|Spatial pattern of PN concentration. Inset shows wind direction. Credit: ACS, Hudda et al. Click to enlarge.|
Results of a new study suggest that emissions particle emissions from airplane traffic at Los Angeles International Airport (LAX) are a major source of particle number (PN) concentrations in the Los Angeles area that are of the same general magnitude as the entire urban freeway network. The results also indicate that the air quality impact areas of major airports may have been seriously underestimated.
The study by a team from the University of Southern California and the University of Washington, published in the ACS journal Environmental Science & Technology, measured the spatial pattern of particle number (PN) concentrations downwind from the Los Angeles International Airport (LAX) with an instrumented vehicle (a gasoline hybrid) that enabled coverage of larger areas than allowed by traditional stationary measurements.
Scott Fruin, Neelakshi Hudda and colleagues noted that past research has measured pollution from air traffic before, but most of these studies only sampled air within a couple of miles, at most, from airports.
Over a period of 29 days, the scientists measured at least a 2-fold increase in PN concentrations over unimpacted baseline PN concentrations during most hours of the day in an area of about 60 km2 (23 square miles) that extended to 16 km (10 miles) downwind and a 4- to 5-fold increase to 8−10 km (5−6 miles) downwind.
The maximum PN concentrations were aligned to eastern, downwind jet trajectories during prevailing westerly winds and to 8 km downwind concentrations exceeded 75,000 particles/cm3—more than the average freeway PN concentration in Los Angeles.
During infrequent northerly winds, the impact area remained large but shifted to south of the airport. They calculated that the freeway length that would cause an equivalent impact to that measured in this study (i.e., PN concentration increases weighted by the area impacted) was 280−790 km (174-491 miles). The total freeway length in Los Angeles is 1500 km (932 miles).
Based on their calculations, the scientists concluded that within the area they found to have elevated pollution from the airport, automobiles contributed less than 5% of the PN levels.
The emissions from LAX are likely not unique on a per-activity basis. The large area of impact from LAX suggests that air pollution studies involving PN, localized roadway impacts, or other sources whose impacts are in the influence zone of a large airport should carefully consider wind conditions and whether measurements are influenced by airport emissions.
Source apportionment of specific airport sources or activities was beyond the scope of our study but would be necessary to evaluate the effectiveness of possible mitigation options. Differing NO2 to NOx ratios at different levels of engine thrust20 might be used to distinguish the contributions of jet landing, idling or takeoff activities. Takeoff and idling emission also differ in surface properties (i.e., the ratio of active surface area to surface bound photoionizable species) and particle size distributions differ between aircraft and ground support equipment emissions.—Hudda et al.
Neelakshi Hudda, Tim Gould, Kris Hartin, Timothy V. Larson, and Scott A. Fruin (2014) “Emissions from an International Airport Increase Particle Number Concentrations 4-fold at 10 km Downwind,” Environmental Science & Technology doi: 10.1021/es5001566