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Detailed knowledge of the physical and chemical properties and sources of particles that form clouds is especially important in pristine areas like the Arctic, where particle concentrations are often low and observations are sparse. Here, we present in situ cloud and aerosol measurements from the central Arctic Ocean in August-September 2018 combined with air parcel source analysis. We provide direct experimental evidence that Aitken mode particles (particles with diameters less than or similar to 70 nm) significantly contribute to cloud condensation nuclei (CCN) or cloud droplet residuals, especially after the freeze-up of the sea ice in the transition toward fall. These Aitken mode particles were associated with air that spent more time over the pack ice, while size distributions dominated by accumulation mode particles (particles with diameters greater than or similar to 70 nm) showed a stronger contribution of oceanic air and slightly different source regions. This was accompanied by changes in the average chemical composition of the accumulation mode aerosol with an increased relative contribution of organic material toward fall. Addition of aerosol mass due to aqueous-phase chemistry during in-cloud processing was probably small over the pack ice given the fact that we observed very similar particle size distributions in both the whole-air and cloud droplet residual data. These aerosol-cloud interaction observations provide valuable insight into the origin and physical and chemical properties of CCN over the pristine central Arctic Ocean., Journal of Geophysical Research: Atmospheres, 127 (11), ISSN:0148-0227, ISSN:2169-897X

NO2 concentrations were measured by various instruments during the NO3Comp campaign at the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich, Germany, in June 2007. Analytical methods included photolytic conversion with chemiluminescence (PC-CLD), broadband cavity ring-down spectroscopy (BBCRDS), pulsed cavity ring-down spectroscopy (CRDS), incoherent broadband cavity-enhanced absorption spectroscopy (IBB\-CEAS), and laser-induced fluorescence (LIF). All broadband absorption spectrometers were optimized for the detection of the main target species of the campaign, NO3, but were also capable of detecting NO2 simultaneously with reduced sensitivity. NO2 mixing ratios in the chamber were within a range characteristic of polluted, urban conditions, with a maximum mixing ratio of approximately 75 ppbv. The overall agreement between measurements of all instruments was excellent. Linear fits of the combined data sets resulted in slopes that differ from unity only within the stated uncertainty of each instrument. Possible interferences from species such as water vapor and ozone were negligible under the experimental conditions.

The intertidal beach is very dynamic and is characterized by high sediment transport rates which may result in large topographic changes. Measuring techniques are well developed for both sediment transport and beach topography but the quantification of transport remains difficult. This paper provides an in-depth review of studies that cross-checked sediment transport measured underwater to transport derived from topographic change and/or predictive formulas to optimize future measuring campaigns in the intertidal zone. Based on these studies it is strongly recommended to measure sediment transport at multiple locations in the intertidal zone, although it is recognized that this is costly. When the suspended sediment is mixed and vertically stratified, it should be gauged over the entire water column. Acoustic backscatter intensity can be used for this purpose but needs to be corrected for grain size and turbulence. When cross-checking measured sediment transport rates with beach volume changes topographic profiles may not be sufficient. Instead, laser scanning of the beach is recommended. Additionally, valuable insights can be obtained from continuously measuring the beach topography. When beach topography is only measured during low tide, wind-driven transport should be taken into account during energetic conditions. It is deemed necessary to improve sensors to measure bed load transport and suspended sediment transport close to the bed and to further improve formulas to predict sediment transport. With the suggestions given in this paper it is encouraged to perform field investigations of sediment transport in the intertidal zone to improve our knowledge of the intertidal beach morphodynamics.

Remote sensing helps foster our understanding of inland water processes allowing a synoptic view of water quality parameters. In the context of global monitoring of inland waters, we demonstrate the benefit of combining in-situ water analysis, hydrodynamic modelling and remote sensing for investigating biogeochemical processes. This methodology has the potential to be used at global scales. We take the example of four Landsat-8 scenes acquired by the OLI sensor and MODIS-Aqua imagery over Lake Geneva (France—Switzerland) from spring to early summer 2014. Remotely sensed data suggest a strong temporal and spatial variability during this period. We show that combining the complementary spatial, spectral and temporal resolutions of these sensors allows for a comprehensive characterization of estuarine, littoral and pelagic near-surface features. Moreover, by combining in-situ measurements, biogeochemical analysis and hydrodynamic modelling with remote sensing data, we can link these features to river intrusion and calcite precipitation processes, which regularly occur in late spring or early summer. In this context, we propose a procedure that can be used to monitor whiting events in temperate lakes worldwide.