Atmospheric chemistry

Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary approach of research and draws on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. Research is increasingly connected with other areas of study such as climatology. The composition and chemistry of the Earth's atmosphere is of importance for several reasons, but primarily because of the interactions between the atmosphere and living organisms. The composition of the Earth's atmosphere changes as result of natural processes such as volcano emissions, lightning and bombardment by solar particles from corona. It has also been changed by human activity and some of these changes are harmful to human health, crops and ecosystems. Examples of problems which have been addressed by atmospheric chemistry include acid rain, ozone depletion, photochemical smog, greenhouse gases and global warming. Atmospheric chemists seek to understand the causes of these problems, and by obtaining a theoretical understanding of them, allow possible solutions to be tested and the effects of changes in government policy evaluated. Besides the more major components listed above, Earth's atmosphere also has many trace gas species that vary significantly depending on nearby sources and sinks. These trace gases can include compounds such as CFCs/HCFCs which are particularly damaging to the ozone layer, and H2S which has a characteristic foul odor of rotten eggs and can be smelt in concentrations as low as 0.47 ppb. Some approximate amounts near the surface of some additional gases are listed below. In addition to gases, the atmosphere contains particulates as aerosol, which includes for example droplets, ice crystals, bacteria, and dust. The ancient Greeks regarded air as one of the four elements.

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Flowing Gas Experiments Reveal Mechanistic Details of Interfacial Reactions on a Molecular Level at Knudsen Flow Conditions

Christian Ludwig, Michel Rossi, Riccardo Iannarelli

Knudsen flow experiments and its interpretation in terms of adsorption/desorption kinetics as well as quantitative uptake on substrates of interest is presented together with the description of critical design parameters of the Knudsen Flow Reactor (KFR). Hitherto focused almost exclusively on the uptake phase exposing a virgin substrate to interacting gases, we now extend the experiment and its interpretation to the desorption phase at ambient temperature. We present analytical expressions for different experimental situations in terms of adsorption (ka), desorption (kd) and effusion (ke) rate constants. The measurement of kd leads to surface residence times (1/kd) obtained under the same experimental conditions as the uptake (ka) that results in the determination of the Langmuir equilibrium constant KL = ka/kd. We emphasize the interaction of semivolatile organic probe gases and small polar molecules with amorphous carbon and mineral dust materials at ambient temperatures. The latter leads to a molecular characterization scheme based on the use of up to ten different reactive probe gases. After saturation of the uptake of each probe gas this results in a reactivity map of the interface. Several examples are used to underline the broad applicability of the technique such as the silver/air (Ag) interface and the reactivity of TiO2 materials towards uptake of CO2 and CH3OH. Following characterization of several types of amorphous carbon a model incorporating several structural elements in agreement with the reactive gas titration is proposed. For instance, an interface that is at the same time weakly basic and strongly reducing is composed of pyrones and hydroquinones whose simultaneous occurrence leads to stable free radicals that may play a role in atmospheric chemistry (EPFR). The question is raised what makes an interface hydrophobic in terms of surface functional groups when interacting with small polar molecules such as H2O(D2O), HCl, NO2 and NH2OH. Multidiagnostic studies of heterogeneous reactions are enabled using stirred-flow reactors (SRF) that are a logical extension of the KFR approach thus relaxing the Knudsen flow requirements. Previous work using SRF on low-temperature substrates such as H2O ices is highlighted that may be of interest to the exoplanetary and space sciences community.

2022

Exploring the coupled ocean and atmosphere system with a data science approach applied to observations from the Antarctic Circumnavigation Expedition

Julia Schmale, Andrea Baccarini, Alireza Moallemi, Irina Gorodetskaya, Christel Sybille Hassler, Katherine Colby Leonard, Robin Lewis Modini, Jenny Thomas, Sebastian Johannes Heinz-Josef Landwehr, Fernando Perez Cruz

The Southern Ocean is a critical component of Earth's climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small scale to the large scale. As a result, our knowledge of this vast region remains largely incomplete. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, and ocean biogeochemistry and microbiology. This circumpolar cruise included visits to 12 remote islands, the marginal ice zone, and the Antarctic coast. Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter-term variations, geographic setting of environmental processes, and interactions between them over the duration of 90 d. To reduce the dimensionality and complexity of the dataset and make the relations between variables interpretable we applied an unsupervised machine learning method, the sparse principal component analysis (sPCA), which describes environmental processes through 14 latent variables. To derive a robust statistical perspective on these processes and to estimate the uncertainty in the sPCA decomposition, we have developed a bootstrap approach. Our results provide a proof of concept that sPCA with uncertainty analysis is able to identify temporal patterns from diurnal to seasonal cycles, as well as geographical gradients and “hotspots” of interaction between environmental compartments. While confirming many well known processes, our analysis provides novel insights into the Southern Ocean water cycle (freshwater fluxes), trace gases (interplay between seasonality, sources, and sinks), and microbial communities (nutrient limitation and island mass effects at the largest scale ever reported). More specifically, we identify the important role of the oceanic circulations, frontal zones, and islands in shaping the nutrient availability that controls biological community composition and productivity; the fact that sea ice controls sea water salinity, dampens the wave field, and is associated with increased phytoplankton growth and net community productivity possibly due to iron fertilisation and reduced light limitation; and the clear regional patterns of aerosol characteristics that have emerged, stressing the role of the sea state, atmospheric chemical processing, and source processes near hotspots for the availability of cloud condensation nuclei and hence cloud formation. A set of key variables and their combinations, such as the difference between the air and sea surface temperature, atmospheric pressure, sea surface height, geostrophic currents, upper-ocean layer light intensity, surface wind speed and relative humidity played an important role in our analysis, highlighting the necessity for Earth system models to represent them adequately. In conclusion, our study highlights the use of sPCA to identify key ocean–atmosphere interactions across physical, chemical, and biological processes and their associated spatio-temporal scales. It thereby fills an important gap between simple correlation analyses and complex Earth system models. The sPCA processing code is available as open-access from the following link: https://renkulab.io/gitlab/ACE-ASAID/spca-decomposition (last access: 29 March 2021). As we show here, it can be used for an exploration of environmental data that is less prone to cognitive biases (and confirmation biases in particular) compared to traditional regression analysis that might be affected by the underlying research question.

2021

In-situ observations of aerosol-cloud interactions in Ny-Ålesund, Svalbard, during fall 2019 and spring 2020

Athanasios Nenes, Ghislain Gilles Jean-Michel Motos, Paraskevi Georgakaki, Jörg Wieder

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). Specifically, the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., under review), could strongly vary between the fall to winter months, with pristine-like conditions, and the higher particle concentrations generally found in spring, known as the arctic haze. First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of spring 2021 compared to those of fall 2020. In addition, we found relatively low values of the aerosol hygroscopic parameter κ, generally below 0.3, consistently with previous studies in the arctic region (Moore et al., 2011). Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A. and Nenes, A.: On the drivers of droplet variability in Alpine mixed-phase clouds, , 34, under review. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Moore, R. H., Bahreini, R., Brock, C. A., Froyd, K. D., Cozic, J., Holloway, J. S., Middlebrook, A. M., Murphy, D. M. and Nenes, A.: Hygroscopicity and composition of Alaskan Arctic CCN during April 2008, Atmospheric Chemistry and Physics, 11(22), 11807–11825, https://doi.org/10.5194/acp-11-11807-2011, 2011.

2021

Air pollution

Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. It is also the contamination of indoor or outdoor surrounding either by chemical activities, physical or biological agents that alters the natural features of the atmosphere. There are many different types of air pollutants, such as gases (including ammonia, carbon monoxide, sulfur dioxide, nitrous oxides, methane and chlorofluorocarbons), particulates (both organic and inorganic), and biological molecules.

Atmospheric chemistry

Ozone–oxygen cycle

The ozone–oxygen cycle is the process by which ozone is continually regenerated in Earth's stratosphere, converting ultraviolet radiation (UV) into heat. In 1930 Sydney Chapman resolved the chemistry involved. The process is commonly called the Chapman cycle by atmospheric scientists. Most of the ozone production occurs in the tropical upper stratosphere and mesosphere. The total mass of ozone produced per day over the globe is about 400 million metric tons.

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