporating volatile and semi-volatile particles. An EEPS spectrometer (Model 3090 from TSI Inc.) was used in this research to determine particle size distribution from the GA aircraft engine exhausts. It measures particle count from 5.6 to 560 nanometers, reporting a total of 32 channels (16 channels of size per decade). Integrat- ing over the 32 channels, the research team obtained total particle concentration from the particle size distribution. In addition, once an effective density, weightings for surface area, volume, and mass (PM) are entered into the EEPS data analysis software, the software will report the calcu- lated statistics via numerical integration over the 32 channels. The calculated properties include median diameter, geometric mean diameter, and total particle surface, volume and mass. In this report, total particle concentration and mass were obtained via the EEPS measurements. Compared to the direct measurement of non-volatile black carbon mass from the MAAP, the EEPS results on particle mass are calculated values, which are based on assumed input parameters (e.g., particle effective density and shape).
