Laser induced fluorescence instrument for NO 2 measurements: Observations at a central Italy background site Cesare Dari-Salisburgo a, b , Piero Di Carlo a, b, * , Franco Giammaria b , Yoshizumi Kajii c , Alfonso D’Altorio b a Center of Excellence CETEMPS, Universita’ degli studi di L’Aquila, Via Vetoio, 67010 Coppito, L’Aquila, Italy b Dipartimento di Fisica, Universita’ degli studi di L’Aquila, Via Vetoio, 67010 Coppito, L’Aquila, Italy c Department of Applied Chemistry, Graduate School of Engineering, Tokyo Metropolitan University,1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan article info Article history: Received 23 April 2008 Received in revised form 27 September 2008 Accepted 16 October 2008 Keywords: Nitrogen dioxide Ozone Boundary layer Urban pollution Laser induced fluorescence abstract A laser induced fluorescence (LIF) instrument has been developed to measure tropospheric NO 2 with low detection limit. The instrument design, development and first measurements are reported. There are also details of the temporal gate system built for the fluorescence acquisition. The instrument is able to make fast measurements (up to 4 Hz) and shows a limit of detection of 10 pptv/60 s. Continuous observations (2 weeks in summer 2007) in a small town in central Italy were used to test the performance of the instrument and to study the photochemistry of ozone in a background site. LIF and a commercial chemiluminescence (CL) instrument simultaneous observations of NO 2 show a good linearity (LIF ¼ 1.02 CL þ 0.6 (ppb), R 2 ¼ 0.98) but there is a bias of the commercial instrument of about 0.60 ppbv on average. The overestimation of the CL system is probably due to conversion of NO y species into NO by the molybdenum converter used in the CL instrument to detect NO 2 . Analysis of 1 s data is used to test the instrument response and the coupling between nitrogen oxides and ozone. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Nitrogen oxides (NO x ¼ NO þ NO 2 ) are key species in the control of tropospheric ozone production, which is the pollutant of most concern for human health and ecosystems (European Environment Agency (EEA), 2005; Hall et al., 1992). Moreover nitrogen oxides play a role in the oxidation capacity of the atmosphere through the control of the course of the oxidation reaction sequences started by hydroxyl radicals (OH) (Levy, 1971; Weinstock, 1969). The primary sources of NO x are: (1) fossil fuel combustion at high temperature (motor vehicles, electric utilities and all the other activities burning fuel), (2) natural sources such as lightning (important in the free upper troposphere) and soil emission, more significant in the atmospheric surface layer. The fast economic growth experienced by China and East Asian countries in the last years led to an increase of NO x emissions. In fact in these regions the analysis of the column amount of NO 2 retrieved from GOME and SCIAMACHY satellite instrument shows an increase of more than 50% over the years 1996–2004 (Richter et al., 2005). On the other hand in the US and Europe has been recorded a decrease of NO 2 emission and, over the years 1990–2000 in Europe has been estimated a decrease of the emission of more than 25% (Lovblad et al., 2004). The expected further reduction of NO 2 concentrations in Europe and the US for the next years asks for instruments with a better limit of detection (the lower measurable concentration) (European Environment Agency (EEA), 2008). NO 2 concentration has a dynamical range of more than 10 4 , in fact it varies from few pptv (parts per trillion by volume) in remote clean troposphere to more than 100 ppbv (parts per billion by volume) in very polluted urban areas. Measurements of NO 2 are challenging not only for the dynamic range of its concentration but for the rapid changes of the concentration with time (Thornton et al., 2000) and also for the difficulty of selective detection against the interferences due to species like: nitric acid (HNO 3 ) and peroxyacetyl nitrate (PAN) that may easily decompose into NO 2 . In the last decades a variety of techniques have been used for in situ observations of tropospheric NO 2 , such as chemiluminescence (CL) (Fehsenfeld et al., 1990), Differential Optical Absorption Spectros- copy (DOAS) (Harder et al., 1997), Tunable Diode Laser Absorption Spectroscopy (TDLAS) (Herndon et al., 2004), Cavity Ring Down Spectroscopy (CARS) (Osthoff et al., 2006; Hargrove et al., 2006) and Laser Induced Fluorescence (LIF) (Thornton et al., 2000; Mat- sumoto and Kajii, 2003; Taketani et al., 2007). Among these tech- niques, CL is the most common and commercially available. CL is used in almost all the networks for air quality observations because of its low cost and easy use, but the big shortcoming is that NO 2 is * Corresponding author. Center of Excellence CETEMPS, Universita’ degli studi di L’Aquila, Via Vetoio, 67010 Coppito, L’Aquila, Italy. Tel.: þ390862433084; fax: þ390862433089. E-mail address: piero.dicarlo@aquila.infn.it (P. Di Carlo). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.10.037 Atmospheric Environment 43 (2009) 970–977