Intercomparison of four airborne imaging DOAS systems for tropospheric NO<sub>2</sub> mapping – the AROMAPEX campaign

Abstract

Abstract. We present an intercomparison study of four airborne imaging DOAS instruments, dedicated to the retrieval and high-resolution mapping of tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs). The AROMAPEX campaign took place in Berlin, Germany, in April 2016 with the primary objective to test and intercompare the performance of experimental airborne imagers. The imaging DOAS instruments were operated simultaneously from two manned aircraft, performing synchronised flights: APEX (VITO–BIRA-IASB) was operated from DLR's DO-228 D-CFFU aircraft at 6.2 km in altitude, while AirMAP (IUP-Bremen), SWING (BIRA-IASB), and SBI (TNO–TU Delft–KNMI) were operated from the FUB Cessna 207T D-EAFU at 3.1 km. Two synchronised flights took place on 21 April 2016. NO2 slant columns were retrieved by applying differential optical absorption spectroscopy (DOAS) in the visible wavelength region and converted to VCDs by the computation of appropriate air mass factors (AMFs). Finally, the NO2 VCDs were georeferenced and mapped at high spatial resolution. For the sake of harmonising the different data sets, efforts were made to agree on a common set of parameter settings, AMF look-up table, and gridding algorithm. The NO2 horizontal distribution, observed by the different DOAS imagers, shows very similar spatial patterns. The NO2 field is dominated by two large plumes related to industrial compounds, crossing the city from west to east. The major highways A100 and A113 are also identified as line sources of NO2. Retrieved NO2 VCDs range between 1×1015 molec cm−2 upwind of the city and 20×1015 molec cm−2 in the dominant plume, with a mean of 7.3±1.8×1015 molec cm−2 for the morning flight and between 1 and 23×1015 molec cm−2 with a mean of 6.0±1.4×1015 molec cm−2 for the afternoon flight. The mean NO2 VCD retrieval errors are in the range of 22 % to 36 % for all sensors. The four data sets are in good agreement with Pearson correlation coefficients better than 0.9, while the linear regression analyses show slopes close to unity and generally small intercepts.

Observations of Atmospheric NO2 Using a New Low-Cost MAX-DOAS System

“…Table 2 presents the main technical characteristics of the Avantes UV-Vis spectrometer. [23,24,30,35].…”

“…The MAX-DOAS observations can be performed using static or mobile observations from cars, unmanned aerial vehicles (UAV), ships, airplanes, etc. [21][22][23][24].…”

The Airborne ROmanian Measurements of Aerosols and Trace gases (AROMAT) campaigns

“…To some extent, these quantities can be measured from an aircraft with the type of instrumentation deployed in the AROMAT activity. The ground albedo can be retrieved with the DOAS instruments by normalizing uncalibrated airborne radiances to a reference area with known albedo (Meier et al, 2017) or by using a radiometrically calibrated DOAS sensor (Tack et al, 2019). The NO 2 and aerosol profiles can be measured with in-situ instruments such as a CAPS NO 2 monitor and a nephelometer.…”

“…The unprecedented horizontal resolution enabled by the last generation of air-quality space-based instruments motivated preparatory field studies around polluted areas in North America (DISCOVER-AQ, https://discover-aq.larc.nasa.gov), Europe (AROMAT and AROMAPEX, Tack et al,2019) and Korea (KORUS-AQ, https://www-air.larc.nasa.gov/missions/korus-aq/). These campaign activities quantified key pollutants (NO 2 , SO 2 , O 3 , H 2 CO, and aerosols) and assessed practical observation capabilities of future satellite instruments while preparing for their validation.…”

“…In Europe, the two AROMAT campaigns, which took place in Romania in September 2014 and August 2015, demonstrated a suite of new instruments such as the Airborne imaging DOAS instrument for Measurements of Atmospheric Pollution (AirMAP, Schönhardt et al,2015;Meier et al,2017), the NO 2 sonde (Sluis et al, 2010), and the Small Whiskbroom Imager for atmospheric compositioN monitorinG (SWING, Merlaud et al,2018). Different airborne imagers were intercompared and further characterized during the AROMAPEX campaign in April 2016 (Tack et al, 2019).…”