Interferences on aerosol acidity quantification due to gas-phase ammonia uptake onto acidic sulfate filter samples

Measurements of the mass concentration and chemical speciation of aerosols are important to investigate their chemical and physical processing from near emission sources to the most remote regions of the atmosphere. A common method to analyze aerosols is to collect them onto filters and analyze the filters offline; however, biases in some chemical components are possible due to changes in the accumulated particles during the handling of the samples. Any biases would impact the measured chemical composition, which in turn affects our understanding of numerous physicochemical processes and aerosol radiative properties. We show, using filters collected onboard the NASA DC-8 and NSF C-130 during six different aircraft campaigns, a consistent, substantial difference in ammonium mass concentration and ammonium-to-anion ratios when comparing the aerosols collected on filters versus an Aerodyne aerosol mass spectrometer (AMS). Another online measurement is consistent with the AMS in showing that the aerosol has lower ammonium-to-anion ratios than obtained by the filters. Using a gas uptake model with literature values for accommodation coefficients, we show that for ambient ammonia mixing ratios greater than 10 ppbv, the timescale for ammonia reacting with acidic aerosol on filter substrates is less than 30 s (typical filter handling time in the aircraft) for typical aerosol volume distributions. Measurements of gas-phase ammonia inside the cabin of the DC-8 show ammonia mixing ratios of 45±20 ppbv, consistent with mixing ratios observed in other indoor environments. This analysis enables guidelines for filter handling to reduce ammonia uptake. Finally, a more meaningful limit of detection for University of New Hampshire Soluble Acidic Gases and Aerosol (SAGA) filters collected during airborne campaigns is ∼0.2 µg sm−3 of ammonium, which is substantially higher than the limit of detection of ion chromatography. A similar analysis should be conducted for filters that collect inorganic aerosol and do not have ammonia scrubbers and/or are handled in the presence of human ammonia emissions

An in situ gas chromatograph with automatic detector switching between PTR- and EI-TOF-MS: isomer-resolved measurements of indoor air

We have developed a field-deployable gas chromatograph (GC) with thermal desorption preconcentration (TDPC), which is demonstrated here with automatic detector switching between two high-resolution time-of-flight mass spectrometers (TOF-MSs) for in situ measurements of volatile organic compounds (VOCs). This system provides many analytical advances, including acquisition of fast time&ndash;response data in tandem with molecular speciation and two types of mass spectral information for each resolved GC peak: molecular ion identification from Vocus proton transfer reaction (PTR) TOF-MS and fragmentation pattern from electron ionization (EI) TOF-MS detection. This system was deployed during the 2018 ATHLETIC campaign at the University of Colorado Dal Ward Athletic Center in Boulder, Colorado, where it was used to characterize VOC emissions in the indoor environment. The addition of the TDPC-GC increased the Vocus sensitivity by a factor of 50 due to preconcentration over a 6&thinsp;min GC sample time versus direct air sampling with the Vocus, which was operated with a time resolution of 1&thinsp;Hz. The GC-TOF methods demonstrated average limits of detection of 1.6&thinsp;ppt across a range of monoterpenes and aromatics. Here, we describe the method to use the two-detector system to conclusively identify a range of VOCs including hydrocarbons, oxygenates, and halocarbons, along with detailed results including the quantification of anthropogenic monoterpenes, where limonene accounted for 47&thinsp;%&ndash;80&thinsp;% of the indoor monoterpene composition. We also report the detection of dimethylsilanediol (DMSD), an organosiloxane degradation product, which was observed with dynamic temporal behavior distinct from volatile organosiloxanes (e.g., decamethylcyclopentasiloxane, D5 siloxane). Our results suggest DMSD is produced from humidity-dependent heterogeneous reactions occurring on surfaces in the indoor environment, rather than formed through gas-phase oxidation of volatile siloxanes. &nbsp;</p

Genomic organization, expression, and phylogenetic analysis of Ca2+ channel β4 genes in 13 vertebrate species

The Ca2+ channel β-subunits, encoded by CACNB genes 1–4, are membrane-associated guanylate kinase (MAGUK) proteins. As auxiliary subunits of voltage-gated Ca2+ channels, the β-subunits facilitate membrane trafficking of the pore-forming α1 subunits and regulate voltage-dependent channel gating. In this report, we investigate whether two zebrafish β4 genes, β4.1 and β4.2, have diverged in structure and function over time. Comparative expression analyses indicated that β4.1 and β4.2 were expressed in separable domains within the developing brain and other tissues. Alternative splicing in both genes was subject to differential temporal and spatial regulation, with some organs expressing different subsets of β4.1 and β4.2 transcript variants. We used several genomic tools to identify and compare predicted cDNAs for eight teleost and five tetrapod β4 genes. Teleost species had either one or two β4 paralogs, whereas each tetrapod species contained only one. Teleost β4.1 and β4.2 genes had regions of sequence divergence, but compared with tetrapod β4s, they exhibited similar exon/intron structure, strong conservation of residues involved in α1 subunit binding, and similar 5′ alternative splicing. Phylogenetic results are consistent with the duplicate teleost β4 genes resulting from the teleost whole genome duplication. Following duplication, the β4.1 genes have evolved faster than β4.2 genes. We identified disproportionately large second and third introns in several β4 genes, which we propose may provide regulatory elements contributing to their differential tissue expression. In sum, both mRNA expression data and phylogenetic analysis support the evolutionary divergence of β4.1 and β4.2 subunit function

Overview of ICARUSA Curated, Open Access, Online Repository for Atmospheric Simulation Chamber Data

Atmospheric simulation chambers continue to be indispensable tools for research in the atmospheric sciences. Insights from chamber studies are integrated into atmospheric chemical transport models, which are used for science-informed policy decisions. However, a centralized data management and access infrastructure for their scientific products had not been available in the United States and many parts of the world. ICARUS (Integrated Chamber Atmospheric data Repository for Unified Science) is an open access, searchable, web-based infrastructure for storing, sharing, discovering, and utilizing atmospheric chamber data [https://icarus.ucdavis.edu]. ICARUS has two parts: a data intake portal and a search and discovery portal. Data in ICARUS are curated, uniform, interactive, indexed on popular search engines, mirrored by other repositories, version-tracked, vocabulary-controlled, and citable. ICARUS hosts both legacy data and new data in compliance with open access data mandates. Targeted data discovery is available based on key experimental parameters, including organic reactants and mixtures that are managed using the PubChem chemical database, oxidant information, nitrogen oxide (NOx) content, alkylperoxy radical (RO2) fate, seed particle information, environmental conditions, and reaction categories. A discipline-specific repository such as ICARUS with high amounts of metadata works to support the evaluation and revision of atmospheric model mechanisms, intercomparison of data and models, and the development of new model frameworks that can have more predictive power in the current and future atmosphere. The open accessibility and interactive nature of ICARUS data may also be useful for teaching, data mining, and training machine learning models