Aviation effects on air quality and climate in present day and mid-century

The projected increase in global air traffic raises concerns about the potential impact aviation emissions have on climate and air quality. Previous studies have shown that aircraft cruise emissions (emitted between 9-11 km in altitude) can actually affect surface air quality, especially ozone (O3) and fine particles (PM2.5). Aviation emissions also have important climate implications by altering the concentrations of O3 and other radiatively important gases and particles in the upper troposphere/lower stratosphere (UTLS). Here, we examine the impacts of aviation cruise emissions on surface air quality for present day and mid-century (2050) using the Community Atmosphere Model with Chemistry, version 5 (CAM5). The mid-century effects of aviation on climate are also examined. The evaluation of the aviation impact at mid-century involves two fuel scenarios, one that assumes further technological improvements have been made in the energy efficiency of future aircraft (Scenario 1 or SC1) and another that replaces jet fuel with biofuels (Alternative Fuel or Alt Fuel). The biofuels have the advantage of no sulfur emissions and 50% less black carbon production. Results from the present day simulations show a northern hemisphere (NH) mean surface O3 increase of 1.3 ppb (2.7% of the background) and a NH mean surface PM2.5 increase of 0.002 μg/m3. Mid-century simulations show slightly greater surface increases for O3 (1.8 ppb (4.1%) for both scenarios) and PM2.5 (0.01 μg/m3 for SC1 and 0.004 μg/m3 for Alt Fuel). While these perturbations do not significantly increase the frequency of extreme air quality events (increase is ~1%), they do contribute a small amount to the background concentrations of O3 and PM2.5, making it easier for urban areas to surpass these standards. The impact of aviation on climate in mid-century shows a short-term O3 radiative forcing (RF) of 56.3 mW m-2 for both mid-century scenarios, which while still quite small, is a 50% increase relative to present day simulations. Switching to biofuels would mainly reduce the aviation-induced changes in aerosols, notably sulfate, which reflects incoming solar radiation. Soot, which absorbs both solar and terrestrial radiation, is also reduced, though the perturbation of soot is much lower than that of sulfate