Summary

Here, a new UAV-borne measurement system ALADINA (Application of Light-weight Aircraft for Detecting In situ Aerosol) has been developed. It has a payload of approx. 2.8 kg and is equipped with instruments to measure basic meteorology (Fig. 2) and aerosol number concentrations in different size channels between 5 nm and 10 µm (Fig.3).

Aerosol instrumentation on ALADINA

Two Condensation Particle Counters (CPC, Type3007, TSI Inc., St. Paul, USA) were modified to measure number concentrations larger than 5 nm (CPC1, N₅) and larger than 10 nm (CPC2, N₁₀) with a time resolution of 1.5 s. The difference between both CPCs results in the number concentration between 5 and 10 nm N_5-10.

Ground-based aerosol measurements in Melpitz

A Neutral cluster and Air Ion Spectrometer (NAIS) measures mobility distributions in the size range from 1 to 40 nm with a time resolution of 5 min. Measurements of meteorologocal, trace gas and other aerosol parameters are performed continuously at the measurement site Melpitz.

On April 3, 2014 nine measurement flights were performed with ALADINA between 6:20 and 12:30 UTC. During these flights mainly vertical profiles up to 1000 m asl (above sea level) were flown to measure the vertical distrubution of ultrafine particle number concentrations (N_5-10), potential temperature Θ, mixing ratio m, correlation (cor) between Θ and m, structure parameters C_q² and C_T² and σ_T, σ_q.

Fig.1 shows a strong inversion at 200 m asl above a shallow convective boundary layer (SCBL) with constant N₅, N₁₀ below with high temperature and humidity fluctuation, expressed by large C_T² and C_q². Above the inversion, a layer with up to 20000 cm^-3 in N₅ and N₁₀ is present between 400 an 500 m but no significant values in N_5-10. This changes at 9:58 UTC (Fig.2) where the height of the well-mixed layer reached 400 m asl and 25000 cm^-3 particles were measured in N_5-10 within a distinct layer between 400 and 500 m. At 10:04 UTC (Fig.3) the SCBL breaks through the inversion and thus the layer with increased N_5-10 is mixed downwards.

This results in an increasing vertical thickness of this layer from 300 to 500 m asl. The following profile at 10:45 UTC (Fig.4) shows a nearly well-mixed layer below ~550 m asl and increased values in N_5-10 of 10000 - 40000 cm^-3 over all heights, also close to the ground. This corresponds to NAIS measurements (Fig.5), showing that the N_5-10 measured on ground start to increase around 10:30 UTC.