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Technical note: Preparation and purification of atmospherically relevant α-hydroxynitrate esters of monoterpenes

This report describes a simple, safe and effective method to prepare nitrate esters of terpenes (carene, limonene, perillic alcohol, beta-pinene and alpha-pinene) which are key oxidation products in the atmosphere. These compounds are implicated in the formation of secondary organic aerosols. A compilation of the relevant spectroscopic data has been presented. The availability of these compounds and their characterization data will enable further study of the structure–reactivity relationships.

Supercooled liquid water cloud observed, analysed, and modelled at the top ofthe planetary boundary layer above Dome C, Antarctica

Thin (~ 100 m) supercooled liquid water (SLW, water staying in liquid phase below 0 °C) clouds have been detected, analysed, and modelled over the Dome C (Concordia, Antarctica) station during the austral summer 2018–2019 using observations and meteorological analyses. The SLW clouds were observed at the top of the planetary boundary layer and the SLW content was always strongly underestimated by the model indicating an incorrect simulation of the surface energy budget of the Antarctic Plateau.

Description and Evaluation of the specified-dynamics experiment in the Chemistry-Climate Model Initiative

Atmospheric composition is strongly influenced by global-scale winds that are not always properly simulated in computer models. A common approach to correct for this bias is to relax or nudge to the observed winds. Here we systematically evaluate how well this technique performs across a large suite of chemistry–climate models in terms of its ability to reproduce key aspects of both the tropospheric and stratospheric circulations.

Technical note: LIMS observations of lower stratospheric ozone in the southern polar springtime of 1978

The Nimbus 7 limb infrared monitor of the stratosphere (LIMS) instrument operated from October 25, 1978, through May 28, 1979. This note focuses on the lower stratosphere of the southern hemisphere, subpolar regions in relation to the position of the polar vortex. Both LIMS ozone and nitric acid show reductions within the edge of the polar vortex at 46 hPa near 60° S from late October through mid-November 1978, indicating that there was a chemical loss of Antarctic ozone some weeks earlier.

LIMS observations of lower stratospheric ozone in the southern polar springtime of 1978">Read more

Methane emissions from the Munich Oktoberfest

We demonstrate for the first time that large festivals can be significant methane sources, though they are not included in emission inventories. We combined in situ measurements with a Gaussian plume model to determine the Oktoberfest emissions and show that they are not due solely to human biogenic emissions, but are instead primarily fossil fuel related. Our study provides the foundation to develop reduction policies for such events and new pathways to mitigate fossil fuel methane emissions.

Deconvolution of boundary layer depth and aerosol constraints on cloud water path in subtropical stratocumulus decks

Cloud water content and the number of droplets inside clouds covary with boundary layer depth. This covariation may amplify the change in water content due to a change in droplet number inferred from long-term observations. Taking this into account shows that the change in water content for increased droplet number in observations and high-resolution simulations agrees in shallow boundary layers. Meanwhile, deep boundary layers are under-sampled in process-scale simulations and observations.

Methanethiol, dimethyl sulfide and acetone over biologically productive waters in the southwest Pacific Ocean

Methanethiol (MeSH) is a reduced sulfur gas originating from phytoplankton, with a global ocean source of ~ 17 % of dimethyl sulfide (DMS). It has been little studied and is rarely observed over the ocean. In this work, MeSH was measured at much higher levels than previously observed (3–36 % of parallel DMS mixing ratios). MeSH could be a significant source of atmospheric sulfur over productive regions of the ocean, but its distribution, and its atmospheric impact, requires more investigation.

Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic

Using observations from instruments deployed to a small island in the southeast Atlantic, we study days when the atmospheric concentrations of particles near the surface are exceptionally low. Interestingly, these ultra-clean boundary layers occur in the same months as the smokiest boundary layers associated with biomass burning in Africa. We find evidence that enhancements in drizzle scavenging, on top of a seasonal maximum in cloudiness and precipitation, likely drive these conditions.

A new look at the environmental conditions favorable to secondary ice production

This study attempts identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals. It was found that in both mesoscale convective systems and frontal clouds, SIP was observed right above the melting layer and extended to the higher altitudes with colder temperatures. A principal conclusion of this work is that the freezing drop shattering mechanism is plausibly accounting for the measured ice concentrations in the observed condition.

Mapping the drivers of uncertainty in atmospheric selenium deposition with global sensitivity analysis

The amount of the micronutrient selenium in food largely depends on the amount and form of selenium in soil. The atmosphere acts as a source of selenium to soils through deposition, yet little information is available about atmospheric selenium cycling. Therefore, we built the first global atmospheric selenium model. Through sensitivity and uncertainty analysis we determine that selenium can be transported thousands of kilometers and that measurements of selenium emissions should be prioritized.

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