A Comprehensive Data Composite of NO and NOy in the Upper Troposphere and Lower Stratosphere from CARIBIC Airborne Measurements

Abstract:

As a key precursor for tropospheric ozone, nitrogen oxides (NO_x) play an important role in atmospheric chemistry. The NO_x distribution in the upper troposphere and lower stratosphere (UTLS) is controlled by different sources and processes, such as long-range transport, uplift of emissions from the boundary layer, lightning, and air traffic emissions. The combination of comparatively short lifetime, variety of sources, and complex chemistry entails large spatial variations in the abundance of nitrogen oxides. Insufficient knowledge of the NO_x background concentrations in the UTLS implicates uncertainties in the determination of the ozone production, which depends non-linear on the background NO_xmixing ratios. To evaluate model simulations, a sound observational data base of nitrogen oxides in the UTLS is required.

Within the framework of CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) nitrogen oxide measurements are performed regularly aboard a passenger aircraft. A total of 330 flights were conducted from May 2005 through April 2013 between Frankfurt/Germany and destinations in the USA, Canada, Brazil, Venezuela, Chile, Argentina, Colombia, South Africa, China, South Korea, Japan, India, Thailand, and the Philippines. We present data averages of NO and NO_y for the different regions and for different seasons. At mid-latitudes, observed NO_y and NO generally show clear seasonal cycles in the upper troposphere with a maximum in summer and a minimum in winter. Mean NO_y mixing ratios vary between 1.36 nmol/mol in summer and 0.27 nmol/mol in winter. Mean NO mixing ratios range between 0.05 nmol/mol and 0.22 nmol/mol. Regions in the sub-tropics and tropics show no consistent seasonal dependence of the NO and NO_yabundance.

These measurements represent one of the most comprehensive NO and NO_y dataset presently available for the tropopause region and is a suitable basis for establishing a climatology. It can be used for the evaluation of global chemistry-climate models.