Porous Aerogels and Adsorption of Pollutants from Water and Air: A Review

Aerogels are open, three-dimensional, porous materials characterized by outstanding properties, such as low density, high porosity, and high surface area. They have been used in various fields as adsorbents, catalysts, materials for thermal insulation, or matrices for drug delivery. Aerogels have been successfully used for environmental applications to eliminate toxic and harmful substances—such as metal ions or organic dyes—contained in wastewater, and pollutants—including aromatic or oxygenated volatile organic compounds (VOCs)—contained in the air. This updated review on the use of different aerogels—for instance, graphene oxide-, cellulose-, chitosan-, and silica-based aerogels—provides information on their various applications in removing pollutants, the results obtained, and potential future developments.

Atmospheric Impacts of COVID-19 on NOx and VOC Levels over China Based on TROPOMI and IASI Satellite Data and Modeling

China was the first country to undergo large-scale lockdowns in response to the pandemic in early 2020 and a progressive return to normalization after April 2020. Spaceborne observations of atmospheric nitrogen dioxide (NO2) and oxygenated volatile organic compounds (OVOCs), including formaldehyde (HCHO), glyoxal (CHOCHO), and peroxyacetyl nitrate (PAN), reveal important changes over China in 2020, relative to 2019, in response to the pandemic-induced shutdown and the subsequent drop in pollutant emissions. In February, at the peak of the shutdown, the observed declines in OVOC levels were generally weaker (less than 20%) compared to the observed NO2 reductions (−40%). In May 2020, the observations reveal moderate decreases in NO2 (−15%) and PAN (−21%), small changes in CHOCHO (−3%) and HCHO (6%). Model simulations using the regional model MAGRITTEv1.1 with anthropogenic emissions accounting for the reductions due to the pandemic explain to a large extent the observed changes in lockdown-affected regions. The model results suggest that meteorological variability accounts for a minor but non-negligible part (~−5%) of the observed changes for NO2, whereas it is negligible for CHOCHO but plays a more substantial role for HCHO and PAN, especially in May. The interannual variability of biogenic and biomass burning emissions also contribute to the observed variations, explaining e.g., the important column increases of NO2 and OVOCs in February 2020, relative to 2019. These changes are well captured by the model simulations.

Oxidation of low-molecular-weight organic compounds in cloud droplets: development of the Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC) in CAABA/MECCA (version 4.5.0)

The Jülich Aqueous-phase Mechanism of Organic Chemistry (JAMOC) is developed and implemented in the Module Efficiently Calculating the Chemistry of the Atmosphere (MECCA; version 4.5.0). JAMOC is an explicit in-cloud oxidation scheme for oxygenated volatile organic compounds (OVOCs), suitable for global model applications. It is based on a subset of the comprehensive Cloud Explicit Physico-chemical Scheme (CLEPS; version 1.0). The phase transfer of species containing up to 10 carbon atoms is included, and a selection of species containing up to 4 carbon atoms reacts in the aqueous phase. In addition, the following main advances are implemented: (1) simulating hydration and dehydration explicitly; (2) taking oligomerisation of formaldehyde, glyoxal, and methylglyoxal into account; (3) adding further photolysis reactions; and (4) considering gas-phase oxidation of new outgassed species. The implementation of JAMOC in MECCA makes a detailed in-cloud OVOC oxidation model readily available for box as well as for regional and global simulations that are affordable with modern supercomputing facilities. The new mechanism is tested inside the box model Chemistry As A Boxmodel Application (CAABA), yielding reduced gas-phase concentrations of most oxidants and OVOCs except for the nitrogen oxides.

Measurement report: Observation-based formaldehyde production rates and their relation to OH reactivity around the Arabian Peninsula

Formaldehyde (HCHO) is the most abundant aldehyde in the troposphere. While its background-mixing ratio is mostly determined by the oxidation of methane, in many environments, especially in the boundary layer, HCHO can have a large variety of precursors, in particular biogenic and anthropogenic volatile organic compounds (VOCs) and their oxidation products. Here we present shipborne observations of HCHO, hydroxyl radical (OH) and OH reactivity (R(OH)), obtained during the Air Quality and Climate Change in the Arabian Basin (AQABA) campaign in summer 2017. The loss rate of HCHO was inferred from its reaction with OH, measured photolysis rates, and dry deposition. In photo-stationary state, the HCHO loss is balanced by production via OH initiated degradation of volatile organic compounds (VOCs), photolysis of oxygenated volatile organic compounds (OVOCs) and the ozonolysis of alkenes. The slope α from a scatter plot of the HCHO production rate versus the product of R(OH) and OH yields the fraction of R(OH) that contributes to HCHO production. Values of α varied between less than 2 % in rather clean air over the Arabian Sea and the southern Red Sea, and up to 32 % over the polluted Arabian Gulf (also known as the Persian Gulf), signifying that polluted areas harbour a larger variety of HCHO precursors. The HCHO yield from R(OH) depends on the absolute and relative contributions of alkanes, alkenes, oxygenated volatile organic compounds (OVOCs) and aromatics to R(OH), while no significant correlation to NOx mixing ratios was found, indicating that HCHO production was not NOx limited.

On-line SPME derivatization for the sensitive determination of multi-oxygenated volatile compounds in air

Multi-oxygenated volatile organic compounds are important markers of air pollution and precursors of ozone and secondary aerosols in both polluted and remote environments. Herein, their accurate determination was enhanced. The approach was based on an automated system for active sampling and on-fiber derivatization coupled with GC-MS technique. The method capability was determined for different compound families, such as aldehydes, ketones, α-dicarbonyls, hydroxy-aldehydes, hydroxy-ketones and, carboxylic acids. A good accuracy (