Search for: All records

Emissions from large-scale fires significantly contribute to the atmospheric burden of primary organic aerosol (OA). 

Relative humidity, NO_x, and NH₃can all alter the molecular, optical, and hygroscopic properties of naphthalene SOAs, with a complex synergy between these factors. 

Abstract. Secondary organic aerosol (SOA) generated from the photooxidationof aromatic compounds in the presence of oxides of nitrogen (NOx) isknown to efficiently absorb ultraviolet and visible radiation. With exposureto sunlight, the photodegradation of chromophoric compounds in the SOAcauses this type of SOA to slowly photobleach. These photodegradationreactions may occur in cloud droplets, which are characterized by lowconcentrations of solutes, or in aerosol particles, which can have highlyviscous organic phases and aqueous phases with high concentrations ofinorganic salts. To investigate the effects of the surrounding matrix on therates and mechanisms of photodegradation of SOA compounds, SOA was preparedin a smog chamber by photooxidation of toluene in the presence of NOx.The collected SOA was photolyzed for up to 24 h using near-UV radiation(300–400 nm) from a xenon arc lamp under different conditions: directly onthe filter, dissolved in pure water, and dissolved in 1 M ammonium sulfate.The SOA mass absorption coefficient was measured as a function ofirradiation time to determine photobleaching rates. Electrospray ionizationhigh-resolution mass spectrometry coupled to liquid chromatographyseparation was used to observe changes in SOA composition resulting from theirradiation. The rate of decrease in SOA mass absorption coefficient due tophotobleaching was the fastest in water, with the presence of 1 M ammoniumsulfate modestly slowing down the photobleaching. By contrast,photobleaching directly on the filter was slower. The high-resolutionmass spectrometry analysis revealed an efficient photodegradation ofnitrophenol compounds on the filter but not in the aqueous phases, withrelatively little change observed in the composition of the SOA irradiatedin water or 1 M ammonium sulfate despite faster photobleaching than in theon-filter samples. This suggests that photodegradation of nitrophenolscontributes much more significantly to photobleaching in the organic phasethan in the aqueous phase. We conclude that the SOA absorption coefficientlifetime with respect to photobleaching and lifetimes of individualchromophores in SOA with respect to photodegradation will depend strongly onthe sample matrix in which SOA compounds are exposed to sunlight. 

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.