The impact of aviation on the nitrogen oxide distribution: An analysis using CARIBIC observations and the AERO2K global aviation emissions inventories

Abstract

As a precursor for tropospheric ozone, nitrogen oxide (NOx) plays a key role in photochemistry. By this, NOx also impact on the radiative forcing. The NOx concentration in the upper troposphere and lower stratosphere (UTLS) is controlled by different sources and processes, such as long-range transport, lofting from the boundary layer, lightning, and air traffic emissions. Insufficient knowledge about the NOx background concentration in the UTLS is responsible for uncertainties concerning the ozone production, since it depends in a non-linear way on the background NOx mixing ratios. Therefore, models show uncertainties in radiative forcing due to aviation-NOx. Within the framework of CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) nitrogen oxide measurements are performed aboard a passenger aircraft. The destinations of the aircraft are located in North and South America, Africa, and Asia. Since 2005 unique records of NO, NOy (the sum of reactive nitrogen oxides), further trace gases and aerosols have been obtained in the UTLS. This large dataset gives a comprehensive view of the seasonal and regional distribution of NO and NOy in the UTLS. In this work, the contribution of aircraft-NOy to the measured NOy budget in the UTLS is investigated using the AERO2K global aviation emissions inventories for 2002 and backward trajectories. Overall 157 CARIBIC flights between 2006 and 2011 were analyzed. A regional as well as a seasonal variability concerning the contribution of aircraft-NOy to the measured NOy budget were found. Since the calculated aviation NOy shows no distinct seasonality, the seasonal cycle is mainly caused by the seasonal cycle of the measured NOy. In the northern regions (north of 35° N) calculated aviation NOy has a mean contribution of about 12 % to the measured tropospheric NOy. However, in the more southern regions (35° S – 35° N), the mean contribution is about 4 %.