Dusty Origins: The formation of cirrus clouds begins with the production of ice nuclei, on which water vapor then condenses. Cziczo et al. (p. 1320 , published online 9 May) determined the kinds of particles on which cirrus ice crystals form by sublimating samples collected by research aircraft and analyzing the chemical and physical properties of the residual seeds. Most of the seed particles were either mineral dust or metallic.

The Total Carbon Column Observing Network (TCCON) produces precise measurements of the column average dry-air mole fractions of CO₂, CO, CH₄, N₂O and H₂O at a variety of sites worldwide. These observations rely on spectroscopic parameters that are not known with sufficient accuracy to compute total columns that can be used in combination with in situ measurements. The TCCON must therefore be calibrated to World Meteorological Organization (WMO) in situ trace gas measurement scales. We present a calibration of TCCON data using WMO-scale instrumentation aboard aircraft that measured profiles over four TCCON stations during 2008 and 2009. These calibrations are compared with similar observations made in 2004 and 2006. The results indicate that a single, global calibration factor for each gas accurately captures the TCCON total column data within error.

In this paper, we describe a new flexible and robust NH₃ retrieval algorithm from measurements of the Infrared Atmospheric Sounding Interferometer (IASI). The method is based on the calculation of a spectral hyperspectral range index (HRI) and subsequent conversion to NH₃ columns via a neural network. It is an extension of the method presented in Van Damme et al. (2014a) who used lookup tables (LUT) for the radiance‐concentration conversion. The new method inherits the advantages of the LUT‐based method while providing several significant improvements. These include the following: (1) Complete temperature and humidity vertical profiles can be accounted for. (2) Third‐party NH₃ vertical profile information can be used. (3) Reported positive biases of LUT retrieval are reduced, and finally (4) a full measurement uncertainty characterization is provided. A running theme in this study, related to item (2), is the importance of the assumed vertical NH₃ profile. We demonstrate the advantages of allowing variable profile shapes in the retrieval. As an example, we analyze how the retrievals change when all NH₃ is assumed to be confined to the boundary layer. We analyze different averaging procedures in use for NH₃ in the literature, introduced to cope with the variable measurement sensitivity and derive global averaged distributions for the year 2013. A comparison with a GEOS‐Chem modeled global distribution is also presented, showing a general good correspondence (within ±3 × 10¹⁵ molecules.cm⁻²) over most of the Northern Hemisphere. However, IASI finds mean columns about 1–1.5 × 10¹⁶ molecules.cm⁻² (∼50–60%) lower than GEOS‐Chem for India and the North China plain.

We use aircraft observations of Asian outflow from the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) mission over the NW Pacific in March–April 2001 to estimate the export efficiency of black carbon (BC) aerosol during lifting to the free troposphere, as limited by scavenging from the wet processes (warm conveyor belts and convection) associated with this lifting. Our estimate is based on the enhancement ratio of BC relative to CO in Asian outflow observed at different altitudes and is normalized to the enhancement ratio observed in boundary layer outflow (0–1 km). We similarly estimate export efficiencies of sulfur oxides (SO_x = SO₂(g) + fine SO₄²⁻) and total inorganic nitrate (HNO₃^T = HNO₃(g) + fine NO₃⁻) for comparison to BC. Normalized export efficiencies for BC are 0.63–0.74 at 2–4 km altitude and 0.27–0.38 at 4–6 km. Values at 2–4 km altitude are higher than for SO_x (0.48–0.66) and HNO₃^T (0.29–0.62), implying that BC is scavenged in wet updrafts but not as efficiently as sulfate or nitrate. Simulation of the TRACE‐P period with a global three‐dimensional model (GEOS‐CHEM) indicates that a model timescale of 1 ± 1 days for conversion of fresh hydrophobic to hydrophilic BC provides a successful fit to the export efficiencies observed in TRACE‐P. The resulting mean atmospheric lifetime of BC is 5.8 ± 1.8 days, the global burden is 0.11 ± 0.03 Tg C, and the decrease in Arctic snow albedo due to BC deposition is 3.1 ± 2.5%.