Abstract. Through measurements of NO2, O3 and NO3 during the PARADE campaign (PArticles and RAdicals, Diel observations of mEchanisms of oxidation) in the German Taunus mountains we derive nighttime steady-state lifetimes (τss) of NO3 and N2O5. During some nights, high NO3 (∼ 200 pptv) and N2O5 (∼ 1 ppbv) mixing ratios were associated with values of τss that exceeded 1 h for NO3 and 3 h for N2O5 near the ground. Such long boundary-layer lifetimes for NO3 and N2O5 are usually only encountered in very clean/unreactive air masses, whereas the PARADE measurement site is impacted by both biogenic emissions from the surrounding forest and anthropogenic emissions from the nearby urbanised/industrialised centres. Measurement of several trace gases which are reactive towards NO3 indicates that the inferred lifetimes are significantly longer than those calculated from the summed loss rate. Several potential causes for the apparently extended NO3 and N2O5 lifetimes are examined, including additional routes to formation of NO3 and the presence of a low-lying residual layer. Overall, the most likely cause of the anomalous lifetimes are related to the meteorological conditions, though additional NO3 formation due to reactions of Criegee intermediates may contribute.

Airborne trace gas, microphysical, and radiation measurements were performed during the AIRcraft TOwed Sensor Shuttle -Inhomogeneous Cirrus Experiment over northern Germany in 2013. Based on high-precision nitrous oxide (N 2 O) and carbon monoxide (CO) in situ data, stratospheric air could be identified, which contained cirrus cloud particles. Consistent with the stratospheric N 2 O data, backward trajectories indicate that the sampled air masses crossed the dynamical tropopause in the last 3 h before the measurement. These air masses contained cirrus particles, which were formed during slow ascent in the troposphere and subsequently mixed with stratospheric air. From the CO-N 2 O correlation the irreversibility of this transport is deduced. To our knowledge, this is the first in situ detection of cirrus particles mixed with stratospheric air in the midlatitudes.

IAGOS (In-service Aircraft for a Global Observing System) performs long-term routine in situ observations of atmospheric chemical composition (O, CO, NO, NO, CO, CH), water vapour, aerosols, clouds, and temperature on a global scale by operating compact instruments on board of passenger aircraft. The unique characteristics of the IAGOS data set originate from the global scale sampling on air traffic routes with similar instrumentation such that the observations are truly comparable and well suited for atmospheric research on a statistical basis. Here, we present the analysis of 15 months of simultaneous observations of relative humidity with respect to ice (RH) and ice crystal number concentration in cirrus (N) from July 2014 to October 2015. The joint data set of 360 hours of RH-N observations in the global upper troposphere and tropopause region is analysed with respect to the in-cloud distribution of RH and related cirrus properties. The majority of the observed cirrus is thin with N < 0.1 cm. The respective fractions of all cloud observations range from 90% over the mid-latitude North Atlantic Ocean and the Eurasian Continent to 67% over the subtropical and tropical Pacific Ocean. The in-cloud RH distributions do not depend on the geographical region of sampling. Types of cirrus origin (in situ origin, liquid origin) are inferred for different N regimes and geographical regions. Most importantly, we found that in-cloud RH shows a strong correlation to N with slightly supersaturated dynamic equilibrium RH associated with higher N values in stronger updrafts.

This study presents the analysis of the structure and air mass characteristics of the lower atmosphere during the field campaign PARADE (PArticles and RAdicals: Diel observations of the impact of urban and biogenic Emissions) on Mount Kleiner Feldberg in southwestern Germany during late summer 2011. We analysed measurements of meteorological variables (temperature, moisture, pressure, wind speed and direction) from radio soundings and of chemical tracers (carbon dioxide, ozone) from aircraft measurements. We focus on the thermodynamic and dynamic properties that control the chemical distribution of atmospheric constituents in the boundary layer. We show that the evolution of tracer profiles of CO2 and O-3 indicate mixing across the inversion layer (or entrainment zone). This finding is supported by the analysis of tracer-tracer correlations which are indicative for mixing and the relation of tracer profiles in relation to the evolution of the boundary layer height deduced from radio soundings. The study shows the relevance of entrainment processes for the lower troposphere in general and specifically that the tracer-tracer correlation method can be used to identify mixing and irreversible exchange processes across the inversion layer