Our group studies the chemical composition of the Earth's atmosphere, not only through the analysis of data of significant atmospheric compounds but also through the design and the development of efficient and complex measuring instruments.
The study of the Atmosphere's chemical composition and, in particular, of the Troposphere, which represents its region in direct contact with the Earth's surface, has become one of the topics of greatest scientific interest in recent decades, not only because of the close correlation between atmospheric compounds and climate change, but also for the effects of these on human health and, more generally, on living beings in the Earth system.
The main activity carried out in this sector is the design and development of the TD-LIF system.
An instrument based on the laser induced fluorescence technique (LIF) for direct measurements of nitrogen dioxide (NO2), a key species in the study of the tropospheric ozone budget (O3), has been developed by this group since 2006. Coupled to it there is a thermodissociation system of three groups of reservoir species of the NO2: peroxynitrates (ΣPNs), alkylnitrates (ΣANs) and nitric acid (HNO3). These species are then converted to NO2 by heating the air samples at 200°C, 400°C e 550°C. The NO2 molecules are excited by means of a 532nm YAG pulsed laser and the emitted fluorescence light measured by photomultipliers (PMT). The pressure inside the measuring cells is maintained in the order of some Torr, so as to minimize the effect of the quench of the NO2 and to lengthen the duration of the fluorescence signal. The background in the same cells is reduced by means of both optical filters and a temporal filter which opens the gate of the PMT after the laser pulse. The TD-LIF has a high sensitivity (9.6 ppt of detection limit for NO2) and allows to perform measurements at high sampling frequency (10 Hz) making this instrument particularly suitable for the flow of NO2, ΣPNs and HNO3 flows through the Eddy Covariance technique. Overall, the analysis of all these species allows a more complex and complete evaluation of the tropospheric ozone budget and its production. In 2010, this instrument was certified to be installed on board the English instrumental aircraft BAe146 (FAAM, Cranfield). The TD-LIF has been used in many measuring campaigns both on land and in the air.