Abstract
Abstract. A novel imaging-DOAS (differential optical absorption spectroscopy) instrument IMPACT (Imaging MaPper for AtmospheriC observaTions) is presented combining full-azimuthal pointing (360∘) with a large vertical coverage (∼41∘). Complete panoramic scans are acquired at a temporal resolution of ∼15 min, enabling the retrieval of NO2 vertical profiles over the entire panorama around the measurement site. IMPACT showed excellent agreement (correlation >99 %) with coincident multiaxis DOAS (MAX-DOAS) measurements during the Second Cabauw Intercomparison of Nitrogen Dioxide measuring Instruments (CINDI-2) campaign. The temporal variability of NO2 slant columns within a typical MAX-DOAS vertical scanning sequence could be resolved and was as large as 20 % in a case study under good viewing conditions. The variation of corresponding profiles and surface concentrations was even larger (40 %). This variability is missed when retrieving trace gas profiles based on standard MAX-DOAS measurements. The azimuthal distribution of NO2 around the measurement site showed inhomogeneities (relative differences) up to 120 % (on average 35 %) on short timescales (individual panoramic scans). This is more than expected for the semirural location. We explain this behavior by the transport of pollution. Exploiting the instrument's advantages, the plume's trajectory during a prominent transport event could be reconstructed. Finally, the potential for retrieving information about the aerosol phase function from O4 slant columns along multiple almucantar scans of IMPACT is demonstrated, with promising results for future studies.
Highlights
Nitrogen dioxide (NO2) is a prominent pollutant in the atmosphere and harmful for human health, causing damage to the respiratory system (Kampa and Castanas, 2008)
In contrast to most imagingDOAS instruments reported far, IMPACT is not restricted to selected scenes but provides full-azimuthal coverage around the measurement site
A complete panoramic scan is achieved in ∼ 15 min, allowing the retrieval of tropospheric trace gas profiles around the measurement site at high temporal resolution
Summary
Nitrogen dioxide (NO2) is a prominent pollutant in the atmosphere and harmful for human health, causing damage to the respiratory system (Kampa and Castanas, 2008). It originates primarily from NO that is produced in the equilibrium between N2 and O2 at high temperatures in combustion processes. The emitted NO reacts with ozone (O3) to form NO2. The sum of NO and NO2 is called NOx. The UV photolysis of NO2 produces NO and O atoms, which react with O2 in air to form O3. Under certain conditions for NOx and O3 in the troposphere, the Leighton photostationary state is achieved:
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