Abstract
Abstract. GANDALF (Gas Analyzer for Nitrogen Dioxide Applying Laser-induced Fluorescence), a new instrument for the detection of nitrogen dioxide based on the laser-induced fluorescence (LIF) technique, is presented in this paper. GANDALF is designed for ground-based and airborne deployment with a robust calibration system. In the current set-up, it uses a multi-mode diode laser (447–450 nm) and performs in situ, continuous, and autonomous measurements with a laser pulse repetition rate of 5 MHz. The performance of GANDALF was tested during the summer of year 2011 (15 August–10 September) in a field experiment at Kleiner Feldberg, Germany. The location is within a forested region with an urban influence, where NOx levels were between 0.12 and 22 parts per billion by volume (ppb). Based on the field results, the limit of detection is estimated at 5–10 parts per trillion by volume (ppt) in 60 s at a signal-to-noise ratio (SNR) of 2. The overall accuracy and precision of the instrument are better than 5 % (1σ) and 0.5 %+3 ppt (1σ min−1), respectively. A comparison of nitrogen dioxide measurements based on several techniques during the field campaign PARADE 2011 is presented to explore methodic differences.
Highlights
Tropospheric nitric oxide (NO) and nitrogen dioxide (NO2) are key species in atmospheric chemistry and are strongly coupled due to their fast photochemical interconversion generally combined as NOx (= NO + NO2)
It is determined using NO2 concentrations generated by gas phase titration of NO to NO2 by means of O3 (Reaction R3) similar to the one described by Ryerson et al (2000)
GANDALF has been tailored towards a compact design with a low detection limit (5–10 ppt min−1) and high precision (0.5 % + 3 ppt min−1), making it capable of measuring NO2 throughout the troposphere with a time resolution of 1 min
Summary
Tropospheric nitric oxide (NO) and nitrogen dioxide (NO2) are key species in atmospheric chemistry and are strongly coupled due to their fast photochemical interconversion generally combined as NOx (= NO + NO2). Techniques like cavity ring-down absorption spectroscopy (Osthoff et al, 2006), tunable diode laser absorption spectroscopy (Herndon et al, 2004), cavity-enhanced absorption spectroscopy (Wojtas et al, 2007), cavity-enhanced differential optical absorption spectroscopy (Platt et al, 2009), and cavity attenuated phase shift spectroscopy (Ge et al, 2013) provide direct in situ detection of NO2. The LIF method for NO2 provides highly selective and sensitive measurements and it has already been demonstrated successfully in the past with detection limits reaching down to about 5 ppt min−1 (Thornton et al, 2000; Matsumoto and Kajii, 2003). Being the first deployment of GANDALF, this opportunity provided the means for a detailed comparison to other methods under real atmospheric conditions
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