Simulating the global atmospheric black carbon cycle: a revisit to the contribution of aircraft emissions

[摘要] The black carbon (BC) burden of the uppertroposphere and lowermost stratosphere (UTLS) is investigatedwith the general circulation model (GCM) ECHAM4. The special focus isthe contribution of aircraft emissions to the UTLS BC loading.Previous studies on the role of aircraft emissions in the global BC cycleeither neglect BC sources located at the Earth's surface or simplifythe BC cycle by assuming pre-defined BC residence times. Here,the global BC cycle including emissions, transport, and removalis explicitly simulated. The BC emissions considered includesurface sources as well as BC from aviation. This enables a consistentcalculation of the relative contribution of aviation to the global atmosphericBC cycle. As a further extension to the previous studies, the aviation-inducedperturbation of the UTLS BC particle number concentration is investigated.The uncertainties associated with the model predictions are evaluatedby means of several sensitivity studies. Especially, the sensitivity of theresults to different assumptions on the BC hygroscopic properties is analysed.The simulated UTLS BC concentrations are compared to in-situ observations.The simulations suggest that the large-scale contribution of aviationto the UTLS BC mass budget typically amounts to only a few percent, even inthe most frequented flight regions. The aviation impact far away fromthese regions is negligible. The simulated aircraft contributions to theUTLS BC particle number concentration are much larger compared to thecorresponding mass perturbations. The simulations suggest that aviation cancause large-scale increases in the UTLS BC particle number concentrationof more than 30% in regions highly frequented by aircraft.The relative effect shows a pronounced annual variation withthe largest relative aviation impact occurring during winter.

[学科分类] 大气科学