On enhancing air quality model predictions of particulate matter from aircraft emissions

Aviation is an important mode of transportation and usage is expected to continually grow. However, aircraft emit numerous pollutants that adversely impact air quality. The goal of this work is to provide additional certainty in air quality estimates of one of those pollutants, aircraft-attributable PM2.5, during landing and takeoff cycles using the Community Air Quality (CMAQ) Model and its enhancements.;First, CMAQ's response to secondary organic aerosol (SOA) concentrations, a component of PM2.5, formed from aircraft emissions was examined. It was determined that at coarser model resolutions (36-km and 12-km), aircraft NOx emissions lowered free radical concentrations and thereby reduced SOA precursor oxidation. This directly resulted in the reduction of SOA concentrations, primarily biogenic SOA. At a finer grid resolution (4-km), aircraft primary organic aerosol (POA) emissions provided additional mass for SOA to partition onto, promoting semi-volatile organic carbon species to partition from the particle phase to the gas phase, increasing SOA concentrations.;Secondly, a new formation pathway for modeled PM2.5 (based on recent sampling and smog chamber data) was incorporated into CMAQ to account for non-traditional SOA (NTSOA), SOA formed from aircraft emissions of semi and intermediate volatile organic compounds. This new pathway added 1.7% in January and 7.4% in July to aircraft-attributable PM2.5 at the Hartsfield-Jackson Atlanta International Airport. Downwind of the Atlanta airport, NTSOA averaged 4.6-17.9% of aircraft- attributable PM2.5. These contributions were generally low compared to smog chamber results due to considerably lower ambient organic aerosol concentrations in CMAQ versus those in the smog chamber experiments.;Thirdly, alternative aircraft PM emission estimates based on a 1-D plume model were coupled with a plume in grid (PinG) treatment for aircraft in CMAQ. This treatment increased grid-based monthly and contiguous U.S. average aircraft-attributable PM2.5 by 40% (from 1.9 ng m-3 to 2.7 ng m -3) in a winter month and 12% (from 2.4 ng m-3 to 2.6 ng m-3) in a summer month. Maximum modeled hourly subgrid scale aircraft-attributable PM2.5 concentrations were 23.7 microg m -3 in a winter month and 59.3 microg m-3 in a summer month, considerably higher than typical grid-based aircraft contributions (~0.1 microg m-3).