The station, installed at the Environmental Climatic Observatory of Lecce, is designed to measure the concentration and turbulent vertical flows of particles by number using the eddy covariance technique. The instruments are housed on a telescopic pole at a height of 20 m from the street level. A 100Hz Gill R3 ultrasonic anemometer is used to measure the three components of wind speed and sonic temperature. The micrometeorological station includes a condensation particle counter (TSI 3776) for measuring the concentration by number of particles at a sampling rate of 10Hz. The CPC measures particles with a diameter between 9 nm and 1mm). The digital output of the CPC is connected to the analog input of the anemometer through a digital-analog interface. The micrometeorological station also includes an optical particle counter (OPC, Grimm 1.109). With the latter we can measure the concentration in number of particles (1Hz) and the related flows in 16 different dimensional ranges (from 0.25 to 3 μm). A thermohygrometer (Rotronic MP100) is used to measure the temperature and relative humidity at the top of the pole. A single inlet is used in this experimental setup for sampling both CPC and OPC. This inlet is fixed to a horizontal bar at a small distance (about 17cm) from the anemometer sampling volume. The air sample is transported inside the observatory by means of a 10 m long silicone rubber tube (internal diameter 26 mm). At the end of the tube we have a two-way flow splitter 15 cm long (25 mm in diameter) to ensure a flow of air to both the CPC and the OPC. A constant flow of 50 L / min is guaranteed by a pump (Thomas Gardner Denver, mod. Picolino) in suction from the flow splitter, allowing to maintain a turbulent flow (with a Reynolds number of about 2803) minimizing the time distortion of the fluctuations in concentration. OPC is connected to the flow splitter by means of a 50 cm (4 mm in diameter) silicone rubber hose and operates with a flow of 1.2 L / min. While a portion at 1.5 l / min is sampled by the CPC connected with a 42 cm (6 mm in diameter) tube.
