Abstract
Abstract. Aviation emissions are unique from other transportation emissions, e.g., from road transportation and shipping, in that they occur at higher altitudes as well as at the surface. Aviation emissions of carbon dioxide, soot, and water vapor have direct radiative impacts on the Earth's climate system while emissions of nitrogen oxides (NOx), sulfur oxides, carbon monoxide (CO), and hydrocarbons (HC) impact air quality and climate through their effects on ozone, methane, and clouds. The most accurate estimates of the impact of aviation on air quality and climate utilize three-dimensional chemistry-climate models and gridded four dimensional (space and time) aviation emissions datasets. We compare five available aviation emissions datasets currently and historically used to evaluate the impact of aviation on climate and air quality: NASA-Boeing 1992, NASA-Boeing 1999, QUANTIFY 2000, Aero2k 2002, and AEDT 2006 and aviation fuel usage estimates from the International Energy Agency. Roughly 90% of all aviation emissions are in the Northern Hemisphere and nearly 60% of all fuelburn and NOx emissions occur at cruise altitudes in the Northern Hemisphere. While these datasets were created by independent methods and are thus not strictly suitable for analyzing trends they suggest that commercial aviation fuelburn and NOx emissions increased over the last two decades while HC emissions likely decreased and CO emissions did not change significantly. The bottom-up estimates compared here are consistently lower than International Energy Agency fuelburn statistics although the gap is significantly smaller in the more recent datasets. Overall the emissions distributions are quite similar for fuelburn and NOx with regional peaks over the populated land masses of North America, Europe, and East Asia. For CO and HC there are relatively larger differences. There are however some distinct differences in the altitude distribution of emissions in certain regions for the Aero2k dataset.
Highlights
Aviation contributes greatly to the world’s economy
Military aviation emissions which are estimated to account for ∼ 15 % of fuelburn and nitrogen oxides (NOx) emissions remain highly uncertain
The uncertainties and variability in military emissions may account for the largest source of uncertainty in estimating total aviation emissions, they are often not included in aviation emissions datasets in part due to the difficulty in quantifying them
Summary
Aviation contributes greatly to the world’s economy. Its total economic impact is estimated to be nearly 8 % of global economic activity and it carries about 40 % of the value of freight (ATAG, 2008). They are estimated to account for 10–15 % of total emissions (e.g., Mortlock et al, 1998; Waitz et al, 2005) Evaluating these emission databases is necessary to provide overall context to the emissions databases, to determine whether there are fundamental differences in aviation emissions distributions over time, and perhaps most importantly to provide a footing for comparing the past and future model simulations evaluating the impact of aviation on air quality and climate which make use of one or more of these datasets. The datasets are not strictly suitable for emission trend analyses since they were created independently with different models and assumptions it is still informative to examine differences as a function of time
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