Secondary organic aerosol produced from aircraft emissions at the Atlanta Airport: An advanced diagnostic investigation using process analysis

Efforts using the Community Multiscale Air Quality (CMAQ) model to investigate the impacts of aircraft emissions from the Hartsfield-Jackson Atlanta International Airport have previously shown aircraft emissions increased total daily PM2.5 concentrations by up to 9.4% (0.94 μg m−3) with overall impacts varying by modeled grid resolution. However, those results also indicated that secondary organic aerosol (SOA) concentrations in the airport grid cell were reduced due to aircraft emissions at coarser grid resolutions (36-km and 12-km) but not at a finer resolution (4-km). To investigate this anomaly, this study instruments the CMAQ model with process analysis, an advanced diagnostic modeling tool, and focuses on changes to SOA concentrations due to aircraft emissions in the grid cells containing the Atlanta airport at grid resolutions of 36-km, 12-km, and 4-km. Model results indicated aircraft emissions reduced hourly anthropogenic and biogenic SOA concentrations at the 36-km and 12-km grid resolutions by up to 6.2% (0.052 μg m−3) by removing nitrate, hydroxyl, and hydroperoxy radicals through chemistry. At the 4-km resolution, however, hourly modeled SOA concentrations increased (primarily due to changes in biogenic SOA) by up to 11.5% (0.081 μg m−3) due to primary organic aerosol emissions from aircraft, with the additional organic mass shifting partitioning of SOA semi-volatile gas phase species into the particle phase.