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25 CHAPTER 6 Gaseous and Particulate Matter Emissions Literature Review This section focuses on collecting and summarizing relevant contributing to volatile PM via uptake on existing particles published articles, results of existing literature reviews, and (Wey et al. 2006). available documentation that addresses the current issues Lubrication Oil. Lubrication oil may also influence and informational needs of the airport community on gaseous volatile PM composition, particularly during transient and particulate emissions at airports. The reader is encouraged periods when engine thrust level is switched from one level to read Chapter 1, Primer on Particulate Matter Emissions to the next. APEX3 data indicated that up to 90% of the from Aviation. Chapter 6 is intended to augment the infor- organic PM emitted by some engines may be lubrication mation presented in Chapter 1. oil (Timko, Onasch et al. 2008). For less efficient engines, lubrication oil makes up as little as about 10% of the total organic PM. In general, lubrication oil is least important in 6.1 Characteristics of Aircraft PM engines with low combustion efficiencies, and under- As discussed in Chapter 1, aircraft PM is categorized either standing of lubrication oil emissions continues to grow. as primary PM or as contributing to secondary PM. Primary PM can be described as either volatile or non-volatile. Non- The total PM reported by EDMS as calculated using the FOA volatile PM has a size distribution that differs from the is an estimate of the non-volatile and volatile primary PM. volatile PM generated by aircraft gas turbine engines. The di- Secondary volatile PM forms on the timescale of minutes to ameters of non-volatile carbonaceous particles (soot) generated days and may continue to form in air masses moving hundreds by aircraft gas turbine engines range from approximately of kilometers (or miles) from the source. Nitrogen oxides, 0.02 to 0.06 m (20 to 60 nm) in diameter. The EPA classifies sulfur oxides, and HC emissions are important contributors such PM as PM2.5, which includes particles less than 2.5 m to secondary volatile PM formation. After atmospheric pro- in aerodynamic diameter. The diameter of volatile PM ranges cessing, these species are absorbed into existing particles, some from approximately 0.001 to 0.015 m (1 to 15 nm), and also of which are non-volatile particles. Nitric acid (HNO3) is pro- is classified as PM2.5 (Lukachko et al. 2008). duced by the photochemical processing of NO2. Ammonium Primary volatile PM is initially formed in the near-field nitrate (NH4NO3) found in PM provides evidence that HNO3 plume (<1 min from emission). Volatile PM is composed of contributes to formation of secondary volatile PM. A regional- a variety of compounds whose emissions indices and relative scale model is needed to calculate the quantities and compo- contributions depend on a number of factors including sition of secondary volatile PM that is formed. ambient air conditions, thrust setting, and fuel sulfur content Several factors can alter aircraft PM properties. Engine (Anderson et al. 2005). Research suggests volatile PM may be technology influences particle size. Fuel sulfur content also composed of the following compounds: influences primary volatile PM properties since volatile PM concentrations tend to increase with higher fuel sulfur con- Sulfuric Acid. Sulfuric acid (H2SO4) resulting from fuel tent (Kugele et al. 2005). Organic emissions also contribute sulfur nucleates as (H2SO4)n(H2O)m, where n and m are to primary volatile PM composition and mass. Secondary PM small integers, to form volatile PM (Lukachko et al. 2008). properties are influenced by coexisting pollutants emitted H2SO4 molecules also condense onto preexisting aerosol from other sources (U.S. EPA Jul 2004). Therefore, PM sourced surfaces (Lukachko et al. 2008). to aircraft can change as emissions from other sources evolve. Hydrocarbons. Hydrocarbons may nucleate as indepen- To date, the studies conducted by Spicer et al. (1992, 1994) dent PM sources but may play a more important role in have been the primary source of hazardous air pollutant (HAP)