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85 Appendix D Links Between Emissions and Air Quality in the Terminal and Fence Line The focus of this project has been the quantification of HAP appeared elevated. For example, NOx concentrations were emissions from aircraft as a function of ambient conditions usually between 1214 ppb at the 1st location (5:45 pm to and engine type. The most immediate use of emission indices 6:07 in Figure D-1) and reached concentrations as high as is for the generation of emission inventories, as required for 200 ppb for short durations, with an average concentration of environmental impact statements. Such emission inventories 37 ppbv. At the 2nd location (after 6:20 pm in Figure D-1), are also a crucial input for air quality models. Most air quality [NOx] was rarely below 22 ppbv and most spikes were less models, however, do not have the spatial resolution to predict than 70 ppbv, but the average concentration was a very similar differences in air quality between the airport ground and the 36 ppbv. Similar results were observed for HCHO: the back- airport fence line. Data collected as part of this project can ground (in-between-plume) concentration in the 1st position partially elucidate the nature of air quality at these locations, was 0.4 ppbv, with an average value of 2.6 ppb caused by a as well as in downwind neighborhoods. Overall the emerg- small number of short spikes that exceeded 50 ppbv. At the ing conclusion is that the air on airport grounds and near 2nd sampling location, [HCHO] was usually between 0.9 and airports is usually not well mixed, and characterized by 3.7 ppbv, with an average value of 1.8 ppbv. "background urban" air most of the time punctuated by Do the concentrations and ratios of concentrations of differ- occasional plumes of high concentrations that, depending on ent species provide information that can be used to apportion pollutant, can increase the average concentration considerably. the different emission sources (aircraft, GSE, etc)? Analysis of Below we discuss examples at or near three airports: MDW the data will surely contribute to an answer to this question. (on the runway), ORD (on the runway and at the fence line), For example, a quick analysis of a one-minute section of data and OAK (2 km downwind). from 6:30 pm to 6:31 pm indicates a combined NOx emission index of 6 g/kg fuel and an HCHO emission index of 0.3 g/kg. Comparison of these numbers to tabulated values for differ- Mixed Airport Emissions at ORD ent emission sources may provide clues to the predominant After sampling the advected plumes at ORD and before sources. The NOx emission index is within the (wide) range the dedicated tests of the two united aircraft, the mobile lab known for gasoline, diesel, and aircraft. The HCHO emis- was stationed for 25 minutes at the downwind perimeter of sion index, however, far exceeds that for gasoline and diesel the airport grounds, approximately 100 m from the closest vehicles, which are typically between 0.01 and 0.13 g/kg, but idling aircraft and over 200 m from the terminals where there is lower than the values reported at these temperatures for was constant activity by GSE (ground support equipment) CFM56-3x and CFM56-7x engines. This indicates a significant vehicles. Earlier on the airport grounds there was a clear dis- aircraft contribution. Further analysis of all species measured tinction between the "background" concentrations of the vari- can provide more information. ous pollutants measured and the exhaust plumes from nearby aircraft and GSE vehicles, which appear as short "spikes" in the Midway On-Runway Measurements time series data (Figure D-1 between 5:45 and 6:00 pm.) At the downwind location (6:25 pm onward in Figure D-1), Similar measurements were recorded on February 17, the numerous exhaust plumes were more spread out in 2010 on the MDW runway. Figure D-2 shows particle time (and therefore space) and the plumes had combined number density, formaldehyde, CO2, and CO during a 30- enough that the background concentrations observed earlier minute time period. The air observed consisted of relatively

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86 Figure D-1. Time series of four pollutants measured at ORD. Between 5:45 and 6:07, the mobile lab was positioned near the runways and observed short "spikes" of exhaust plumes. Between 6:20 and 6:50, the mobile lab was positioned several 100 meters downwind of aircraft and GSE activity, and observed an overall increase in the concentrations of all species, with "smoother" plumes that cannot always be individually identified. Figure D-2. Time series of data recorded on the MDW runway.

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87 clean air most of the time punctuated by occasional short transients of very high concentrations of most pollutants measured. The average formaldehyde and particle number concentrations in between the occasional plumes were 0.2 ppbv and 103 particles/cm3, respectively. As a result of the ~12 aircraft whose exhaust was sampled during this 35 minute time period, the average concentrations were increased to 1.4 ppbv and 187 103 particles/cm3--results very similar to the ORD data shown above. San Leandro Measurements At the conclusion of the JETS-APEX2 study, the Aerodyne Mobile Laboratory spent two days at the San Leandro Marina (Figure D-3), which is ~2 km downwind of the OAK runway. Winds were consistently from the northwest. Although lim- Figure D-3. San Leandro Marina and Oakland ited in duration, these measurements are unique in that they International Airport. enabled observations of diluted airport emissions with no interferences from non-airport sources, since there is no land in between the emissions and the measurement site. A 6-hour time-series of HCHO, CO, NOx, CO2, and PM ground value observed on the airport grounds). More impor- number concentration is shown in Figure D-4. Individual air- tantly, a dilution factor of ~5000 can be inferred for most of the craft exhaust plumes resulting from idle, take-off, and landing observed plumes based on comparison of the observed CO2 activity could be resolved. The average HCHO concentration to known CO2 concentrations at the exit of a high bypass in the time series shown is 1.3 ppb, while the interpolated turbine engine. Such a simplified source-receptor scheme background value is approximately 0.8 (similar to the back- would be an ideal scenario for testing dispersion models. Figure D-4. Time series of measurements recorded 2 km downwind of OAK.