Abstract. A Zeppelin airship was used as a platform for in situ measurements of greenhouse gases and short-lived air pollutants within the planetary boundary layer (PBL) in Germany. A novel quantum cascade laser-based multi-compound gas analyzer (MIRO Analytical AG) was deployed to simultaneously measure in situ concentrations of greenhouse gases (CO2, N2O, H2O, and CH4) and air pollutants (CO, NO, NO2, O3, SO2, and NH3) with high precision at a measurement rate of 1 Hz. These measurements were complemented by electrochemical sensors for NO, NO2, Ox (NO2 + O3), and CO, an optical particle counter, temperature, humidity, altitude, and position monitoring. Instruments were operated remotely without the need for on-site interactions. Three 2-week campaigns were conducted in 2020 comprising commercial passenger as well as targeted flights over multiple German cities including Cologne, Mönchengladbach, Düsseldorf, Aachen, Frankfurt, but also over industrial areas and highways. Vertical profiles of trace gases were obtained during the airship landing and take-off. Diurnal variability of the Zeppelin vertical profiles was compared to measurements from ground-based monitoring stations with a focus on nitrogen oxides and ozone. We find that their variability can be explained by the increasing nocturnal boundary layer height from early morning towards midday, an increase in emissions during rush hour traffic, and the rapid photochemical activity midday. Higher altitude (250–450 m) NOx to CO ratios are further compared to the 2015 EDGAR emission inventory to find that pollutant concentrations are influenced by transportation and residential emissions as well as manufacturing industries and construction activity. Finally, we report NOx and CO concentrations from one plume transect originating from a coal power plant and compare it to the EURopean Air pollution Dispersion-Inverse Modell (EURAD-IM) model to find agreement within 15 %. However, due to the increased contribution of solar and wind energy and the impact of lockdown measures the power plant was operating at max. 50 % capacity; therefore, possible overestimation of emissions by the model cannot be excluded.

Air quality measurements usually consist of ground-based instrumentation at fixed locations. However, vertical profiles of pollutants are of interest for understanding processes, distribution, dilution and concentration. Therefore, a multicopter system has been developed to investigate the vertical distribution of the concentration of aerosol particles, black carbon, ozone, nitrogen oxides (NOx) and carbon monoxide and the meteorological parameters of temperature and humidity. This article presents the requirements by different users, the setup of the quadrocopter system, the instrumentation and the results of first applications. The vertical distribution of particulate matter next to a highway was strongly related to atmospheric stratification, with different concentrations below and above the temperature inversion present in the morning. After the qualification phase described in this article, two identically equipped multicopters will be used upwind and downwind of line or diffuse sources such as highways or urban areas to quantify the influence of their emissions on the local air quality.

<p>For the Jülich Atmospheric Chemistry Project campaign (JULIAC) at Forschungszentrum Jülich (FZJ), Germany, the atmospheric simulation chamber SAPHIR was used as a large photochemical flow reactor to study tropospheric chemistry in a rural environment. From an inlet at 50 m height above ground, ambient air was continuously fed through the chamber and exposed to natural solar radiation. A large set of instrumentation allowed for the measurement of NO, NO<sub>2</sub>, NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, ClNO<sub>2</sub>, HCHO, HONO, RO<sub>2</sub>, HO<sub>2</sub>, OH, k<sub>OH</sub>, CO, CO<sub>2</sub>, CH<sub>4</sub>, H2O, VOCs, aerosols, and O<sub>3</sub> in the sampled air. Intensive measurement phases were performed for one month in each season of 2019. One goal of the JULIAC project was to test our understanding of the chemistry of tropospheric ozone formation.</p><p>To determine the photochemical net ozone production rate in atmospheric air, O<sub>X</sub> (O<sub>3</sub> + NO<sub>2</sub>) was measured by commercial instruments at the inlet and inside the well mixed chamber. Through careful characterization of the flow reactor it is possible to predict a reference concentration of O<sub>X</sub> from the inflow measurements which excludes photochemistry. The measured O<sub>X</sub> concentration in the chamber was compared with the reference. At night, both concentrations agreed, but during daytime the chamber concentration was enhanced due to photochemical O<sub>X</sub> production. The difference was used to determine diurnal profiles of the net ozone production with 1 hour time resolution. Production rates up to 15 ppbv/h were observed with an accuracy of 1 ppb<sub>V</sub>/h. Uncertainties in the offsets of the instruments measuring at the inlet and inside the chamber were identified as large contributors (~0.5 ppb<sub>V</sub>/h) to the overall error. The measured net ozone production rates are compared to production rates that are expected from the reactions of peroxy radicals (HO<sub>2</sub>, RO<sub>2</sub>) with NO, all of which were concurrently measured. The analysis includes other chemical reactions that may produce or destroy ozone or NO<sub>2</sub> in the lower troposphere.</p><p>Good agreement (within 10%) between measured and calculated ozone production rates during the spring and summer campaigns confirms that the main contributions to daytime O<sub>X</sub> production and destruction in the troposphere are overall governed by the reactions of HO<sub>2</sub> and RO<sub>2</sub> with NO and the reaction of OH radicals with NO<sub>2</sub> in the rural environment studied in this project. The presentation will include a discussion of the role of the OH reactivity from VOCs for the local photochemical ozone production.</p>

SupplementFigure S1: (a) Electronical and mechanical components of the sensor setup we currently use. It is slightly modified, mainly for weight 10 and space reasons, compared to what was used for this study, but the functionality is the same. (b) Bottom view of the setup. PCB: printed circuit board; ECS: electrochemical sensor; T & RH: temperature and relative humidity.

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