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.
This work reported new voltammetric/amperometric-based protocols using a commercial boron-doped diamond (BDD) electrode for simple and fast simultaneous detection of sulfide and nitrite from water. Square-wave voltammetry operated under the optimized working conditions of 0.01 V step potential, 0.5 V modulation amplitude and 10 Hz frequency allowed achieving the best electroanalytical parameters for the simultaneous detection of nitrite and sulfide. For practical in-field detection applications, the multiple-pulsed amperometry technique was operated under optimized conditions, i.e., −0.5 V/SCE for a duration of 0.3 s as conditioning step, +0.85 V/SCE for a duration of 3 s that assure the sulfide oxidation and +1.25 V/SCE for a duration of 0.3 s, where the nitrite oxidation occurred, which allowed the simultaneously detection of sulfide and nitrite without interference between them. Good accuracy was found for this protocol in comparison with standardized methods for each anion. Also, no interference effect was found for the cation and anion species, which are common in the water matrix.
Abstract. The Airborne ROmanian Measurements of Aerosols and Trace gases (AROMAT) campaigns took place in Romania in September 2014 and August 2015. They focused on two sites: the Bucharest urban area and large power plants in the Jiu Valley. The main objectives of the campaigns were to test recently developed airborne observation systems dedicated to air quality studies and to verify their applicability for the validation of space-borne atmospheric missions such as the TROPOspheric Monitoring Instrument (TROPOMI)/Sentinel-5 Precursor (S5P). We present the AROMAT campaigns from the perspective of findings related to the validation of tropospheric NO2, SO2, and H2CO. We also quantify the emissions of NOx and SO2 at both measurement sites. We show that tropospheric NO2 vertical column density (VCD) measurements using airborne mapping instruments are well suited for satellite validation in principle. The signal-to-noise ratio of the airborne NO2 measurements is an order of magnitude higher than its space-borne counterpart when the airborne measurements are averaged at the TROPOMI pixel scale. However, we show that the temporal variation of the NO2 VCDs during a flight might be a significant source of comparison error. Considering the random error of the TROPOMI tropospheric NO2 VCD (σ), the dynamic range of the NO2 VCDs field extends from detection limit up to 37 σ (2.6×1016 molec. cm−2) and 29 σ (2×1016 molec. cm−2) for Bucharest and the Jiu Valley, respectively. For both areas, we simulate validation exercises applied to the TROPOMI tropospheric NO2 product. These simulations indicate that a comparison error budget closely matching the TROPOMI optimal target accuracy of 25 % can be obtained by adding NO2 and aerosol profile information to the airborne mapping observations, which constrains the investigated accuracy to within 28 %. In addition to NO2, our study also addresses the measurements of SO2 emissions from power plants in the Jiu Valley and an urban hotspot of H2CO in the centre of Bucharest. For these two species, we conclude that the best validation strategy would consist of deploying ground-based measurement systems at well-identified locations.
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