Vertical measurements of aerosols in the high Arctic during the winter-spring transition using a tethered balloon.

Aerosol number size distributions, along with thermodynamic and dynamic parameters, were measured from the surface to 600 m using a tethered balloon, the Helikite. The field measurements were carried out at Villum Research Station in Northern Greenland from 23^rd March to 2^nd May 2024. During the transition from winter to spring, three types of atmospheric regimes were identified: (1) a background regime with a profile of uniformly distributed aerosols, represented by low particle number concentrations as well as number size distributions along the vertical axis similar to the surface number size distribution, (2) a winter-type regime characterized by a pollution layer observable at altitudes above 500 m and not observed at the surface, (3) new particle formation episodes in late April and beginning of May, which accompanied a warm airmass intrusion event that had trigged surface melt. Most of the profiles presented a temperature inversion below 200 m, and a low-level jet was sometimes visible between 50 m and 100 m. These recently acquired measurements helped to clarify when ground-based aerosol observations were representative for higher altitude aerosol populations. By capturing a warm airmass intrusion, a comparison could be established with previous events to better understand its impact on the Arctic climate.

Aerosol number size distributions from the Helikite ranged from 8 nm to 3 µm measured with a Miniaturized Scanning Electrical Mobility Sizer (mSEMS, Brechtel) and a Portable Optical Particle Spectrometer (POPS, Hendix). Wind speed and direction were obtained with a SmartTether (Anasphere), and temperature and relative humidity with SHT85 sensors (Sensirion). Observations from the Helikite were complemented by measurements from the Villum Research Station with a ceilometer (Vaisala CL51) for cloud heights, a Scanning Mobility Particle Sizer (SMPS, TSI) for surface aerosol number size distributions and a stand-alone condensation particle counter (CPC, TSI) for number closure, and a 9-meter meteorological mast (temperature, relative humidity, wind, shortwave radiation). Back trajectories from the Lagrangian Analysis Tool LAGRANTO were also used to shed light on the warm airmass intrusion event.