Response to the Reviewer 3

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 setup, 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 field experiment at a forested location with urban influence where 20 NO x levels were between 0.12 and 22 parts per billion by volume (ppb v). Based on the field results, the limit of detection is estimated at 5-10 parts per trillion by volume (ppt v) in 60 s at a signal to noise ratio (SNR) of 2. The overall accuracy and precision of the instrument are better than 5 % (1 σ) and 0.5 % + 3 ppt v (1 σ min-1), respectively. A comparison of nitrogen dioxide measurements based on several techniques during the field campaign is presented to explore methodic differences.